Red Hat ENTERPRISE LINUX 5.4 - SYSTEMTAP BEGINNERS GUIDE System information

SUSE Linux
Enterprise Server
11 SP3
October 16, 2014
www.suse.com
System Analysis and Tuning Guide
System Analysis and Tuning Guide
Copyright © 2006–2014 SUSE LLC and contributors. All rights reserved.
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU
Free Documentation License, Version 1.2 or (at your option) version 1.3; with the Invariant Section
being this copyright notice and license. A copy of the license version 1.2 is included in the section
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Contents
About This Guide
ix
1 Available Documentation ......................................................................... x
2 Feedback ............................................................................................. xii
3 Documentation Conventions .................................................................. xiii
I Basics
1
1 General Notes on System Tuning
3
1.1 Be Sure What Problem to Solve ............................................................. 3
1.2 Rule Out Common Problems ................................................................. 4
1.3 Finding the Bottleneck .......................................................................... 4
1.4 Step-by-step Tuning ............................................................................. 5
II System Monitoring
7
2 System Monitoring Utilities
9
2.1 Multi-Purpose Tools ............................................................................. 9
2.2 System Information ............................................................................ 17
2.3 Processes ........................................................................................... 21
2.4 Memory ............................................................................................ 28
2.5 Networking ........................................................................................ 31
2.6 The /proc File System ..................................................................... 35
2.7 Hardware Information ......................................................................... 39
2.8 Files and File Systems ........................................................................ 40
2.9 User Information ................................................................................ 43
2.10 Time and Date ................................................................................. 43
2.11 Graph Your Data: RRDtool ............................................................... 44
3 Monitoring with Nagios
51
3.1 Features of Nagios ............................................................................. 51
3.2 Installing Nagios ................................................................................. 51
3.3 Nagios Configuration Files .................................................................. 52
3.4 Configuring Nagios ............................................................................ 55
3.5 Troubleshooting ................................................................................. 58
3.6 For More Information ......................................................................... 59
4 Analyzing and Managing System Log Files
61
4.1 System Log Files in /var/log/ ........................................................ 61
4.2 Viewing and Parsing Log Files ............................................................. 64
4.3 Managing Log Files with logrotate ................................................. 64
4.4 Monitoring Log Files with logwatch ................................................. 66
4.5 Using logger to Make System Log Entries .......................................... 67
III Kernel Monitoring
5 SystemTap—Filtering and Analyzing System Data
69
71
5.1 Conceptual Overview .......................................................................... 71
5.2 Installation and Setup .......................................................................... 74
5.3 Script Syntax ..................................................................................... 76
5.4 Example Script .................................................................................. 83
5.5 User-Space Probing ............................................................................ 84
5.6 For More Information ......................................................................... 85
6 Kernel Probes
87
6.1 Supported Architectures ...................................................................... 88
6.2 Types of Kernel Probes ....................................................................... 88
6.3 Kernel probes API .............................................................................. 89
6.4 Debugfs Interface ............................................................................... 90
6.5 For More Information ......................................................................... 91
7 Perfmon2—Hardware-Based Performance Monitoring
93
7.1 Conceptual Overview .......................................................................... 93
7.2 Installation ......................................................................................... 95
7.3 Using Perfmon ................................................................................... 96
7.4 Retrieving Metrics From DebugFS ....................................................... 99
7.5 For More Information ....................................................................... 102
8 OProfile—System-Wide Profiler
105
8.1 Conceptual Overview ........................................................................ 105
8.2 Installation and Requirements ............................................................. 106
8.3 Available OProfile Utilities ................................................................ 106
8.4 Using OProfile ................................................................................. 106
8.5 Using OProfile's GUI ........................................................................ 109
8.6 Generating Reports ........................................................................... 110
8.7 For More Information ....................................................................... 110
IV Resource Management
113
9 General System Resource Management
115
9.1 Planning the Installation .................................................................... 115
9.2 Disabling Unnecessary Services .......................................................... 117
9.3 File Systems and Disk Access ............................................................ 118
10 Kernel Control Groups
121
10.1 Technical Overview and Definitions .................................................. 121
10.2 Scenario ......................................................................................... 122
10.3 Control Group Subsystems ............................................................... 124
10.4 Using Controller Groups .................................................................. 127
10.5 For More Information ..................................................................... 130
11 Power Management
133
11.1 Power Management at CPU Level ..................................................... 133
11.2 The Linux Kernel CPUfreq Infrastructure .......................................... 137
11.3 Viewing, Monitoring and Tuning Power-related Settings ....................... 139
11.4 Special Tuning Options .................................................................... 146
11.5 Creating and Using Power Management Profiles ................................. 149
11.6 Troubleshooting .............................................................................. 150
11.7 For More Information ..................................................................... 151
V Kernel Tuning
153
12 Installing Multiple Kernel Versions
155
12.1 Enabling and Configuring Multiversion Support .................................. 156
12.2 Installing/Removing Multiple Kernel Versions with YaST ..................... 157
12.3 Installing/Removing Multiple Kernel Versions with zypper ................... 158
13 Tuning I/O Performance
161
13.1 Switching I/O Scheduling ................................................................. 161
13.2 Available I/O Elevators .................................................................... 162
13.3 I/O Barrier Tuning .......................................................................... 164
14 Tuning the Task Scheduler
165
14.1 Introduction ................................................................................... 165
14.2 Process Classification ...................................................................... 166
14.3 O(1) Scheduler ............................................................................... 167
14.4 Completely Fair Scheduler ............................................................... 168
14.5 For More Information ..................................................................... 176
15 Tuning the Memory Management Subsystem
179
15.1 Memory Usage ............................................................................... 180
15.2 Reducing Memory Usage ................................................................. 182
15.3 Virtual Memory Manager (VM) Tunable Parameters ............................ 183
15.4 Non-Uniform Memory Access (NUMA) ............................................ 185
15.5 Monitoring VM Behavior ................................................................. 186
16 Tuning the Network
187
16.1 Configurable Kernel Socket Buffers .................................................. 187
16.2 Detecting Network Bottlenecks and Analyzing Network Traffic ............. 189
16.3 Netfilter ......................................................................................... 189
16.4 For More Information ..................................................................... 190
VI Handling System Dumps
17 Tracing Tools
191
193
17.1 Tracing System Calls with strace ....................................................... 193
17.2 Tracing Library Calls with ltrace ....................................................... 197
17.3 Debugging and Profiling with Valgrind .............................................. 198
17.4 For More Information ..................................................................... 203
18 kexec and kdump
205
18.1 Introduction ................................................................................... 205
18.2 Required Packages .......................................................................... 206
18.3 kexec Internals ............................................................................... 206
18.4 Basic kexec Usage .......................................................................... 207
18.5 How to Configure kexec for Routine Reboots ..................................... 208
18.6 Basic kdump Configuration .............................................................. 209
18.7 Analyzing the Crash Dump .............................................................. 213
18.8 Advanced kdump Configuration ....................................................... 217
18.9 For More Information ..................................................................... 218
A GNU Licenses
221
A.1 GNU Free Documentation License ..................................................... 221
About This Guide
SUSE Linux Enterprise Server is used for a broad range of usage scenarios in enterprise and scientific data centers. SUSE has ensured SUSE Linux Enterprise Server
is set up in a way that it accommodates different operation purposes with optimal
performance. However, SUSE Linux Enterprise Server must meet very different demands when employed on a number crunching server compared to a file server, for
example.
Generally it is not possible to ship a distribution that will by default be optimized for
all kinds of workloads. Due to the simple fact that different workloads vary substantially in various aspects—most importantly I/O access patterns, memory access patterns, and process scheduling. A behavior that perfectly suits a certain workload might
t reduce performance of a completely different workload (for example, I/O intensive
databases usually have completely different requirements compared to CPU-intensive
tasks, such as video encoding). The great versatility of Linux makes it possible to configure your system in a way that it brings out the best in each usage scenario.
This manual introduces you to means to monitor and analyze your system. It describes
methods to manage system resources and to tune your system. This guide does not
offer recipes for special scenarios, because each server has got its own different demands. It rather enables you to thoroughly analyze your servers and make the most out
of them.
General Notes on System Tuning
Tuning a system requires a carefully planned proceeding. Learn which steps are
necessary to successfully improve your system.
Part II, “System Monitoring” (page 7)
Linux offers a large variety of tools to monitor almost every aspect of the system.
Learn how to use these utilities and how to read and analyze the system log files.
Part III, “Kernel Monitoring” (page 69)
The Linux kernel itself offers means to examine every nut, bolt and screw of the
system. This part introduces you to SystemTap, a scripting language for writing
kernel modules that can be used to analyze and filter data. Collect debugging information and find bottlenecks by using kernel probes and use perfmon2 to access the CPU's performance monitoring unit. Last, monitor applications with the
help of Oprofile.
Part IV, “Resource Management” (page 113)
Learn how to set up a tailor-made system fitting exactly the server's need. Get to
know how to use power management while at the same time keeping the performance of a system at a level that matches the current requirements.
Part V, “Kernel Tuning” (page 153)
The Linux kernel can be optimized either by using sysctl or via the /proc file
system. This part covers tuning the I/O performance and optimizing the way how
Linux schedules processes. It also describes basic principles of memory management and shows how memory management could be fine-tuned to suit needs of
specific applications and usage patterns. Furthermore, it describes how to optimize network performance.
Part VI, “Handling System Dumps” (page 191)
This part enables you to analyze and handle application or system crashes. It introduces tracing tools such as strace or ltrace and describes how to handle system
crashes using Kexec and Kdump.
TIP: Getting the SUSE Linux Enterprise SDK
Some programs or packages mentioned in this guide are only available
from the SUSE Linux Enterprise SDK. The SDK is an add-on product for
SUSE Linux Enterprise Server and is available for download from http://
www.novell.com/developer/sle_sdk.html.
Many chapters in this manual contain links to additional documentation resources.
This includes additional documentation that is available on the system as well as documentation available on the Internet.
For an overview of the documentation available for your product and the latest documentation updates, refer to http://www.suse.com/doc or to the following section:
1 Available Documentation
We provide HTML and PDF versions of our books in different languages. The following manuals for users and administrators are available for this product:
x
System Analysis and Tuning Guide
Deployment Guide (↑Deployment Guide)
Shows how to install single or multiple systems and how to exploit the product
inherent capabilities for a deployment infrastructure. Choose from various approaches, ranging from a local installation or a network installation server to a
mass deployment using a remote-controlled, highly-customized, and automated
installation technique.
Administration Guide (↑Administration Guide)
Covers system administration tasks like maintaining, monitoring, and customizing
an initially installed system.
Security Guide (↑Security Guide)
Introduces basic concepts of system security, covering both local and network security aspects. Shows how to make use of the product inherent security software
like AppArmor (which lets you specify per program which files the program may
read, write, and execute), and the auditing system that reliably collects information about any security-relevant events.
Security and Hardening (↑Security and Hardening)
Deals with the particulars of installing and setting up a secure SUSE Linux Enterprise Server, and additional post-installation processes required to further secure and harden that installation. Supports the administrator with security-related
choices and decisions.
System Analysis and Tuning Guide (page i)
An administrator's guide for problem detection, resolution and optimization. Find
how to inspect and optimize your system by means of monitoring tools and how
to efficiently manage resources. Also contains an overview of common problems
and solutions, and of additional help and documentation resources.
Virtualization with Xen (↑Virtualization with Xen)
Offers an introduction to virtualization technology of your product. It features an
overview of the various fields of application and installation types of each of the
platforms supported by SUSE Linux Enterprise Server as well as a short description of the installation procedure.
Virtualization with KVM for IBM System z (↑Virtualization with KVM for IBM System z)
Offers an introduction to setting up and managing virtualization with KVM (Kernel-based Virtual Machine) on SUSE Linux Enterprise Server. Learn how to manAbout This Guide
xi
age KVM with libvirt or QEMU. The guide also contains detailed information
about requirements, limitations, and support status.
AutoYaST (↑AutoYaST)
AutoYaST is a system for installing one or more SUSE Linux Enterprise systems
automatically and without user intervention, using an AutoYaST profile that contains installation and configuration data. The manual guides you through the basic
steps of auto-installation: preparation, installation, and configuration.
Storage Administration Guide (↑Storage Administration Guide)
Provides information about how to manage storage devices on a SUSE Linux Enterprise Server.
In addition to the comprehensive manuals, several quick start guides are available:
Installation Quick Start (↑Installation Quick Start)
Lists the system requirements and guides you step-by-step through the installation
of SUSE Linux Enterprise Server from DVD, or from an ISO image.
Linux Audit Quick Start
Gives a short overview how to enable and configure the auditing system and how
to execute key tasks such as setting up audit rules, generating reports, and analyzing the log files.
AppArmor Quick Start
Helps you understand the main concepts behind AppArmor®.
Virtualization with Linux Containers (LXC) (↑Virtualization with Linux Containers
(LXC))
Gives a short introduction to LXC (a lightweight “virtualization” method) and
shows how to set up an LXC host and LXC containers.
Find HTML versions of most product manuals in your installed system under /usr/
share/doc/manual or in the help centers of your desktop. Find the latest documentation updates at http://www.suse.com/doc where you can download
PDF or HTML versions of the manuals for your product.
2 Feedback
Several feedback channels are available:
xii
System Analysis and Tuning Guide
Bugs and Enhancement Requests
For services and support options available for your product, refer to http://
www.suse.com/support/.
To report bugs for a product component, log in to the Novell Customer Center
from http://www.suse.com/support/ and select My Support > Service
Request.
User Comments
We want to hear your comments about and suggestions for this manual and the
other documentation included with this product. Use the User Comments feature at the bottom of each page in the online documentation or go to http://
www.suse.com/doc/feedback.html and enter your comments there.
Mail
For feedback on the documentation of this product, you can also send a mail to
doc-team@suse.de. Make sure to include the document title, the product
version, and the publication date of the documentation. To report errors or suggest enhancements, provide a concise description of the problem and refer to the
respective section number and page (or URL).
3 Documentation Conventions
The following typographical conventions are used in this manual:
• /etc/passwd: directory names and filenames
• placeholder: replace placeholder with the actual value
• PATH: the environment variable PATH
• ls, --help: commands, options, and parameters
• user: users or groups
• Alt, Alt + F1: a key to press or a key combination; keys are shown in uppercase as
on a keyboard
• File, File > Save As: menu items, buttons
About This Guide
xiii
• #amd64 em64t ipf: This paragraph is only relevant for the architectures amd64,
em64t, and ipf. The arrows mark the beginning and the end of the text block. ◄
#ipseries zseries: This paragraph is only relevant for the architectures System z
and ipseries. The arrows mark the beginning and the end of the text block. ◄
• Dancing Penguins (Chapter Penguins, ↑Another Manual): This is a reference to a
chapter in another manual.
xiv
System Analysis and Tuning Guide
Part I. Basics
General Notes on System
Tuning
This manual discusses how to find the reasons for performance problems and provides means to solve these problems. Before you start tuning your system, you should
make sure you have ruled out common problems and have found the cause (bottleneck) for the problem. You should also have a detailed plan on how to tune the
system, because applying random tuning tips will not help (and could make things
worse).
1
Procedure 1.1: General Approach When Tuning a System
1 Be sure what problem to solve
2 Rule out common problems
3 Find the bottleneck
3a Monitor the system and/or application
3b Analyze the data
4 Step-by-step tuning
1.1 Be Sure What Problem to Solve
Before you start tuning your system, try to describe the problem as exactly as possible.
Obviously, a simple and general “The system is too slow!” is no helpful problem deGeneral Notes on System Tuning
3
scription. If you plan to tune your Web server for faster delivery of static pages, for
example, it makes a difference whether you need to generally improve the speed or
whether it only needs to be improved at peak times.
Furthermore, make sure you can apply a measurement to your problem, otherwise you
will not be able to control if the tuning was a success or not. You should always be
able to compare “before” and “after”.
1.2 Rule Out Common Problems
A performance problem often is caused by network or hardware problems, bugs, or
configuration issues. Make sure to rule out problems such as the ones listed below before attempting to tune your system:
• Check /var/log/warn and /var/log/messages for unusual entries.
• Check (using top or ps) whether a certain process misbehaves by eating up unusual amounts of CPU time or memory.
• Check for network problems by inspecting /proc/net/dev.
• In case of I/O problems with physical disks, make sure it is not caused by hardware
problems (check the disk with the smartmontools) or by a full disk.
• Ensure that background jobs are scheduled to be carried out in times the server load
is low. Those jobs should also run with low priority (set via nice).
• If the machine runs several services using the same resources, consider moving services to another server.
• Last, make sure your software is up-to-date.
1.3 Finding the Bottleneck
Finding the bottleneck very often is the hardest part when tuning a system. SUSE Linux Enterprise Server offers a lot of tools helping you with this task. See Part II, “System Monitoring” (page 7) for detailed information on general system monitoring applications and log file analysis. If the problem requires a long-time in-depth
4
System Analysis and Tuning Guide
analysis, the Linux kernel offers means to perform such analysis. See Part III, “Kernel
Monitoring” (page 69) for coverage.
Once you have collected the data, it needs to be analyzed. First, inspect if the server's
hardware (memory, CPU, bus) and its I/O capacities (disk, network) are sufficient. If
these basic conditions are met, the system might benefit from tuning.
1.4 Step-by-step Tuning
Make sure to carefully plan the tuning itself. It is of vital importance to only do one
step at a time. Only by doing so you will be able to measure if the change provided an
improvement or even had a negative impact. Each tuning activity should be measured
over a sufficient time period in order to ensure you can do an analysis based on significant data. If you cannot measure a positive effect, do not make the change permanent. Chances are, that it might have a negative effect in the future.
General Notes on System Tuning
5
Part II. System Monitoring
System Monitoring Utilities
There are number of programs, tools, and utilities which you can use to examine the
status of your system. This chapter introduces some of them and describes their most
important and frequently used parameters.
2
For each of the described commands, examples of the relevant outputs are presented. In the examples, the first line is the command itself (after the > or # sign prompt).
Omissions are indicated with square brackets ([...]) and long lines are wrapped
where necessary. Line breaks for long lines are indicated by a backslash (\).
# command -x -y
output line 1
output line 2
output line 3 is annoyingly long, so long that \
we have to break it
output line 4
[...]
output line 98
output line 99
The descriptions have been kept short so that we can include as many utilities as possible. Further information for all the commands can be found in the manual pages.
Most of the commands also understand the parameter --help, which produces a
brief list of possible parameters.
2.1 Multi-Purpose Tools
While most of the Linux system monitoring tools are specific to monitor a certain aspect of the system, there are a few “swiss army knife” tools showing various aspects
System Monitoring Utilities
9
of the system at a glance. Use these tools first in order to get an overview and find out
which part of the system to examine further.
2.1.1 vmstat
vmstat collects information about processes, memory, I/O, interrupts and CPU. If
called without a sampling rate, it displays average values since the last reboot. When
called with a sampling rate, it displays actual samples:
Example 2.1: vmstat Output on a Lightly Used Machine
tux@mercury:~> vmstat -a 2
procs -----------memory---------- ---swap-- -----io---- -system-- -----cpu------r b
swpd
free inact active
si
so
bi
bo
in
cs us sy id wa st
0 0
0 750992 570648 548848
0
0
0
1
8
9 0 0 100 0 0
0 0
0 750984 570648 548912
0
0
0
0
63
48 1 0 99
0 0
0 0
0 751000 570648 548912
0
0
0
0
55
47 0 0 100 0 0
0 0
0 751000 570648 548912
0
0
0
0
56
50 0 0 100 0 0
0 0
0 751016 570648 548944
0
0
0
0
57
50 0 0 100 0 0
Example 2.2: vmstat Output on a Heavily Used Machine (CPU bound)
tux@mercury:~> vmstat 2
procs -----------memory----------- ---swap-- -----io---r b
swpd
free
buff
cache
si
so
bi
bo
32 1 26236 459640 110240 6312648
0
0 9944
2
23 1 26236 396728 110336 6136224
0
0 9588
0
35 0 26236 554920 110508 6166508
0
0 7684 27992
28 0 26236 518184 110516 6039996
0
0 10830
4
21 5 26236 716468 110684 6074872
0
0 8734 20534
-system-in
cs
4552 6597
4468 6273
4474 4700
4446 4670
4512 4061
-----cpu-----us sy id wa st
95 5 0 0 0
94 6 0 0 0
95 5 0 0 0
94 6 0 0 0
96 4 0 0 0
TIP
The first line of the vmstat output always displays average values since the
last reboot.
The columns show the following:
r
10
Shows the number of processes in the run queue. These processes are waiting for
a free CPU slot to be executed. If the number of processes in this column is constantly higher than the number of CPUs available, this is an indication of insufficient CPU power.
System Analysis and Tuning Guide
b
Shows the number of processes waiting for a resource other than a CPU. A high
number in this column may indicate an I/O problem (network or disk).
swpd
The amount of swap space (KB) currently used.
free
The amount of unused memory (KB).
inact
Recently unused memory that can be reclaimed. This column is only visible when
calling vmstat with the parameter -a (recommended).
active
Recently used memory that normally does not get reclaimed. This column is only
visible when calling vmstat with the parameter -a (recommended).
buff
File buffer cache (KB) in RAM. This column is not visible when calling vmstat
with the parameter -a (recommended).
cache
Page cache (KB) in RAM. This column is not visible when calling vmstat with
the parameter -a (recommended).
si
so
bi
bo
Amount of data (KB) that is moved from swap to RAM per second. High values over a long period of time in this column are an indication that the machine
would benefit from more RAM.
Amount of data (KB) that is moved from RAM to swap per second. High values over a longer period of time in this column are an indication that the machine
would benefit from more RAM.
Number of blocks per second received from a block device (e.g. a disk read).
Note that swapping also impacts the values shown here.
Number of blocks per second sent to a block device (e.g. a disk write). Note that
swapping also impacts the values shown here.
System Monitoring Utilities
11
in
cs
us
sy
id
wa
st
Interrupts per second. A high value indicates a high I/O level (network and/or
disk).
Number of context switches per second. Simplified this means that the kernel has
to replace executable code of one program in memory with that of another program.
Percentage of CPU usage from user processes.
Percentage of CPU usage from system processes.
Percentage of CPU time spent idling. If this value is zero over a longer period of
time, your CPU(s) are working to full capacity. This is not necessarily a bad sign
—rather refer to the values in columns r and b to determine if your machine is
equipped with sufficient CPU power.
If "wa" time is non-zero, it indicates throughput lost due to waiting for I/O. This
may be inevitable, for example, if a file is being read for the first time, background writeback cannot keep up, and so on. It can also be an indicator for a
hardware bottleneck (network or hard disk). Lastly, it can indicate a potential
for tuning the virtual memory manager (refer to Chapter 15, Tuning the Memory
Management Subsystem (page 179)).
Percentage of CPU time used by virtual machines.
See vmstat --help for more options.
2.1.2 System Activity Information: sar and
sadc
sar can generate extensive reports on almost all important system activities, among
them CPU, memory, IRQ usage, IO, or networking. It can either generate reports on
12
System Analysis and Tuning Guide
the fly or query existing reports gathered by the system activity data collector (sadc).
sar and sadc both gather all their data from the /proc file system.
NOTE: sysstat Package
sar and sadc are part of sysstat package. You need to install the package either with YaST, or with zypper in sysstat.
2.1.2.1 Automatically Collecting Daily Statistics
With sadc
If you want to monitor your system about a longer period of time, use sadc to automatically collect the data. You can read this data at any time using sar. To start
sadc, simply run /etc/init.d/boot.sysstat start. This will add a link
to /etc/cron.d/ that calls sadc with the following default configuration:
• All available data will be collected.
• Data is written to /var/log/sa/saDD, where DD stands for the current day. If a
file already exists, it will be archived.
• The summary report is written to /var/log/sa/sarDD, where DD stands for
the current day. Already existing files will be archived.
• Data is collected every ten minutes, a summary report is generated every 6 hours
(see /etc/sysstat/sysstat.cron).
• The data is collected by the /usr/lib64/sa/sa1 script (or /usr/lib/sa/
sa1 on 32-bit systems)
• The summaries are generated by the script /usr/lib64/sa/sa2 (or /usr/
lib/sa/sa2 on 32-bit systems)
If you need to customize the configuration, copy the sa1 and sa2 scripts and adjust
them according to your needs. Replace the link /etc/cron.d/sysstat with a
customized copy of /etc/sysstat/sysstat.cron calling your scripts.
2.1.2.2 Generating reports with sar
To generate reports on the fly, call sar with an interval (seconds) and a count. To
generate reports from files specify a filename with the option -f instead of interval
System Monitoring Utilities
13
and count. If filename, interval and count are not specified, sar attempts to generate
a report from /var/log/sa/saDD, where DD stands for the current day. This is
the default location to where sadc writes its data. Query multiple files with multiple
-f options.
sar 2 10
seconds
sar -f ~/reports/sar_2010_05_03
sar
cd /var/log/sa &&\
sar -f sa01 -f sa02
# on-the-fly report, 10 times every 2
# queries file sar_2010_05_03
# queries file from today in /var/log/sa/
# queries files /var/log/sa/0[12]
Find examples for useful sar calls and their interpretation below. For detailed information on the meaning of each column, please refer to the man (1) of sar. Also
refer to the man page for more options and reports—sar offers plenty of them.
CPU Utilization Report: sar
When called with no options, sar shows a basic report about CPU usage. On multi-processor machines, results for all CPUs are summarized. Use the option -P ALL
to also see statistics for individual CPUs.
mercury:~ # sar 10 5
Linux 2.6.31.12-0.2-default (mercury) 03/05/10
14:15:43
14:15:53
14:16:03
14:16:13
14:16:23
14:16:33
Average:
CPU
all
all
all
all
all
all
%user
38.55
12.59
56.59
58.45
86.46
49.94
%nice
0.00
0.00
0.00
0.00
0.00
0.00
%system
6.10
4.90
8.16
3.00
4.70
5.38
_x86_64_
%iowait
0.10
0.33
0.44
0.00
0.00
0.18
(2 CPU)
%steal
0.00
0.00
0.00
0.00
0.00
0.00
%idle
55.25
82.18
34.81
38.55
8.85
44.50
If the value for %iowait (percentage of the CPU being idle while waiting for I/O) is
significantly higher than zero over a longer period of time, there is a bottleneck in the
I/O system (network or hard disk). If the %idle value is zero over a longer period of
time, your CPU(s) are working to full capacity.
Memory Usage Report: sar -r
Generate an overall picture of the system memory (RAM) by using the option -r:
mercury:~ # sar -r 10 5
Linux 2.6.31.12-0.2-default (mercury) 03/05/10
_x86_64_
(2 CPU)
16:12:12 kbmemfree kbmemused %memused kbbuffers kbcached kbcommit %commit
16:12:22
548188
1507488
73.33
20524
64204 2338284
65.10
14
System Analysis and Tuning Guide
16:12:32
16:12:42
16:12:52
16:13:02
Average:
259320
381096
642668
311984
428651
1796356
1674580
1413008
1743692
1627025
87.39
81.46
68.74
84.82
79.15
20808
21084
21392
21712
21104
72660
75460
81212
84040
75515
2229080
2328192
1938820
2212024
2209280
62.06
64.82
53.98
61.58
61.51
The last two columns (kbcommit and %commit) show an approximation of the total
amount of memory (RAM plus swap) the current workload would need in the worst
case (in kilobyte or percent respectively).
Paging Statistics Report: sar -B
Use the option -B to display the kernel paging statistics.
mercury:~ # sar -B 10 5
Linux 2.6.31.12-0.2-default (mercury) 03/05/10
_x86_64_
(2 CPU)
16:11:43 pgpgin/s pgpgout/s
fault/s majflt/s pgfree/s pgscank/s pgscand/s pgsteal/s
16:11:53
225.20
104.00 91993.90
0.00 87572.60
0.00
0.00
0.00
16:12:03
718.32
601.00 82612.01
2.20 99785.69
560.56
839.24
1132.23
16:12:13 1222.00
1672.40 103126.00
1.70 106529.00
1136.00
982.40
1172.20
16:12:23
112.18
77.84 113406.59
0.10 97581.24
35.13
127.74
159.38
16:12:33
817.22
81.28 121312.91
9.41 111442.44
0.00
0.00
0.00
Average:
618.72
507.20 102494.86
2.68 100578.98
346.24
389.76
492.60
%vmeff
0.00
80.89
55.33
97.86
0.00
66.93
The majflt/s (major faults per second) column shows how many pages are loaded
from disk (swap) into memory. A large number of major faults slows down the system and is an indication of insufficient main memory. The %vmeff column shows
the number of pages scanned (pgscand/s) in relation to the ones being reused from the
main memory cache or the swap cache (pgsteal/s). It is a measurement of the efficiency of page reclaim. Healthy values are either near 100 (every inactive page swapped
out is being reused) or 0 (no pages have been scanned). The value should not drop below 30.
Block Device Statistics Report: sar -d
Use the option -d to display the block device (hdd, optical drive, USB storage device, ...). Make sure to use the additional option -p (pretty-print) to make the DEV
column readable.
mercury:~ # sar -d -p 10 5
Linux 2.6.31.12-0.2-default (neo)
03/05/10
_x86_64_ (2 CPU)
16:28:31 DEV
16:28:41 sdc
16:28:41 scd0
tps
11.51
0.00
rd_sec/s
98.50
0.00
wr_sec/s
653.45
0.00
avgrq-sz
65.32
0.00
avgqu-sz
0.10
0.00
await
8.83
0.00
svctm
4.87
0.00
%util
5.61
0.00
16:28:41
16:28:51
tps
15.38
rd_sec/s
329.27
wr_sec/s
465.93
avgrq-sz
51.69
avgqu-sz
0.10
await
6.39
svctm
4.70
%util
7.23
DEV
sdc
System Monitoring Utilities
15
16:28:51 scd0
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
16:28:51 DEV
16:29:01 sdc
16:29:01 scd0
tps rd_sec/s
32.47
876.72
0.00
0.00
wr_sec/s
647.35
0.00
avgrq-sz
46.94
0.00
avgqu-sz
0.33
0.00
await
10.20
0.00
svctm
3.67
0.00
%util
11.91
0.00
16:29:01 DEV
16:29:11 sdc
16:29:11 scd0
tps rd_sec/s
48.75 2852.45
0.00
0.00
wr_sec/s
366.77
0.00
avgrq-sz
66.04
0.00
avgqu-sz
0.82
0.00
await
16.93
0.00
svctm
4.91
0.00
%util
23.94
0.00
16:29:11 DEV
16:29:21 sdc
16:29:21 scd0
tps rd_sec/s
13.20
362.40
0.00
0.00
wr_sec/s
412.00
0.00
avgrq-sz
58.67
0.00
avgqu-sz
0.16
0.00
await
12.03
0.00
svctm
6.09
0.00
%util
8.04
0.00
Average: DEV
Average: sdc
Average: scd0
tps rd_sec/s
24.26
903.52
0.00
0.00
wr_sec/s
509.12
0.00
avgrq-sz
58.23
0.00
avgqu-sz
0.30
0.00
await
12.49
0.00
svctm
4.68
0.00
%util
11.34
0.00
If your machine uses multiple disks, you will receive the best performance, if I/O requests are evenly spread over all disks. Compare the Average values for tps, rd_sec/s,
and wr_sec/s of all disks. Constantly high values in the svctm and %util columns could
be an indication that the amount of free space on the disk is insufficient.
Network Statistics Reports: sar -n KEYWORD
The option -n lets you generate multiple network related reports. Specify one of the
following keywords along with the -n:
• DEV: Generates a statistic report for all network devices
• EDEV: Generates an error statistics report for all network devices
• NFS: Generates a statistic report for an NFS client
• NFSD: Generates a statistic report for an NFS server
• SOCK: Generates a statistic report on sockets
• ALL: Generates all network statistic reports
2.1.2.3 Visualizing sar Data
sar reports are not always easy to parse for humans. kSar, a Java application visualizing your sar data, creates easy-to-read graphs. It can even generate PDF reports.
kSar takes data generated on the fly as well as past data from a file. kSar is licensed
under the BSD license and is available from http://ksar.atomique.net/.
16
System Analysis and Tuning Guide
2.2 System Information
2.2.1 Device Load Information: iostat
iostat monitors the system device loading. It generates reports that can be useful
for better balancing the load between physical disks attached to your system.
The first iostat report shows statistics collected since the system was booted. Subsequent reports cover the time since the previous report.
tux@mercury:~> iostat
Linux 2.6.32.7-0.2-default (geeko@buildhost)
avg-cpu:
Device:
sda
sda1
sda2
sda3
%user
0,49
%nice %system %iowait
0,01
0,10
0,31
tps
1,34
0,00
0,87
0,47
Blk_read/s
5,59
0,01
5,11
0,47
02/24/10
%steal
0,00
Blk_wrtn/s
25,37
0,00
17,83
7,54
_x86_64_
%idle
99,09
Blk_read
1459766
1519
1335365
122578
Blk_wrtn
6629160
0
4658152
1971008
When invoked with the -n option, iostat adds statistics of network file systems
(NFS) load. The option -x shows extended statistics information.
You can also specify which device should be monitored at what time intervals. For example, iostat -p sda 3 5 will display five reports at three second intervals for
device sda.
NOTE: sysstat Package
iostat is part of sysstat package. To use it, install the package with zypper in sysstat
2.2.2 Processor Activity Monitoring:
mpstat
The utility mpstat examines activities of each available processor. If your system
has one processor only, the global average statistics will be reported.
System Monitoring Utilities
17
With the -P option, you can specify the number of processors to be reported (note
that 0 is the first processor). The timing arguments work the same way as with the
iostat command. Entering mpstat -P 1 2 5 prints five reports for the second
processor (number 1) at 2 second intervals.
tux@mercury:~> mpstat -P 1 2 5
Linux 2.6.32.7-0.2-default (geeko@buildhost)
08:57:10 CPU
%usr
%guest
%idle
08:57:12
1
4.46
0.00
89.11
08:57:14
1
1.98
0.00
93.07
08:57:16
1
2.50
0.00
93.50
08:57:18
1
14.36
0.00
83.17
08:57:20
1
2.51
0.00
91.46
Average:
1
5.17
0.00
90.05
%nice
02/24/10
_x86_64_
%sys %iowait
%irq
%soft
%steal
\
0.00
5.94
0.50
0.00
0.00
0.00
\
0.00
2.97
0.99
0.00
0.99
0.00
\
0.00
3.00
0.00
0.00
1.00
0.00
\
0.00
1.98
0.00
0.00
0.50
0.00
\
0.00
4.02
0.00
0.00
2.01
0.00
\
0.00
3.58
0.30
0.00
0.90
0.00
\
2.2.3 Task Monitoring: pidstat
If you need to see what load a particular task applies to your system, use pidstat
command. It prints activity of every selected task or all tasks managed by Linux kernel if no task is specified. You can also set the number of reports to be displayed and
the time interval between them.
For example, pidstat -C top 2 3 prints the load statistic for tasks whose command name includes the string “top”. There will be three reports printed at two second
intervals.
tux@mercury:~> pidstat -C top 2 3
Linux 2.6.27.19-5-default (geeko@buildhost)
18
03/23/2009
_x86_64_
09:25:42 AM
09:25:44 AM
PID
23576
%usr %system
37.62
61.39
%guest
0.00
%CPU
99.01
CPU
1
Command
top
09:25:44 AM
09:25:46 AM
PID
23576
%usr %system
37.00
62.00
%guest
0.00
%CPU
99.00
CPU
1
Command
top
09:25:46 AM
09:25:48 AM
PID
23576
%usr %system
38.00
61.00
%guest
0.00
%CPU
99.00
CPU
1
Command
top
Average:
Average:
PID
23576
%usr %system
37.54
61.46
%guest
0.00
%CPU
99.00
CPU
-
Command
top
System Analysis and Tuning Guide
2.2.4 Kernel Ring Buffer: dmesg
The Linux kernel keeps certain messages in a ring buffer. To view these messages,
enter the command dmesg:
tux@mercury:~> dmesg
[...]
end_request: I/O error, dev fd0, sector 0
subfs: unsuccessful attempt to mount media (256)
e100: eth0: e100_watchdog: link up, 100Mbps, half-duplex
NET: Registered protocol family 17
IA-32 Microcode Update Driver: v1.14 <tigran@veritas.com>
microcode: CPU0 updated from revision 0xe to 0x2e, date = 08112004
IA-32 Microcode Update Driver v1.14 unregistered
bootsplash: status on console 0 changed to on
NET: Registered protocol family 10
Disabled Privacy Extensions on device c0326ea0(lo)
IPv6 over IPv4 tunneling driver
powernow: This module only works with AMD K7 CPUs
bootsplash: status on console 0 changed to on
Older events are logged in the files /var/log/messages and /var/log/warn.
2.2.5 List of Open Files: lsof
To view a list of all the files open for the process with process ID PID, use -p. For
example, to view all the files used by the current shell, enter:
tux@mercury:~> lsof -p $$
COMMAND PID
USER
FD
TYPE DEVICE SIZE/OFF NODE NAME
bash
5552 tux cwd
DIR
3,3
1512 117619 /home/tux
bash
5552 tux rtd
DIR
3,3
584
2 /
bash
5552 tux txt
REG
3,3 498816 13047 /bin/bash
bash
5552 tux mem
REG
0,0
0 [heap] (stat: No such
bash
5552 tux mem
REG
3,3 217016 115687 /var/run/nscd/passwd
bash
5552 tux mem
REG
3,3 208464 11867 /usr/lib/locale/en_GB.
[...]
bash
5552 tux mem
REG
3,3
366
9720 /usr/lib/locale/en_GB.
bash
5552 tux mem
REG
3,3
97165
8828 /lib/ld-2.3.6.so
bash
5552 tux
0u
CHR 136,5
7 /dev/pts/5
bash
5552 tux
1u
CHR 136,5
7 /dev/pts/5
bash
5552 tux
2u
CHR 136,5
7 /dev/pts/5
bash
5552 tux 255u
CHR 136,5
7 /dev/pts/5
The special shell variable $$, whose value is the process ID of the shell, has been
used.
The command lsof lists all the files currently open when used without any parameters. There are often thousands of open files, therefore, listing all of them is rarely
System Monitoring Utilities
19
useful. However, the list of all files can be combined with search functions to generate useful lists. For example, list all used character devices:
tux@mercury:~> lsof | grep CHR
bash
3838
tux
0u
bash
3838
tux
1u
bash
3838
tux
2u
bash
3838
tux 255u
bash
5552
tux
0u
bash
5552
tux
1u
bash
5552
tux
2u
bash
5552
tux 255u
X
5646
root mem
lsof
5673
tux
0u
lsof
5673
tux
2u
grep
5674
tux
1u
grep
5674
tux
2u
CHR 136,0
CHR 136,0
CHR 136,0
CHR 136,0
CHR 136,5
CHR 136,5
CHR 136,5
CHR 136,5
CHR
1,1
CHR 136,5
CHR 136,5
CHR 136,5
CHR 136,5
2 /dev/pts/0
2 /dev/pts/0
2 /dev/pts/0
2 /dev/pts/0
7 /dev/pts/5
7 /dev/pts/5
7 /dev/pts/5
7 /dev/pts/5
1006 /dev/mem
7 /dev/pts/5
7 /dev/pts/5
7 /dev/pts/5
7 /dev/pts/5
When used with -i, lsof lists currently open Internet files as well:
tux@mercury:~> lsof -i
[...]
pidgin
4349 tux
17r IPv4 15194
0t0 TCP \
jupiter.example.com:58542->www.example.net:https (ESTABLISHED)
pidgin
4349 tux
21u IPv4 15583
0t0 TCP \
jupiter.example.com:37051->aol.example.org:aol (ESTABLISHED)
evolution 4578 tux
38u IPv4 16102
0t0 TCP \
jupiter.example.com:57419->imap.example.com:imaps (ESTABLISHED)
npviewer. 9425 tux
40u IPv4 24769
0t0 TCP \
jupiter.example.com:51416->www.example.com:http (CLOSE_WAIT)
npviewer. 9425 tux
49u IPv4 24814
0t0 TCP \
jupiter.example.com:43964->www.example.org:http (CLOSE_WAIT)
ssh
17394 tux
3u IPv4 40654
0t0 TCP \
jupiter.example.com:35454->saturn.example.com:ssh (ESTABLISHED)
2.2.6 Kernel and udev Event Sequence
Viewer: udevadm monitor
udevadm monitor listens to the kernel uevents and events sent out by a udev rule
and prints the device path (DEVPATH) of the event to the console. This is a sequence
of events while connecting a USB memory stick:
NOTE: Monitoring udev Events
Only root user is allowed to monitor udev events by running the udevadm
command.
20
System Analysis and Tuning Guide
UEVENT[1138806687]
UEVENT[1138806687]
UEVENT[1138806687]
UEVENT[1138806687]
UDEV [1138806687]
UDEV [1138806687]
UDEV [1138806687]
UDEV [1138806687]
UEVENT[1138806692]
UEVENT[1138806692]
UEVENT[1138806692]
UEVENT[1138806692]
UDEV [1138806693]
UDEV [1138806693]
UDEV [1138806693]
UDEV [1138806693]
UEVENT[1138806694]
UDEV [1138806694]
UEVENT[1138806694]
UEVENT[1138806697]
add@/devices/pci0000:00/0000:00:1d.7/usb4/4-2/4-2.2
add@/devices/pci0000:00/0000:00:1d.7/usb4/4-2/4-2.2/4-2.2
add@/class/scsi_host/host4
add@/class/usb_device/usbdev4.10
add@/devices/pci0000:00/0000:00:1d.7/usb4/4-2/4-2.2
add@/devices/pci0000:00/0000:00:1d.7/usb4/4-2/4-2.2/4-2.2
add@/class/scsi_host/host4
add@/class/usb_device/usbdev4.10
add@/devices/pci0000:00/0000:00:1d.7/usb4/4-2/4-2.2/4-2.2
add@/block/sdb
add@/class/scsi_generic/sg1
add@/class/scsi_device/4:0:0:0
add@/devices/pci0000:00/0000:00:1d.7/usb4/4-2/4-2.2/4-2.2
add@/class/scsi_generic/sg1
add@/class/scsi_device/4:0:0:0
add@/block/sdb
add@/block/sdb/sdb1
add@/block/sdb/sdb1
mount@/block/sdb/sdb1
umount@/block/sdb/sdb1
2.2.7 Information on Security Events:
audit
The Linux audit framework is a complex auditing system that collects detailed information about all security related events. These records can be consequently analyzed
to discover if, for example, a violation of security policies occurred. For more information on audit, see Part “The Linux Audit Framework” (↑Security Guide).
2.3 Processes
2.3.1 Interprocess Communication: ipcs
The command ipcs produces a list of the IPC resources currently in use:
------ Shared Memory Segments -------key
shmid
owner
perms
0x00000000 58261504
tux
600
0x00000000 58294273
tux
600
0x00000000 83886083
tux
666
0x00000000 83951622
tux
666
bytes
393216
196608
43264
192000
nattch
2
2
2
2
status
dest
dest
System Monitoring Utilities
21
0x00000000 83984391
0x00000000 84738056
tux
root
666
644
282464
151552
------ Semaphore Arrays -------key
semid
owner
perms
0x4d038abf 0
tux
600
------ Message Queues -------key
msqid
owner
2
2
dest
nsems
8
perms
used-bytes
messages
2.3.2 Process List: ps
The command ps produces a list of processes. Most parameters must be written without a minus sign. Refer to ps --help for a brief help or to the man page for extensive help.
To list all processes with user and command line information, use ps axu:
tux@mercury:~> ps axu
USER
PID %CPU %MEM
VSZ
RSS TTY
root
1 0.0 0.0
696
272 ?
root
2 0.0 0.0
0
0 ?
root
3 0.0 0.0
0
0 ?
[...]
tux
4047 0.0 6.0 158548 31400 ?
tux
4057 0.0 0.7
9036 3684 ?
tux
4067 0.0 0.1
2204
636 ?
tux
4072 0.0 1.0 15996 5160 ?
tux
4114 0.0 3.7 130988 19172 ?
tux
4818 0.0 0.3
4192 1812 pts/0
tux
4959 0.0 0.1
2324
816 pts/0
STAT
S
SN
S<
Ssl
Sl
S
Ss
SLl
Ss
R+
START
12:59
12:59
12:59
13:02
13:02
13:02
13:02
13:06
15:59
16:17
TIME
0:01
0:00
0:00
0:06
0:00
0:00
0:00
0:04
0:00
0:00
COMMAND
init [5]
[ksoftirqd
[events
mono-best
/opt/gnome
/opt/gnome
gnome-scre
sound-juic
-bash
ps axu
To check how many sshd processes are running, use the option -p together with the
command pidof, which lists the process IDs of the given processes.
tux@mercury:~>
PID TTY
3524 ?
4813 ?
4817 ?
ps -p $(pidof sshd)
STAT
TIME COMMAND
Ss
0:00 /usr/sbin/sshd -o PidFile=/var/run/sshd.init.pid
Ss
0:00 sshd: tux [priv]
R
0:00 sshd: tux@pts/0
The process list can be formatted according to your needs. The option -L returns a
list of all keywords. Enter the following command to issue a list of all processes sorted
by memory usage:
tux@mercury:~> ps ax --format pid,rss,cmd --sort rss
PID
RSS CMD
2
0 [ksoftirqd/0]
22
System Analysis and Tuning Guide
3
4
5
11
12
472
473
[...]
4028
4118
4114
4023
0
0
0
0
0
0
0
17556
17800
19172
25144
[events/0]
[khelper]
[kthread]
[kblockd/0]
[kacpid]
[pdflush]
[pdflush]
nautilus --no-default-window --sm-client-id default2
ksnapshot
sound-juicer
gnome-panel --sm-client-id default1
Useful ps Calls
ps aux --sort column
Sort the output by column. Replace column with
pmem for physical memory ratio
pcpu for CPU ratio
rss for resident set size (non-swapped physical memory)
ps axo pid,%cpu,rss,vsz,args,wchan
Shows every process, their PID, CPU usage ratio, memory size (resident and virtual), name, and their syscall.
ps axfo pid,args
Show a process tree.
2.3.3 Process Tree: pstree
The command pstree produces a list of processes in the form of a tree:
tux@mercury:~> pstree
init-+-NetworkManagerD
|-acpid
|-3*[automount]
|-cron
|-cupsd
|-2*[dbus-daemon]
|-dbus-launch
|-dcopserver
|-dhcpcd
|-events/0
|-gpg-agent
|-hald-+-hald-addon-acpi
System Monitoring Utilities
23
|
`-hald-addon-stor
|-kded
|-kdeinit-+-kdesu---su---kdesu_stub---yast2---y2controlcenter
|
|-kio_file
|
|-klauncher
|
|-konqueror
|
|-konsole-+-bash---su---bash
|
|
`-bash
|
`-kwin
|-kdesktop---kdesktop_lock---xmatrix
|-kdesud
|-kdm-+-X
|
`-kdm---startkde---kwrapper
[...]
The parameter -p adds the process ID to a given name. To have the command lines
displayed as well, use the -a parameter:
2.3.4 Table of Processes: top
The command top, which stands for table of processes, displays a list of
processes that is refreshed every two seconds. To terminate the program, press Q. The
parameter -n 1 terminates the program after a single display of the process list. The
following is an example output of the command top -n 1:
tux@mercury:~> top -n 1
top - 17:06:28 up 2:10, 5 users, load average: 0.00, 0.00, 0.00
Tasks: 85 total,
1 running, 83 sleeping,
1 stopped,
0 zombie
Cpu(s): 5.5% us, 0.8% sy, 0.8% ni, 91.9% id, 1.0% wa, 0.0% hi, 0.0% si
Mem:
515584k total,
506468k used,
9116k free,
66324k buffers
Swap:
658656k total,
0k used,
658656k free,
353328k cached
PID
1
2
3
4
5
11
12
472
473
475
474
681
839
923
1343
1587
24
USER
root
root
root
root
root
root
root
root
root
root
root
root
root
root
root
root
PR
16
34
10
10
10
10
20
20
15
11
15
10
10
13
10
20
NI
0
19
-5
-5
-5
-5
-5
0
0
-5
0
-5
-5
-4
-5
0
VIRT
700
0
0
0
0
0
0
0
0
0
0
0
0
1712
0
0
System Analysis and Tuning Guide
RES
272
0
0
0
0
0
0
0
0
0
0
0
0
552
0
0
SHR
236
0
0
0
0
0
0
0
0
0
0
0
0
344
0
0
S %CPU %MEM
S 0.0 0.1
S 0.0 0.0
S 0.0 0.0
S 0.0 0.0
S 0.0 0.0
S 0.0 0.0
S 0.0 0.0
S 0.0 0.0
S 0.0 0.0
S 0.0 0.0
S 0.0 0.0
S 0.0 0.0
S 0.0 0.0
S 0.0 0.1
S 0.0 0.0
S 0.0 0.0
TIME+
0:01.33
0:00.00
0:00.27
0:00.01
0:00.00
0:00.05
0:00.00
0:00.00
0:00.06
0:00.00
0:00.07
0:00.01
0:00.02
0:00.67
0:00.00
0:00.00
COMMAND
init
ksoftirqd/0
events/0
khelper
kthread
kblockd/0
kacpid
pdflush
pdflush
aio/0
kswapd0
kseriod
reiserfs/0
udevd
khubd
shpchpd_event
1746
1752
2151
2165
2166
2171
2235
2289
2403
2709
2714
root
root
root
messageb
root
root
root
root
root
root
root
15
15
16
16
15
16
15
16
23
19
16
0
0
0
0
0
0
0
0
0
0
0
0
0
0 S
0
0
0 S
1464 496 416 S
3340 1048 792 S
1840 752 556 S
1600 516 320 S
1736 800 652 S
4192 2852 1444 S
1756 600 524 S
2668 1076 944 S
1756 648 564 S
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.1
0.2
0.1
0.1
0.2
0.6
0.1
0.2
0.1
0:00.00
0:00.00
0:00.00
0:00.64
0:00.01
0:00.00
0:00.10
0:02.05
0:00.00
0:00.00
0:00.56
w1_control
w1_bus_master1
acpid
dbus-daemon
syslog-ng
klogd
resmgrd
hald
hald-addon-acpi
NetworkManagerD
hald-addon-stor
By default the output is sorted by CPU usage (column %CPU, shortcut Shift + P). Use
following shortcuts to change the sort field:
Shift + M: Resident Memory (RES)
Shift + N: Process ID (PID)
Shift + T: Time (TIME+)
To use any other field for sorting, press F and select a field from the list. To toggle
the sort order, Use Shift + R.
The parameter -U UID monitors only the processes associated with a particular
user. Replace UID with the user ID of the user. Use top -U $(id -u) to show
processes of the current user
2.3.5 System z hypervisor monitor:
hyptop
hyptop provides a dynamic real-time view of a System z hypervisor environment,
using the kernel infrastructure via debugfs. It works with either the z/VM or the
LPAR hypervisor. Depending on the available data it, for example, shows CPU and
memory consumption of active LPARs or z/VM guests. It provides a curses based
user interface similar to the top command. hyptop provides two windows:
• sys_list: Shows a list of systems that the currently hypervisor is running
• sys: Shows one system in more detail
You can run hyptop in interactive mode (default) or in batch mode with the -b option. Help in the interactive mode is available by pressing ? after hyptop is started.
System Monitoring Utilities
25
Output for the sys_list window under LPAR:
12:30:48 | CPU-T: IFL(18) CP(3) UN(3)
system #cpu
cpu
mgm
Cpu+ Mgm+
(str)
(#)
(%)
(%)
(hm) (hm)
H05LP30
10 461.14 10.18 1547:41 8:15
H05LP33
4 133.73 7.57 220:53 6:12
H05LP50
4 99.26 0.01 146:24 0:12
H05LP02
1 99.09 0.00 269:57 0:00
TRX2CFA
1
2.14 0.03
3:24 0:04
H05LP13
6
1.36 0.34
4:23 0:54
TRX1
19
1.22 0.14
13:57 0:22
TRX2
20
1.16 0.11
26:05 0:25
H05LP55
2
0.00 0.00
0:22 0:00
H05LP56
3
0.00 0.00
0:00 0:00
413 823.39 23.86 3159:57 38:08
?=help
online
(dhm)
11:05:59
11:05:54
10:04:24
11:05:58
11:06:01
11:05:56
11:06:01
11:06:00
11:05:52
11:05:52
11:06:01
Output for the "sys_list" window under z/VM:
12:32:21 | CPU-T: UN(16)
?=help
system
#cpu
cpu
Cpu+
online memuse memmax wcur
(str)
(#)
(%)
(hm)
(dhm) (GiB) (GiB) (#)
T6360004
6 100.31 959:47 53:05:20
1.56
2.00 100
T6360005
2
0.44
1:11 3:02:26
0.42
0.50 100
T6360014
2
0.27
0:45 10:18:41
0.54
0.75 100
DTCVSW1
1
0.00
0:00 53:16:42
0.01
0.03 100
T6360002
6
0.00 166:26 40:19:18
1.87
2.00 100
OPERATOR
1
0.00
0:00 53:16:42
0.00
0.03 100
T6360008
2
0.00
0:37 30:22:55
0.32
0.75 100
T6360003
6
0.00 3700:57 53:03:09
4.00
4.00 100
NSLCF1
1
0.00
0:02 53:16:41
0.03
0.25 500
EREP
1
0.00
0:00 53:16:42
0.00
0.03 100
PERFSVM
1
0.00
0:53 2:21:12
0.04
0.06
0
TCPIP
1
0.00
0:01 53:16:42
0.01
0.12 3000
DATAMOVE
1
0.00
0:05 53:16:42
0.00
0.03 100
DIRMAINT
1
0.00
0:04 53:16:42
0.01
0.03 100
DTCVSW2
1
0.00
0:00 53:16:42
0.01
0.03 100
RACFVM
1
0.00
0:00 53:16:42
0.01
0.02 100
75 101.57 5239:47 53:16:42 15.46 22.50 3000
Output for the sys window under LPAR:
14:08:41 | H05LP30 |
cpuid
type
cpu
(#)
(str)
(%)
0
IFL 96.91
1
IFL 81.82
2
IFL 88.00
3
IFL 92.27
4
IFL 83.32
5
IFL 92.46
6
IFL
0.00
7
IFL
0.00
26
CPU-T: IFL(18) CP(3) UN(3)
? = help
mgm visual.
(%) (vis)
1.96 |############################################ |
1.46 |#####################################
|
2.43 |########################################
|
1.29 |##########################################
|
1.05 |#####################################
|
2.59 |##########################################
|
0.00 |
|
0.00 |
|
System Analysis and Tuning Guide
8
9
IFL
IFL
0.00 0.00 |
0.00 0.00 |
534.79 10.78
|
|
Output for the sys window under z/VM:
15:46:57 | T6360003 | CPU-T: UN(16)
? = help
cpuid
cpu visual
(#)
(%) (vis)
0
548.72 |#########################################
|
548.72
2.3.6 A top-like I/O Monitor: iotop
The iotop utility displays a table of I/O usage by processes or threads.
TIP
iotop is not installed by default. You need to install it manually with zypper
in iotop as root.
iotop displays columns for the I/O bandwidth read and written by each process during the sampling period. It also displays the percentage of time the process spent while
swapping in and while waiting on I/O. For each process, its I/O priority (class/level) is
shown. In addition, the total I/O bandwidth read and written during the sampling period is displayed at the top of the interface.
Use the left and right arrows to change the sorting, R to reverse the sorting order, O to
toggle the --only option, P to toggle the --processes option, A to toggle the -accumulated option, Q to quit or I to change the priority of a thread or a process'
thread(s). Any other key will force a refresh.
Following is an example output of the command iotop --only, while find and
emacs are running:
tux@mercury:~> iotop --only
Total DISK READ: 50.61 K/s | Total DISK WRITE: 11.68
TID PRIO USER
DISK READ DISK WRITE SWAPIN
3416 be/4 ke
50.61 K/s
0.00 B/s 0.00 %
275 be/3 root
0.00 B/s
3.89 K/s 0.00 %
5055 be/4 ke
0.00 B/s
3.89 K/s 0.00 %
K/s
IO>
COMMAND
4.05 % find /
2.34 % [jbd2/sda2-8]
0.04 % emacs
iotop can be also used in a batch mode (-b) and its output stored in a file for later
analysis. For a complete set of options, see the manual page (man 1 iotop).
System Monitoring Utilities
27
2.3.7 Modify a process' niceness: nice
and renice
The kernel determines which processes require more CPU time than others by the
process' nice level, also called niceness. The higher the “nice” level of a process is, the
less CPU time it will take from other processes. Nice levels range from -20 (the least
“nice” level) to 19. Negative values can only be set by root.
Adjusting the niceness level is useful when running a non time-critical process that
lasts long and uses large amounts of CPU time, such as compiling a kernel on a system that also performs other tasks. Making such a process “nicer”, ensures that the
other tasks, for example a Web server, will have a higher priority.
Calling nice without any parameters prints the current niceness:
tux@mercury:~> nice
0
Running nice command increments the current nice level for the given command
by 10. Using nice -n level command lets you specify a new niceness relative
to the current one.
To change the niceness of a running process, use renice priority -p
process id, for example:
renice +5 3266
To renice all processes owned by a specific user, use the option -u user. Process
groups are reniced by the option -g process group id.
2.4 Memory
2.4.1 Memory Usage: free
The utility free examines RAM and swap usage. Details of both free and used memory and swap areas are shown:
tux@mercury:~> free
total
Mem:
2062844
-/+ buffers/cache:
28
used
2047444
995928
System Analysis and Tuning Guide
free
15400
1066916
shared
0
buffers
129580
cached
921936
Swap:
2104472
0
2104472
The options -b, -k, -m, -g show the output in bytes, KB, MB, or GB, respectively. The parameter -d delay ensures that the display is refreshed every delay seconds. For example, free -d 1.5 produces an update every 1.5 seconds.
2.4.2 Detailed Memory Usage: /proc/
meminfo
Use /proc/meminfo to get more detailed information on memory usage than with
free. Actually free uses some of the data from this file. See an example output
from a 64-bit system below. Note that it slightly differs on 32-bit systems due to different memory management):
tux@mercury:~> cat /proc/meminfo
MemTotal:
8182956 kB
MemFree:
1045744 kB
Buffers:
364364 kB
Cached:
5601388 kB
SwapCached:
1936 kB
Active:
4048268 kB
Inactive:
2674796 kB
Active(anon):
663088 kB
Inactive(anon):
107108 kB
Active(file):
3385180 kB
Inactive(file): 2567688 kB
Unevictable:
4 kB
Mlocked:
4 kB
SwapTotal:
2096440 kB
SwapFree:
2076692 kB
Dirty:
44 kB
Writeback:
0 kB
AnonPages:
756108 kB
Mapped:
147320 kB
Slab:
329216 kB
SReclaimable:
300220 kB
SUnreclaim:
28996 kB
PageTables:
21092 kB
NFS_Unstable:
0 kB
Bounce:
0 kB
WritebackTmp:
0 kB
CommitLimit:
6187916 kB
Committed_AS:
1388160 kB
VmallocTotal:
34359738367 kB
VmallocUsed:
133384 kB
VmallocChunk:
34359570939 kB
HugePages_Total:
0
HugePages_Free:
0
System Monitoring Utilities
29
HugePages_Rsvd:
HugePages_Surp:
Hugepagesize:
DirectMap4k:
DirectMap2M:
0
0
2048 kB
2689024 kB
5691392 kB
The most important entries are:
MemTotal
Total amount of usable RAM
MemFree
Total amount of unused RAM
Buffers
File buffer cache in RAM
Cached
Page cache (excluding buffer cache) in RAM
SwapCached
Page cache in swap
Active
Recently used memory that normally is not reclaimed. This value is the sum of
memory claimed by anonymous pages (listed as Active(anon)) and file-backed
pages (listed as Active(file))
Inactive
Recently unused memory that can be reclaimed. This value is the sum of memory claimed by anonymous pages (listed as Inactive(anon)) and file-backed pages
(listed as Inactive(file)).
SwapTotal
Total amount of swap space
SwapFree
Total amount of unused swap space
Dirty
Amount of memory that will be written to disk
Writeback
Amount of memory that currently is written to disk
30
System Analysis and Tuning Guide
Mapped
Memory claimed with the mmap system call
Slab
Kernel data structure cache
SReclaimable
Reclaimable slab caches (inode, dentry, etc.)
Committed_AS
An approximation of the total amount of memory (RAM plus swap) the current
workload needs in the worst case.
2.4.3 Process Memory Usage: smaps
Exactly determining how much memory a certain process is consuming is not possible with standard tools like top or ps. Use the smaps subsystem, introduced in Kernel 2.6.14, if you need exact data. It can be found at /proc/pid/smaps and shows
you the number of clean and dirty memory pages the process with the ID PID is using at that time. It differentiates between shared and private memory, so you are able
to see how much memory the process is using without including memory shared with
other processes.
2.5 Networking
2.5.1 Basic Network Diagnostics: ifconfig
ifconfig is a powerful tool to set up and control network interfaces. As well as
this, you can use it to quickly view basic statistics about one or all network interfaces
present in the system, such as whether the interface is up, the number of errors or
dropped packets, or packet collisions.
If you run ifconfig with no additional parameter, it lists all active network interfaces. ifconfig -a lists all (even inactive) network interfaces, while ifconfig
net_interface lists statistics for the specified interface only.
# ifconfig br0
br0
Link encap:Ethernet HWaddr 00:25:90:98:6A:00
inet addr:10.100.2.76 Bcast:10.100.63.255 Mask:255.255.192.0
System Monitoring Utilities
31
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:68562268 errors:0 dropped:4609817 overruns:0 frame:0
TX packets:113273547 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:5375024474 (5126.0 Mb) TX bytes:321602834105 (306704.3
Mb)
2.5.2 Ethernet Cards in Detail: ethtool
ethtool can display and change detailed aspects of your ethernet network device.
By default it prints the current setting of the specified device.
# ethtool eth0
Settings for eth0:
Supported ports: [ TP ]
Supported link modes:
10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Full
Supports auto-negotiation: Yes
Advertised link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Full
Advertised pause frame use: No
[...]
Link detected: yes
The following table shows ethtool's options that you can use to query the device
for specific information:
Table 2.1: List of ethtool's Query Options
32
ethtool's option
it queries the device for
-a
pause parameter information
-c
interrupt coalescing information
-g
Rx/Tx (receive/transmit) ring parameter information
-i
associated driver information
-k
offload information
-S
NIC and driver-specific statistics
System Analysis and Tuning Guide
2.5.3 Show the Network Status: netstat
netstat shows network connections, routing tables (-r), interfaces (-i), masquerade connections (-M), multicast memberships (-g), and statistics (-s).
tux@mercury:~> netstat -r
Kernel IP routing table
Destination
Gateway
192.168.2.0
*
link-local
*
loopback
*
default
192.168.2.254
Genmask
255.255.254.0
255.255.0.0
255.0.0.0
0.0.0.0
tux@mercury:~> netstat -i
Kernel Interface table
Iface
MTU Met
RX-OK RX-ERR RX-DRP RX-OVR
eth0
1500
0 1624507 129056
0
0
BMNRU
lo
16436
0
23728
0
0
0
Flags
U
U
U
UG
MSS
0
0
0
0
Window
0
0
0
0
irtt
0
0
0
0
Iface
eth0
eth0
lo
eth0
TX-OK TX-ERR TX-DRP TX-OVR Flg
7055
0
0
0
23728
0
0
0 LRU
When displaying network connections or statistics, you can specify the socket type to
display: TCP (-t), UDP (-u), or raw (-r). The -p option shows the PID and name
of the program to which each socket belongs.
The following example lists all TCP connections and the programs using these connections.
mercury:~ # netstat -t -p
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address Foreign Address
State
PID/Pro
[...]
tcp
0
0 mercury:33513
www.novell.com:www-http ESTABLISHED 6862/
fi
tcp
0
352 mercury:ssh
mercury2.:trc-netpoll
ESTABLISHED
19422/s
tcp
0
0 localhost:ssh localhost:17828
ESTABLISHED -
In the following, statistics for the TCP protocol are displayed:
tux@mercury:~> netstat -s -t
Tcp:
2427 active connections openings
2374 passive connection openings
0 failed connection attempts
0 connection resets received
1 connections established
27476 segments received
26786 segments send out
54 segments retransmited
0 bad segments received.
6 resets sent
[...]
System Monitoring Utilities
33
TCPAbortOnLinger: 0
TCPAbortFailed: 0
TCPMemoryPressures: 0
2.5.4 Interactive Network Monitor: iptraf
The iptraf utility is a menu based Local Area Network (LAN) monitor. It generates network statistics, including TCP and UDP counts, Ethernet load information, IP
checksum errors and others.
TIP
iptraf is not installed by default, install it with zypper in iptraf as
root
If you enter the command without any option, it runs in an interactive mode. You can
navigate through graphical menus and choose the statistics that you want iptraf to
report. You can also specify which network interface to examine.
Figure 2.1: iptraf Running in Interactive Mode
The command iptraf understands several options and can be run in a batch mode
as well. The following example will collect statistics for network interface eth0 (-i)
for 1 minute (-t). It will be run in the background (-B) and the statistics will be written to the iptraf.log file in your home directory (-L).
tux@mercury:~> iptraf -i eth0 -t 1 -B -L ~/iptraf.log
You can examine the log file with the more command:
tux@mercury:~> more ~/iptraf.log
Mon Mar 23 10:08:02 2010; ******** IP traffic monitor started ********
34
System Analysis and Tuning Guide
Mon Mar 23 10:08:02 2010;
\
239.255.255.253:427
Mon Mar 23 10:08:02 2010;
224.0.0.18
Mon Mar 23 10:08:03 2010;
224.0.0.18
Mon Mar 23 10:08:03 2010;
224.0.0.18
[...]
Mon Mar 23 10:08:06 2010;
10.20.7.255:111
Mon Mar 23 10:08:06 2010;
10.20.7.255:8765
Mon Mar 23 10:08:06 2010;
\
10.20.7.255:111
Mon Mar 23 10:08:06 2010;
224.0.0.18
--More--(7%)
UDP; eth0; 107 bytes; from 192.168.1.192:33157 to
VRRP; eth0; 46 bytes; from 192.168.1.252 to \
VRRP; eth0; 46 bytes; from 192.168.1.252 to \
VRRP; eth0; 46 bytes; from 192.168.1.252 to \
UDP; eth0; 132 bytes; from 192.168.1.54:54395 to \
UDP; eth0; 46 bytes; from 192.168.1.92:27258 to \
UDP; eth0; 124 bytes; from 192.168.1.139:43464 to
VRRP; eth0; 46 bytes; from 192.168.1.252 to \
2.6 The /proc File System
The /proc file system is a pseudo file system in which the kernel reserves important
information in the form of virtual files. For example, display the CPU type with this
command:
tux@mercury:~> cat /proc/cpuinfo
processor
: 0
vendor_id
: GenuineIntel
cpu family
: 15
model
: 4
model name
: Intel(R) Pentium(R) 4 CPU 3.40GHz
stepping
: 3
cpu MHz
: 2800.000
cache size
: 2048 KB
physical id
: 0
[...]
Query the allocation and use of interrupts with the following command:
tux@mercury:~> cat /proc/interrupts
CPU0
0:
3577519
XT-PIC timer
1:
130
XT-PIC i8042
2:
0
XT-PIC cascade
5:
564535
XT-PIC Intel 82801DB-ICH4
7:
1
XT-PIC parport0
8:
2
XT-PIC rtc
9:
1
XT-PIC acpi, uhci_hcd:usb1, ehci_hcd:usb4
System Monitoring Utilities
35
10:
11:
12:
14:
15:
NMI:
LOC:
ERR:
MIS:
0
71772
101150
33146
149202
0
0
0
0
XT-PIC
XT-PIC
XT-PIC
XT-PIC
XT-PIC
uhci_hcd:usb3
uhci_hcd:usb2, eth0
i8042
ide0
ide1
Some of the important files and their contents are:
/proc/devices
Available devices
/proc/modules
Kernel modules loaded
/proc/cmdline
Kernel command line
/proc/meminfo
Detailed information about memory usage
/proc/config.gz
gzip-compressed configuration file of the kernel currently running
Further information is available in the text file /usr/src/linux/Documenta​
tion/filesystems/proc.txt (this file is available when the package kernel-source is installed). Find information about processes currently running in the
/proc/NNN directories, where NNN is the process ID (PID) of the relevant process.
Every process can find its own characteristics in /proc/self/:
tux@mercury:~> ls -l /proc/self
lrwxrwxrwx 1 root root 64 2007-07-16 13:03 /proc/self -> 5356
tux@mercury:~> ls -l /proc/self/
total 0
dr-xr-xr-x 2 tux users 0 2007-07-16 17:04 attr
-r-------- 1 tux users 0 2007-07-16 17:04 auxv
-r--r--r-- 1 tux users 0 2007-07-16 17:04 cmdline
lrwxrwxrwx 1 tux users 0 2007-07-16 17:04 cwd -> /home/tux
-r-------- 1 tux users 0 2007-07-16 17:04 environ
lrwxrwxrwx 1 tux users 0 2007-07-16 17:04 exe -> /bin/ls
dr-x------ 2 tux users 0 2007-07-16 17:04 fd
-rw-r--r-- 1 tux users 0 2007-07-16 17:04 loginuid
-r--r--r-- 1 tux users 0 2007-07-16 17:04 maps
-rw------- 1 tux users 0 2007-07-16 17:04 mem
-r--r--r-- 1 tux users 0 2007-07-16 17:04 mounts
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System Analysis and Tuning Guide
-rw-r--r--r--r--r-lrwxrwxrwx
-rw-------r--r--r--r--r--r-[...]
dr-xr-xr-x
-r--r--r--
1
1
1
1
1
1
tux
tux
tux
tux
tux
tux
users
users
users
users
users
users
0
0
0
0
0
0
2007-07-16
2007-07-16
2007-07-16
2007-07-16
2007-07-16
2007-07-16
17:04
17:04
17:04
17:04
17:04
17:04
oom_adj
oom_score
root -> /
seccomp
smaps
stat
3 tux users 0 2007-07-16 17:04 task
1 tux users 0 2007-07-16 17:04 wchan
The address assignment of executables and libraries is contained in the maps file:
tux@mercury:~> cat /proc/self/maps
08048000-0804c000 r-xp 00000000 03:03
0804c000-0804d000 rw-p 00004000 03:03
0804d000-0806e000 rw-p 0804d000 00:00
b7d27000-b7d5a000 r--p 00000000 03:03
b7d5a000-b7e32000 r--p 00000000 03:03
b7e32000-b7e33000 rw-p b7e32000 00:00
b7e33000-b7f45000 r-xp 00000000 03:03
b7f45000-b7f46000 r--p 00112000 03:03
b7f46000-b7f48000 rw-p 00113000 03:03
b7f48000-b7f4c000 rw-p b7f48000 00:00
b7f52000-b7f53000 r--p 00000000 03:03
[...]
b7f5b000-b7f61000 r--s 00000000 03:03
b7f61000-b7f62000 r--p 00000000 03:03
b7f62000-b7f76000 r-xp 00000000 03:03
b7f76000-b7f78000 rw-p 00013000 03:03
bfd61000-bfd76000 rw-p bfd61000 00:00
ffffe000-fffff000 ---p 00000000 00:00
17753
17753
0
11867
11868
0
8837
8837
8837
0
11842
/bin/cat
/bin/cat
[heap]
/usr/lib/locale/en_GB.utf8/
/usr/lib/locale/en_GB.utf8/
9109
9720
8828
8828
0
0
/usr/lib/gconv/gconv-module
/usr/lib/locale/en_GB.utf8/
/lib/ld-2.3.6.so
/lib/ld-2.3.6.so
[stack]
[vdso]
/lib/libc-2.3.6.so
/lib/libc-2.3.6.so
/lib/libc-2.3.6.so
/usr/lib/locale/en_GB.utf8/
2.6.1 procinfo
Important information from the /proc file system is summarized by the command
procinfo:
tux@mercury:~> procinfo
Linux 2.6.32.7-0.2-default (geeko@buildhost) (gcc 4.3.4) #1 2CPU
Memory:
Mem:
Swap:
Total
2060604
2104472
Used
2011264
112
Bootup: Wed Feb 17 03:39:33 2010
user :
nice :
system:
IOwait:
hw irq:
2:43:13.78
1d 22:21:27.87
13:39:57.57
18:02:18.59
0:03:39.44
0.8%
14.7%
4.3%
5.7%
0.0%
Free
49340
2104360
Shared
0
Buffers
200664
Load average: 0.86 1.10 1.11 3/118 21547
page
page
page
page
page
in :
71099181
out: 690734737
act: 138388345
dea:
29639529
flt: 9539791626
disk 1:
2827023r 968
System Monitoring Utilities
37
sw irq:
idle :
uptime:
1:15:35.25
9d 16:07:56.79
6d 13:07:11.14
0.4%
73.8%
irq 0: 141399308 timer
irq 1:
73784 i8042
irq 4:
2
irq 6:
5 floppy [2]
irq 7:
2
irq 8:
0 rtc
irq 9:
0 acpi
irq 12:
3
swap in :
swap out:
context :
69
209
542720687
irq 14:
5074312 ide0
irq 50:
1938076 uhci_hcd:usb1, ehci_
irq 58:
0 uhci_hcd:usb2
irq 66:
872711 uhci_hcd:usb3, HDA I
irq 74:
15 uhci_hcd:usb4
irq 82: 178717720 0
PCI-MSI e
irq169: 44352794 nvidia
irq233:
8209068 0
PCI-MSI l
To see all the information, use the parameter -a. The parameter -nN produces updates of the information every N seconds. In this case, terminate the program by
pressing q.
By default, the cumulative values are displayed. The parameter -d produces the differential values. procinfo -dn5 displays the values that have changed in the last
five seconds:
2.6.2 System Control Parameters: /proc/
sys/
System control parameters are used to modify the Linux kernel parameters at runtime.
They can be checked with the sysctl command, or by looking into /proc/sys/.
A brief description of some of /proc/sys/'s subdirectories follows.
/proc/sys/vm/
Entries in this path relate to information about the virtual memory, swapping, and
caching.
/proc/sys/kernel/
Entries in this path represent information about the task scheduler, system shared
memory, and other kernel-related parameters.
/proc/sys/fs/
Entries in this path relate to used file handles, quotas, and other file system-oriented parameters.
/proc/sys/net/
Entries in this path relate to information about network bridges, and general network parameters (mainly the ipv4/ subdirectory).
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System Analysis and Tuning Guide
2.7 Hardware Information
2.7.1 PCI Resources: lspci
NOTE: Accessing PCI configuration.
Most operating systems require root user privileges to grant access to the
computer's PCI configuration.
The command lspci lists the PCI resources:
mercury:~ # lspci
00:00.0 Host bridge: Intel Corporation 82845G/GL[Brookdale-G]/GE/PE \
DRAM Controller/Host-Hub Interface (rev 01)
00:01.0 PCI bridge: Intel Corporation 82845G/GL[Brookdale-G]/GE/PE \
Host-to-AGP Bridge (rev 01)
00:1d.0 USB Controller: Intel Corporation 82801DB/DBL/DBM \
(ICH4/ICH4-L/ICH4-M) USB UHCI Controller #1 (rev 01)
00:1d.1 USB Controller: Intel Corporation 82801DB/DBL/DBM \
(ICH4/ICH4-L/ICH4-M) USB UHCI Controller #2 (rev 01)
00:1d.2 USB Controller: Intel Corporation 82801DB/DBL/DBM \
(ICH4/ICH4-L/ICH4-M) USB UHCI Controller #3 (rev 01)
00:1d.7 USB Controller: Intel Corporation 82801DB/DBM \
(ICH4/ICH4-M) USB2 EHCI Controller (rev 01)
00:1e.0 PCI bridge: Intel Corporation 82801 PCI Bridge (rev 81)
00:1f.0 ISA bridge: Intel Corporation 82801DB/DBL (ICH4/ICH4-L) \
LPC Interface Bridge (rev 01)
00:1f.1 IDE interface: Intel Corporation 82801DB (ICH4) IDE \
Controller (rev 01)
00:1f.3 SMBus: Intel Corporation 82801DB/DBL/DBM (ICH4/ICH4-L/ICH4-M) \
SMBus Controller (rev 01)
00:1f.5 Multimedia audio controller: Intel Corporation 82801DB/DBL/DBM \
(ICH4/ICH4-L/ICH4-M) AC'97 Audio Controller (rev 01)
01:00.0 VGA compatible controller: Matrox Graphics, Inc. G400/G450 (rev 85)
02:08.0 Ethernet controller: Intel Corporation 82801DB PRO/100 VE (LOM) \
Ethernet Controller (rev 81)
Using -v results in a more detailed listing:
mercury:~ # lspci -v
[...]
00:03.0 Ethernet controller: Intel Corporation 82540EM Gigabit Ethernet \
Controller (rev 02)
Subsystem: Intel Corporation PRO/1000 MT Desktop Adapter
Flags: bus master, 66MHz, medium devsel, latency 64, IRQ 19
Memory at f0000000 (32-bit, non-prefetchable) [size=128K]
I/O ports at d010 [size=8]
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39
Capabilities: [dc] Power Management version 2
Capabilities: [e4] PCI-X non-bridge device
Kernel driver in use: e1000
Kernel modules: e1000
Information about device name resolution is obtained from the file /usr/share/
pci.ids. PCI IDs not listed in this file are marked “Unknown device.”
The parameter -vv produces all the information that could be queried by the program. To view the pure numeric values, use the parameter -n.
2.7.2 USB Devices: lsusb
The command lsusb lists all USB devices. With the option -v, print a more detailed list. The detailed information is read from the directory /proc/bus/usb/.
The following is the output of lsusb with these USB devices attached: hub, memory
stick, hard disk and mouse.
mercury:/ # lsusb
Bus 004 Device 007: ID 0ea0:2168
2.0 / Astone USB Drive
Bus 004 Device 006: ID 04b4:6830
Adapter
Bus 004 Device 005: ID 05e3:0605
Bus 004 Device 001: ID 0000:0000
Bus 003 Device 001: ID 0000:0000
Bus 002 Device 001: ID 0000:0000
Bus 001 Device 005: ID 046d:c012
Bus 001 Device 001: ID 0000:0000
Ours Technology, Inc. Transcend JetFlash \
Cypress Semiconductor Corp. USB-2.0 IDE \
Genesys Logic, Inc.
Logitech, Inc. Optical Mouse
2.8 Files and File Systems
2.8.1 Determine the File Type: file
The command file determines the type of a file or a list of files by checking /
usr/share/misc/magic.
tux@mercury:~> file /usr/bin/file
/usr/bin/file: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), \
for GNU/Linux 2.6.4, dynamically linked (uses shared libs), stripped
The parameter -f list specifies a file with a list of filenames to examine. The -z
allows file to look inside compressed files:
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System Analysis and Tuning Guide
tux@mercury:~> file /usr/share/man/man1/file.1.gz
/usr/share/man/man1/file.1.gz: gzip compressed data, from Unix, max
compression
tux@mercury:~> file -z /usr/share/man/man1/file.1.gz
/usr/share/man/man1/file.1.gz: troff or preprocessor input text \
(gzip compressed data, from Unix, max compression)
The parameter -i outputs a mime type string rather than the traditional description.
tux@mercury:~> file -i /usr/share/misc/magic
/usr/share/misc/magic: text/plain charset=utf-8
2.8.2 File Systems and Their Usage:
mount, df and du
The command mount shows which file system (device and type) is mounted at which
mount point:
tux@mercury:~> mount
/dev/sda2 on / type ext4 (rw,acl,user_xattr)
proc on /proc type proc (rw)
sysfs on /sys type sysfs (rw)
debugfs on /sys/kernel/debug type debugfs (rw)
devtmpfs on /dev type devtmpfs (rw,mode=0755)
tmpfs on /dev/shm type tmpfs (rw,mode=1777)
devpts on /dev/pts type devpts (rw,mode=0620,gid=5)
/dev/sda3 on /home type ext3 (rw)
securityfs on /sys/kernel/security type securityfs (rw)
fusectl on /sys/fs/fuse/connections type fusectl (rw)
gvfs-fuse-daemon on /home/tux/.gvfs type fuse.gvfs-fuse-daemon \
(rw,nosuid,nodev,user=tux)
Obtain information about total usage of the file systems with the command df. The
parameter -h (or --human-readable) transforms the output into a form understandable for common users.
tux@mercury:~> df -h
Filesystem
/dev/sda2
devtmpfs
tmpfs
/dev/sda3
Size
20G
1,6G
1,6G
208G
Used Avail Use% Mounted on
5,9G
13G 32% /
236K 1,6G
1% /dev
668K 1,6G
1% /dev/shm
40G 159G 20% /home
Display the total size of all the files in a given directory and its subdirectories with
the command du. The parameter -s suppresses the output of detailed information
and gives only a total for each argument. -h again transforms the output into a human-readable form:
System Monitoring Utilities
41
tux@mercury:~> du -sh /opt
192M
/opt
2.8.3 Additional Information about ELF
Binaries
Read the content of binaries with the readelf utility. This even works with ELF
files that were built for other hardware architectures:
tux@mercury:~> readelf --file-header /bin/ls
ELF Header:
Magic:
7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00
Class:
ELF64
Data:
2's complement, little endian
Version:
1 (current)
OS/ABI:
UNIX - System V
ABI Version:
0
Type:
EXEC (Executable file)
Machine:
Advanced Micro Devices X86-64
Version:
0x1
Entry point address:
0x402540
Start of program headers:
64 (bytes into file)
Start of section headers:
95720 (bytes into file)
Flags:
0x0
Size of this header:
64 (bytes)
Size of program headers:
56 (bytes)
Number of program headers:
9
Size of section headers:
64 (bytes)
Number of section headers:
32
Section header string table index: 31
2.8.4 File Properties: stat
The command stat displays file properties:
tux@mercury:~> stat /etc/profile
File: `/etc/profile'
Size: 9662
Blocks: 24
IO Block: 4096
regular file
Device: 802h/2050d Inode: 132349
Links: 1
Access: (0644/-rw-r--r--) Uid: (
0/
root)
Gid: (
0/
root)
Access: 2009-03-20 07:51:17.000000000 +0100
Modify: 2009-01-08 19:21:14.000000000 +0100
Change: 2009-03-18 12:55:31.000000000 +0100
The parameter --file-system produces details of the properties of the file system in which the specified file is located:
tux@mercury:~> stat /etc/profile --file-system
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System Analysis and Tuning Guide
File: "/etc/profile"
ID: d4fb76e70b4d1746 Namelen: 255
Type: ext2/ext3
Block size: 4096
Fundamental block size: 4096
Blocks: Total: 2581445
Free: 1717327
Available: 1586197
Inodes: Total: 655776
Free: 490312
2.9 User Information
2.9.1 User Accessing Files: fuser
It can be useful to determine what processes or users are currently accessing certain
files. Suppose, for example, you want to unmount a file system mounted at /mnt.
umount returns "device is busy." The command fuser can then be used to determine what processes are accessing the device:
tux@mercury:~> fuser -v /mnt/*
/mnt/notes.txt
USER
tux
PID ACCESS COMMAND
26597 f.... less
Following termination of the less process, which was running on another terminal,
the file system can successfully be unmounted. When used with -k option, fuser
will kill processes accessing the file as well.
2.9.2 Who Is Doing What: w
With the command w, find out who is logged onto the system and what each user is
doing. For example:
tux@mercury:~> w
14:58:43 up 1 day, 1:21, 2 users, load average: 0.00, 0.00, 0.00
USER
TTY
LOGIN@
IDLE
JCPU
PCPU WHAT
tux
:0
12:25
?xdm?
1:23
0.12s /bin/sh /usr/bin/startkde
root
pts/4
14:13
0.00s 0.06s 0.00s w
If any users of other systems have logged in remotely, the parameter -f shows the
computers from which they have established the connection.
2.10 Time and Date
System Monitoring Utilities
43
2.10.1 Time Measurement with time
Determine the time spent by commands with the time utility. This utility is available
in two versions: as a shell built-in and as a program (/usr/bin/time).
tux@mercury:~> time find . > /dev/null
real
user
sys
0m4.051s
0m0.042s
0m0.205s
The real time that elapsed from the command's start-up until it finished.
CPU time of the user as reported by the times system call.
CPU time of the system as reported by the times system call.
2.11 Graph Your Data: RRDtool
There are a lot of data in the world around you, which can be easily measured in time.
For example, changes in the temperature, or the number of data sent or received by
your computer's network interface. RRDtool can help you store and visualize such data in detailed and customizable graphs.
RRDtool is available for most UNIX platforms and Linux distributions. SUSE® Linux Enterprise Server ships RRDtool as well. Install it either with YaST or by entering
zypper install rrdtool in the command line as root.
TIP
There are Perl, Python, Ruby, or PHP bindings available for RRDtool, so that
you can write your own monitoring scripts with your preferred scripting language.
2.11.1 How RRDtool Works
RRDtool is a shortcut of Round Robin Database tool. Round Robin is a method for
manipulating with a constant amount of data. It uses the principle of a circular buffer,
where there is no end nor beginning to the data row which is being read. RRDtool uses Round Robin Databases to store and read its data.
44
System Analysis and Tuning Guide
As mentioned above, RRDtool is designed to work with data that change in time. The
ideal case is a sensor which repeatedly reads measured data (like temperature, speed
etc.) in constant periods of time, and then exports them in a given format. Such data
are perfectly ready for RRDtool, and it is easy to process them and create the desired
output.
Sometimes it is not possible to obtain the data automatically and regularly. Their format needs to be pre-processed before it is supplied to RRDtool, and often you need to
manipulate RRDtool even manually.
The following is a simple example of basic RRDtool usage. It illustrates all three important phases of the usual RRDtool workflow: creating a database, updating measured values, and viewing the output.
2.11.2 Simple Real Life Example
Suppose we want to collect and view information about the memory usage in the Linux system as it changes in time. To make the example more vivid, we measure the
currently free memory for the period of 40 seconds in 4-second intervals. During the
measuring, the three hungry applications that usually consume a lot of system memory have been started and closed: the Firefox Web browser, the Evolution e-mail client,
and the Eclipse development framework.
2.11.2.1 Collecting Data
RRDtool is very often used to measure and visualize network traffic. In such case,
Simple Network Management Protocol (SNMP) is used. This protocol can query network devices for relevant values of their internal counters. Exactly these values are to
be stored with RRDtool. For more information on SNMP, see http://www.netsnmp.org/.
Our situation is different - we need to obtain the data manually. A helper script
free_mem.sh repetitively reads the current state of free memory and writes it to
the standard output.
tux@mercury:~> cat free_mem.sh
INTERVAL=4
for steps in {1..10}
do
DATE=`date +%s`
FREEMEM=`free -b | grep "Mem" | awk '{ print $4 }'`
System Monitoring Utilities
45
sleep $INTERVAL
echo "rrdtool update free_mem.rrd $DATE:$FREEMEM"
done
Points to Notice
• The time interval is set to 4 seconds, and is implemented with the sleep command.
• RRDtool accepts time information in a special format - so called Unix time. It is defined as the number of seconds since the midnight of January 1, 1970 (UTC). For
example, 1272907114 represents 2010-05-03 17:18:34.
• The free memory information is reported in bytes with free -b. Prefer to supply
basic units (bytes) instead of multiple units (like kilobytes).
• The line with the echo ... command contains the future name of the database
file (free_mem.rrd), and together creates a command line for the purpose of
updating RRDtool values.
After running free_mem.sh, you see an output similar to this:
tux@mercury:~>
rrdtool update
rrdtool update
rrdtool update
rrdtool update
rrdtool update
rrdtool update
rrdtool update
rrdtool update
rrdtool update
rrdtool update
sh free_mem.sh
free_mem.rrd 1272974835:1182994432
free_mem.rrd 1272974839:1162817536
free_mem.rrd 1272974843:1096269824
free_mem.rrd 1272974847:1034219520
free_mem.rrd 1272974851:909438976
free_mem.rrd 1272974855:832454656
free_mem.rrd 1272974859:829120512
free_mem.rrd 1272974863:1180377088
free_mem.rrd 1272974867:1179369472
free_mem.rrd 1272974871:1181806592
It is convenient to redirect the command's output to a file with
sh free_mem.sh > free_mem_updates.log
to ease its future execution.
2.11.2.2 Creating Database
Create the initial Robin Round database for our example with the following command:
46
System Analysis and Tuning Guide
rrdtool create free_mem.rrd --start 1272974834 --step=4 \
DS:memory:GAUGE:600:U:U RRA:AVERAGE:0.5:1:24
Points to Notice
• This command creates a file called free_mem.rrd for storing our measured values in a Round Robin type database.
• The --start option specifies the time (in Unix time) when the first value will be
added to the database. In this example, it is one less than the first time value of the
free_mem.sh output (1272974835).
• The --step specifies the time interval in seconds with which the measured data
will be supplied to the database.
• The DS:memory:GAUGE:600:U:U part introduces a new data source for the
database. It is called memory, its type is gauge, the maximum number between two
updates is 600 seconds, and the minimal and maximal value in the measured range
are unknown (U).
• RRA:AVERAGE:0.5:1:24 creates Round Robin archive (RRA) whose stored
data are processed with the consolidation functions (CF) that calculates the average
of data points. 3 arguments of the consolidation function are appended to the end of
the line .
If no error message is displayed, then free_mem.rrd database is created in the
current directory:
tux@mercury:~> ls -l free_mem.rrd
-rw-r--r-- 1 tux users 776 May 5 12:50 free_mem.rrd
2.11.2.3 Updating Database Values
After the database is created, you need to fill it with the measured data. In Section 2.11.2.1, “Collecting Data” (page 45), we already prepared the file
free_mem_updates.log which consists of rrdtool update commands.
These commands do the update of database values for us.
tux@mercury:~> sh free_mem_updates.log; ls -l free_mem.rrd
-rw-r--r-- 1 tux users 776 May 5 13:29 free_mem.rrd
As you can see, the size of free_mem.rrd remained the same even after updating
its data.
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47
2.11.2.4 Viewing Measured Values
We have already measured the values, created the database, and stored the measured
value in it. Now we can play with the database, and retrieve or view its values.
To retrieve all the values from our database, enter the following on the command line:
tux@mercury:~> rrdtool fetch free_mem.rrd AVERAGE --start 1272974830 \
--end 1272974871
memory
1272974832: nan
1272974836: 1.1729059840e+09
1272974840: 1.1461806080e+09
1272974844: 1.0807572480e+09
1272974848: 1.0030243840e+09
1272974852: 8.9019289600e+08
1272974856: 8.3162112000e+08
1272974860: 9.1693465600e+08
1272974864: 1.1801251840e+09
1272974868: 1.1799787520e+09
1272974872: nan
Points to Notice
• AVERAGE will fetch average value points from the database, because only one data
source is defined (Section 2.11.2.2, “Creating Database” (page 46)) with AVERAGE processing and no other function is available.
• The first line of the output prints the name of the data source as defined in Section 2.11.2.2, “Creating Database” (page 46).
• The left results column represents individual points in time, while the right one represents corresponding measured average values in scientific notation.
• The nan in the last line stands for “not a number”.
Now a graph representing representing the values stored in the database is drawn:
tux@mercury:~> rrdtool graph free_mem.png \
--start 1272974830 \
--end 1272974871 \
--step=4 \
DEF:free_memory=free_mem.rrd:memory:AVERAGE \
LINE2:free_memory#FF0000 \
--vertical-label "GB" \
--title "Free System Memory in Time" \
--zoom 1.5 \
--x-grid SECOND:1:SECOND:4:SECOND:10:0:%X
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System Analysis and Tuning Guide
Points to Notice
• free_mem.png is the filename of the graph to be created.
• --start and --end limit the time range within which the graph will be drawn.
• --step specifies the time resolution (in seconds) of the graph.
• The DEF:... part is a data definition called free_memory. Its data are read from
the free_mem.rrd database and its data source called memory. The average value points are calculated, because no others were defined in Section 2.11.2.2, “Creating Database” (page 46).
• The LINE... part specifies properties of the line to be drawn into the graph. It is
2 pixels wide, its data come from the free_memory definition, and its color is red.
• --vertical-label sets the label to be printed along the y axis, and --title
sets the main label for the whole graph.
• --zoom specifies the zoom factor for the graph. This value must be greater than
zero.
• --x-grid specifies how to draw grid lines and their labels into the graph. Our example places them every second, while major grid lines are placed every 4 seconds.
Labels are placed every 10 seconds under the major grid lines.
Figure 2.2: Example Graph Created with RRDtool
2.11.3 For More Information
RRDtool is a very complex tool with a lot of sub-commands and command line options. Some of them are easy to understand, but you have to really study RRDtool to
make it produce the results you want and fine-tune them according to your liking.
System Monitoring Utilities
49
Apart form RRDtool's man page (man 1 rrdtool) which gives you only basic information, you should have a look at the RRDtool home page [http://
oss.oetiker.ch/rrdtool/]. There is a detailed documentation [http://
oss.oetiker.ch/rrdtool/doc/index.en.html] of the rrdtool
command and all its sub-commands. There are also several tutorials [http://
oss.oetiker.ch/rrdtool/tut/index.en.html] to help you understand
the common RRDtool workflow.
If you are interested in monitoring network traffic, have a look at MRTG [http://
oss.oetiker.ch/mrtg/]. It stands for Multi Router Traffic Grapher and can
graph the activity of all sorts of network devices. It can easily make use of RRDtool.
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3
Monitoring with Nagios
Nagios is a stable, scalable and extensible enterprise-class network and system monitoring tool which allows administrators to monitor network and host resources such as
HTTP, SMTP, POP3, disk usage and processor load. Originally Nagios was designed
to run under Linux, but it can also be used on several UNIX operating systems. This
chapter covers the installation and parts of the configuration of Nagios (http://
www.nagios.org/).
3.1 Features of Nagios
The most important features of Nagios are:
• Monitoring of network services (SMTP, POP3, HTTP, NNTP, etc.).
• Monitoring of host resources (processor load, disk usage, etc.).
• Simple plug-in design that allows administrators to develop further service checks.
• Support for redundant Nagios servers.
3.2 Installing Nagios
Install Nagios either with zypper or using YaST.
Monitoring with Nagios
51
For further information on how to install packages see:
• Section “Using Zypper” (Chapter 6, Managing Software with Command Line Tools,
↑Administration Guide)
• Section “Installing and Removing Packages or Patterns” (Chapter 9, Installing or
Removing Software, ↑Deployment Guide)
Both methods install the packages nagios and nagios-www. The later RPM package contains a Web interface for Nagios which allows, for example, to view the service status and the problem history. However, this is not absolutely necessary.
Nagios is modular designed and, thus, uses external check plug-ins to verify whether a
service is available or not. It is recommended to install the nagios-plugin RPM
package that contains ready-made check plug-ins. However, it is also possible to write
your own, custom check plug-ins.
3.3 Nagios Configuration Files
Nagios organizes the configuration files as follows:
/etc/nagios/nagios.cfg
Main configuration file of Nagios containing a number of directives which define how Nagios operates. See http://nagios.sourceforge.net/
docs/3_0/configmain.html for a complete documentation.
/etc/nagios/resource.cfg
Containing path to all Nagios plug-ins (default: /usr/lib/nagios/plug​
ins).
/etc/nagios/command.cfg
Defining the programs to be used to determine the availability of services or the
commands which are used to send e-mail notifications.
/etc/nagios/cgi.cfg
Contains options regarding the Nagios Web interface.
/etc/nagios/objects/
A directory containing object definition files. See Section 3.3.1, “Object Definition Files” (page 53) for a more complete documentation.
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System Analysis and Tuning Guide
3.3.1 Object Definition Files
In addition to those configuration files Nagios comes with very flexible and highly
customizable configuration files called Object Definition configuration files. Those
configuration files are very important since they define the following objects:
• Hosts
• Services
• Contacts
The flexibility lies in the fact that objects are easily enhanceable. Imagine you are responsible for a host with only one service running. However, you want to install another service on the same host machine and you want to monitor that service as well.
It is possible to add another service object and assign it to the host object without
huge efforts.
Right after the installation, Nagios offers default templates for object definition configuration files. They can be found at /etc/nagios/objects. In the following
see a description on how hosts, services and contacts are added:
Example 3.1: A Host Object Definition
define host {
name
host_name
address
use
check_period
check_interval
retry_interval
max_check_attempts
notification_period
notification_interval
notification_options
}
SRV1
SRV1
192.168.0.1
generic-host
24x7
5
1
10
workhours
120
d,u,r
The host_name option defines a name to identify the host that has to be monitored.
address is the IP address of this host. The use statement tells Nagios to inherit
other configuration values from the generic-host template. check_period defines
whether the machine has to be monitored 24x7. check_interval makes Nagios
checking the service every 5 minutes and retry_interval tells Nagios to schedule host check retries at 1 minute intervals. Nagios tries to execute the checks multiple times when they do not pass. You can define how many attempts Nagios should do
Monitoring with Nagios
53
with the max_check_attempts directive. All configuration flags beginning with
notification handle how Nagios should behave when a failure of a monitored
service occurs. In the host definition above, Nagios notifies the administrators only
on working hours. However, this can be adjusted with notification_period.
According to notification_interval notifications will be resend every two
hours. notification_options contains four different flags: d, u, r and
n. They control in which state Nagios should notify the administrator. d stands for a
down state, u for unreachable and r for recoveries. n does not send any notifications anymore.
Example 3.2: A Service Object Definition
define service {
use
host_name
service_description
contact_groups
check_command
}
generic-service
SRV1
PING
router-admins
check_ping!100.0,20%!500.0,60%
The first configuration directive use tells Nagios to inherit from the gener​
ic-service template. host_name is the name that assigns the service to the host
object. The host itself is defined in the host object definition. A description can be set
with service_description. In the example above the description is just PING.
Within the contact_groups option it is possible to refer to a group of people who
will be contacted on a failure of the service. This group and its members are later defined in a contact group object definition. check_command sets the program that
checks whether the service is available, or not.
Example 3.3: A Contact and Contactgroup Definition
define contact {
contact_name
use
alias
e-mail
}
admins
generic-contact
Nagios Admin
nagios@localhost
define contactgroup {
contactgroup_name
alias
members
}
router-admins
Administrators
admins
The example listing above shows the direct contact definition and its proper contactgroup. The contact definition contains the e-mail address and the name of
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System Analysis and Tuning Guide
the person who is contacted on a failure of a service. Usually this is the responsible
administrator. use inherits configuration values from the generic-contact definition.
An overview of all Nagios objects and further information about them can
be found at: http://nagios.sourceforge.net/docs/3_0/
objectdefinitions.html.
3.4 Configuring Nagios
Learn step-by-step how to configure Nagios to monitor different things like remote
services or remote host-resources.
3.4.1 Monitoring Remote Services with
Nagios
This section explains how to monitor remote services with Nagios. Proceed as follows
to monitor a remote service:
Procedure 3.1: Monitoring a Remote HTTP Service with Nagios
1 Create a directory inside /etc/nagios/objects using mkdir. You can use
any desired name for it.
2 Open /etc/nagios/nagios.conf and set cfg_dir (configuration directory) to the directory you have created in the first step.
3 Change to the configuration directory created in the first step and create the following files: hosts.cfg, services.cfg and contacts.cfg
4 Insert a host object in hosts.cfg:
define host {
name
host_name
address
use
check_period
check_interval
retry_interval
host.name.com
host.name.com
192.168.0.1
generic-host
24x7
5
1
Monitoring with Nagios
55
max_check_attempts
contact_groups
notification_interval
notification_options
10
admins
60
d,u,r
}
5 Insert a service object in services.cfg:
define service {
use
host_name
service_description
contact_groups
check_command
}
generic-service
host.name.com
HTTP
router-admins
check_http
6 Insert a contact and contactgroup object in contacts.cfg:
define contact {
contact_name
use
alias
e-mail
}
max-mustermann
generic-contact
Webserver Administrator
mmustermann@localhost
define contactgroup {
contactgroup_name
alias
members
}
admins
Administrators
max-mustermann
7 Execute rcnagios restart to (re)start Nagios.
8 Execute cat /var/log/nagios/nagios.log and verify whether the following content appears:
[1242115343]
[1242115343]
[1242115343]
[1242115343]
Nagios 3.0.6 starting... (PID=10915)
Local time is Tue May 12 10:02:23 CEST 2009
LOG VERSION: 2.0
Finished daemonizing... (New PID=10916)
If you need to monitor a different remote service, it is possible to adjust
check_command in step Step 5 (page 56). A full list of all available check
programs can be obtained by executing ls /usr/lib/nagios/plugins/check_*
See Section 3.5, “Troubleshooting” (page 58) if an error occurred.
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System Analysis and Tuning Guide
3.4.2 Monitoring Remote Host-Resources
with Nagios
This section explains how to monitor remote host resources with Nagios.
Proceed as follows on the Nagios server:
Procedure 3.2: Monitoring a Remote Host Resource with Nagios (Server)
1 Install nagios-nsca (for example, zypper in nagios-nsca).
2 Set the following options in /etc/nagios/nagios.cfg:
check_external_commands=1
accept_passive_service_checks=1
accept_passive_host_checks=1
command_file=/var/spool/nagios/nagios.cmd
3 Set the command_file option in /etc/nagios/nsca.conf to the same
file defined in /etc/nagios/nagios.conf.
4 Add another host and service object:
define host {
name
host_name
address
use
check_period
check_interval
retry_interval
max_check_attempts
active_checks_enabled
passive_checks_enabled
contact_groups
notification_interval
notification_options
}
foobar
foobar
10.10.4.234
generic-host
24x7
0
1
1
0
1
router-admins
60
d,u,r
define service {
use
host_name
service_description
active_checks_enabled
passive_checks_enabled
contact_groups
check_command
}
generic-service
foobar
diskcheck
0
1
router-admins
check_ping
Monitoring with Nagios
57
5 Execute rcnagios restart and rcnsca restart.
Proceed as follows on the client you want to monitor:
Procedure 3.3: Monitoring a Remote Host Resource with Nagios (client)
1 Install nagios-nsca-client on the host you want to monitor.
2 Write your test scripts (for example a script that checks the disk usage) like this:
#!/bin/bash
NAGIOS_SERVER=10.10.4.166
THIS_HOST=foobar
#
# Write own test algorithm here
#
# Execute On SUCCESS:
echo "$THIS_HOST;diskcheck;0;OK: test ok" \
| send_nsca -H $NAGIOS_SERVER -p 5667 -c /etc/nagios/
send_nsca.cfg -d ";"
# Execute On Warning:
echo "$THIS_HOST;diskcheck;1;Warning: test warning" \
| send_nsca -H $NAGIOS_SERVER -p 5667 -c /etc/nagios/
send_nsca.cfg -d ";"
# Execute On FAILURE:
echo "$THIS_HOST;diskcheck;2;CRITICAL: test critical" \
| send_nsca -H $NAGIOS_SERVER -p 5667 -c /etc/nagios/
send_nsca.cfg -d ";"
3 Insert a new cron entry with crontab -e. A typical cron entry could look like
this:
*/5 * * * * /directory/to/check/program/check_diskusage
3.5 Troubleshooting
Error: ABC 'XYZ' specified in ... '...' is not defined
anywhere!
Make sure that you have defined all necessary objects correctly. Be careful with
the spelling.
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System Analysis and Tuning Guide
(Return code of 127 is out of bounds - plugin may be
missing)
Make sure that you have installed nagios-plugins.
E-mail notification does not work
Make sure that you have installed and configured a mail server like postfix or exim correctly. You can verify if your mail server works with echo
"Mail Server Test!" | mail foo@bar.com which sends an e-mail
to foo@bar.com. If this e-mail arrives, your mail server is working correctly. Otherwise, check the log files of the mail server.
3.6 For More Information
The complete Nagios documentation
http://nagios.sourceforge.net/docs/3_0/toc.html
Object Configuration Overview
http://nagios.sourceforge.net/docs/3_0/
configobject.html
Object Definitions
http://nagios.sourceforge.net/docs/3_0/
objectdefinitions.html
Nagios Plugins
http://nagios.sourceforge.net/docs/3_0/plugins.html
Monitoring with Nagios
59
Analyzing and Managing
System Log Files
4
System log file analysis is one of the most important tasks when analyzing the system.
In fact, looking at the system log files should be the first thing to do when maintaining
or troubleshooting a system. SUSE Linux Enterprise Server automatically logs almost
everything that happens on the system in detail. Normally, system log files are written
in plain text and therefore, can be easily read using an editor or pager. They are also
parsable by scripts, allowing you to easily filter their content.
4.1 System Log Files in /var/log/
System log files are always located under the /var/log directory. The following
list presents an overview of all system log files from SUSE Linux Enterprise Server
present after a default installation. Depending on your installation scope, /var/log
also contains log files from other services and applications not listed here. Some files
and directories described below are “placeholders” and are only used, when the corresponding application is installed. Most log files are only visible for the user root.
acpid
Log of the advanced configuration and power interface event daemon (acpid),
a daemon to notify user-space programs of ACPI events. acpid will log all of its
activities, as well as the STDOUT and STDERR of any actions to syslog.
apparmor
AppArmor log files. See Part “Confining Privileges with AppArmor” (↑Security
Guide) for details of AppArmor.
Analyzing and Managing System Log Files
61
audit
Logs from the audit framework. See Part “The Linux Audit
Framework” (↑Security Guide) for details.
boot.msg
Log of the system init process—this file contains all boot messages from the Kernel, the boot scripts and the services started during the boot sequence.
Check this file to find out whether your hardware has been correctly initialized or
all services have been started successfully.
boot.omsg
Log of the system shutdown process - this file contains all messages issued on the
last shutdown or reboot.
ConsoleKit/*
Logs of the ConsoleKit daemon (daemon for tracking what users are logged
in and how they interact with the computer).
cups/
Access and error logs of the Common UNIX Printing System (cups).
faillog
Database file that contains all login failures. Use the faillog command to
view. See man 8 faillog for more information.
firewall
Firewall logs.
gdm/*
Log files from the GNOME display manager.
krb5
Log files from the Kerberos network authentication system.
lastlog
The lastlog file is a database which contains info on the last login of each user.
Use the command lastlog to view. See man 8 lastlog for more information.
localmessages
Log messages of some boot scripts, for example the log of the DHCP client.
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System Analysis and Tuning Guide
mail*
Mail server (postfix, sendmail) logs.
messages
This is the default place where all Kernel and system log messages go and should
be the first place (along with /var/log/warn) to look at in case of problems.
NetworkManager
NetworkManager log files
news/*
Log messages from a news server.
ntp
Logs from the Network Time Protocol daemon (ntpd).
pk_backend_zypp
PackageKit (with libzypp backend) log files.
puppet/*
Log files from the data center automation tool puppet.
samba/*
Log files from samba, the Windows SMB/CIFS file server.
SaX.log
Logs from SaX2, the SUSE advanced X11 configuration tool.
scpm
Logs from the system configuration profile management (scpm).
warn
Log of all system warnings and errors. This should be the first place (along with /
var/log/messages) to look at in case of problems.
wtmp
Database of all login/logout activities, runlevel changes and remote connections.
Use the command last to view. See man 1 last for more information.
xinetd.log
Log files from the extended Internet services daemon (xinetd).
Analyzing and Managing System Log Files
63
Xorg.0.log
X startup log file. Refer to this in case you have problems starting X. Copies from
previous X starts are numbered Xorg.?.log.
YaST2/*
All YaST log files.
zypp/*
libzypp log files. Refer to these files for the package installation history.
zypper.log
Logs from the command line installer zypper.
4.2 Viewing and Parsing Log Files
To view log files, you can use your favorite text editor. There is also a simple YaST
module for viewing /var/log/messages, available in the YaST Control Center
under Miscellaneous > System Log.
For viewing log files in a text console, use the commands less or more. Use head
and tail to view the beginning or end of a log file. To view entries appended to a
log file in real-time use tail -f. For information about how to use these tools, see
their man pages.
To search for strings or regular expressions in log files use grep. awk is useful for
parsing and rewriting log files.
4.3 Managing Log Files with
logrotate
Log files under /var/log grow on a daily basis and quickly become very big.
logrotate is a tool for large amounts of log files and helps you to manage these
files and to control their growth. It allows automatic rotation, removal, compression, and mailing of log files. Log files can be handled periodically (daily, weekly, or
monthly) or when exceeding a particular size.
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System Analysis and Tuning Guide
logrotate is usually run as a daily cron job. It does not modify any log files more
than once a day unless the log is to be modified because of its size, because logrotate is being run multiple times a day, or the --force option is used.
The main configuration file of logrotate is /etc/logrotate.conf. System
packages as well as programs that produce log files (for example, apache2) put their
own configuration files in the /etc/logrotate.d/ directory. The content of /
etc/logrotate.d/ is included via /etc/logrotate.conf.
Example 4.1: Example for /etc/logrotate.conf
# see "man logrotate" for details
# rotate log files weekly
weekly
# keep 4 weeks worth of backlogs
rotate 4
# create new (empty) log files after rotating old ones
create
# use date as a suffix of the rotated file
dateext
# uncomment this if you want your log files compressed
#compress
# comment these to switch compression to use gzip or another
# compression scheme
compresscmd /usr/bin/bzip2
uncompresscmd /usr/bin/bunzip2
# RPM packages drop log rotation information into this directory
include /etc/logrotate.d
IMPORTANT
The create option pays heed to the modes and ownerships of files specified in /etc/permissions*. If you modify these settings, make sure no
conflicts arise.
logrotate is controlled through cron and is called daily by /etc/
cron.daily/logrotate. Use /var/lib/logrotate.status to find out
when a particular file has been rotated lastly.
Analyzing and Managing System Log Files
65
4.4 Monitoring Log Files with
logwatch
logwatch is a customizable, pluggable log-monitoring script. It parses system logs,
extracts the important information and presents them in a human readable manner. To
use logwatch, install the logwatch package.
logwatch can either be used at the command-line to generate on-the-fly reports,
or via cron to regularly create custom reports. Reports can either be printed on the
screen, saved to a file, or be mailed to a specified address. The latter is especially useful when automatically generating reports via cron.
The command-line syntax is easy. You basically tell logwatch for which service,
time span and to which detail level to generate a report:
# Detailed report on all kernel messages from yesterday
logwatch --service kernel --detail High --range Yesterday --print
# Low detail report on all sshd events recorded (incl. archived logs)
logwatch --service sshd --detail Low --range All --archives --print
# Mail a report on all smartd messages from May 5th to May 7th to root@localhost
logwatch --service smartd --range 'between 5/5/2005 and 5/7/2005' \
--mailto root@localhost --print
The --range option has got a complex syntax—see logwatch --range help
for details. A list of all services that can be queried is available with the following
command:
ls /usr/share/logwatch/default.conf/services/ | sed 's/\.conf//g'
logwatch can be customized to great detail. However, the default configuration
should be sufficient in most cases. The default configuration files are located under
/usr/share/logwatch/default.conf/. Never change them because they
would get overwritten again with the next update. Rather place custom configuration
in /etc/logwatch/conf/ (you may use the default configuration file as a template, though). A detailed HOWTO on customizing logwatch is available at /usr/
share/doc/packages/logwatch/HOWTO-Customize-LogWatch. The
following config files exist:
logwatch.conf
The main configuration file. The default version is extensively commented. Each
configuration option can be overwritten on the command line.
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System Analysis and Tuning Guide
ignore.conf
Filter for all lines that should globally be ignored by logwatch.
services/*.conf
The service directory holds configuration files for each service you can generate a
report for.
logfiles/*.conf
Specifications on which log files should be parsed for each service.
4.5 Using logger to Make System
Log Entries
logger is a tool for making entries in the system log. It provides a shell command
interface to the syslog(3) system log module. For example, the following line outputs
its message in /var/log/messages:
logger -t Test "This messages comes from $USER"
Depending on the current user and hostname, /var/log/messages contains a
line similar to this:
Sep 28 13:09:31 venus Test: This messages comes from tux
Analyzing and Managing System Log Files
67
Part III. Kernel Monitoring
SystemTap—Filtering and
Analyzing System Data
5
SystemTap provides a command line interface and a scripting language to examine
the activities of a running Linux system, particularly the kernel, in fine detail. SystemTap scripts are written in the SystemTap scripting language, are then compiled
to C-code kernel modules and inserted into the kernel. The scripts can be designed
to extract, filter and summarize data, thus allowing the diagnosis of complex performance problems or functional problems. SystemTap provides information similar to
the output of tools like netstat, ps, top, and iostat. However, more filtering
and analysis options can be used for the collected information.
5.1 Conceptual Overview
Each time you run a SystemTap script, a SystemTap session is started. A number of
passes are done on the script before it is allowed to run, at which point the script is
compiled into a kernel module and loaded. In case the script has already been executed before and no changes regarding any components have occurred (for example, regarding compiler version, kernel version, library path, script contents), SystemTap does not compile the script again, but uses the *.c and *.ko data stored
in the SystemTap cache (~/.systemtap). The module is unloaded when the tap
has finished running. For an example, see the test run in Section 5.2, “Installation and
Setup” (page 74) and the respective explanation.
SystemTap—Filtering and Analyzing System Data
71
5.1.1 SystemTap Scripts
SystemTap usage is based on SystemTap scripts (*.stp). They tell SystemTap which
type of information to collect, and what to do once that information is collected.
The scripts are written in the SystemTap scripting language that is similar to AWK
and C. For the language definition, see http://sourceware.org/system​
tap/langref/.
The essential idea behind a SystemTap script is to name events, and to give them
handlers. When SystemTap runs the script, it monitors for certain events. When an
event occurs, the Linux kernel runs the handler as a sub-routine, then resumes. Thus,
events serve as the triggers for handlers to run. Handlers can record specified data and
print it in a certain manner.
The SystemTap language only uses a few data types (integers, strings, and associative
arrays of these), and full control structures (blocks, conditionals, loops, functions). It
has a lightweight punctuation (semicolons are optional) and does not need detailed declarations (types are inferred and checked automatically).
For more information about SystemTap scripts and their syntax, refer to Section 5.3,
“Script Syntax” (page 76) and to the stapprobes and stapfuncs man pages,
that are available with the systemtap-docs package.
5.1.2 Tapsets
Tapsets are a library of pre-written probes and functions that can be used in SystemTap scripts. When a user runs a SystemTap script, SystemTap checks the script's
probe events and handlers against the tapset library. SystemTap then loads the corresponding probes and functions before translating the script to C. Like SystemTap
scripts themselves, tapsets use the filename extension *.stp.
However, unlike SystemTap scripts, tapsets are not meant for direct execution—they
constitute the library from which other scripts can pull definitions. Thus, the tapset library is an abstraction layer designed to make it easier for users to define events and
functions. Tapsets provide useful aliases for functions that users may want to specify
as an event (knowing the proper alias is mostly easier than remembering specific kernel functions that might vary between kernel versions).
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System Analysis and Tuning Guide
5.1.3 Commands and Privileges
The main commands associated with SystemTap are stap and staprun. To execute them, you either need root privileges or must be a member of the stapdev or
stapusr group.
stap
SystemTap front-end. Runs a SystemTap script (either from file, or from standard input). It translates the script into C code, compiles it, and loads the resulting kernel module into a running Linux kernel. Then, the requested system trace
or probe functions are performed.
staprun
SystemTap back-end. Loads and unloads kernel modules produced by the SystemTap front-end.
For a list of options for each command, use --help. For details, refer to the stap
and the staprun man pages.
To avoid giving root access to users just for running SystemTap, you can make use
of the following SystemTap groups. They are not available by default on SUSE Linux
Enterprise, but you can create the groups and modify the access rights accordingly.
stapdev
Members of this group can run SystemTap scripts with stap, or run SystemTap instrumentation modules with staprun. As running stap involves compiling scripts into kernel modules and loading them into the kernel, members of this
group still have effective root access.
stapusr
Members of this group are only allowed to run SystemTap instrumentation modules with staprun. In addition, they can only run those modules from /lib/
modules/kernel_version/systemtap/. This directory must be owned
by root and must only be writable for the root user.
5.1.4 Important Files and Directories
The following list gives an overview of the SystemTap main files and directories.
/lib/modules/kernel_version/systemtap/
Holds the SystemTap instrumentation modules.
SystemTap—Filtering and Analyzing System Data
73
/usr/share/systemtap/tapset/
Holds the standard library of tapsets.
/usr/share/doc/packages/systemtap/examples
Holds a number of example SystemTap scripts for various purposes. Only available if the systemtap-docs package is installed.
~/.systemtap/cache
Data directory for cached SystemTap files.
/tmp/stap*
Temporary directory for SystemTap files, including translated C code and kernel
object.
5.2 Installation and Setup
As SystemTap needs information about the kernel, some kernel-related packages
must be installed in addition to the SystemTap packages. For each kernel you want to
probe with SystemTap, you need to install a set of the following packages that exactly
matches the kernel version and flavor (indicated by * in the overview below).
IMPORTANT: Repository for Packages with Debugging Information
If you subscribed your system for online updates, you can find “debuginfo”
packages in the *-Debuginfo-Updates online installation repository relevant for SUSE Linux Enterprise Server 11 SP3. Use YaST to enable the
repository.
For the classic SystemTap setup, install the following packages (using either YaST or
zypper).
• systemtap
• systemtap-server
• systemtap-docs (optional)
• kernel-*-base
• kernel-*-debuginfo
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System Analysis and Tuning Guide
• kernel-*-devel
• kernel-source-*
• gcc
To get access to the man pages and to a helpful collection of example SystemTap
scripts for various purposes, additionally install the systemtap-docs package.
To check if all packages are correctly installed on the machine and if SystemTap is
ready to use, execute the following command as root.
stap -v -e 'probe vfs.read {printf("read performed\n"); exit()}'
It probes the currently used kernel by running a script and returning an output. If the
output is similar to the following, SystemTap is successfully deployed and ready to
use:
Pass
: parsed user script and 59 library script(s) in 80usr/0sys/214real ms.
Pass
: analyzed script: 1 probe(s), 11 function(s), 2 embed(s), 1 global(s)
in
140usr/20sys/412real ms.
Pass
: translated to C into
"/tmp/stapDwEk76/stap_1856e21ea1c246da85ad8c66b4338349_4970.c" in
160usr/0sys/408real ms.
Pass
: compiled C into "stap_1856e21ea1c246da85ad8c66b4338349_4970.ko" in
2030usr/360sys/10182real ms.
Pass
: starting run.
read performed
Pass
(page 75): run completed in 10usr/20sys/257real ms.
Checks the script against the existing tapset library in /usr/share/sys​
temtap/tapset/ for any tapsets used. Tapsets are scripts that form a library
of pre-written probes and functions that can be used in SystemTap scripts.
Examines the script for its components.
Translates the script to C. Runs the system C compiler to create a kernel module from it. Both the resulting C code (*.c) and the kernel module (*.ko) are
stored in the SystemTap cache, ~/.systemtap.
Loads the module and enables all the probes (events and handlers) in the script
by hooking into the kernel. The event being probed is a Virtual File System
(VFS) read. As the event occurs on any processor, a valid handler is executed
(prints the text read performed) and closed with no errors.
After the SystemTap session is terminated, the probes are disabled, and the kernel module is unloaded.
SystemTap—Filtering and Analyzing System Data
75
In case any error messages appear during the test, check the output for hints about any
missing packages and make sure they are installed correctly. Rebooting and loading
the appropriate kernel may also be needed.
5.3 Script Syntax
SystemTap scripts consist of the following two components:
SystemTap Events (Probe Points) (page 77)
Name the kernel events at the associated handler should be executed. Examples
for events are entering or exiting a certain function, a timer expiring, or starting
or terminating a session.
SystemTap Handlers (Probe Body) (page 78)
Series of script language statements that specify the work to be done whenever a
certain event occurs. This normally includes extracting data from the event context, storing them into internal variables, or printing results.
An event and its corresponding handler is collectively called a probe. SystemTap
events are also called probe points. A probe's handler is also referred to as
probe body.
Comments can be inserted anywhere in the SystemTap script in various styles: using
either #, /* */, or // as marker.
5.3.1 Probe Format
A SystemTap script can have multiple probes. They must be written in the following
format:
probe event {statements}
Each probe has a corresponding statement block. This statement block must be enclosed in { } and contains the statements to be executed per event.
Example 5.1: Simple SystemTap Script
The following example shows a simple SystemTap script.
probe begin
{
printf ("hello world\n")
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exit ()
}
Start of the probe.
Event begin (the start of the SystemTap session).
Start of the handler definition, indicated by {.
First function defined in the handler: the printf function.
String to be printed by the printf function, followed by a line break (/n).
Second function defined in the handler: the exit() function. Note that the
SystemTap script will continue to run until the exit() function executes. If
you want to stop the execution of the script before, stop it manually by pressing
Ctrl + C.
End of the handler definition, indicated by }.
The event begin (the start of the SystemTap session) triggers the handler enclosed
in { }, in this case the printf function which prints hello world followed
by a new line , then exits.
If your statement block holds several statements, SystemTap executes these statements in sequence—you do not need to insert special separators or terminators between multiple statements. A statement block can also be nested within another statement blocks. Generally, statement blocks in SystemTap scripts use the same syntax
and semantics as in the C programming language.
5.3.2 SystemTap Events (Probe Points)
SystemTap supports a number of built-in events.
The general event syntax is a dotted-symbol sequence. This allows a breakdown of
the event namespace into parts. Each component identifier may be parametrized by a
string or number literal, with a syntax like a function call. A component may include
a * character, to expand to other matching probe points. A probe point may be followed by a ? character, to indicate that it is optional, and that no error should result if
it fails to expand. Alternately, a probe point may be followed by a ! character to indicate that it is both optional and sufficient.
SystemTap supports multiple events per probe—they need to be separated by a comma (,). If multiple events are specified in a single probe, SystemTap will execute the
handler when any of the specified events occur.
In general, events can be classified into the following categories:
SystemTap—Filtering and Analyzing System Data
77
• Synchronous events: Occur when any process executes an instruction at a particular location in kernel code. This gives other events a reference point (instruction address) from which more contextual data may be available.
An example for a synchronous event is vfs.file_operation: The entry to
the file_operation event for Virtual File System (VFS). For example, in Section 5.2, “Installation and Setup” (page 74), read is the file_operation
event used for VFS.
• Asynchronous events: Not tied to a particular instruction or location in code. This
family of probe points consists mainly of counters, timers, and similar constructs.
Examples for asynchronous events are: begin (start of a SystemTap session—
as soon as a SystemTap script is run, end (end of a SystemTap session), or timer
events. Timer events specify a handler to be executed periodically, like example
timer.s(seconds), or timer.ms(milliseconds).
When used in conjunction with other probes that collect information, timer events
allow you to print out periodic updates and see how that information changes over
time.
Example 5.2: Probe with Timer Event
For example, the following probe would print the text “hello world” every 4 seconds:
probe timer.s(4)
{
printf("hello world\n")
}
For detailed information about supported events, refer to the stapprobes man
page. The See Also section of the man page also contains links to other man pages that
discuss supported events for specific subsystems and components.
5.3.3 SystemTap Handlers (Probe Body)
Each SystemTap event is accompanied by a corresponding handler defined for that
event, consisting of a statement block.
5.3.3.1 Functions
If you need the same set of statements in multiple probes, you can place them in a
function for easy reuse. Functions are defined by the keyword function followed
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by a name. They take any number of string or numeric arguments (by value) and may
return a single string or number.
function function_name(arguments) {statements}
probe event {function_name(arguments)}
The statements in function_name are executed when the probe for event executes. The arguments are optional values passed into the function.
Functions can be defined anywhere in the script. They may take any
One of the functions needed very often was already introduced in Example 5.1, “Simple SystemTap Script” (page 76): the printf function for printing data in a
formatted way. When using the printf function, you can specify how arguments
should be printed by using a format string. The format string is included in quotation
marks and can contain further format specifiers, introduced by a % character.
Which format strings to use depends on your list of arguments. Format strings can
have multiple format specifiers—each matching a corresponding argument. Multiple
arguments can be separated by a comma.
Example 5.3: printf Function with Format Specifiers
printf (" %s (%d ) open\n ", execname(), pid())
Start of the format string, indicated by ".
String format specifier.
Integer format specifier.
End of the format string, indicated by ".
The example above would print the current executable name (execname()) as
string and the process ID (pid()) as integer in brackets, followed by a space, then
the word open and a line break:
[...]
vmware-guestd(2206) open
hald(2360) open
[...]
Apart from the two functions execname()and pid()) used in Example 5.3,
“printf Function with Format Specifiers” (page 79), a variety of other functions can be used as printf arguments.
Among the most commonly used SystemTap functions are the following:
SystemTap—Filtering and Analyzing System Data
79
tid()
ID of the current thread.
pid()
Process ID of the current thread.
uid()
ID of the current user.
cpu()
Current CPU number.
execname()
Name of the current process.
gettimeofday_s()
Number of seconds since UNIX epoch (January 1, 1970).
ctime()
Convert time into a string.
pp()
String describing the probe point currently being handled.
thread_indent()
Useful function for organizing print results. It (internally) stores an indentation
counter for each thread (tid()). The function takes one argument, an indentation delta, indicating how many spaces to add or remove from the thread's indentation counter. It returns a string with some generic trace data along with an
appropriate number of indentation spaces. The generic data returned includes a
time stamp (number of microseconds since the initial indentation for the thread),
a process name, and the thread ID itself. This allows you to identify what functions were called, who called them, and how long they took.
Call entries and exits often do not immediately precede each other (otherwise
it would be easy to match them). In between a first call entry and its exit, usually a number of other call entries and exits are made. The indentation counter
helps you match an entry with its corresponding exit as it indents the next function call in case it is not the exit of the previous one. For an example SystemTap script using thread_indent() and the respective output, refer to the
SystemTap Tutorial: http://sourceware.org/systemtap/tutori​
al/Tracing.html#fig:socket-trace.
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For more information about supported SystemTap functions, refer to the stapfuncs man page.
5.3.3.2 Other Basic Constructs
Apart from functions, you can use several other common constructs in SystemTap
handlers, including variables, conditional statements (like if/else, while loops,
for loops, arrays or command line arguments.
Variables
Variables may be defined anywhere in the script. To define one, simply choose a
name and assign a value from a function or expression to it:
foo = gettimeofday( )
Then you can use the variable in an expression. From the type of values assigned to
the variable, SystemTap automatically infers the type of each identifier (string or
number). Any inconsistencies will be reported as errors. In the example above, foo
would automatically be classified as a number and could be printed via printf()
with the integer format specifier (%d).
However, by default, variables are local to the probe they are used in: They are initialized, used and disposed of at each handler evocation. To share variables between
probes, declare them global anywhere in the script. To do so, use the global keyword outside of the probes:
Example 5.4: Using Global Variables
global count_jiffies, count_ms
probe timer.jiffies(100) { count_jiffies ++ }
probe timer.ms(100) { count_ms ++ }
probe timer.ms(12345)
{
hz=(1000*count_jiffies) / count_ms
printf ("jiffies:ms ratio %d:%d => CONFIG_HZ=%d\n",
count_jiffies, count_ms, hz)
exit ()
}
This example script computes the CONFIG_HZ setting of the kernel by using timers
that count jiffies and milliseconds, then computing accordingly. (A jiffy is the duration of one tick of the system timer interrupt. It is not an absolute time interval
unit, since its duration depends on the clock interrupt frequency of the particular
SystemTap—Filtering and Analyzing System Data
81
hardware platform). With the global statement it is possible to use the variables
count_jiffies and count_ms also in the probe timer.ms(12345). With +
+ the value of a variable is incremented by 1.
Conditional Statements
There are a number of conditional statements that you can use in SystemTap scripts.
The following are probably most common:
If/Else Statements
They are expressed in the following format:
if (condition) statement1
else statement2
The if statement compares an integer-valued expression to zero. If the condition
expression is non-zero, the first statement is executed. If the condition expression is zero, the second statement is executed. The else clause ( and ) is
optional. Both and can also be statement blocks.
While Loops
They are expressed in the following format:
while (condition) statement
As long as condition is non-zero, the statement is executed. can also be a
statement block. It must change a value so condition will eventually be zero.
For Loops
They are basically a shortcut for while loops and are expressed in the following
format:
for (initialization ; conditional ; increment ) statement
The expression specified in is used to initialize a counter for the number of
loop iterations and is executed before execution of the loop starts. The execution of the loop continues until the loop condition is false. (This expression is
checked at the beginning of each loop iteration). The expression specified in
is used to increment the loop counter. It is executed at the end of each loop iteration.
Conditional Operators
The following operators can be used in conditional statements:
==: Is equal to
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System Analysis and Tuning Guide
!=: Is not equal to
>=: Is greater than or equal to
<=: Is less than or equal to
5.4 Example Script
If you have installed the systemtap-docs package, you can find a number of
useful SystemTap example scripts in /usr/share/doc/packages/system​
tap/examples.
This section describes a rather simple example script in more detail: /
usr/share/doc/packages/systemtap/examples/net​
work/tcp_connections.stp.
Example 5.5: Monitoring Incoming TCP Connections with tcp_connections.stp
#! /usr/bin/env stap
probe begin {
printf("%6s %16s %6s %6s %16s\n",
"UID", "CMD", "PID", "PORT", "IP_SOURCE")
}
probe kernel.function("tcp_accept").return?,
kernel.function("inet_csk_accept").return? {
sock = $return
if (sock != 0)
printf("%6d %16s %6d %6d %16s\n", uid(), execname(), pid(),
inet_get_local_port(sock), inet_get_ip_source(sock))
}
This SystemTap script monitors the incoming TCP connections and helps to identify
unauthorized or unwanted network access requests in real time. It shows the following
information for each new incoming TCP connection accepted by the computer:
• User ID (UID)
• Command accepting the connection (CMD)
• Process ID of the command (PID)
• Port used by the connection (PORT)
SystemTap—Filtering and Analyzing System Data
83
• IP address from which the TCP connection originated (IP_SOUCE)
To run the script, execute
stap /usr/share/doc/packages/systemtap/examples/network/tcp_connections.stp
and follow the output on the screen. To manually stop the script, press Ctrl + C.
5.5 User-Space Probing
For debugging user-space applications (like DTrace can do), SUSE Linux Enterprise
Server 11 SP3 supports user-space probing with SystemTap: Custom probe points can
be inserted in any user-space application. Thus, SystemTap lets you use both Kerneland user-space probes to debug the behavior of the whole system.
To get the required utrace infrastructure and the uprobes Kernel module for userspace probing, you need to install the kernel-trace package in addition to the
packages listed in Section 5.2, “Installation and Setup” (page 74).
Basically, utrace implements a framework for controlling user-space tasks. It provides
an interface that can be used by various tracing “engines”, implemented as loadable
Kernel modules. The engines register callback functions for specific events, then attach to whichever thread they wish to trace. As the callbacks are made from “safe”
places in the Kernel, this allows for great leeway in the kinds of processing the functions can do. Various events can be watched via utrace, for example, system call entry and exit, fork(), signals being sent to the task, etc. More details about the utrace
infrastructure are available at http://sourceware.org/systemtap/wi​
ki/utrace.
SystemTap includes support for probing the entry into and return from a function in
user-space processes, probing predefined markers in user-space code, and monitoring
user-process events.
To check if the currently running Kernel provides the needed utrace support, use the
following command:
grep CONFIG_UTRACE /boot/config-`uname -r`
For more details about user-space probing, refer to https://
sourceware.org/systemtap/SystemTap_Beginners_Guide/user​
space-probing.html.
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5.6 For More Information
This chapter only provides a short SystemTap overview. Refer to the following links
for more information about SystemTap:
http://sourceware.org/systemtap/
SystemTap project home page.
http://sourceware.org/systemtap/wiki/
Huge collection of useful information about SystemTap, ranging from detailed
user and developer documentation to reviews and comparisons with other tools,
or Frequently Asked Questions and tips. Also contains collections of SystemTap
scripts, examples and usage stories and lists recent talks and papers about SystemTap.
http://sourceware.org/systemtap/documentation.html
Features a SystemTap Tutorial, a SystemTap Beginner's Guide, a Tapset Developer's
Guide, and a SystemTap Language Reference in PDF and HTML format. Also
lists the relevant man pages.
You can also find the SystemTap language reference and SystemTap tutorial in your
installed system under /usr/share/doc/packages/systemtap. Example
SystemTap scripts are available from the example subdirectory.
SystemTap—Filtering and Analyzing System Data
85
6
Kernel Probes
Kernel probes are a set of tools to collect Linux kernel debugging and performance
information. Developers and system administrators usually use them either to debug
the kernel, or to find system performance bottlenecks. The reported data can then be
used to tune the system for better performance.
You can insert these probes into any kernel routine, and specify a handler to be invoked after a particular break-point is hit. The main advantage of kernel probes is
that you no longer need to rebuild the kernel and reboot the system after you make
changes in a probe.
To use kernel probes, you typically need to write or obtain a specific kernel module.
Such module includes both the init and the exit function. The init function (such as
register_kprobe()) registers one or more probes, while the exit function unregisters them. The registration function defines where the probe will be inserted and
which handler will be called after the probe is hit. To register or unregister a group of
probes at one time, you can use relevant register_<probe_type>probes()
or unregister_<probe_type>probes() functions.
Debugging and status messages are typically reported with the printk kernel
routine. printk is a kernel-space equivalent of a user-space printf routine.
For more information on printk, see Logging kernel messages [http://
www.win.tue.nl/~aeb/linux/lk/lk-2.html#ss2.8]. Normally, you
can view these messages by inspecting /var/log/messages or /var/log/
syslog. For more information on log files, see Chapter 4, Analyzing and Managing
System Log Files (page 61).
Kernel Probes
87
6.1 Supported Architectures
Kernel probes are fully implemented on the following architectures:
• i386
• x86_64 (AMD-64, EM64T)
• ppc64
• arm
• ppc
Kernel probes are partially implemented on the following architectures:
• ia64 (does not support probes on instruction slot1)
• sparc64 (return probes not yet implemented)
6.2 Types of Kernel Probes
There are three types of kernel probes: kprobes, jprobes, and kretprobes. Kretprobes are sometimes referred to as return probes. You can find vivid source code
examples of all three type of kernel probes in the /usr/src/linux/sam​
ples/kprobes/ directory (package kernel-source).
6.2.1 Kprobe
Kprobe can be attached to any instruction in the Linux kernel. When it is registered,
it inserts a break-point at the first bytes of the probed instruction. When the processor
hits this break-point, the processor registers are saved, and the processing passes to
kprobes. First, a pre-handler is executed, then the probed instruction is stepped, and,
finally a post-handler is executed. The control is then passed to the instruction following the probe point.
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6.2.2 Jprobe
Jprobe is implemented through the kprobe mechanism. It is inserted on a function's
entry point and allows direct access to the arguments of the function which is being
probed. Its handler routine must have the same argument list and return value as the
probed function. It also has to end by calling the jprobe_return() function.
When jprobe is hit, the processor registers are saved, and the instruction pointer is
directed to the jprobe handler routine. The control then passes to the handler with
the same register contents as the function being probed. Finally, the handler calls the
jprobe_return() function, and switches the control back to the control function.
In general, you can insert multiple probes on one function. Jprobe is, however, limited
to only one instance per function.
6.2.3 Return Probe
Return probes are also implemented through kprobes. When the
register_kretprobe() function is called, a kprobe is attached to the entry of
the probed function. After hitting the probe, the Kernel probes mechanism saves the
probed function return address and calls a user-defined return handler. The control is
then passed back to the probed function.
Before you call register_kretprobe(), you need to set a maxactive argument, which specifies how many instances of the function can be probed at the same
time. If set too low, you will miss a certain number of probes.
6.3 Kernel probes API
Kprobe's programming interface consists of functions, which are used to register and
unregister all used kernel probes, and associated probe handlers. For a more detailed
description of these functions and their arguments, see the information sources in
Section 6.5, “For More Information” (page 91).
register_kprobe()
Inserts a break-point on a specified address. When the break-point is hit, the
pre_handler and post_handler are called.
Kernel Probes
89
register_jprobe()
Inserts a break-point in the specified address. The address has to be the address of
the first instruction of the probed function. When the break-point is hit, the specified handler is run. The handler should have the same argument list and return
type as the probed.
register_kretprobe()
Inserts a return probe for the specified function. When the probed function returns, a specified handler is run. This function returns 0 on success, or a negative
error number on failure.
unregister_kprobe(), unregister_jprobe(),
unregister_kretprobe()
Removes the specified probe. You can use it any time after the probe has been
registered.
register_kprobes(), register_jprobes(),
register_kretprobes()
Inserts each of the probes in the specified array.
unregister_kprobes(), unregister_jprobes(),
unregister_kretprobes()
Removes each of the probes in the specified array.
disable_kprobe(), disable_jprobe(), disable_kretprobe()
Disables the specified probe temporarily.
enable_kprobe(), enable_jprobe(), enable_kretprobe()
Enables temporarily disabled probes.
6.4 Debugfs Interface
With recent Linux kernels, the Kernel probes instrumentation uses the kernel debugfs
interface. It helps you list all registered probes and globally switch all the probes on or
off.
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System Analysis and Tuning Guide
6.4.1 How to List Registered Kernel
Probes
The list of all currently registered kprobes is in the /sys/kernel/de​
bug/kprobes/list file.
saturn.example.com:~ # cat /sys/kernel/debug/kprobes/list
c015d71a k vfs_read+0x0
[DISABLED]
c011a316 j do_fork+0x0
c03dedc5 r tcp_v4_rcv+0x0
The first column lists the address in the kernel where the probe is inserted. The second column prints the type of the probe: k for kprobe, j for jprobe, and r for return
probe. The third column specifies the symbol, offset and optional module name of the
probe. The following optional columns include the status information of the probe. If
the probe is inserted on a virtual address which is not valid anymore, it is marked with
[GONE]. If the probe is temporarily disabled, it is marked with [DISABLED].
6.4.2 How to Switch All Kernel Probes On
or Off
The /sys/kernel/debug/kprobes/enabled file represents a switch with
which you can globally and forcibly turn on or off all the registered kernel probes. To
turn them off, simply enter
echo "0" > /sys/kernel/debug/kprobes/enabled
on the command line as root. To turn them on again, enter
echo "1" > /sys/kernel/debug/kprobes/enabled
Note that this way you do not change the status of the probes. If a probe is temporarily disabled, it will not be enabled automatically but will remain in the [DISABLED]
state after entering the latter command.
6.5 For More Information
To learn more about kernel probes, look at the following sources of information:
Kernel Probes
91
• Thorough but more technically oriented information about kernel probes is in
/usr/src/linux/Documentation/kprobes.txt (package kenrel-source).
• Examples of all three types of probes (together with related Makefile) are
in the /usr/src/linux/samples/kprobes/ directory (package kenrel-source).
• In-depth information about Linux kernel modules and printk kernel routine is
in The Linux Kernel Module Programming Guide [http://tldp.org/LDP/
lkmpg/2.6/html/lkmpg.html]
• Practical but slightly outdated information about practical use of kernel probes is
in Kernel debugging with Kprobes [http://www.ibm.com/developer​
works/library/l-kprobes.html]
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System Analysis and Tuning Guide
Perfmon2—HardwareBased Performance
Monitoring
7
Perfmon2 is a standardized, generic interface to access the performance monitoring
unit (PMU) of a processor. It is portable across all PMU models and architectures,
supports system-wide and per-thread monitoring, counting and sampling.
7.1 Conceptual Overview
The following subsections give you a brief overview about Perfmon.
7.1.1 Perfmon2 Structure
Performance monitoring is “the action of collecting information related to how an application or system performs”. The information can be obtained from the code or the
CPU/chipset.
Modern processors contain a performance monitoring unit (PMU). The design and
functionality of a PMU is CPU specific: for example, the number of registers, counters and features supported will vary by CPU implementation.
The Perfmon interface is designed to be generic, flexible and extensible. It can monitor at the program (thread) or system levels. In either mode, it is possible to count
or sample your profile information. This uniformity makes it easier to write portable
tools. Figure 7.1, “Architecture of perfmon2” (page 94) gives an overview.
Perfmon2—Hardware-Based Performance Monitoring
93
Figure 7.1: Architecture of perfmon2
pfmon
Userspace
Generic
perfmon
Linux Kernel
Architecture- specific
perfmon
PMU
CPU Hardware
Each PMU model consists of a set of registers: the performance monitor configuration (PMC) and the performance monitor data (PMD). Only PMCs are writeable, but
both can be read. These registers store configuration information and data.
7.1.2 Sampling and Counting
Perfmon2 supports two modes where you can run your profiling: sampling or counting.
Sampling is usually expressed by an interval of time (time-based) or an occurance of
a definied number of events (event-based). Perfmon indirectly supports time-based
sampling by using an event-based sample with constant correlation to time (for example, unhalted_reference_cycles.)
In contrast, Counting is expressed in terms of a number of occurances of an event.
Both methods store their information into a sample. This sample contains information
about, for example, where a thread was or instruction pointers.
The following example demonstrates the counting of the CPU_OP_CYCLES event
and the sampling of this event, generating a sample per 100000 occurances of the
event:
pfmon --no-cmd-output -e CPU_OP_CYCLES_ALL /bin/ls
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System Analysis and Tuning Guide
1306604 CPU_OP_CYCLES_ALL
The following command gives the count of a specific function and the procentual
amount of the total cycles:
pfmon --no-cmd-output --short-smpl-periods=100000
bin/ls
# results for [28119:28119<-[28102]] (/bin/ls)
# total samples
: 12
# total buffer overflows : 0
#
#
event00
#
counts
%self
%cum
code addr
1
8.33%
8.33% 0x2000000000007180
1
8.33% 16.67% 0x20000000000195a0
1
8.33% 25.00% 0x2000000000019260
1
8.33% 33.33% 0x2000000000014e60
1
8.33% 41.67% 0x20000000001f38c0
1
8.33% 50.00% 0x20000000001ea481
1
8.33% 58.33% 0x200000000020b260
1
8.33% 66.67% 0x2000000000203490
1
8.33% 75.00% 0x2000000000203360
1
8.33% 83.33% 0x2000000000203440
1
8.33% 91.67% 0x4000000000002690
1
8.33% 100.00% 0x20000000001cfdf1
-e CPU_OP_CYCLES_ALL /
7.2 Installation
In order to use Perfmon2, first check the following preconditions:
SUSE Linux Enterprise 11
Supported architectures are IA64, x86_64. The package perf (Performance
Counters for Linux) is the supported tool for x86 and PPC64
SUSE Linux Enterprise 11 SP1
Supported architecture is IA64 only
The pfmon on SUSE Linux Enterprise11 supports the following processors (taken
from /usr/share/doc/packages/pfmon/README):
Table 7.1: Supported Processors
Model
Processor
Intel IA-64
Itanium (Merced), Itanium 2 (McKinley, Madison, Deerfield), Itanium 2
Perfmon2—Hardware-Based Performance Monitoring
95
Model
Processor
9000/9100 (Montecito, Montvale)
and Generic
AMD X86
Opteron (K8, fam 10h)
Intel X86
Intel P6 (Pentium II, Pentium Pro,
Pentium III, Pentium M); Yonah
(Core Duo, Core Solo); Netburst
(Pentium 4, Xeon); Core (Merom,
Penryn, Dunnington) Core 2 and
Quad; Atom; Nehalem; architectural
perfmon v1, v2, v3
Install the following packages depending on your architecture:
Table 7.2: Needed Packages
Architecture
Packages
ia64
pfmon
7.3 Using Perfmon
In order to use Perfmon, use the command line tool pfmon to get all your information.
NOTE: Mutual Exclusion of Perfmon and OProfile Sessions
On x86 architectures it is not possible to start a Perfmon session and a OProfile session. Only one can be run at the same time.
7.3.1 Getting Event Information
To get a list of supported events, use the option -l from pfmon to list them. Keep in
mind, this list depends on the host PMU:
pfmon -l
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ALAT_CAPACITY_MISS_ALL
ALAT_CAPACITY_MISS_FP
ALAT_CAPACITY_MISS_INT
BACK_END_BUBBLE_ALL
BACK_END_BUBBLE_FE
BACK_END_BUBBLE_L1D_FPU_RSE
...
CPU_CPL_CHANGES_ALL
CPU_CPL_CHANGES_LVL0
CPU_CPL_CHANGES_LVL1
CPU_CPL_CHANGES_LVL2
CPU_CPL_CHANGES_LVL3
CPU_OP_CYCLES_ALL
CPU_OP_CYCLES_QUAL
CPU_OP_CYCLES_HALTED
DATA_DEBUG_REGISTER_FAULT
DATA_DEBUG_REGISTER_MATCHES
DATA_EAR_ALAT
...
Get an explanation of these entries with the option -i and the event name:
pfmon -i
Name
Code
Counters
Desc
Umask
EAR
ETB
MaxIncr
Qual
Type
Set
CPU_OP_CYCLES_ALL
: CPU_OP_CYCLES_ALL
: 0x12
: [ 4 5 6 7 8 9 10 11 12 13 14 15 ]
: CPU Operating Cycles -- All CPU cycles counted
: 0x0
: None
: No
: 1 (Threshold 0)
: None
: Causal
: None
7.3.2 Enabling System-Wide Sessions
Use the --system-wide option to enable monitoring all processes that execute on
a specific CPU or sets of CPUs. You do not have to be root to do so; per default,
user level is turned on for all events (option -u).
It is possible that one system-wide session can run concurrently with other system-wide sessions as long as they do not monitor the same set of CPUs. However, you
cannot run a system-wide session together with any per-thread session.
The following examples are taken from a Itanium IA64 Montecito processor. To execute a system-wide session, perform the following procedure:
1 Detect your CPU set:
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97
pfmon -v --system-wide
...
selected CPUs (2 CPU in set, 2 CPUs online): CPU0 CPU1
2 Delimit your session. The following list describes options which are used in the examples below (refer to the man page for more details):
-e/--events
Profile only selected events. See Section 7.3.1, “Getting Event
Information” (page 96) for how to get a list.
--cpu-list
Specifies the list of processors to monitor. Without this options, all available
processors are monitored.
-t/--session-timeout
Specifies the duration of the monitor session expressed in seconds.
Use one of the three methods to start your profile session.
• Use the default events:
pfmon --cpu-list=0-2 --system-wide -k -e
CPU_OP_CYCLES_ALL,IA64_INST_RETIRED
<press ENTER to stop session>
CPU0
7670609 CPU_OP_CYCLES_ALL
CPU0
4380453 IA64_INST_RETIRED
CPU1
7061159 CPU_OP_CYCLES_ALL
CPU1
4143020 IA64_INST_RETIRED
CPU2
7194110 CPU_OP_CYCLES_ALL
CPU2
4168239 IA64_INST_RETIRED
• Use a timeout expressed in seconds:
pfmon --cpu-list=0-2 --system-wide --session-timeout=10 -k -e
CPU_OP_CYCLES_ALL,IA64_INST_RETIRED
<session to end in 10 seconds>
CPU0
69263547 CPU_OP_CYCLES_ALL
CPU0
38682141 IA64_INST_RETIRED
CPU1
87189093 CPU_OP_CYCLES_ALL
CPU1
54684852 IA64_INST_RETIRED
CPU2
64441287 CPU_OP_CYCLES_ALL
CPU2
37883915 IA64_INST_RETIRED
• Execute a command. The session is automatically started when the program
starts and automatically stopped when the program is finished:
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pfmon --cpu-list=0-1 --system-wide -u -e
CPU_OP_CYCLES_ALL,IA64_INST_RETIRED -- ls -l /dev/null
crw-rw-rw- 1 root root 1, 3 27. Mär 03:30 /dev/null
CPU0
38925 CPU_OP_CYCLES_ALL
CPU0
7510 IA64_INST_RETIRED
CPU1
9825 CPU_OP_CYCLES_ALL
CPU1
1676 IA64_INST_RETIRED
3 Press the Enter key to stop a session:
4 If you want to aggregate counts, use the -aggr option after the previous command:
pfmon --cpu-list=0-1 --system-wide -u -e
CPU_OP_CYCLES_ALL,IA64_INST_RETIRED --aggr
<press ENTER to stop session>
52655 CPU_OP_CYCLES_ALL
53164 IA64_INST_RETIRED
7.3.3 Monitoring Running Tasks
Perfmon can also monitor an existing thread. This is useful for monitoring system
daemons or programs which take a long time to start. First determine the process ID
you wish to monitor:
ps ax | grep foo
10027 pts/1
R
2:23
foo
Use the found PID for the --attach-task option of pfmon:
pfmon --attach-task=10027
3682190 CPU_OP_CYCLES_ALL
7.4 Retrieving Metrics From
DebugFS
Perfmon can collect statistics which are exported through the debug interface. The
metrics consists of mostly aggregated counts and durations.
Access the data through mounting the debug file system as root under /sys/ker​
nel/debug
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99
The data is located under /sys/kernel/debug/perfmon/ and organized
per CPU. Each CPU contains a set of metrics, accessible as ASCII file. The following data is taken from the /usr/src/linux/Documentation/perf​
mon2-debugfs.txt:
Table 7.3: Read-Only Files in /sys/kernel/debug/perfmon/cpu*/
File
Description
ctxswin_count
Number of PMU context switch in
ctxswin_ns
Number of nanoseconds spent in the
PMU context switch in routine
Average cost of the PMU context
switch in =
ctxswin_ns / ctxswin_count
ctxswout_count
Number of PMU context switch out
ctxswout_ns
Number of nanoseconds spend in the
PMU context switch out routine
Average cost of the PMU context
switch out =
ctxswout_ns / ctxswout_count
fmt_handler_calls
Number of calls to the sampling format routine that handles PMU interrupts (typically the routine that recors
a sample)
fmt_handler_ns
Number of nanoseconds spent in the
routine that handle PMU interrupt in
the sampling format
Average time spent in this
routine =
fmt_handler_ns /
fmt_handler_calls
handle_timeout_count
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Number of times the
pfm_handle_timeout() routine
File
Description
is called (used for timeout-based set
switching)
handle_work_count
Number of times
pfm_handle_work() routine is
called
ovl_intr_all_count
Number of PMU interrupts received
by the kernel
ovfl_intr_nmi_count
Number of non maskeable interrupts
(NMI) received by the kernel from
perfmon (only for X86 hardware)
ovfl_intr_ns
Number of nanoseconds spent in the
perfmon2 PMU interrupt handler routine.
Average time to handle one PMU
interrupt =
ovfl_intr_ns /
ovfl_intr_all_count
ovfl_intr_regular_count
Number of PMU interrupts which are
actually processed by the perfmon interrupt handler
ovfl_intr_replay_count
Number of PMU interrupts which
were replayed on the context switch
in or on event set switching
perfom_intr_spurious_count,
ovfl_intr_spurious_count
Number of PMU interrupts which
were dropped because there was no
active context
pfm_restart_count
Number of times pfm_restart()
is called
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101
File
Description
reset_pmds_count
Number of times
pfm_reset_pmds() is called
set_switch_count
Number of event set switches
set_switch_ns
Number of nanoseconds spent in the
set switching rountine
Average cost of switching sets =
set_switch_ns /
set_switch_count
This might be useful to compare your metrics before and after the perfmon run. For
example, collect your data first:
for i in /sys/kernel/debug/perfmon/cpu0/*; do
echo "$i:"; cat $i
done >> pfmon-before.txt
Run your performance monitoring, maybe restrict it to a specific CPU:
pfmon --cpu-list=0 ...
Collect your data again:
for i in /sys/kernel/debug//perfmon/cpu0/*; do
echo "$i:"; cat $i
done >> pfmon-after.txt
Compare these two files:
diff -u pfmon-before.txt pfmon-after.txt
7.5 For More Information
This chapter only provides a short overview. Refer to the following links for more information:
http://perfmon2.sourceforge.net/
The project home page.
http://www.iop.org/EJ/arti​
cle/1742-6596/119/4/042017/jpconf8_119_042017.pdf
A good overview as PDF.
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Chapter 8, OProfile—System-Wide Profiler (page 105)
Consult this chapter for other performance optimizations.
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OProfile—System-Wide
Profiler
8
OProfile is a profiler for dynamic program analysis. It investigates the behaviour of a
running program and gathers information. This information can be viewed and gives
hints for further optimizations.
It is not necessary to recompile or use wrapper libraries in order to use OProfile. Not
even a Kernel patch is needed. Usually, when you profile an application, a small overhead is expected, depending on work load and sampling frequency.
8.1 Conceptual Overview
OProfile consists of a Kernel driver and a daemon for collecting data. It makes use of
the hardware performance counters provided on Intel, AMD, and other processors.
OProfile is capable of profiling all code including the Kernel, Kernel modules, Kernel
interrupt handlers, system shared libraries, and other applications.
Modern processors support profiling through the hardware by performance counters.
Depending on the processor, there can be many counters and each of these can be
programmed with an event to count. Each counter has a value which determines how
often a sample is taken. The lower the value, the more often it is used.
During the post-processing step, all information is collected and instruction addresses
are mapped to a function name.
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105
8.2 Installation and Requirements
In order to make use of OProfile, install the oprofile package. OProfile works on
IA-64, AMD64, s390, and PPC64 processors.
It is useful to install the *-debuginfo package for the respective application you
want to profile. If you want to profile the Kernel, you need the debuginfo package
as well.
8.3 Available OProfile Utilities
OProfile contains several utilities to handle the profiling process and its profiled data.
The following list is a short summary of programms used in this chapter:
opannotate
Outputs annotated source or assembly listings mixed with profile information.
opcontrol
Controls the profiling sessions (start or stop), dumps profile data, and sets up parameters.
ophelp
Lists available events with short descriptions.
opimport
Converts sample database files from a foreign binary format to the native format.
opreport
Generates reports from profiled data.
8.4 Using OProfile
It is possible with OProfile to profile both Kernel and applications. When profiling
the Kernel, tell OProfile where to find the vmlinuz* file. Use the --vmlinux
option and point it to vmlinuz* (usually in /boot). If you need to profile Kernel modules, OProfile does this by default. However, make sure you read http://
oprofile.sourceforge.net/doc/kernel-profiling.html.
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Applications usually do not need to profile the Kernel, so better use the --no-vmlinux option to reduce the amount of information.
8.4.1 General Steps
In its simplest form, start the daemon, collect data, stop the daemon, and create your
report. This method is described in detail in the following procedure:
1 Open a shell and log in as root.
2 Decide if you want to profile with or without the Linux Kernel:
2a Profile With the Linux Kernel Execute the following commands, because the opcontrol command needs an uncompressed image:
cp /boot/vmlinux-`uname -r`.gz /tmp
gunzip /tmp/vmlinux*.gz
opcontrol --vmlinux=/tmp/vmlinux*
2b Profile Without the Linux Kernel Use the following command:
opcontrol --no-vmlinux
If you want to see which functions call other functions in the output, use additionally the --callgraph option and set a maximum DEPTH:
opcontrol --no-vmlinux --callgraph DEPTH
3 Start the OProfile daemon:
opcontrol --start
Using 2.6+ OProfile kernel interface.
Using log file /var/lib/oprofile/samples/oprofiled.log
Daemon started.
Profiler running.
4 Start your application you want to profile right after the previous step.
5 Stop the OProfile daemon:
opcontrol --stop
6 Dump the collected data to /var/lib/oprofile/samples:
opcontrol --dump
7 Create a report:
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107
opreport
Overflow stats not available
CPU: CPU with timer interrupt, speed 0 MHz (estimated)
Profiling through timer interrupt
TIMER:0|
samples|
%|
-----------------84877 98.3226 no-vmlinux
...
8 Shutdown the OProfile daemon:
opcontrol --shutdown
8.4.2 Getting Event Configurations
The general procedure for event configuration is as follows:
1 Use first the events CPU-CLK_UNHALTED and INST_RETIRED to find optimization opportunities.
2 Use specific events to find bottlenecks. To list them, use the command opcontrol --list-events.
If you need to profile certain events, first check the available events supported by
your processor with the ophelp command (example output generated from Intel
Core i5 CPU):
ophelp
oprofile: available events for CPU type "Intel Architectural Perfmon"
See Intel 64 and IA-32 Architectures Software Developer's Manual
Volume 3B (Document 253669) Chapter 18 for architectural perfmon events
This is a limited set of fallback events because oprofile doesn't know your
CPU
CPU_CLK_UNHALTED: (counter: all))
Clock cycles when not halted (min count: 6000)
INST_RETIRED: (counter: all))
number of instructions retired (min count: 6000)
LLC_MISSES: (counter: all))
Last level cache demand requests from this core that missed the LLC
(min count: 6000)
Unit masks (default 0x41)
---------0x41: No unit mask
LLC_REFS: (counter: all))
Last level cache demand requests from this core (min count: 6000)
Unit masks (default 0x4f)
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---------0x4f: No unit mask
BR_MISS_PRED_RETIRED: (counter: all))
number of mispredicted branches retired (precise) (min count: 500)
You can get the same output from opcontrol --list-events.
Specify the performance counter events with the option --event. Multiple options
are possible. This option needs an event name (from ophelp) and a sample rate, for
example:
opcontrol --event=CPU_CLK_UNHALTED:100000
WARNING: Be Careful with Low Sampling Rates with
CPU_CLK_UNHALTED
Setting sampling rates is dangerous as small rates cause the system to overload and freeze.
8.5 Using OProfile's GUI
The GUI for OProfile can be started as root with oprof_start, see Figure 8.1,
“GUI for OProfile” (page 109). Select your events and change the counter, if necessary. Every green line is added to the list of checked events. Hover the mouse over
the line to see a help text in the status line below. Use the Configuration tab to set the
buffer and CPU size, the verbose option and others. Click on Start to execute OProfile.
Figure 8.1: GUI for OProfile
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109
8.6 Generating Reports
Before generating a report, make sure OProfile has dumped your data to the /var/
lib/oprofile/samples directory using the command opcontrol --dump.
A report can be generated with the commands opreport or opannotate.
Calling oreport without any options gives a complete summary. With an executable
as an argument, retrieve profile data only from this executable. If you analyze applications written in C++, use the --demangle smart option.
The opannotate generates output with annotations from source code. Run it with
the following options:
opannotate --source \
--base-dirs=BASEDIR \
--search-dirs= \
--output-dir=annotated/ \
/lib/libfoo.so
The option --base-dir contains a comma separated list of paths which is stripped
from debug source files. This paths were searched prior than looking in --searchdirs. The --search-dirs option is also a comma separated list of directories to
search for source files.
NOTE: Inaccuracies in Annotated Source
Due to compiler optimization, code can disappear and appear in a different
place. Use the information in http://oprofile.sourceforge.net/
doc/debug-info.html to fully understand its implications.
8.7 For More Information
This chapter only provides a short overview. Refer to the following links for more information:
http://oprofile.sourceforge.net
The project home page.
Manpages
Details descriptions about the options of the different tools.
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/usr/share/doc/packages/oprofile/oprofile.html
Contains the OProfile manual.
http://developer.intel.com/
Architecture reference for Intel processors.
http://www.amd.com/us-en/assets/content_type/
white_papers_and_tech_docs/22007.pdf
Architecture reference for AMD Athlon/Opteron/Phenom/Turion.
http://www-01.ibm.com/chips/techlib/techlib.nsf/product​
families/PowerPC/
Architecture reference for PowerPC64 processors in IBM iSeries, pSeries, and
blade server systems.
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111
Part IV. Resource
Management
General System Resource
Management
Tuning the system is not only about optimizing the kernel or getting the most out of
your application, it begins with setting up a lean and fast system. The way you set up
your partitions and file systems can influence the server's speed. The number of active
services and the way routine tasks are scheduled also affects performance.
9
9.1 Planning the Installation
A carefully planned installation ensures that the system is basically set up exactly as
you need it for the given purpose. It also saves considerable time when fine tuning the
system. All changes suggested in this section can be made in the Installation Settings
step during the installation. See Section “Installation Settings” (Chapter 6, Installation
with YaST, ↑Deployment Guide) for details.
9.1.1 Partitioning
Depending on the server's range of applications and the hardware layout, the partitioning scheme can influence the machine's performance (although to a lesser extend only). It is beyond the scope of this manual to suggest different partition schemes for
particular workloads, however, the following rules will positively affect performance.
Of course they do not apply when using an external storage system.
• Make sure there always is some free space available on the disk, since a full disk
has got inferior performance
• Disperse simultaneous read and write access onto different disks by, for example:
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115
• using separate disks for the operating system, the data, and the log files
• placing a mail server's spool directory on a separate disk
• distributing the user directories of a home server between different disks
9.1.2 Installation Scope
Actually, the installation scope has no direct influence on the machine's performance,
but a carefully chosen scope of packages nevertheless has got advantages. It is recommended to install the minimum of packages needed to run the server. A system with
a minimum set of packages is easier to maintain and has got less potential security issues. Furthermore, a tailor made installation scope also ensures no unnecessary services are started by default.
SUSE Linux Enterprise Server lets you customize the installation scope on the Installation Summary screen. By default, you can select or remove pre-configured patterns for specific tasks, but it is also possible to start the YaST Software Manager for
a fine-grained package based selection.
One or more of the following default patterns may not be needed in all cases:
GNOME Desktop Environment
A server seldomly needs a full-blown desktop environment. In case a graphical
environment is needed, a more economical solution such as as icewm or fvwm
may also be sufficient.
X Window System
When solely administrating the server and its applications via command line, consider to not install this pattern. However, keep in mind that it is needed to run
GUI applications from a remote machine. If your application is managed by a
GUI or if you prefer the GUI version of YaST, keep this pattern.
Print Server
This pattern is only needed when you want to print from the machine.
9.1.3 Default Runlevel
A running X Window system eats up many resources and is seldomly needed on a
server. It is strongly recommended to start the system in runlevel 3 (Full multiuser
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with network, no X). You will still be able to start graphical applications from remote
or use the startx command to start a local graphical desktop.
9.2 Disabling Unnecessary
Services
The default installation starts a number of services (the number varies with the installation scope). Since each service consumes resources, it is recommended to disable the ones not needed. Run YaST > System > System Services (Runlevel) > Expert
Mode to start the services management module. When using the graphical version of
YaST you can click on the column headlines to sort the service list. Use this to get an
overview of which services are currently running or which services are started in the
server's default runlevel. Click a service to see its description. Use the Start/Stop/Refresh drop-down menu to disable the service for the running session. To permanently
disable it, use the Set/Reset drop-down menu.
The following list shows services that are started by default after the installation of
SUSE Linux Enterprise Server. Check which of the components you need, and disable
the others:
alsasound
Loads the Advanced Linux Sound System.
auditd
A daemon for the audit system (see Part “The Linux Audit Framework” (↑Security
Guide) for details). Disable if you do not use Audit.
bluez-coldplug
Handles cold plugging of Bluetooth dongles.
cups
A printer daemon.
java.binfmt_misc
Enables the execution of *.class or *.jar Java programs.
nfs
Services needed to mount NFS file systems.
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117
smbfs
Services needed to mount SMB/CIFS file systems from a Windows server.
splash / splash_early
Shows the splash screen on start-up.
9.3 File Systems and Disk Access
Hard disks are the slowest components in a computer system and therefore often the
cause for a bottleneck. Using the file system that best suits your workload helps to improve performance. Using special mount options or prioritizing a process' I/O priority
are further means to speed up the system.
9.3.1 File Systems
SUSE Linux Enterprise Server ships with a number of different file systems, including BrtFS, Ext3, Ext2, ReiserFS, and XFS. Each file system has its own advantages and disadvantages. Please refer to Chapter 1, Overview of File Systems in Linux
(↑Storage Administration Guide) for detailed information.
9.3.1.1 NFS
NFS (Version 3) tuning is covered in detail in the NFS Howto at http://
nfs.sourceforge.net/nfs-howto/. The first thing to experiment with
when mounting NFS shares is increasing the read write blocksize to 32768 by using
the mount options wsize and rsize.
9.3.2 Disabling Access Time (atime)
Updates
Whenever a file is read on a Linux file system, its access time (atime) is updated. As a
result, each read-only file access in fact causes a write operation. On a journaling file
system two write operations are triggered since the journal will be updated, too. It is
recommended to turn this feature off when you do not need to keep track of access
times. This is possibly true for file and Web servers as well as for a network storage.
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To turn off access time updates, mount the file system with the noatime option. To
do so, either edit /etc/fstab directly, or use the Fstab Options dialog when editing
or adding a partition with the YaST Partitioner.
9.3.3 Prioritizing Disk Access with ionice
The ionice command lets you prioritize disk access for single processes. This enables you to give less I/O priority to non time-critical background processes with
heavy disk access, such as backup jobs. On the other hand ionice lets you raise I/O
priority for a specific process to make sure this process has always immediate access
to the disk. You may set the following three scheduling classes:
Idle
A process from the idle scheduling class is only granted disk access when no other process has asked for disk I/O.
Best effort
The default scheduling class used for any process that has not asked for a specific
I/O priority. Priority within this class can be adjusted to a level from 0 to 7 (with
0 being the highest priority). Programs running at the same best-effort priority
are served in a round-robin fashion. Some kernel versions treat priority within the
best-effort class differently—for details, refer to the ionice(1) man page.
Real-time
Processes in this class are always granted disk access first. Fine-tune the priority
level from 0 to 7 (with 0 being the highest priority). Use with care, since it can
starve other processes.
For more details and the exact command syntax refer to the ionice(1) man page.
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119
10
Kernel Control Groups
Kernel Control Groups (abbreviated known as “cgroups”) are a kernel feature that allows aggregating or partitioning tasks (processes) and all their children into hierarchical organized groups. These hierarchical groups can be configured to show a specialized behavior that helps with tuning the system to make best use of available hardware
and network resources.
10.1 Technical Overview and
Definitions
The following terms are used in this chapter:
• “cgroup” is another name for Control Groups.
• In a cgroup there is a set of tasks (processes) associated with a set of subsystems
that act as parameters constituting an environment for the tasks.
• Subsystems provide the parameters that can be assigned and define CPU sets,
freezer, or—more general—“resource controllers” for memory, disk I/O, network
traffic, etc.
• cgroups are organized in a tree-structured hierarchy. There can be more than one
hierarchy in the system. You use a different or alternate hierarchy to cope with specific situations.
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121
• Every task running in the system is in exactly one of the cgroups in the hierarchy.
10.2 Scenario
See the following resource planning scenario for a better understanding (source: /
usr/src/linux/Documentation/cgroups/cgroups.txt):
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Figure 10.1: Resource Planning
CPUs
Top CPU Set (20%)
CPU Set 1
(60%)
CPU Set 2
(20%)
Professors
Students
Memory
Disk I/O
Professors (50%)
Professors (50%)
Students (30%)
Students (30%)
System (20%)
System (20%)
Network I/O
WWW Browsing (20%)
Professors
(15%)
Students
(5%)
Network File Systems (60%)
Others (20%)
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123
Web browsers such as Firefox will be part of the Web network class, while the NFS
daemons such as (k)nfsd will be part of the NFS network class. On the other side,
Firefox will share appropriate CPU and memory classes depending on whether a professor or student started it.
10.3 Control Group Subsystems
The following subsystems are available and can be classified as two types:
Isolation and Special Controllers
cpuset, freezer, devices, checkpoint/restart
Resource Controllers
cpu (scheduler), cpuacct, memory, disk I/O, network
Either mount each subsystem separately:
mount -t cgroup -o cpu none /cpu
mount -t cgroup -o cpuset none /cpuset
or all subsystems in one go; you can use an arbitrary device name (e.g., none), which
will appear in /proc/mounts:
mount -t cgroup none /sys/fs/cgroup
Some additional information on available subsystems:
Cpuset (Isolation)
Use cpuset to tie processes to system subsets of CPUs and memory (“memory
nodes”). For an example, see Section 10.4.3, “Example: Cpusets” (page 128).
Freezer (Control)
The Freezer subsystem is useful for high-performance computing clusters (HPC
clusters). Use it to freeze (stop) all tasks in a group or to stop tasks, if they reach
a defined checkpoint. For more information, see /usr/src/linux/Docu​
mentation/cgroups/freezer-subsystem.txt.
Here are basic commands to use the freezer subsystem:
mount -t cgroup -o freezer freezer /freezer
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# Create a child cgroup:
mkdir /freezer/0
# Put a task into this cgroup:
echo $task_pid > /freezer/0/tasks
# Freeze it:
echo FROZEN > /freezer/0/freezer.state
# Unfreeze (thaw) it:
echo THAWED > /freezer/0/freezer.state
Checkpoint/Restart (Control)
Save the state of all processes in a cgroup to a dump file. Restart it later (or just
save the state and continue).
Move a “saved container” between physical machines (as VM can do).
Dump all process images of a cgroup to a file.
Devices (Isolation)
A system administrator can provide a list of devices that can be accessed by
processes under cgroups.
It limits access to a device or a file system on a device to only tasks that belong
to the specified cgroup. For more information, see /usr/src/linux/Docu​
mentation/cgroups/devices.txt.
Cpuacct (Control)
The CPU accounting controller groups tasks using cgroups and accounts the CPU
usage of these groups. For more information, see /usr/src/linux/Docu​
mentation/cgroups/cpuacct.txt.
CPU (Resource Control)
Share CPU bandwidth between groups with the group scheduling function of CFS
(the scheduler). Mechanically complicated.
Memory (Resource Control)
• Limits memory usage of user space processes.
• Control swap usage by setting swapaccount=1 as a kernel boot parameter.
• Limit LRU (Least Recently Used) pages.
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125
• Anonymous and file cache.
• No limits for kernel memory.
• Maybe in another subsystem if needed.
For more information, see /usr/src/linux/Documenta​
tion/cgroups/memory.txt.
Blkio (Resource Control)
The blkio (Block IO) controller is now available as a disk I/O controller. With the
blkio controller you can currently set policies for proportional bandwidth and for
throttling.
These are the basic commands to configure proportional weight division of bandwidth by setting weight values in blkio.weight:
# Setup in /sys/fs/cgroup
mkdir /sys/fs/cgroup/blkio
mount -t cgroup -o blkio none /sys/fs/cgroup/blkio
# Start two cgroups
mkdir -p /sys/fs/cgroup/blkio/group1 /sys/fs/cgroup/blkio/group2
# Set weights
echo 1000 > /sys/fs/cgroup/blkio/group1/blkio.weight
echo 500 > /sys/fs/cgroup/blkio/group2/blkio.weight
# Write the PIDs of the processes to be controlled to the
# appropriate groups
command1 &
echo $! > /sys/fs/cgroup/blkio/group1/tasks
command2 &
echo $! > /sys/fs/cgroup/blkio/group2/tasks
These are the basic commands to configure throttling or upper limit policy by
setting values in blkio.throttle.read_bps_device for reads and
blkio.throttle.write_bps_device for writes:
# Setup in /sys/fs/cgroup
mkdir /sys/fs/cgroup/blkio
mount -t cgroup -o blkio none /sys/fs/cgroup/blkio
# Bandwidth rate of a device for the root group; format:
# <major>:<minor> <byes_per_second>
echo "8:16 1048576" > /sys/fs/cgroup/blkio/
blkio.throttle.read_bps_device
For more information about caveats, usage scenarios, and additional parameters, see /usr/src/linux/Documentation/cgroups/blkiocontroller.txt.
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Network Traffic (Resource Control)
With cgroup_tc, a network traffic controller is available. It can be used
to manage traffic that is associated with the tasks in a cgroup. Additionally,
cls_flow can classify packets based on the tc_classid field in the packet.
For example, to limit the traffic from all tasks from a file_server cgroup to
100 Mbps, proceed as follows:
# create a file_transfer cgroup and assign it a unique classid
# of 0x10 - this will be used later to direct packets.
mkdir -p /dev/cgroup
mount -t cgroup tc -otc /dev/cgroup
mkdir /dev/cgroup/file_transfer
echo 0x10 > /dev/cgroup/file_transfer/tc.classid
echo $PID_OF_FILE_XFER_PROCESS > /dev/cgroup/file_transfer/tasks
# Now create an HTB class that rate-limits traffic to 100 mbits and
attach
# a filter to direct all traffic from the file_transfer cgroup
# to this new class.
tc qdisc add dev eth0 root handle 1: htb
tc class add dev eth0 parent 1: classid 1:10 htb rate 100mbit ceil
100mbit
tc filter add dev eth0 parent 1: handle 800 protocol ip prio 1 \
flow map key cgroup-classid baseclass 1:10
This example is taken from https://lwn.net/Articles/291161/,
where you can find more information about this feature.
10.4 Using Controller Groups
10.4.1 Prerequisites
To conveniently use cgroups, install the following additional packages:
• libcgroup1 — basic user space tools to simplify resource management
• cpuset — contains the cset to manipulate cpusets
• libcpuset1 — C API to cpusets
• kernel-source — only needed for documentation purposes
• lxc — Linux container implementation
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10.4.2 Checking the Environment
The kernel shipped with SUSE Linux Enterprise Server supports cgroups. There is no
need to apply additional patches. Execute lxc-checkconfig to see a cgroups environment similar to the following output:
--- Namespaces --Namespaces: enabled
Utsname namespace: enabled
Ipc namespace: enabled
Pid namespace: enabled
User namespace: enabled
Network namespace: enabled
Multiple /dev/pts instances: enabled
--- Control groups --Cgroup: enabled
Cgroup namespace: enabled
Cgroup device: enabled
Cgroup sched: enabled
Cgroup cpu account: enabled
Cgroup memory controller: enabled
Cgroup cpuset: enabled
--- Misc --Veth pair device: enabled
Macvlan: enabled
Vlan: enabled
File capabilities: enabled
To find out which subsystems are available, proceed as follows:
mkdir /cgroups
mount -t cgroup none /cgroups
grep cgroup /proc/mounts
The following subsystems are available: perf_event, blkio, net_cls, freezer, devices,
memory, cpuacct, cpu, cpuset.
10.4.3 Example: Cpusets
With the command line proceed as follows:
1 To determine the number of CPUs and memory nodes see /proc/cpuinfo and
/proc/zoneinfo.
2 Create the cpuset hierarchy as a virtual file system (source: /usr/src/linux/Documentation/cgroups/cpusets.txt):
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mount -t cgroup -ocpuset cpuset /sys/fs/cgroup/cpuset
cd /sys/fs/cgroup/cpuset
mkdir Charlie
cd Charlie
# List of CPUs in this cpuset:
echo 2-3 > cpuset.cpus
# List of memory nodes in this cpuset:
echo 1 > cpuset.mems
echo $$ > tasks
# The subshell 'sh' is now running in cpuset Charlie
# The next line should display '/Charlie'
cat /proc/self/cpuset
3 Remove the cpuset using shell commands:
rmdir /sys/fs/cgroup/cpuset/Charlie
This fails as long as this cpuset is in use. First, you must remove the inside cpusets
or tasks (processes) that belong to it. Check it with:
cat /sys/fs/cgroup/cpuset/Charlie/tasks
For background information and additional configuration flags, see /usr/src/
linux/Documentation/cgroups/cpusets.txt.
With the cset tool, proceed as follows:
# Determine the number of CPUs and memory nodes
cset set --list
# Creating the cpuset hierarchy
cset set --cpu=2-3 --mem=1 --set=Charlie
# Starting processes in a cpuset
cset proc --set Charlie --exec -- stress -c 1 &
# Moving existing processes to a cpuset
cset proc --move --pid PID --toset=Charlie
# List task in a cpuset
cset proc --list --set Charlie
# Removing a cpuset
cset set --destroy Charlie
10.4.4 Example: cgroups
Using shell commands, proceed as follows:
1 Create the cgroups hierarchy:
mount -t cgroup cgroup /sys/fs/cgroup
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129
cd /sys/fs/cgroup/cpuset/cgroup
mkdir priority
cd priority
cat cpu.shares
2 Understanding cpu.shares:
• 1024 is the default (for more information, see /Documentation/sched​
uler/sched-design-CFS.txt) = 50% utilization
• 1524 = 60% utilization
• 2048 = 67% utilization
• 512 = 40% utilization
3 Changing cpu.shares
echo 1024 > cpu.shares
10.5 For More Information
• Kernel documentation (package kernel-source): files in /usr/src/lin​
ux/Documentation/cgroups:
• /usr/src/linux/Documentation/cgroups/blkiocontroller.txt
• /usr/src/linux/Documentation/cgroups/cgroups.txt
• /usr/src/linux/Documentation/cgroups/cpuacct.txt
• /usr/src/linux/Documentation/cgroups/cpusets.txt
• /usr/src/linux/Documentation/cgroups/devices.txt
• /usr/src/linux/Documentation/cgroups/freez​
er-subsystem.txt
• /usr/src/linux/Documentation/cgroups/
memcg_test.txt
• /usr/src/linux/Documentation/cgroups/memory.txt
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• /usr/src/linux/Documentation/cgroups/
resource_counter.txt
• For Linux Containers (LXC) based on cgroups, see Virtualization with Linux Containers (LXC) (↑Virtualization with Linux Containers (LXC)).
• http://lwn.net/Articles/243795/—Corbet, Jonathan: Controlling
memory use in containers (2007).
• http://lwn.net/Articles/236038/—Corbet, Jonathan: Process containers (2007).
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11
Power Management
Power management aims at reducing operating costs for energy and cooling systems
while at the same time keeping the performance of a system at a level that matches
the current requirements. Thus, power management is always a matter of balancing
the actual performance needs and power saving options for a system. Power management can be implemented and used at different levels of the system. A set of specifications for power management functions of devices and the operating system interface to them has been defined in the Advanced Configuration and Power Interface (ACPI). As power savings in server environments can primarily be achieved
on processor level, this chapter introduces some of the main concepts and highlights
some tools for analyzing and influencing relevant parameters.
11.1 Power Management at CPU
Level
At CPU level, you can control power usage in various ways: for example, by using
idling power states (C-states), changing CPU frequency (P-states), and throttling the
CPU (T-states). The following sections give a short introduction to each approach and
its significance for power savings. Detailed specifications can be found at http://
www.acpi.info/spec.htm.
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11.1.1 C-States (Processor Operating
States)
Modern processors have several power saving modes called C-states. They reflect the capability of an idle processor to turn off unused components in order to save
power. Whereas C-states have been available for laptops for some time, they are a
rather recent trend in the server market (for example, with Intel* processors, C-modes
are only available since Nehalem).
When a processor runs in the C0 state, it is executing instructions. A processor running in any other C-state is idle. The higher the C number, the deeper the CPU sleep
mode: more components are shut down to save power. Deeper sleep states are very
efficient concerning power consumption in an idle system. But the downside is that
they introduce higher latency (the time the CPU needs to go back to C0). Depending
on the workload (threads waking up, triggering some CPU utilization and then going
back to sleep again for a short period of time) or hardware (for example, interrupt activity of a network device), disabling the deepest sleep states can significantly increase
overall performance. For details on how to do so, refer to Section 11.3.2.2, “Viewing
and Modifying Kernel Idle Statistics with cpupower” (page 143).
Some states also have submodes with different power saving latency levels. Which Cstates and submodes are supported depends on the respective processor. However, C1
is always available.
Table 11.1, “C-States” (page 134) gives an overview of the most common C-states.
Table 11.1: C-States
134
Mode
Definition
C0
Operational state. CPU fully turned
on.
C1
First idle state. Stops CPU main internal clocks via software. Bus interface
unit and APIC are kept running at full
speed.
C2
Stops CPU main internal clocks via
hardware. State where the proces-
System Analysis and Tuning Guide
Mode
Definition
sor maintains all software-visible
states, but may take longer to wake up
through interrupts.
C3
Stops all CPU internal clocks. The
processor does not need to keep its
cache coherent, but maintains other states. Some processors have variations of the C3 state that differ in
how long it takes to wake the processor through interrupts.
To avoid needless power consumption, it is recommended to test your workloads with
deep sleep states enabled versus deep sleep states disabled. A recent maintenance
update for SUSE Linux Enterprise Server 11 SP3 provides an updated cpupower package with an additional cpupower subcommand. Use it to disable or enable
individual C-states, if necessary. For more information, refer to Section 11.3.2.2,
“Viewing and Modifying Kernel Idle Statistics with cpupower” (page 143) or the
cpupower-idle-set(1) man page.
11.1.2 P-States (Processor Performance
States)
While a processor operates (in C0 state), it can be in one of several CPU performance
states (P-states). Whereas C-states are idle states (all but C0), P-states are
operational states that relate to CPU frequency and voltage.
The higher the P-state, the lower the frequency and voltage at which the processor
runs. The number of P-states is processor-specific and the implementation differs
across the various types. However, P0 is always the highest-performance state. Higher
P-state numbers represent slower processor speeds and lower power consumption. For
example, a processor in P3 state runs more slowly and uses less power than a processor running at P1 state. To operate at any P-state, the processor must be in the C0
state where the processor is working and not idling. The CPU P-states are also defined in the Advanced Configuration and Power Interface (ACPI) specification, see
http://www.acpi.info/spec.htm.
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C-states and P-states can vary independently of one another.
11.1.3 T-States (Processor Throttling
States)
T-states refer to throttling the processor clock to lower frequencies in order to reduce
thermal effects. This means that the CPU is forced to be idle a fixed percentage of
its cycles per second. Throttling states range from T1 (the CPU has no forced idle cycles) to Tn, with the percentage of idle cycles increasing the greater n is.
Note that throttling does not reduce voltage and since the CPU is forced to idle part of
the time, processes will take longer to finish and will consume more power instead of
saving any power.
T-states are only useful if reducing thermal effects is the primary goal. Since T-states
can interfere with C-states (preventing the CPU from reaching higher C-states), they
can even increase power consumption in a modern CPU capable of C-states.
11.1.4 Turbo Features
Since quite some time, CPU power consumption and performance tuning is not only about frequency scaling anymore. In modern processors, a combination of different means is used to achieve the optimum balance between performance and power
savings: deep sleep states, traditional dynamic frequency scaling and hidden boost frequencies. The turbo features (Turbo CORE* or Turbo Boost*) of the latest AMD* or
Intel* processors allow to dynamically increase (boost) the clock speed of active CPU
cores while other cores are in deep sleep states. This increases the performance of active threads while still complying to Thermal Design Power (TDP) limits.
However, the conditions under which a CPU core may use turbo frequencies are very
architecture-specific. Learn how to evaluate the efficiency of those new features in
Section 11.3.2, “Using the cpupower Tools” (page 141).
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11.2 The Linux Kernel CPUfreq
Infrastructure
Processor performance states (P-states) and processor operating states (C-states) are
the capability of a processor to switch between different supported operating frequencies and voltages to modulate power consumption.
In order to dynamically scale processor frequencies at runtime, you can use the
CPUfreq infrastructure to set a static or dynamic power policy for the system. Its
main components are the CPUfreq subsystem (providing a common interface to the
various low-level technologies and high-level policies) , the in-kernel governors (policy governors that can change the CPU frequency based on different criteria) and
CPU-specific drivers that implement the technology for the specific processor.
The dynamic scaling of the clock speed helps to consume less power and generate less
heat when not operating at full capacity.
11.2.1 In-Kernel Governors
You can think of the in-kernel governors as a sort of pre-configured power schemes
for the CPU. The CPUfreq governors use P-states to change frequencies and lower power consumption. The dynamic governors can switch between CPU frequencies, based on CPU utilization to allow for power savings while not sacrificing performance. These governors also allow for some tuning so you can customize and change
the frequency scaling behavior.
The following governors are available with the CPUfreq subsystem:
Performance Governor
The CPU frequency is statically set to the highest possible for maximum performance. Consequently, saving power is not the focus of this governor.
Tuning options: The range of maximum frequencies available to the governor can
be adjusted (for example, with the cpupower command line tool).
Powersave Governor
The CPU frequency is statically set to the lowest possible. This can have severe
impact on the performance, as the system will never rise above this frequency no
matter how busy the processors are.
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However, using this governor often does not lead to the expected power savings
as the highest savings can usually be achieved at idle through entering C-states.
Due to running processes at the lowest frequency with the powersave governor,
processes will take longer to finish, thus prolonging the time for the system to enter any idle C-states.
Tuning options: The range of minimum frequencies available to the governor can
be adjusted (for example, with the cpupower command line tool).
On-demand Governor
The kernel implementation of a dynamic CPU frequency policy: The governor
monitors the processor utilization. As soon as it exceeds a certain threshold, the
governor will set the frequency to the highest available. If the utilization is less
than the threshold, the next lowest frequency is used. If the system continues to
be underemployed, the frequency is again reduced until the lowest available frequency is set.
For SUSE Linux Enterprise, the on-demand governor is the default governor and
the one that has the best test coverage.
Tuning options: The range of available frequencies, the rate at which the governor checks utilization, and the utilization threshold can be adjusted. Another parameter you might want to change for the on-demand governor is
ignore_nice_load. For details, refer to Procedure 11.1, “Ignoring Nice Values in Processor Utilization” (page 147).
Conservative Governor
Similar to the on-demand implementation, this governor also dynamically adjusts frequencies based on processor utilization, except that it allows for a more
gradual increase in power. If processor utilization exceeds a certain threshold, the
governor does not immediately switch to the highest available frequency (as the
on-demand governor does), but only to next higher frequency available.
Tuning options: The range of available frequencies, the rate at which the governor checks utilization, the utilization thresholds, and the frequency step rate can
be adjusted.
11.2.2 Related Files and Directories
If the CPUfreq subsystem in enabled on your system (which it is by default with
SUSE Linux Enterprise Server), you can find the relevant files and directories under
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/sys/devices/system/cpu/. If you list the contents of this directory, you will
find a cpu{0..x} subdirectory for each processor, and several other files and directories. A cpufreq subdirectory in each processor directory holds a number of files
and directories that define the parameters for CPUfreq. Some of them are writable
(for root), some of them are read-only. If your system currently uses the on-demand
or conservative governor, you will see a separate subdirectory for those governors in
cpufreq, containing the parameters for the governors.
NOTE: Different Processor Settings
The settings under the cpufreq directory can be different for each processor. If you want to use the same policies across all processors, you need
to adjust the parameters for each processor. Instead of looking up or modifying the current settings manually (in /sys/devices/system/cpu*/
cpufreq), we advise to use the tools provided by the cpupower package
or by the older cpufrequtils package for that.
11.3 Viewing, Monitoring and
Tuning Power-related Settings
The following command line tools are available for that purpose:
Using the cpufrequtils Tools (page 140)
With the tools of the cpufrequtils package you can view and modify settings of the kernel-related CPUfreq subsystem. The cpufreq* commands are
useful for modifying settings related to P-states, especially frequency scaling and
CPUfreq governors.
Using the cpupower Tools (page 141)
The new cpupower tool was designed to give an overview of all CPU power-related parameters that are supported on a given machine, including turbo (or boost)
states. Use the tool set to view and modify settings of the kernel-related CPUfreq
and cpuidle systems as well as other settings not related to frequency scaling or
idle states. The integrated monitoring framework can access both Kernel-related parameters and hardware statistics and is thus ideally suited for performance
benchmarks. It also helps you to identify the dependencies between turbo and idle
states.
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Monitoring Power Consumption with powerTOP (page 145)
powerTOP combines various sources of information (analysis of programs, device drivers, kernel options, amounts and sources of interrupts waking up processors from sleep states) and shows them in one screen. The tool helps you to identify the reasons for unnecessary high power consumption (for example, processes that are mainly responsible for waking up a processor from its idle state) and to
optimize your system settings to avoid these.
11.3.1 Using the cpufrequtils Tools
NOTE: cpupower and cpufrequtils
All functions of cpufrequtils are also covered by cpupower—a new set
of tools that is more powerful and provides additional features. As cpupower
will replace cpufrequtils sooner or later, we advise to switch to cpupower soon and to adjust your scripts accordingly.
After you have installed the cpufrequtils package, you can make use of the
cpufreq-info and cpufreq-set command line tools.
11.3.1.1 Viewing Current Settings with cpufreqinfo
The cpufreq-info command helps you to retrieve CPUfreq kernel information.
Run without any options, it collects the information available for your system:
Example 11.1: Example Output of cpufreq-info
cpufrequtils 004: cpufreq-info (C) Dominik Brodowski 2004-2006
Report errors and bugs to http://bugs.opensuse.org, please.
analyzing CPU 0:
driver: acpi-cpufreq
CPUs which need to switch frequency at the same time: 0
hardware limits: 2.80 GHz - 3.40 GHz
available frequency steps: 3.40 GHz, 2.80 GHz
available cpufreq governors: conservative, userspace, powersave, ondemand, performance
current policy: frequency should be within 2.80 GHz and 3.40 GHz.
The governor "performance" may decide which speed to use
within this range.
current CPU frequency is 3.40 GHz.
analyzing CPU 1:
driver: acpi-cpufreq
CPUs which need to switch frequency at the same time: 1
hardware limits: 2.80 GHz - 3.40 GHz
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available frequency steps: 3.40 GHz, 2.80 GHz
available cpufreq governors: conservative, userspace, powersave, ondemand, performance
current policy: frequency should be within 2.80 GHz and 3.40 GHz.
The governor "performance" may decide which speed to use
within this range.
current CPU frequency is 3.40 GHz.
Using the appropriate options, you can view the current CPU frequency, the minimum and maximum CPU frequency allowed, show the currently used CPUfreq policy, the available CPUfreq governors, or determine the CPUfreq kernel driver used.
For more details and the available options, refer to the cpufreq-info man page or
run cpufreq-info --help.
11.3.1.2 Modifying Current Settings with cpufreqset
To modify CPUfreq settings, use the cpufreq-set command as root. It allows
you set values for the minimum or maximum CPU frequency the governor may select
or to create a new governor. With the -c option, you can also specify for which of the
processors the settings should be modified. That makes it easy to use a consistent policy across all processors without adjusting the settings for each processor individually.
For more details and the available options, refer to the cpufreq-set man page or
run cpufreq-set --help.
11.3.2 Using the cpupower Tools
After installing the cpupower package, view the available cpupower subcommands with cpupower --help. Access the general man page with
man cpupower, and the man pages of the subcommands with man cpupower-subcommand.
The subcommands frequency-info and frequency-set are mostly equivalent to cpufreq-info and cpufreq-set, respectively. However, they provide
extended output and there are small differences in syntax and behavior:
Syntax Differences Between cpufreq* and cpupower
• To specify the number of the CPU to which the command is applied, both commands have the -c option. Due to the command-subcommand structure, the placement of the -c option is different for cpupower:
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141
cpupower -c 4 frequency-info (versus cpufreq-info -c 4)
cpupower lets you also specify a list of CPUs with -c. For example, the following command would affect the CPUs 1 , 2, 3, and 5:
cpupower -c 1-3,5 frequency-set
• If cpufreq* and cpupower are used without the -c option, the behavior differs:
cpufreq-set automatically applies the command to CPU 0, whereas cpupower frequency-set applies the command to all CPUs in this case. Typically,
cpupower *info subcommands access only CPU 0, whereas cpufreq-info
accesses all CPUs, if not specified otherwise.
11.3.2.1 Viewing Current Settings with cpupower
Similar to cpufreq-info, cpupower frequency-info also shows the statistics of the cpufreq driver used in the Kernel. Additionally, it shows if turbo (boost)
states are supported and enabled in the BIOS. Run without any options, it shows an
output similar to the following:
Example 11.2: Example Output of cpupower frequency-info
analyzing CPU 0:
driver: acpi-cpufreq
CPUs which run at the same hardware frequency: 0 1 2 3
CPUs which need to have their frequency coordinated by software: 0
maximum transition latency: 10.0 us.
hardware limits: 2.00 GHz - 2.83 GHz
available frequency steps: 2.83 GHz, 2.34 GHz, 2.00 GHz
available cpufreq governors: conservative, userspace, powersave, ondemand, performance
current policy: frequency should be within 2.00 GHz and 2.83 GHz.
The governor "ondemand" may decide which speed to use
within this range.
current CPU frequency is 2.00 GHz (asserted by call to hardware).
boost state support:
Supported: yes
Active: yes
To get the current values for all CPUs, use cpupower -c all frequency-info.
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11.3.2.2 Viewing and Modifying Kernel Idle
Statistics with cpupower
The idle-info subcommand shows the statistics of the cpuidle driver used in the
Kernel. It works on all architectures that use the cpuidle Kernel framework.
Example 11.3: Example Output of cpupower idle-info
CPUidle driver: acpi_idle
CPUidle governor: menu
Analyzing CPU 0:
Number of idle states: 3
Available idle states: C1 C2
C1:
Flags/Description: ACPI FFH INTEL MWAIT 0x0
Latency: 1
Usage: 3156464
Duration: 233680359
C2:
Flags/Description: ACPI FFH INTEL MWAIT 0x10
Latency: 1
Usage: 273007117
Duration: 103148860538
After finding out which processor idle states are supported with cpupower idleinfo, individual states can be disabled using the cpupower idle-set command. Typically one wants to disable the deepest sleep state, for example:
cpupower idle-set -d 4
But before making this change permanent by adding the corresponding command to a
current /etc/init.d/* service file, check for performance or power impact.
11.3.2.3 Monitoring Kernel and Hardware
Statistics with cpupower
The most powerful enhancement is the monitor subcommand. Use it to report
processor topology, and monitor frequency and idle power state statistics over a certain period of time. The default interval is 1 second, but it can be changed with the i. Independent processor sleep states and frequency counters are implemented in the
tool—some retrieved from kernel statistics, others reading out hardware registers. The
available monitors depend on the underlying hardware and the system. List them with
cpupower monitor -l. For a description of the individual monitors, refer to the
cpupower-monitor man page.
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The monitor subcommand allows you to execute performance benchmarks and to
compare Kernel statistics with hardware statistics for specific workloads.
Example 11.4: Example cpupower monitor Output
|Mperf
CPU | C0
|
0| 3.71|
1| 100.0|
2| 9.06|
3| 7.43|
Cx
|
96.29|
-0.00|
90.94|
92.57|
|| Idle_Stats
Freq || POLL | C1
| C2
|
2833|| 0.00| 0.00| 0.02|
2833|| 0.00| 0.00| 0.00|
1983|| 0.00| 7.69| 6.98|
2039|| 0.00| 2.60| 12.62|
C3
96.32
0.00
76.45
77.52
Mperf shows the average frequency of a CPU, including boost frequencies, over
a period of time. Additionally, it shows the percentage of time the CPU has
been active (C0) or in any sleep state (Cx). The default sampling rate is 1 second and the values are read directly from the hardware registers. As the turbo
states are managed by the BIOS, it is impossible to get the frequency values at
a given instant. On modern processors with turbo features the Mperf monitor is
the only way to find out about the frequency a certain CPU has been running in.
Idle_Stats shows the statistics of the cpuidle kernel subsystem. The kernel updates these values every time an idle state is entered or left. Therefore there can
be some inaccuracy when cores are in an idle state for some time when the measure starts or ends.
Apart from the (general) monitors in the example above, other architecture-specific
monitors are available. For detailed information, refer to the cpupower-monitor
man page.
By comparing the values of the individual monitors, you can find correlations and dependencies and evaluate how well the power saving mechanism works for a certain
workload. In Example 11.4 (page 144) you can see that CPU 0 is idle (the value of
Cx is near to 100%), but runs at a very high frequency. Additionally, the CPUs 0 and
1 have the same frequency values which means that there is a dependency between
them.
11.3.2.4 Modifying Current Settings with
cpupower
Similar to cpufreq-set, you can use cpupower frequency-set command
as root to modify current settings. It allows you to set values for the minimum or
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maximum CPU frequency the governor may select or to create a new governor. With
the -c option, you can also specify for which of the processors the settings should be
modified. That makes it easy to use a consistent policy across all processors without
adjusting the settings for each processor individually. For more details and the available options, refer to the cpupower-freqency-set man page or run cpupower frequency-set --help.
11.3.3 Monitoring Power Consumption
with powerTOP
Another useful tool for monitoring system power consumption is powerTOP. It
helps you to identify the reasons for unnecessary high power consumption (for example, processes that are mainly responsible for waking up a processor from its
idle state) and to optimize your system settings to avoid these. It supports both Intel and AMD processors. The powertop package is available from the SUSE Linux Enterprise SDK. For information on how to access the SDK, refer to About This
Guide (page ix).
powerTOP combines various sources of information (analysis of programs, device
drivers, kernel options, amounts and sources of interrupts waking up processors from
sleep states) and shows them in one screen. Example 11.5, “Example powerTOP
Output” (page 145) shows which information categories are available:
Example 11.5: Example powerTOP Output
Cn
Avg residency
C0 (cpu running)
(11.6%)
polling
0.0ms
( 0.0%)
C1
4.4ms
(57.3%)
C2
10.0ms
(31.1%)
P-states
2.00 Ghz
2.00 Ghz
1.87 Ghz
1064 Mhz
Wakeups-from-idle per second : 11.2
no ACPI power usage estimate available
Top causes for wakeups:
96.2% (826.0)
<interrupt>
0.9% ( 8.0)
<kernel core>
0.3% ( 2.4)
<interrupt>
0.2% ( 2.0)
<kernel core>
0.2% ( 1.6)
<interrupt>
0.1% ( 1.0)
<interrupt>
:
:
:
:
:
:
(frequencies)
0.1%
0.0%
0.0%
99.9%
interval: 5.0s
extra timer interrupt
usb_hcd_poll_rh_status (rh_timer_func)
megasas
clocksource_watchdog (clocksource_watchdog)
eth1-TxRx-0
eth1-TxRx-4
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[...]
Suggestion:
Enable SATA ALPM link power management via:
echo min_power > /sys/class/scsi_host/host0/link_power_management_policy
or press the S key.
The column shows the C-states. When working, the CPU is in state 0, when
resting it is in some state greater than 0, depending on which C-states are available and how deep the CPU is sleeping.
The column shows average time in milliseconds spent in the particular C-state.
The column shows the percentages of time spent in various C-states. For considerable power savings during idle, the CPU should be in deeper C-states most
of the time. In addition, the longer the average time spent in these C-states, the
more power is saved.
The column shows the frequencies the processor and kernel driver support on
your system.
The column shows the amount of time the CPU cores stayed in different frequencies during the measuring period.
Shows how often the CPU is awoken per second (number of interrupts). The
lower the number the better. The interval value is the powerTOP refresh interval which can be controlled with the -t option. The default time to gather data is 5 seconds.
When running powerTOP on a laptop, this line displays the ACPI information
on how much power is currently being used and the estimated time until discharge of the battery. On servers, this information is not available.
Shows what is causing the system to be more active than needed. powerTOP displays the top items causing your CPU to awake during the sampling period.
Suggestions on how to improve power usage for this machine.
For more information, refer to the powerTOP project page at http://
www.lesswatts.org/projects/powertop/. It also provides tips and tricks
and an informative FAQ section.
11.4 Special Tuning Options
The following sections highlight some of the most relevant settings that you might
want to touch.
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11.4.1 Tuning Options for P-States
The CPUfreq subsystem offers several tuning options for P-states: You can switch between the different governors, influence minimum or maximum CPU frequency to be
used or change individual governor parameters.
To switch to another governor at runtime, use cpupower frequency-set (or
cpufreq-set) with the -g option. For example, running the following command
(as root) will activate the on-demand governor:
cpupower frequency-set -g ondemand
If you want the change in governor to persist also after a reboot or shutdown, use the
pm-profiler as described in Section 11.5, “Creating and Using Power Management
Profiles” (page 149).
To set values for the minimum or maximum CPU frequency the governor may select,
use the -d or -u option, respectively.
Apart from the governor settings that can be influenced with cpupower or
cpufreq*, you can also tune further governor parameters manually, for example,
Ignoring Nice Values in Processor Utilization (page 147).
Procedure 11.1: Ignoring Nice Values in Processor Utilization
One parameter you might want to change for the on-demand or conservative governor
is ignore_nice_load.
Each process has a niceness value associated with it. This value is used by the kernel
to determine which processes require more processor time than others. The higher
the nice value, the lower the priority of the process. Or: the “nicer” a process, the less
CPU it will try to take from other processes.
If the ignore_nice_load parameter for the on-demand or conservative governor is set to 1, any processes with a nice value will not be counted toward the overall processor utilization. When ignore_nice_load is set to 0 (default value), all
processes are counted toward the utilization. Adjusting this parameter can be useful
if you are running something that requires a lot of processor capacity but you do not
care about the runtime.
1 Change to the subdirectory of the governor whose settings you want to modify, for
example:
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cd /sys/devices/system/cpu/cpu0/cpufreq/conservative/
2 Show the current value of ignore_nice_load with:
cat ignore_nice_load
3 To set the value to 1, execute:
echo 1 > ignore_nice_load
TIP: Using the Same Value for All Cores
When setting the ignore_nice_load value for cpu0, the same value is
automatically used for all cores. In this case, you do not need to repeat the
steps above for each of the processors where you want to modify this governor parameter.
Another parameter that significantly impacts the performance loss caused by dynamic frequency scaling is the sampling rate (rate at which the governor checks the current CPU load and adjusts the processor's frequency accordingly). Its default value
depends on a BIOS value and it should be as low as possible. However, in modern systems, an appropriate sampling rate is set by default and does not need manual intervention.
11.4.2 Tuning Options for C-states
By default, SUSE Linux Enterprise Server uses C-states appropriately. The only parameter you might want to touch for optimization is the
sched_mc_power_savings scheduler. Instead of distributing a work load across
all cores with the effect that all cores are used only at a minimum level, the kernel can
try to schedule processes on as few cores as possible so that the others can go idle.
This helps to save power as it allows some processors to be idle for a longer time so
they can reach a higher C-state. However, the actual savings depend on a number of
factors, for example how many processors are available and which C-states are supported by them (especially deeper ones such as C3 to C6).
If sched_mc_power_savings is set to 0 (default value), no special scheduling is
done. If it is set to 1, the scheduler tries to consolidate the work onto the fewest number of processors possible in the case that all processors are a little busy. To modify
this parameter, proceed as follows:
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Procedure 11.2: Scheduling Processes on Cores
1 Become root on a command line.
2 To view the current value of sched_mc_power_savings, use the following
command:
cpupower info -m
3 To set sched_mc_power_savings to 1, execute:
cpupower set -m 1
11.5 Creating and Using Power
Management Profiles
SUSE Linux Enterprise Server includes pm-profiler, intended for server use. It is a
script infrastructure to enable or disable certain power management functions via
configuration files. It allows you to define different profiles, each having a specific configuration file for defining different settings. A configuration template for
new profiles can be found at /usr/share/doc/packages/pm-profil​
er/config.template. The template contains a number of parameters you can
use for your profile, including comments on usage and links to further documentation.
The individual profiles are stored in /etc/pm-profiler/. The profile that will
be activated on system start, is defined in /etc/pm-profiler.conf.
Procedure 11.3: Creating and Switching Power Profiles
To create a new profile, proceed as follows:
1 Create a directory in /etc/pm-profiler/, containing the profile name, for
example:
mkdir /etc/pm-profiler/testprofile
2 To create the configuration file for the new profile, copy the profile template to
the newly created directory:
cp /usr/share/doc/packages/pm-profiler/config.template \
/etc/pm-profiler/testprofile/config
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3 Edit the settings in /etc/pm-profiler/testprofile/config and save
the file. You can also remove variables that you do not need—they will be handled
like empty variables, the settings will not be touched at all.
4 Edit /etc/pm-profiler.conf. The PM_PROFILER_PROFILE variable
defines which profile will be activated on system start. If it has no value, the default system or kernel settings will be used. To set the newly created profile:
PM_PROFILER_PROFILE="testprofile"
The profile name you enter here must match the name you used in the path to the
profile configuration file (/etc/pm-profiler/testprofile/config),
not necessarily the NAME you used for the profile in the /etc/pm-profil​
er/testprofile/config.
5 To activate the profile, run
rcpm-profiler start
or
/usr/lib/pm-profiler/enable-profile testprofile
Though you have to manually create or modify a profile by editing the respective profile configuration file, you can use YaST to switch between different profiles. Start
YaST and select System > Power Management to open the Power Management Settings.
Alternatively, become root and execute yast2 power-management on a command line. The drop-down list shows the available profiles. Default means that the
system default settings will be kept. Select the profile to use and click Finish.
11.6 Troubleshooting
BIOS options enabled?
In order to make use of C-states or P-states, check your BIOS options:
• To use C-states, make sure to enable CPU C State or similar options to
benefit from power savings at idle.
• To use P-states and the CPUfreq governors, make sure to enable
Processor Performance States options or similar.
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In case of a CPU upgrade, make sure to upgrade your BIOS, too. The BIOS needs
to know the new CPU and its valid frequencies steps in order to pass this information on to the operating system.
CPUfreq subsystem enabled?
In SUSE Linux Enterprise Server, the CPUfreq subsystem is enabled by default.
To find out if the subsystem is currently enabled, check for the following path
in your system: /sys/devices/system/cpu/cpufreq (or /sys/de​
vices/system/cpu/cpu*/cpufreq for machines with multiple cores). If
the cpufreq subdirectory exists, the subsystem is enabled.
Log file information?
Check syslog (usually /var/log/messages) for any output regrading the
CPUfreq subsystem. Only severe errors are reported there.
If you suspect problems with the CPUfreq subsystem on your machine, you can
also enable additional debug output. To do so, either use cpufreq.debug=7
as boot parameter or execute the following command as root:
echo 7 > /sys/module/cpufreq/parameters/debug
This will cause CPUfreq to log more information to dmesg on state transitions,
which is useful for diagnosis. But as this additional output of kernel messages can
be rather comprehensive, use it only if you are fairly sure that a problem exists.
11.7 For More Information
• A threepart, comprehensive article about tuning components with regards to power
efficiency is available at the following URLs:
• Reduce Linux power consumption, Part 1: The CPUfreq subsystem, available at http://www.ibm.com/developerworks/linux/li​
brary/l-cpufreq-1/?ca=dgr-lnxw03ReduceLXPWR-P1dthLX&S_TACT=105AGX59&S_CMP=grlnxw03
• Reduce Linux power consumption, Part 2: General and governor-specific settings, available at http://www.ibm.com/developerworks/lin​
ux/library/l-cpufreq-2/?ca=dgr-lnxw03ReduceLXPWRP1dth-LX&S_TACT=105AGX59&S_CMP=grlnxw03
• Reduce Linux power consumption, Part 3: Tuning results, available
at http://www.ibm.com/developerworks/linux/li​
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brary/l-cpufreq-3/?ca=dgr-lnxw03ReduceLXPWR-P1dthLX&S_TACT=105AGX59&S_CMP=grlnxw03
• The LessWatts.org project deals with how to save power, reduce costs and increase efficiency on Linux systems. Find the project home page at http://
www.lesswatts.org/. The project page also holds an informative FAQs
section at http://www.lesswatts.org/documentation/faq/
index.php and provides useful tips and tricks. For tips dealing with the CPU
level, refer to http://www.lesswatts.org/tips/cpu.php. For more
information about powerTOP, refer to http://www.lesswatts.org/
projects/powertop/.
• Platforms with a Baseboard Management Controller (BMC) may have additional power management configuration options accessible via the service processor.
These configurations are vendor specific and therefore not subject of this guide.
For more information, refer to the manuals provided by your vendor. For example, HP ProLiant Server Power Management on SUSE Linux Enterprise Server 11
—Integration Note provides detailed information how the HP platform specific
power management features interact with the Linux Kernel. The paper is available
from http://h18004.www1.hp.com/products/servers/technol​
ogy/whitepapers/os-techwp.html.
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Part V. Kernel Tuning
Installing Multiple Kernel
Versions
12
SUSE Linux Enterprise Server supports the parallel installation of multiple kernel versions. When installing a second kernel, a boot entry and an initrd are automatically
created, so no further manual configuration is needed. When rebooting the machine,
the newly added kernel is available as an additional boot option.
Using this functionality, you can safely test kernel updates while being able to always
fall back to the proven former kernel. To do so, do not use the update tools (such as
the YaST Online Update or the updater applet), but instead follow the process described in this chapter.
WARNING: Support Entitlement
Please be aware that you loose your entire support entitlement for the machine when installing a self-compiled or a third-party kernel. Only kernels
shipped with SUSE Linux Enterprise Server and kernels delivered via the official update channels for SUSE Linux Enterprise Server are supported.
TIP: Check Your Bootloader Configuration Kernel
It is recommended to check your boot loader config after having installed
another kernel in order to set the default boot entry of your choice. See
Section “Configuring the Boot Loader with YaST” (Chapter 10, The Boot
Loader GRUB, ↑Administration Guide) for more information. To change
the default append line for new kernel installations, adjust /etc/syscon​
fig/bootloader prior to installing a new kernel. For more information reInstalling Multiple Kernel Versions
155
fer to Section “The File /etc/sysconfig/bootloader” (Chapter 10, The
Boot Loader GRUB, ↑Administration Guide).
12.1 Enabling and Configuring
Multiversion Support
Installing multiple versions of a software package (multiversion support) is not enabled by default. To enable this feature, proceed as follows:
1 Open /etc/zypp/zypp.conf with the editor of your choice as root.
2 Search for the string multiversion. To enable multiversion for all kernel packages capable of this feature, uncomment the following line
# multiversion = provides:multiversion(kernel)
3 To restrict multiversion support to certain kernel flavors, add the package names
as a comma-separated list, to the multiversion option in /etc/zypp/
zypp.conf—for example
multiversion = kernel-default,kernel-default-base,kernel-source
4 Save your changes.
12.1.1 Automatically Deleting Unused
Kernels
When frequently testing new kernels with multiversion support enabled, the boot
menu quickly becomes confusing. Since a /boot usually has got limited space you
also might run into trouble with /boot overflowing. While you may delete unused
kernel versions manually with YaST or Zypper (as described below), you can also
configure libzypp to automatically delete kernels no longer used. By default no
kernels are deleted.
1 Open /etc/zypp/zypp.conf with the editor of your choice as root.
2 Search for the string multiversion.kernels and activate this option by uncommenting the line. This option takes a comma separated list of the following values
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2.6.32.12-0.7 : keep the kernel with the specified version number
latest: keep the kernel with the highest version number
latest-N: keep the kernel with the Nth highest version number
running keep the running kernel
oldest keep the kernel with the lowest version number (the one that was originally shipped with SUSE Linux Enterprise Server)
oldest+N keep the kernel with the Nth lowest version number
Here are some examples
multiversion.kernels = latest,running
Keep the latest kernel and the one currently running one. This is similar to not
enabling the multiversion feature at all, except that the old kernel is removed
after the next reboot and not immediately after the installation.
multiversion.kernels = latest,latest-1,running
Keep the last two kernels and the one currently running.
multiversion.kernels = latest,running,3.0.rc7-test
Keep the latest kernel, the one currently running and 3.0.rc7-test.
TIP: Keep the running Kernel
Unless using special setups, you probably always want to keep the running kernel.
12.2 Installing/Removing Multiple
Kernel Versions with YaST
1 Start YaST and open the software manager via Software > Software Mannagment.
2 List all packages capable of providing multiple versions by choosing View > Package Groups > Multiversion Packages.
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157
Figure 12.1: The YaST Software Manager - Multiversion View
3 Select a package and open its Version tab in the bottom pane on the left.
4 To install a package, click its check box. A green check mark indicates it is selected for installation.
To remove an already installed package (marked with a white check mark), click
its check box until a red X indicates it is selected for removal.
5 Click Accept to start the installation.
12.3 Installing/Removing Multiple
Kernel Versions with zypper
1 Use the command zypper se -s 'kernel*' to display a list of all kernel
packages available:
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S | Name
| Type
| Version
| Arch
| Repository
--+----------------+------------+-----------------+--------+------------------v | kernel-default | package
| 2.6.32.10-0.4.1 | x86_64 | Alternative Kernel
i | kernel-default | package
| 2.6.32.9-0.5.1 | x86_64 | (System Packages)
| kernel-default | srcpackage | 2.6.32.10-0.4.1 | noarch | Alternative Kernel
i | kernel-default | package
| 2.6.32.9-0.5.1 | x86_64 | (System Packages)
...
2 Specify the exact version when installing:
zypper in kernel-default-2.6.32.10-0.4.1
3 When uninstalling a kernel, use the commands zypper se -si 'kernel*'
to list all kernels installed and zypper rm PACKAGENAME-VERSION to remove the package.
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159
Tuning I/O Performance
I/O scheduling controls how input/output operations will be submitted to storage.
SUSE Linux Enterprise Server offers various I/O algorithms—called elevators—
suiting different workloads. Elevators can help to reduce seek operations, can prioritize I/O requests, or make sure, and I/O request is carried out before a given deadline.
13
Choosing the best suited I/O elevator not only depends on the workload, but on the
hardware, too. Single ATA disk systems, SSDs, RAID arrays, or network storage systems, for example, each require different tuning strategies.
13.1 Switching I/O Scheduling
SUSE Linux Enterprise Server lets you set a default I/O scheduler at boot-time, which
can be changed on the fly per block device. This makes it possible to set different algorithms for e.g. the device hosting the system partition and the device hosting a database.
By default the CFQ (Completely Fair Queuing) scheduler is used. Change this default
by entering the boot parameter
elevator=SCHEDULER
where SCHEDULER is one of cfq, noop, or deadline. See Section 13.2, “Available I/O Elevators” (page 162) for details.
To change the elevator for a specific device in the running system, run the following
command:
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161
echo SCHEDULER > /sys/block/DEVICE/queue/scheduler
where SCHEDULER is one of cfq, noop, or deadline and DEVICE the block device (sda for example).
NOTE: Default Schedulter on IBM System z
On IBM System z the default I/O scheduler for a storage device is set by the
device driver.
13.2 Available I/O Elevators
In the following elevators available on SUSE Linux Enterprise Server are listed. Each
elevator has a set of tunable parameters, which can be set with the following command:
echo VALUE > /sys/block/DEVICE/queue/iosched/TUNABLE
where VALUE is the desired value for the TUNABLE and DEVICE the block device.
To find out which elevator is the current default, run the following command. The
currently selected scheduler is listed in brackets:
jupiter:~ # cat /sys/block/sda/queue/scheduler
noop deadline [cfq]
13.2.1 CFQ (Completely Fair Queuing)
CFQ is a fairness-oriented scheduler and is used by default on SUSE Linux Enterprise
Server. The algorithm assigns each thread a time slice in which it is allowed to submit
I/O to disk. This way each thread gets a fair share of I/O throughput. It also allows assigning tasks I/O priorities which are taken into account during scheduling decisions
(see man 1 ionice). The CFQ scheduler has the following tunable parameters:
/sys/block/<device>/queue/iosched/slice_idle
When a task has no more I/O to submit in its time slice, the I/O scheduler waits
for a while before scheduling the next thread to improve locality of I/O. For media where locality does not play a big role (SSDs, SANs with lots of disks) setting
/sys/block/<device>/queue/iosched/slice_idle to 0 can improve the throughput considerably.
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/sys/block/<device>/queue/iosched/quantum
This option limits the maximum number of requests that are being processed
by the device at once. The default value is 4. For a storage with several disks,
this setting can unnecessarily limit parallel processing of requests. Therefore,
increasing the value can improve performance although this can cause that the
latency of some I/O may be increased due to more requests being buffered inside the storage. When changing this value, you can also consider tuning /sys/
block/<device>/queue/iosched/slice_async_rq (the default value is 2) which limits the maximum number of asynchronous requests—usually
writing requests—that are submitted in one time slice.
/sys/block/<device>/queue/iosched/low_latency
For workloads where the latency of I/O is crucial, setting /sys/block/<de​
vice>/queue/iosched/low_latency to 1 can help.
13.2.2 NOOP
A trivial scheduler that just passes down the I/O that comes to it. Useful for checking whether complex I/O scheduling decisions of other schedulers are not causing I/O
performance regressions.
In some cases it can be helpful for devices that do I/O scheduling themselves, as intelligent storage, or devices that do not depend on mechanical movement, like SSDs.
Usually, the DEADLINE I/O scheduler is a better choice for these devices, but due to
less overhead NOOP may produce better performance on certain workloads.
13.2.3 DEADLINE
DEADLINE is a latency-oriented I/O scheduler. Each I/O request has got a deadline assigned. Usually, requests are stored in queues (read and write) sorted by sector numbers. The DEADLINE algorithm maintains two additional queues (read and
write) where the requests are sorted by deadline. As long as no request has timed out,
the “sector” queue is used. If timeouts occur, requests from the “deadline” queue are
served until there are no more expired requests. Generally, the algorithm prefers reads
over writes.
This scheduler can provide a superior throughput over the CFQ I/O scheduler in cases where several threads read and write and fairness is not an issue. For example, for
Tuning I/O Performance
163
several parallel readers from a SAN and for databases (especially when using “TCQ”
disks). The DEADLINE scheduler has the following tunable parameters:
/sys/block/<device>/queue/iosched/writes_starved
Controls how many reads can be sent to disk before it is possible to send writes.
A value of 3 means, that three read operations are carried out for one write operation.
/sys/block/<device>/queue/iosched/read_expire
Sets the deadline (current time plus the read_expire value) for read operations in
milliseconds. The default is 500.
/sys/block/<device>/queue/iosched/write_expire
/sys/block/<device>/queue/iosched/read_expire Sets the
deadline (current time plus the read_expire value) for read operations in milliseconds. The default is 500.
13.3 I/O Barrier Tuning
Most file systems (XFS, ext3, ext4, reiserfs) send write barriers to disk after fsync or
during transaction commits. Write barriers enforce proper ordering of writes, making
volatile disk write caches safe to use (at some performance penalty). If your disks are
battery-backed in one way or another, disabling barriers may safely improve performance.
Sending write barriers can be disabled using the barrier=0 mount option (for ext3,
ext4, and reiserfs), or using the nobarrier mount option (for XFS).
WARNING
Disabling barriers when disks cannot guarantee caches are properly written
in case of power failure can lead to severe file system corruption and data
loss.
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Tuning the Task Scheduler
14
Modern operating systems, such as SUSE® Linux Enterprise Server, normally run
many different tasks at the same time. For example, you can be searching in a text
file while receiving an e-mail and copying a big file to an external hard drive. These
simple tasks require many additional processes to be run by the system. To provide
each task with its required system resources, the Linux kernel needs a tool to distribute available system resources to individual tasks. And this is exactly what the task
scheduler does.
The following sections explain the most important terms related to a process scheduling. They also introduce information about the task scheduler policy, scheduling algorithm, description of the task scheduler used by SUSE Linux Enterprise Server, and
references to other sources of relevant information.
14.1 Introduction
The Linux kernel controls the way tasks (or processes) are managed in the running
system. The task scheduler, sometimes called process scheduler, is the part of the kernel that decides which task to run next. It is one of the core components of a multitasking operating system (such as Linux), being responsible for best utilizing system
resources to guarantee that multiple tasks are being executed simultaneously.
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165
14.1.1 Preemption
The theory behind task scheduling is very simple. If there are runnable processes in
a system, at least one process must always be running. If there are more runnable
processes than processors in a system, not all the processes can be running all the
time.
Therefore, some processes need to be stopped temporarily, or suspended, so that others can be running again. The scheduler decides what process in the queue will run
next.
As already mentioned, Linux, like all other Unix variants, is a multitasking operating
system. That means that several tasks can be running at the same time. Linux provides
a so called preemptive multitasking, where the scheduler decides when a process is
suspended. This forced suspension is called preemption. All Unix flavors have been
providing preemptive multitasking since the beginning.
14.1.2 Timeslice
The time period for which a process will be running before it is preempted is defined
in advance. It is called a process' timeslice and represents the amount of processor time
that is provided to each process. By assigning timeslices, the scheduler makes global
decisions for the running system, and prevents individual processes from dominating
over the processor resources.
14.1.3 Process Priority
The scheduler evaluates processes based on their priority. To calculate the current
priority of a process, the task scheduler uses complex algorithms. As a result, each
process is given a value according to which it is “allowed” to run on a processor.
14.2 Process Classification
Processes are usually classified according to their purpose and behavior. Although the
borderline is not always clearly distinct, generally two criteria are used to sort them.
These criteria are independent and do not exclude each other.
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One approach is to classify a process either I/O-bound or processor-bound.
I/O-bound
I/O stands for Input/Output devices, such as keyboards, mice, or optical and hard
disks. I/O-bound processes spend the majority of time submitting and waiting for
requests. They are run very frequently, but for short time intervals, not to block
other processes waiting for I/O requests.
processor-bound
On the other hand, processor-bound tasks use their time to execute a code, and
usually run until they are preempted by the scheduler. They do not block processes waiting for I/O requests, and, therefore, can be run less frequently but for
longer time intervals.
Another approach is to divide processes by either being interactive, batch, or real-time
ones.
• Interactive processes spend a lot of time waiting for I/O requests, such as keyboard
or mouse operations. The scheduler must wake up such process quickly on user request, or the user will find the environment unresponsive. The typical delay is approximately 100 ms. Office applications, text editors or image manipulation programs represent typical interactive processes.
• Batch processes often run in the background and do not need to be responsive. They
usually receive lower priority from the scheduler. Multimedia converters, database
search engines, or log files analyzers are typical examples of batch processes.
• Real-time processes must never be blocked by low-priority processes, and the
scheduler guarantees a short response time to them. Applications for editing multimedia content are a good example here.
14.3 O(1) Scheduler
The Linux kernel version 2.6 introduced a new task scheduler, called O(1)
scheduler (see Big O notation [http://en.wikipedia.org/wi​
ki/Big_O_notation]), It was used as the default scheduler up to Kernel version
2.6.22. Its main task is to schedule tasks within a fixed amount of time, no matter how
many runnable processes there are in the system.
Tuning the Task Scheduler
167
The scheduler calculates the timeslices dynamically. However, to determine the appropriate timeslice is a complex task: Too long timeslices cause the system to be less
interactive and responsive, while too short ones make the processor waste a lot of time
on the overhead of switching the processes too frequently. The default timeslice is
usually rather low, for example 20ms. The scheduler determines the timeslice based
on priority of a process, which allows the processes with higher priority to run more
often and for a longer time.
A process does not have to use all its timeslice at once. For instance, a process with
a timeslice of 150ms does not have to be running for 150ms in one go. It can be running in five different schedule slots for 30ms instead. Interactive tasks typically benefit from this approach because they do not need such a large timeslice at once while
they need to be responsive as long as possible.
The scheduler also assigns process priorities dynamically. It monitors the processes'
behavior and, if needed, adjusts its priority. For example, a process which is being
suspended for a long time is brought up by increasing its priority.
14.4 Completely Fair Scheduler
Since the Linux kernel version 2.6.23, a new approach has been taken to the scheduling of runnable processes. Completely Fair Scheduler (CFS) became the default
Linux kernel scheduler. Since then, important changes and improvements have been
made. The information in this chapter applies to SUSE Linux Enterprise Server with
kernel version 2.6.32 and higher (including 3.x kernels). The scheduler environment
was divided into several parts, and three main new features were introduced:
Modular Scheduler Core
The core of the scheduler was enhanced with scheduling classes. These classes are
modular and represent scheduling policies.
Completely Fair Scheduler
Introduced in kernel 2.6.23 and extended in 2.6.24, CFS tries to assure that each
process obtains its “fair” share of the processor time.
Group Scheduling
For example, if you split processes into groups according to which user is running
them, CFS tries to provide each of these groups with the same amount of processor time.
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As a result, CFS brings more optimized scheduling for both servers and desktops.
14.4.1 How CFS Works
CFS tries to guarantee a fair approach to each runnable task. To find the most balanced way of task scheduling, it uses the concept of red-black tree. A red-black tree
is a type of self-balancing data search tree which provides inserting and removing entries in a reasonable way so that it remains well balanced. For more information, see the wiki pages of Red-black tree [http://en.wikipedia.org/wi​
ki/Red_black_tree].
When a task enters into the run queue (a planned time line of processes to be executed next), the scheduler records the current time. While the process waits for processor
time, its “wait” value gets incremented by an amount derived from the total number
of tasks currently in the run queue and the process priority. As soon as the processor
runs the task, its “wait” value gets decremented. If the value drops below a certain level, the task is preempted by the scheduler and other tasks get closer to the processor.
By this algorithm, CFS tries to reach the ideal state where the “wait” value is always
zero.
14.4.2 Grouping Processes
Since the Linux kernel version 2.6.24, CFS can be tuned to be fair to users or groups
rather than to tasks only. Runnable tasks are then grouped to form entities, and CFS
tries to be fair to these entities instead of individual runnable tasks. The scheduler also
tries to be fair to individual tasks within these entities.
Tasks can be grouped in two mutually exclusive ways:
• By user IDs
• By kernel control groups.
The way the kernel scheduler lets you group the runnable tasks depends on setting the kernel compile-time options CONFIG_FAIR_USER_SCHED and
CONFIG_FAIR_CGROUP_SCHED. The default setting in SUSE® Linux Enterprise
Server 11 SP3 is to use control groups, which lets you create groups as needed. For
more information, see Chapter 10, Kernel Control Groups (page 121).
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169
14.4.3 Kernel Configuration Options
Basic aspects of the task scheduler behavior can be set through the kernel configuration options. Setting these options is part of the kernel compilation process. Because
kernel compilation process is a complex task and out of this document's scope, refer
to relevant source of information.
WARNING: Kernel Compilation
If you run SUSE Linux Enterprise Server on a kernel that was not shipped
with it, for example on a self-compiled kernel, you loose the entire support entitlement.
14.4.4 Terminology
Documents regarding task scheduling policy often use several technical terms which
you need to know to understand the information correctly. Here are some of them:
Latency
Delay between the time a process is scheduled to run and the actual process execution.
Granularity
The relation between granularity and latency can be expressed by the following
equation:
gran = ( lat / rtasks ) - ( lat / rtasks / rtasks )
where gran stands for granularity, lat stand for latency, and rtasks is the number
of running tasks.
14.4.4.1 Scheduling Policies
The Linux kernel supports the following scheduling policies:
SCHED_FIFO
Scheduling policy designed for special time-critical applications. It uses the First
In-First Out scheduling algorithm.
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SCHED_BATCH
Scheduling policy designed for CPU-intensive tasks.
SCHED_IDLE
Scheduling policy intended for very low prioritized tasks.
SCHED_OTHER
Default Linux time-sharing scheduling policy used by the majority of processes.
SCHED_RR
Similar to SCHED_FIFO, but uses the Round Robin scheduling algorithm.
14.4.5 Changing Real-time Attributes
of Processes with chrt
The chrt command sets or retrieves the real-time scheduling attributes of a running
process, or runs a command with the specified attributes. You can get or retrieve both
the scheduling policy and priority of a process.
In the following examples, a process whose PID is 16244 is used.
To retrieve the real-time attributes of an existing task:
saturn.example.com:~ # chrt -p 16244
pid 16244's current scheduling policy: SCHED_OTHER
pid 16244's current scheduling priority: 0
Before setting a new scheduling policy on the process, you need to find out the minimum and maximum valid priorities for each scheduling algorithm:
saturn.example.com:~ # chrt -m
SCHED_OTHER min/max priority : 0/0
SCHED_FIFO min/max priority : 1/99
SCHED_RR min/max priority : 1/99
SCHED_BATCH min/max priority : 0/0
SCHED_IDLE min/max priority : 0/0
In the above example, SCHED_OTHER, SCHED_BATCH, SCHED_IDLE polices
only allow for priority 0, while that of SCHED_FIFO and SCHED_RR can range
from 1 to 99.
To set SCHED_BATCH scheduling policy:
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171
saturn.example.com:~ # chrt -b
saturn.example.com:~ # chrt -p
pid 16244's current scheduling
pid 16244's current scheduling
-p 0 16244
16244
policy: SCHED_BATCH
priority: 0
For more information on chrt, see its man page (man 1 chrt).
14.4.6 Runtime Tuning with sysctl
The sysctl interface for examining and changing kernel parameters at runtime introduces important variables by means of which you can change the default behavior
of the task scheduler. The syntax of the sysctl is simple, and all the following commands must be entered on the command line as root.
To read a value from a kernel variable, enter
sysctl variable
To assign a value, enter
sysctl variable=value
To get a list of all scheduler related sysctl variables, enter
sysctl -A | grep "sched" | grep -v"domain"
saturn.example.com:~ # sysctl -A | grep "sched" | grep -v "domain"
kernel.sched_child_runs_first = 0
kernel.sched_min_granularity_ns = 1000000
kernel.sched_latency_ns = 5000000
kernel.sched_wakeup_granularity_ns = 1000000
kernel.sched_shares_ratelimit = 250000
kernel.sched_tunable_scaling = 1
kernel.sched_shares_thresh = 4
kernel.sched_features = 15834238
kernel.sched_migration_cost = 500000
kernel.sched_nr_migrate = 32
kernel.sched_time_avg = 1000
kernel.sched_rt_period_us = 1000000
kernel.sched_rt_runtime_us = 950000
kernel.sched_compat_yield = 0
Note that variables ending with “_ns” and “_us” accept values in nanoseconds and microseconds, respectively.
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A list of the most important task scheduler sysctl tuning variables (located at /
proc/sys/kernel/) with a short description follows:
sched_child_runs_first
A freshly forked child runs before the parent continues execution. Setting this parameter to 1 is beneficial for an application in which the child performs an execution after fork. For example make -j<NO_CPUS> performs better when
sched_child_runs_first is turned off. The default value is 0.
sched_compat_yield
Enables the aggressive yield behavior of the old 0(1) scheduler. Java applications
that use synchronization extensively perform better with this value set to 1. Only
use it when you see a drop in performance. The default value is 0.
Expect applications that depend on the sched_yield() syscall behavior to perform
better with the value set to 1.
sched_migration_cost
Amount of time after the last execution that a task is considered to be “cache hot”
in migration decisions. A “hot” task is less likely to be migrated, so increasing this
variable reduces task migrations. The default value is 500000 (ns).
If the CPU idle time is higher than expected when there are runnable processes,
try reducing this value. If tasks bounce between CPUs or nodes too often, try increasing it.
sched_latency_ns
Targeted preemption latency for CPU bound tasks. Increasing this variable increases a CPU bound task's timeslice. A task's timeslice is its weighted fair share
of the scheduling period:
timeslice = scheduling period * (task's weight/total weight of tasks in the run
queue)
The task's weight depends on the task's nice level and the scheduling policy. Minimum task weight for a SCHED_OTHER task is 15, corresponding to nice 19.
The maximum task weight is 88761, corresponding to nice -20.
Timeslices become smaller as the load increases. When the number of runnable
tasks exceeds sched_latency_ns/sched_min_granularity_ns, the
slice becomes number_of_running_tasks * sched_min_granularity_ns.
Prior to that, the slice is equal to sched_latency_ns.
Tuning the Task Scheduler
173
This value also specifies the maximum amount of time during which a sleeping
task is considered to be running for entitlement calculations. Increasing this variable increases the amount of time a waking task may consume before being preempted, thus increasing scheduler latency for CPU bound tasks. The default value
is 20000000 (ns).
sched_min_granularity_ns
Minimal preemption granularity for CPU bound tasks. See
sched_latency_ns for details. The default value is 4000000 (ns).
sched_wakeup_granularity_ns
The wake-up preemption granularity. Increasing this variable reduces wake-up
preemption, reducing disturbance of compute bound tasks. Lowering it improves
wake-up latency and throughput for latency critical tasks, particularly when a
short duty cycle load component must compete with CPU bound components.
The default value is 5000000 (ns).
WARNING
Settings larger than half of sched_latency_ns will result in zero wakeup preemption and short duty cycle tasks will be unable to compete with
CPU hogs effectively.
sched_rt_period_us
Period over which real-time task bandwidth enforcement is measured. The default value is 1000000 (µs).
sched_rt_runtime_us
Quantum allocated to real-time tasks during sched_rt_period_us. Setting to -1 disables RT bandwidth enforcement. By default, RT tasks may consume 95%CPU/
sec, thus leaving 5%CPU/sec or 0.05s to be used by SCHED_OTHER tasks.
sched_features
Provides information about specific debugging features.
sched_stat_granularity_ns
Specifies the granularity for collecting task scheduler statistics.
sched_nr_migrate
Controls how many tasks can be moved across processors through migration software interrupts (softirq). If a large number of tasks is created by
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SCHED_OTHER policy, they will all be run on the same processor. The default value is 32. Increasing this value gives a performance boost to large
SCHED_OTHER threads at the expense of increased latencies for real-time
tasks.
14.4.7 Debugging Interface and
Scheduler Statistics
CFS comes with a new improved debugging interface, and provides runtime statistics
information. Relevant files were added to the /proc file system, which can be examined simply with the cat or less command. A list of the related /proc files follows with their short description:
/proc/sched_debug
Contains the current values of all tunable variables (see Section 14.4.6, “Runtime
Tuning with sysctl” (page 172)) that affect the task scheduler behavior,
CFS statistics, and information about the run queue on all available processors.
saturn.example.com:~ # less /proc/sched_debug
Sched Debug Version: v0.09, 2.6.32.8-0.3-default #1
now at 2413026096.408222 msecs
.jiffies
: 4898148820
.sysctl_sched_latency
: 5.000000
.sysctl_sched_min_granularity
: 1.000000
.sysctl_sched_wakeup_granularity
: 1.000000
.sysctl_sched_child_runs_first
: 0.000000
.sysctl_sched_features
: 15834238
.sysctl_sched_tunable_scaling
: 1 (logaritmic)
cpu#0, 1864.411 MHz
.nr_running
.load
.nr_switches
.nr_load_updates
[...]
cfs_rq[0]:/
.exec_clock
.MIN_vruntime
.min_vruntime
.max_vruntime
[...]
rt_rq[0]:/
.rt_nr_running
.rt_throttled
.rt_time
.rt_runtime
:
:
:
:
1
1024
37539000
22950725
:
:
:
:
52940326.803842
0.000001
54410632.307072
0.000001
:
:
:
:
0
0
0.000000
950.000000
Tuning the Task Scheduler
175
runnable tasks:
task PID
tree-key
switches prio exec-runtime
sum-exec sumsleep
-------------------------------------------------------------------------R cat 16884 54410632.307072
0
120 54410632.307072 13.836804
0.000000
/proc/schedstat
Displays statistics relevant to the current run queue. Also domain-specific statistics for SMP systems are displayed for all connected processors. Because the output format is not user-friendly, read the contents of /usr/src/linux/Doc​
umentation/scheduler/sched-stats.txt for more information.
/proc/PID/sched
Displays scheduling information on the process with id PID.
saturn.example.com:~ # cat /proc/`pidof nautilus`/sched
nautilus (4009, #threads: 1)
--------------------------------------------------------se.exec_start
:
2419575150.560531
se.vruntime
:
54549795.870151
se.sum_exec_runtime
:
4867855.829415
se.avg_overlap
:
0.401317
se.avg_wakeup
:
3.247651
se.avg_running
:
0.323432
se.wait_start
:
0.000000
se.sleep_start
:
2419575150.560531
[...]
nr_voluntary_switches
:
938552
nr_involuntary_switches
:
71872
se.load.weight
:
1024
policy
:
0
prio
:
120
clock-delta
:
109
14.5 For More Information
To get a compact knowledge about Linux kernel task scheduling, you need to explore
several information sources. Here are some of them:
• For task scheduler System Calls description, see the relevant manual page (for example man 2 sched_setaffinity).
• General information on scheduling is described in Scheduling [http://
en.wikipedia.org/wiki/Scheduling_(computing)] wiki page.
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System Analysis and Tuning Guide
• General information on Linux task scheduling is described in Inside the Linux scheduler [http://www.ibm.com/developerworks/linux/li​
brary/l-scheduler/].
• Information specific to Completely Fair Scheduler is available in Multiprocessing
with the Completely Fair Scheduler [http://www.ibm.com/developer​
works/linux/library/l-cfs/?ca=dgr-lnxw06CFC4Linux]
• Information specific to tuning Completely Fair Scheduler is available
in Tuning the Linux Kernel’s Completely Fair Scheduler [http://
www.hotaboutlinux.com/2010/01/tuning-the-linux-ker​
nels-completely-fair-scheduler/]
• A useful lecture on Linux scheduler policy and algorithm is available in
http://www.inf.fu-berlin.de/lehre/SS01/OS/Lec​
tures/Lecture08.pdf.
• A good overview of Linux process scheduling is given in Linux Kernel Development by Robert Love (ISBN-10: 0-672-32512-8). See http://
www.informit.com/articles/article.aspx?p=101760.
• A very comprehensive overview of the Linux kernel internals is given in Understanding the Linux Kernel by Daniel P. Bovet and Marco Cesati (ISBN
978-0-596-00565-8).
• Technical information about task scheduler is covered in files under /usr/src/
linux/Documentation/scheduler.
Tuning the Task Scheduler
177
Tuning the Memory
Management Subsystem
15
In order to understand and tune the memory management behavior of the kernel, it is
important to first have an overview of how it works and cooperates with other subsystems.
The memory management subsystem, also called the virtual memory manager, will
subsequently be referred to as “VM”. The role of the VM is to manage the allocation
of physical memory (RAM) for the entire kernel and user programs. It is also responsible for providing a virtual memory environment for user processes (managed via
POSIX APIs with Linux extensions). Finally, the VM is responsible for freeing up
RAM when there is a shortage, either by trimming caches or swapping out “anonymous” memory.
The most important thing to understand when examining and tuning VM is how its
caches are managed. The basic goal of the VM's caches is to minimize the cost of I/O
as generated by swapping and file system operations (including network file systems).
This is achieved by avoiding I/O completely, or by submitting I/O in better patterns.
Free memory will be used and filled up by these caches as required. The more memory is available for caches and anonymous memory, the more effectively caches and
swapping will operate. However, if a memory shortage is encountered, caches will be
trimmed or memory will be swapped out.
For a particular workload, the first thing that can be done to improve performance
is to increase memory and reduce the frequency that memory must be trimmed or
swapped. The second thing is to change the way caches are managed by changing kernel parameters.
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179
Finally, the workload itself should be examined and tuned as well. If an application is
allowed to run more processes or threads, effectiveness of VM caches can be reduced,
if each process is operating in its own area of the file system. Memory overheads are
also increased. If applications allocate their own buffers or caches, larger caches will
mean that less memory is available for VM caches. However, more processes and
threads can mean more opportunity to overlap and pipeline I/O, and may take better
advantage of multiple cores. Experimentation will be required for the best results.
15.1 Memory Usage
Memory allocations in general can be characterized as “pinned” (also known as “unreclaimable”), “reclaimable” or “swappable”.
15.1.1 Anonymous Memory
Anonymous memory tends to be program heap and stack memory (for example,
>malloc()). It is reclaimable, except in special cases such as mlock or if there is
no available swap space. Anonymous memory must be written to swap before it can
be reclaimed. Swap I/O (both swapping in and swapping out pages) tends to be less
efficient than pagecache I/O, due to allocation and access patterns.
15.1.2 Pagecache
A cache of file data. When a file is read from disk or network, the contents are stored
in pagecache. No disk or network access is required, if the contents are up-to-date in
pagecache. tmpfs and shared memory segments count toward pagecache.
When a file is written to, the new data is stored in pagecache before being written
back to a disk or the network (making it a write-back cache). When a page has new
data not written back yet, it is called “dirty”. Pages not classified as dirty are “clean”.
Clean pagecache pages can be reclaimed if there is a memory shortage by simply
freeing them. Dirty pages must first be made clean before being reclaimed.
15.1.3 Buffercache
This is a type of pagecache for block devices (for example, /dev/sda). A file system
typically uses the buffercache when accessing its on-disk “meta-data” structures such
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as inode tables, allocation bitmaps, and so forth. Buffercache can be reclaimed similarly to pagecache.
15.1.4 Buffer Heads
Buffer heads are small auxiliary structures that tend to be allocated upon pagecache
access. They can generally be reclaimed easily when the pagecache or buffercache
pages are clean.
15.1.5 Writeback
As applications write to files, the pagecache (and buffercache) becomes dirty. When
pages have been dirty for a given amount of time, or when the amount of dirty memory reaches a particular percentage of RAM, the kernel begins writeback. Flusher
threads perform writeback in the background and allow applications to continue running. If the I/O cannot keep up with applications dirtying pagecache, and dirty data
reaches a critical percentage of RAM, then applications begin to be throttled to prevent dirty data exceeding this threshold.
15.1.6 Readahead
The VM monitors file access patterns and may attempt to perform readahead. Readahead reads pages into the pagecache from the file system that have not been requested
yet. It is done in order to allow fewer, larger I/O requests to be submitted (more efficient). And for I/O to be pipelined (I/O performed at the same time as the application
is running).
15.1.7 VFS caches
15.1.7.1 Inode Cache
This is an in-memory cache of the inode structures for each file system. These contain
attributes such as the file size, permissions and ownership, and pointers to the file data.
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181
15.1.7.2 Directory Entry Cache
This is an in-memory cache of the directory entries in the system. These contain a
name (the name of a file), the inode which it refers to, and children entries. This
cache is used when traversing the directory structure and accessing a file by name.
15.2 Reducing Memory Usage
15.2.1 Reducing malloc (Anonymous)
Usage
Applications running on SUSE Linux Enterprise Server 11 SP3 can allocate more
memory compared to SUSE Linux Enterprise Server 10. This is due to glibc
changing its default behavior while allocating userspace memory. Please see
http://www.gnu.org/s/libc/manual/html_node/Malloc-Tun​
able-Parameters.html for explanation of these parameters.
To restore a SUSE Linux Enterprise Server 10-like behavior,
M_MMAP_THRESHOLD should be set to 128*1024. This can be done with mallopt() call from the application, or via setting MALLOC_MMAP_THRESHOLD environment variable before running the application.
15.2.2 Reducing Kernel Memory
Overheads
Kernel memory that is reclaimable (caches, described above) will be trimmed automatically during memory shortages. Most other kernel memory cannot be easily reduced but is a property of the workload given to the kernel.
Reducing the requirements of the userspace workload will reduce the kernel memory
usage (fewer processes, fewer open files and sockets, etc.)
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15.2.3 Memory Controller (Memory
Cgroups)
If the memory cgroups feature is not needed, it can be switched off by passing
cgroup_disable=memory on the kernel command line, reducing memory consumption
of the kernel a bit.
15.3 Virtual Memory Manager (VM)
Tunable Parameters
When tuning the VM it should be understood that some of the changes will take
time to affect the workload and take full effect. If the workload changes throughout
the day, it may behave very differently at different times. A change that increases
throughput under some conditions may decrease it under other conditions.
15.3.1 Reclaim Ratios
/proc/sys/vm/swappiness
This control is used to define how aggressively the kernel swaps out anonymous
memory relative to pagecache and other caches. Increasing the value increases the
amount of swapping. The default value is 60.
Swap I/O tends to be much less efficient than other I/O. However, some pagecache pages will be accessed much more frequently than less used anonymous
memory. The right balance should be found here.
If swap activity is observed during slowdowns, it may be worth reducing this parameter. If there is a lot of I/O activity and the amount of pagecache in the system is rather small, or if there are large dormant applications running, increasing
this value might improve performance.
Note that the more data is swapped out, the longer the system will take to swap
data back in when it is needed.
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183
/proc/sys/vm/vfs_cache_pressure
This variable controls the tendency of the kernel to reclaim the memory which is
used for caching of VFS caches, versus pagecache and swap. Increasing this value
increases the rate at which VFS caches are reclaimed.
It is difficult to know when this should be changed, other than by experimentation. The slabtop command (part of the package procps) shows top
memory objects used by the kernel. The vfs caches are the "dentry" and the
"*_inode_cache" objects. If these are consuming a large amount of memory in relation to pagecache, it may be worth trying to increase pressure. Could also help
to reduce swapping. The default value is 100.
/proc/sys/vm/min_free_kbytes
This controls the amount of memory that is kept free for use by special reserves
including “atomic” allocations (those which cannot wait for reclaim). This should
not normally be lowered unless the system is being very carefully tuned for memory usage (normally useful for embedded rather than server applications). If
“page allocation failure” messages and stack traces are frequently seen in logs,
min_free_kbytes could be increased until the errors disappear. There is no need
for concern, if these messages are very infrequent. The default value depends on
the amount of RAM.
15.3.2 Writeback Parameters
One important change in writeback behavior since SUSE Linux Enterprise Server 10
is that modification to file-backed mmap() memory is accounted immediately as dirty
memory (and subject to writeback). Whereas previously it would only be subject to
writeback after it was unmapped, upon an msync() system call, or under heavy memory pressure.
Some applications do not expect mmap modifications to be subject to such writeback
behavior, and performance can be reduced. Berkeley DB (and applications using it)
is one known example that can cause problems. Increasing writeback ratios and times
can improve this type of slowdown.
/proc/sys/vm/dirty_background_ratio
This is the percentage of the total amount of free and reclaimable memory. When
the amount of dirty pagecache exceeds this percentage, writeback threads start
writing back dirty memory. The default value is 10 (%).
/proc/sys/vm/dirty_ratio
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System Analysis and Tuning Guide
Similar percentage value as above. When this is exceeded, applications that want
to write to the pagecache are blocked and start performing writeback as well. The
default value is 40 (%).
These two values together determine the pagecache writeback behavior. If these
values are increased, more dirty memory is kept in the system for a longer time.
With more dirty memory allowed in the system, the chance to improve throughput
by avoiding writeback I/O and to submitting more optimal I/O patterns increases.
However, more dirty memory can either harm latency when memory needs to be reclaimed or at data integrity (sync) points when it needs to be written back to disk.
15.3.3 Readahead parameters
/sys/block/<bdev>/queue/read_ahead_kb
If one or more processes are sequentially reading a file, the kernel reads some data in advance (ahead) in order to reduce the amount of time that processes have
to wait for data to be available. The actual amount of data being read in advance
is computed dynamically, based on how much "sequential" the I/O seems to be.
This parameter sets the maximum amount of data that the kernel reads ahead
for a single file. If you observe that large sequential reads from a file are not fast
enough, you can try increasing this value. Increasing it too far may result in readahead thrashing where pagecache used for readahead is reclaimed before it can
be used, or slowdowns due to a large amount of useless I/O. The default value is
512 (kb).
15.3.4 Further VM Parameters
For the complete list of the VM tunable parameters, see /usr/src/linux/Doc​
umentation/sysctl/vm.txt (available after having installed the kernel-source package).
15.4 Non-Uniform Memory Access
(NUMA)
Another increasingly important role of the VM is to provide good NUMA allocation
strategies. NUMA stands for non-uniform memory access, and most of today's mulTuning the Memory Management Subsystem
185
ti-socket servers are NUMA machines. NUMA is a secondary concern to managing
swapping and caches in terms of performance, and there are lots of documents about
improving NUMA memory allocations. One particular parameter interacts with page
reclaim:
/proc/sys/vm/zone_reclaim_mode
This parameter controls whether memory reclaim is performed on a local NUMA
node even if there is plenty of memory free on other nodes. This parameter is automatically turned on on machines with more pronounced NUMA characteristics.
If the VM caches are not being allowed to fill all of memory on a NUMA machine, it could be due to zone_reclaim_mode being set. Setting to 0 will disable
this behavior.
15.5 Monitoring VM Behavior
Some simple tools that can help monitor VM behavior:
1. vmstat: This tool gives a good overview of what the VM is doing. See Section 2.1.1,
“vmstat” (page 10) for details.
2. /proc/meminfo: This file gives a detailed breakdown of where memory is being used. See Section 2.4.2, “Detailed Memory Usage: /proc/
meminfo” (page 29) for details.
3. slabtop: This tool provides detailed information about kernel slab memory
usage. buffer_head, dentry, inode_cache, ext3_inode_cache, etc. are the major
caches. This command is available with the package procps.
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16
Tuning the Network
The network subsystem is rather complex and its tuning highly depends on the system
use scenario and also on external factors such as software clients or hardware components (switches, routers, or gateways) in your network. The Linux kernel aims more at
reliability and low latency than low overhead and high throughput. Other settings can
mean less security, but better performance.
16.1 Configurable Kernel Socket
Buffers
Networking is largely based on the TCP/IP protocol and a socket interface for communication; for more information about TCP/IP, see Chapter 21, Basic Networking
(↑Administration Guide). The Linux kernel handles data it receives or sends via the
socket interface in socket buffers. These kernel socket buffers are tunable.
IMPORTANT: TCP Autotuning
Since kernel version 2.6.17 full autotuning with 4 MB maximum buffer size
exists. This means that manual tuning in most cases will not improve networking performance considerably. It is often the best not to touch the following variables, or, at least, to check the outcome of tuning efforts carefully.
If you update from an older kernel, it is recommended to remove manual TCP
tunings in favor of the autotuning feature.
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187
The special files in the /proc file system can modify the size and behavior of kernel
socket buffers; for general information about the /proc file system, see Section 2.6,
“The /proc File System” (page 35). Find networking related files in:
/proc/sys/net/core
/proc/sys/net/ipv4
/proc/sys/net/ipv6
General net variables are explained in the kernel documentation (linux/Docu​
mentation/sysctl/net.txt). Special ipv4 variables are explained in lin​
ux/Documentation/networking/ip-sysctl.txt and linux/Docu​
mentation/networking/ipvs-sysctl.txt.
In the /proc file system, for example, it is possible to either set the Maximum Socket Receive Buffer and Maximum Socket Send Buffer for all protocols, or both these
options for the TCP protocol only (in ipv4) and thus overriding the setting for all
protocols (in core).
/proc/sys/net/ipv4/tcp_moderate_rcvbuf
If /proc/sys/net/ipv4/tcp_moderate_rcvbuf is set to 1, autotuning
is active and buffer size is adjusted dynamically.
/proc/sys/net/ipv4/tcp_rmem
The three values setting the minimum, initial, and maximum size of the Memory Receive Buffer per connection. They define the actual memory usage, not just
TCP window size.
/proc/sys/net/ipv4/tcp_wmem
The same as tcp_rmem, but just for Memory Send Buffer per connection.
/proc/sys/net/core/rmem_max
Set to limit the maximum receive buffer size that applications can request.
/proc/sys/net/core/wmem_max
Set to limit the maximum send buffer size that applications can request.
Via /proc it is possible to disable TCP features that you do not need (all TCP features are switched on by default). For example, check the following files:
/proc/sys/net/ipv4/tcp_timestamps
TCP timestamps are defined in RFC1323.
/proc/sys/net/ipv4/tcp_window_scaling
TCP window scaling is also defined in RFC1323.
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/proc/sys/net/ipv4/tcp_sack
Select acknowledgments (SACKS).
Use sysctl to read or write variables of the /proc file system. sysctl is preferable to cat (for reading) and echo (for writing), because it also reads settings
from /etc/sysctl.conf and, thus, those settings survive reboots reliably. With
sysctl you can read all variables and their values easily; as root use the following
command to list TCP related settings:
sysctl -a | grep tcp
NOTE: Side-Effects of Tuning Network Variables
Tuning network variables can affect other system resources such as CPU or
memory use.
16.2 Detecting Network Bottlenecks
and Analyzing Network Traffic
Before starting with network tuning, it is important to isolate network bottlenecks and
network traffic patterns. There are some tools that can help you with detecting those
bottlenecks.
The following tools can help analyzing your network traffic: netstat, tcpdump,
and wireshark. Wireshark is a network traffic analyzer.
16.3 Netfilter
The Linux firewall and masquerading features are provided by the Netfilter kernel
modules. This is a highly configurable rule based framework. If a rule matches a
packet, Netfilter accepts or denies it or takes special action (“target”) as defined by
rules such as address translation.
There are quite some properties, Netfilter is able to take into account. Thus, the more
rules are defined, the longer packet processing may last. Also advanced connection
tracking could be rather expensive and, thus, slowing down overall networking.
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When the kernel queue becomes full, all new packets are dropped, causing existing connections to fail. The 'fail-open' feature, available since SUSE Linux Enterprise Server 11 SP3, allows a user to temporarily disable the packet inspection and maintain the connectivity under heavy network traffic. For reference, see
https://home.regit.org/netfilter-en/using-nfqueue-andlibnetfilter_queue/.
For more information, see the home page of the Netfilter and iptables project,
http://www.netfilter.org
16.4 For More Information
• Eduardo Ciliendo, Takechika Kunimasa: “Linux Performance and
Tuning Guidelines” (2007), esp. sections 1.5, 3.5, and 4.7: http://
www.redbooks.ibm.com/redpapers/abstracts/redp4285.html
• John Heffner, Matt Mathis: “Tuning TCP for Linux 2.4 and 2.6” (2006): http://
www.psc.edu/networking/projects/tcptune/#Linux
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Part VI. Handling
System Dumps
17
Tracing Tools
SUSE Linux Enterprise Server comes with a number of tools that help you obtain useful information about your system. You can use the information for various purposes,
for example, to debug and find problems in your program, to discover places causing
performance drops, or to trace a running process to find out what system resources
it uses. The tools are mostly part of the installation media, otherwise you can install
them from the downloadable SUSE Software Development Kit.
NOTE: Tracing and Impact on Performance
While a running process is being monitored for system or library calls, the
performance of the process is heavily reduced. You are advised to use tracing tools only for the time you need to collect the data.
17.1 Tracing System Calls with
strace
The strace command traces system calls of a process and signals received by the
process. strace can either run a new command and trace its system calls, or you can
attach strace to an already running command. Each line of the command's output
contains the system call name, followed by its arguments in parenthesis and its return
value.
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To run a new command and start tracing its system calls, enter the command to be
monitored as you normally do, and add strace at the beginning of the command
line:
tux@mercury:~> strace ls
execve("/bin/ls", ["ls"], [/* 52 vars */]) = 0
brk(0)
= 0x618000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) \
= 0x7f9848667000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) \
= 0x7f9848666000
access("/etc/ld.so.preload", R_OK)
= -1 ENOENT \
(No such file or directory)
open("/etc/ld.so.cache", O_RDONLY)
= 3
fstat(3, {st_mode=S_IFREG|0644, st_size=200411, ...}) = 0
mmap(NULL, 200411, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f9848635000
close(3)
= 0
open("/lib64/librt.so.1", O_RDONLY)
= 3
[...]
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) \
= 0x7fd780f79000
write(1, "Desktop\nDocuments\nbin\ninst-sys\n", 31Desktop
Documents
bin
inst-sys
) = 31
close(1)
= 0
munmap(0x7fd780f79000, 4096)
= 0
close(2)
= 0
exit_group(0)
= ?
To attach strace to an already running process, you need to specify the -p with the
process ID (PID) of the process that you want to monitor:
tux@mercury:~> strace -p `pidof mysqld`
Process 2868 attached - interrupt to quit
select(15, [13 14], NULL, NULL, NULL)
= 1 (in [14])
fcntl(14, F_SETFL, O_RDWR|O_NONBLOCK)
= 0
accept(14, {sa_family=AF_FILE, NULL}, [2]) = 31
fcntl(14, F_SETFL, O_RDWR)
= 0
getsockname(31, {sa_family=AF_FILE, path="/var/run/mysql"}, [28]) = 0
fcntl(31, F_SETFL, O_RDONLY)
= 0
fcntl(31, F_GETFL)
= 0x2 (flags O_RDWR)
fcntl(31, F_SETFL, O_RDWR|O_NONBLOCK)
= 0
[...]
setsockopt(31, SOL_IP, IP_TOS, [8], 4) = -1 EOPNOTSUPP (Operation \
not supported)
clone(child_stack=0x7fd1864801f0, flags=CLONE_VM|CLONE_FS|CLONE_ \
FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_ \
PARENT_SETTID|CLONE_CHILD_CLEARTID, parent_tidptr=0x7fd1864809e0, \
tls=0x7fd186480910, child_tidptr=0x7fd1864809e0) = 21993
select(15, [13 14], NULL, NULL, NULL
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The -e option understands several sub-options and arguments. For example, to trace
all attempts to open or write to a particular file, use the following:
tux@mercury:~> strace -e trace=open,write ls ~
open("/etc/ld.so.cache", O_RDONLY)
= 3
open("/lib64/librt.so.1", O_RDONLY)
= 3
open("/lib64/libselinux.so.1", O_RDONLY) = 3
open("/lib64/libacl.so.1", O_RDONLY)
= 3
open("/lib64/libc.so.6", O_RDONLY)
= 3
open("/lib64/libpthread.so.0", O_RDONLY) = 3
[...]
open("/usr/lib/locale/cs_CZ.utf8/LC_CTYPE", O_RDONLY) = 3
open(".", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 3
write(1, "addressbook.db.bak\nbin\ncxoffice\n"..., 311) = 311
To trace only network related system calls, use -e trace=network:
tux@mercury:~> strace -e trace=network -p 26520
Process 26520 attached - interrupt to quit
socket(PF_NETLINK, SOCK_RAW, 0)
= 50
bind(50, {sa_family=AF_NETLINK, pid=0, groups=00000000}, 12) = 0
getsockname(50, {sa_family=AF_NETLINK, pid=26520, groups=00000000}, \
[12]) = 0
sendto(50, "\24\0\0\0\26\0\1\3~p\315K\0\0\0\0\0\0\0\0", 20, 0,
{sa_family=AF_NETLINK, pid=0, groups=00000000}, 12) = 20
[...]
The -c calculates the time the kernel spent on each system call:
tux@mercury:~> strace -c find /etc -name xorg.conf
/etc/X11/xorg.conf
% time
seconds usecs/call
calls
errors syscall
------ ----------- ----------- --------- --------- ---------------32.38
0.000181
181
1
execve
22.00
0.000123
0
576
getdents64
19.50
0.000109
0
917
31 open
19.14
0.000107
0
888
close
4.11
0.000023
2
10
mprotect
0.00
0.000000
0
1
write
[...]
0.00
0.000000
0
1
getrlimit
0.00
0.000000
0
1
arch_prctl
0.00
0.000000
0
3
1 futex
0.00
0.000000
0
1
set_tid_address
0.00
0.000000
0
4
fadvise64
0.00
0.000000
0
1
set_robust_list
------ ----------- ----------- --------- --------- ---------------100.00
0.000559
3633
33 total
To trace all child processes of a process, use -f:
tux@mercury:~> strace -f rcapache2 status
execve("/usr/sbin/rcapache2", ["rcapache2", "status"], [/* 81 vars */]) = 0
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brk(0)
= 0x69e000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) \
= 0x7f3bb553b000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) \
= 0x7f3bb553a000
[...]
[pid 4823] rt_sigprocmask(SIG_SETMASK, [], <unfinished ...>
[pid 4822] close(4 <unfinished ...>
[pid 4823] <... rt_sigprocmask resumed> NULL, 8) = 0
[pid 4822] <... close resumed> )
= 0
[...]
[pid 4825] mprotect(0x7fc42cbbd000, 16384, PROT_READ) = 0
[pid 4825] mprotect(0x60a000, 4096, PROT_READ) = 0
[pid 4825] mprotect(0x7fc42cde4000, 4096, PROT_READ) = 0
[pid 4825] munmap(0x7fc42cda2000, 261953) = 0
[...]
[pid 4830] munmap(0x7fb1fff10000, 261953) = 0
[pid 4830] rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0
[pid 4830] open("/dev/tty", O_RDWR|O_NONBLOCK) = 3
[pid 4830] close(3)
[...]
read(255, "\n\n# Inform the caller not only v"..., 8192) = 73
rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0
rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0
exit_group(0)
If you need to analyze the output of strace and the output messages are too long to
be inspected directly in the console window, use -o. In that case, unnecessary messages, such as information about attaching and detaching processes, are suppressed.
You can also suppress these messages (normally printed on the standard output) with
-q. To optionally prepend timestamps to each line with a system call, use -t:
tux@mercury:~> strace -t -o strace_sleep.txt sleep 1; more strace_sleep.txt
08:44:06 execve("/bin/sleep", ["sleep", "1"], [/* 81 vars */]) = 0
08:44:06 brk(0)
= 0x606000
08:44:06 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, \
-1, 0) = 0x7f8e78cc5000
[...]
08:44:06 close(3)
= 0
08:44:06 nanosleep({1, 0}, NULL)
= 0
08:44:07 close(1)
= 0
08:44:07 close(2)
= 0
08:44:07 exit_group(0)
= ?
The behavior and output format of strace can be largely controlled. For more information, see the relevant manual page (man 1 strace).
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17.2 Tracing Library Calls with
ltrace
ltrace traces dynamic library calls of a process. It is used in a similar way to
strace, and most of their parameters have a very similar or identical meaning. By
default, ltrace uses /etc/ltrace.conf or ~/.ltrace.conf configuration
files. You can, however, specify an alternative one with the -F config_file option.
In addition to library calls, ltrace with the -S option can trace system calls as well:
tux@mercury:~> ltrace -S -o ltrace_find.txt find /etc -name \
xorg.conf; more ltrace_find.txt
SYS_brk(NULL)
= 0x00628000
SYS_mmap(0, 4096, 3, 34, 0xffffffff)
= 0x7f1327ea1000
SYS_mmap(0, 4096, 3, 34, 0xffffffff)
= 0x7f1327ea0000
[...]
fnmatch("xorg.conf", "xorg.conf", 0)
= 0
free(0x0062db80)
= <void>
__errno_location()
= 0x7f1327e5d698
__ctype_get_mb_cur_max(0x7fff25227af0, 8192, 0x62e020, -1, 0) = 6
__ctype_get_mb_cur_max(0x7fff25227af0, 18, 0x7f1327e5d6f0, 0x7fff25227af0,
0x62e031) = 6
__fprintf_chk(0x7f1327821780, 1, 0x420cf7, 0x7fff25227af0, 0x62e031
<unfinished ...>
SYS_fstat(1, 0x7fff25227230)
= 0
SYS_mmap(0, 4096, 3, 34, 0xffffffff)
= 0x7f1327e72000
SYS_write(1, "/etc/X11/xorg.conf\n", 19)
= 19
[...]
You can change the type of traced events with the -e option. The following example
prints library calls related to fnmatch and strlen functions:
tux@mercury:~> ltrace -e fnmatch,strlen find /etc -name xorg.conf
[...]
fnmatch("xorg.conf", "xorg.conf", 0)
= 0
strlen("Xresources")
= 10
strlen("Xresources")
= 10
strlen("Xresources")
= 10
fnmatch("xorg.conf", "Xresources", 0)
= 1
strlen("xorg.conf.install")
= 17
[...]
To display only the symbols included in a specific library, use -l /path/to/library:
tux@mercury:~> ltrace -l /lib64/librt.so.1 sleep 1
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clock_gettime(1, 0x7fff4b5c34d0, 0, 0, 0)
= 0
clock_gettime(1, 0x7fff4b5c34c0, 0xffffffffff600180, -1, 0) = 0
+++ exited (status 0) +++
You can make the output more readable by indenting each nested call by the specified
number of space with the -n num_of_spaces.
17.3 Debugging and Profiling with
Valgrind
Valgrind is a set of tools to debug and profile your programs so that they can run
faster and with less errors. Valgrind can detect problems related to memory management and threading, or can also serve as a framework for building new debugging
tools.
17.3.1 Installation
Valgrind is not shipped with standard SUSE Linux Enterprise Server distribution. To
install it on your system, you need to obtain SUSE Software Development Kit, and either install it as an Add-On product and run
zypper install valgrind
or browse through the SUSE Software Development Kit directory tree, locate the Valgrind package and install it with
rpm -i valgrind-version_architecture.rpm
17.3.2 Supported Architectures
Valgrind runs on the following architectures:
• i386
• x86_64 (AMD-64)
• ppc
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• ppc64
• System z
17.3.3 General Information
The main advantage of Valgrind is that it works with existing compiled executables.
You do not have to recompile or modify your programs to make use of it. Run Valgrind like this:
valgrind valgrind_options your-prog your-program-options
Valgrind consists of several tools, and each provides specific functionality. Information in this section is general and valid regardless of the used tool. The most important
configuration option is --tool . This option tells Valgrind which tool to run. If you
omit this option, memcheck is selected by default. For example, if you want to run
find ~ -name .bashrc with Valgrind's memcheck tools, enter the following
in the command line:
valgrind --tool=memcheck find ~ -name .bashrc
A list of standard Valgrind tools with a brief description follows:
memcheck
Detects memory errors. It helps you tune your programs to behave correctly.
cachegrind
Profiles cache prediction. It helps you tune your programs to run faster.
callgrind
Works in a similar way to cachegrind but also gathers additional cache-profiling information.
exp-drd
Detects thread errors. It helps you tune your multi-threaded programs to behave
correctly.
helgrind
Another thread error detector. Similar to exp-drd but uses different techniques
for problem analysis.
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massif
A heap profiler. Heap is an area of memory used for dynamic memory allocation.
This tool helps you tune your program to use less memory.
lackey
An example tool showing instrumentation basics.
17.3.4 Default Options
Valgrind can read options at start-up. There are three places which Valgrind checks:
1. The file .valgrindrc in the home directory of the user who runs Valgrind.
2. The environment variable $VALGRIND_OPTS
3. The file .valgrindrc in the current directory where Valgrind is run from.
These resources are parsed exactly in this order, while later given options take
precedence over earlier processed options. Options specific to a particular Valgrind
tool must be prefixed with the tool name and a colon. For example, if you want
cachegrind to always write profile data to the /tmp/cachegrind_PID.log,
add the following line to the .valgrindrc file in your home directory:
--cachegrind:cachegrind-out-file=/tmp/cachegrind_%p.log
17.3.5 How Valgrind Works
Valgrind takes control of your executable before it starts. It reads debugging information from the executable and related shared libraries. The executable's code is redirected to the selected Valgrind tool, and the tool adds its own code to handle its debugging. Then the code is handed back to the Valgrind core and the execution continues.
For example, memcheck adds its code, which checks every memory access. As a
consequence, the program runs much slower than in the native execution environment.
Valgrind simulates every instruction of your program. Therefore, it not only checks
the code of your program, but also all related libraries (including the C library), libraries used for graphical environment, and so on. If you try to detect errors with Val200
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grind, it also detects errors in associated libraries (like C, X11, or Gtk libraries). Because you probably do not need these errors, Valgrind can selectively, suppress these
error messages to suppression files. The --gen-suppressions=yes tells Valgrind to report these suppressions which you can copy to a file.
Note that you should supply a real executable (machine code) as an Valgrind argument. Therefore, if your application is run, for example, from a shell or a Perl script
you will by mistake get error reports related to /bin/sh (or /usr/bin/perl). In
such case, you can use --trace-children=yes or, which is better, supply a real
executable to avoid any processing confusion.
17.3.6 Messages
During its runtime, Valgrind reports messages with detailed errors and important
events. The following example explains the messages:
tux@mercury:~> valgrind --tool=memcheck find ~ -name .bashrc
[...]
==6558== Conditional jump or move depends on uninitialised value(s)
==6558==
at 0x400AE79: _dl_relocate_object (in /lib64/ld-2.11.1.so)
==6558==
by 0x4003868: dl_main (in /lib64/ld-2.11.1.so)
[...]
==6558== Conditional jump or move depends on uninitialised value(s)
==6558==
at 0x400AE82: _dl_relocate_object (in /lib64/ld-2.11.1.so)
==6558==
by 0x4003868: dl_main (in /lib64/ld-2.11.1.so)
[...]
==6558== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 0 from 0)
==6558== malloc/free: in use at exit: 2,228 bytes in 8 blocks.
==6558== malloc/free: 235 allocs, 227 frees, 489,675 bytes allocated.
==6558== For counts of detected errors, rerun with: -v
==6558== searching for pointers to 8 not-freed blocks.
==6558== checked 122,584 bytes.
==6558==
==6558== LEAK SUMMARY:
==6558==
definitely lost: 0 bytes in 0 blocks.
==6558==
possibly lost: 0 bytes in 0 blocks.
==6558==
still reachable: 2,228 bytes in 8 blocks.
==6558==
suppressed: 0 bytes in 0 blocks.
==6558== Rerun with --leak-check=full to see details of leaked memory.
The ==6558== introduces Valgrind's messages and contains the process ID number
(PID). You can easily distinguish Valgrind's messages from the output of the program
itself, and decide which messages belong to a particular process.
To make Valgrind's messages more detailed, use -v or even -v -v.
Basically, you can make Valgrind send its messages to three different places:
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1. By default, Valgrind sends its messages to the file descriptor 2, which is the standard error output. You can tell Valgrind to send its messages to any other file descriptor with the --log-fd=file_descriptor_number option.
2. The second and probably more useful way is to send Valgrind's messages to a file
with --log-file=filename. This option accepts several variables, for example, %p gets replaced with the PID of the currently profiled process. This way
you can send messages to different files based on their PID. %q{env_var} is replaced with the value of the related env_var environment variable.
The following example checks for possible memory errors during the Apache Web
server restart, while following children processes and writing detailed Valgrind's
messages to separate files distinguished by the current process PID:
tux@mercury:~> valgrind -v --tool=memcheck --trace-children=yes \
--log-file=valgrind_pid_%p.log rcapache2 restart
This process created 52 log files in the testing system, and took 75 seconds instead
of the usual 7 seconds needed to run rcapache2 restart without Valgrind,
which is approximately 10 times more.
tux@mercury:~> ls -1 valgrind_pid_*log
valgrind_pid_11780.log
valgrind_pid_11782.log
valgrind_pid_11783.log
[...]
valgrind_pid_11860.log
valgrind_pid_11862.log
valgrind_pid_11863.log
3. You may also prefer to send the Valgrind's messages over the network. You need
to specify the aa.bb.cc.dd IP address and port_num port number of the network socket with the --log-socket=aa.bb.cc.dd:port_num option. If
you omit the port number, 1500 will be used.
It is useless to send Valgrind's messages to a network socket if no application is capable of receiving them on the remote machine. That is why valgrind-listener, a simple listener, is shipped together with Valgrind. It accepts connections
on the specified port and copies everything it receives to the standard output.
17.3.7 Error Messages
Valgrind remembers all error messages, and if it detects a new error, the error is compared against old error messages. This way Valgrind checks for duplicate error mes-
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sages. In case of a duplicate error, it is recorded but no message is shown. This mechanism prevents you from being overwhelmed by millions of duplicate errors.
The -v option will add a summary of all reports (sorted by their total count) to the
end of the Valgrind's execution output. Moreover, Valgrind stops collecting errors if it
detects either 1000 different errors, or 10 000 000 errors in total. If you want to suppress this limit and wish to see all error messages, use --error-limit=no.
Some errors usually cause other ones. Therefore, fix errors in the same order as they
appear and re-check the program continuously.
17.4 For More Information
• For a complete list of options related to the described tracing tools, see the corresponding man page (man 1 strace, man 1 ltrace, and man 1 valgrind).
• To describe advanced usage of Valgrind is beyond the scope of this document. It is
very well documented, see Valgrind User Manual [http://valgrind.org/
docs/manual/manual.html]. These pages are indispensable if you need
more advanced information on Valgrind or the usage and purpose of its standard
tools.
Tracing Tools
203
kexec and kdump
kexec is a tool to boot to another kernel from the currently running one. You can perform faster system reboots without any hardware initialization. You can also prepare
the system to boot to another kernel if the system crashes.
18
18.1 Introduction
With kexec, you can replace the running kernel with another one without a hard reboot. The tool is useful for several reasons:
• Faster system rebooting
If you need to reboot the system frequently, kexec can save you significant time.
• Avoiding unreliable firmware and hardware
Computer hardware is complex and serious problems may occur during the system
start-up. You cannot always replace unreliable hardware immediately. kexec boots
the kernel to a controlled environment with the hardware already initialized. The
risk of unsuccessful system start is then minimized.
• Saving the dump of a crashed kernel
kexec preserves the contents of the physical memory. After the production kernel
fails, the capture kernel (an additional kernel running in a reserved memory range)
saves the state of the failed kernel. The saved image can help you with the subsequent analysis.
kexec and kdump
205
• Booting without GRUB or LILO configuration
When the system boots a kernel with kexec, it skips the boot loader stage. Normal
booting procedure can fail due to an error in the boot loader configuration. With
kexec, you do not depend on a working boot loader configuration.
18.2 Required Packages
If you intend to use kexec on SUSE® Linux Enterprise Server to speed up reboots
or avoid potential hardware problems, you need to install the kexec-tools package. It contains a script called kexec-bootloader, which reads the boot loader
configuration and runs kexec with the same kernel options as the normal boot loader
does. kexec-bootloader -h gives you the list of possible options.
To set up an environment that helps you obtain useful debug information in case of a
kernel crash, you need to install makedumpfile in addition.
The preferred method to use kdump in SUSE Linux Enterprise Server is through the
YaST kdump module. Install the package yast2-kdump by entering zypper install yast2-kdump in the command line as root.
18.3 kexec Internals
The most important component of kexec is the /sbin/kexec command. You can
load a kernel with kexec in two different ways:
• kexec -l kernel_image loads the kernel to the address space of a production kernel for a regular reboot. You can later boot to this kernel with kexec -e.
• kexec -p kernel_image loads the kernel to a reserved area of memory.
This kernel will be booted automatically when the system crashes.
If you want to boot another kernel and preserve the data of the production kernel
when the system crashes, you need to reserve a dedicated area of the system memory.
The production kernel never loads to this area because it must be always available. It
is used for the capture kernel so that the memory pages of the production kernel can
be preserved. You reserve the area with crashkernel = size@offset as a command line parameter of the production kernel. Note that this is not a parameter of the
capture kernel. The capture kernel does not use kexec at all.
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The capture kernel is loaded to the reserved area and waits for the kernel to crash.
Then kdump tries to invoke the capture kernel because the production kernel is no
longer reliable at this stage. This means that even kdump can fail.
To load the capture kernel, you need to include the kernel boot parameters. Usually,
the initial RAM file system is used for booting. You can specify it with --initrd
= filename. With --append = cmdline , you append options to the command
line of the kernel to boot. It is helpful to include the command line of the production
kernel if these options are necessary for the kernel to boot. You can simply copy the
command line with --append = "$(cat /proc/cmdline)" or add more options with --append = "$(cat /proc/cmdline) more_options" .
You can always unload the previously loaded kernel. To unload a kernel that was
loaded with the -l option, use the kexec -u command. To unload a crash kernel
loaded with the -p option, use kexec -p -u command.
18.4 Basic kexec Usage
To verify if your kexec environment works properly, follow these steps:
1 Make sure no users are currently logged in and no important services are running
on the system.
2 Log in as root.
3 Switch to runlevel 1 with telinit 1
4 Load the new kernel to the address space of the production kernel with the following command:
kexec -l /boot/vmlinuz --append="$(cat /proc/cmdline)"
--initrd=/boot/initrd
5 Unmount all mounted file systems except the root file system with umount -a
IMPORTANT: Unmounting Root Filesystem
Unmounting all file systems will most likely produce a device is busy
warning message. The root file system cannot be unmounted if the system
is running. Ignore the warning.
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207
6 Remount the root file system in read-only mode:
mount -o remount,ro /
7 Initiate the reboot of the kernel that you loaded in Step 4 (page 207) with kexec -e
It is important to unmount the previously mounted disk volumes in read-write mode.
The reboot system call acts immediately upon calling. Hard drive volumes mounted
in read-write mode neither synchronize nor unmount automatically. The new kernel
may find them “dirty”. Read-only disk volumes and virtual file systems do not need
to be unmounted. Refer to /etc/mtab to determine which file systems you need to
unmount.
The new kernel previously loaded to the address space of the older kernel rewrites it
and takes control immediately. It displays the usual start-up messages. When the new
kernel boots, it skips all hardware and firmware checks. Make sure no warning messages appear. All the file systems are supposed to be clean if they had been unmounted.
18.5 How to Configure kexec for
Routine Reboots
kexec is often used for frequent reboots. For example, if it takes a long time to run
through the hardware detection routines or if the start-up is not reliable.
NOTE: Rebooting with kexec
In previous versions of SUSE® Linux Enterprise Server, you had to manually
edit the configuration file /etc/sysconfig/shutdown and the init script /
etc/init.d/halt to use kexec to reboot the system. You no longer need
to edit any system files, since version 11 is already configured for kexec reboots.
Note that firmware as well as the boot loader are not used when the system reboots
with kexec. Any changes you make to the boot loader configuration will be ignored
until the computer performs a hard reboot.
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System Analysis and Tuning Guide
18.6 Basic kdump Configuration
You can use kdump to save kernel dumps. If the kernel crashes, it is useful to copy
the memory image of the crashed environment to the file system. You can then debug
the dump file to find the cause of the kernel crash. This is called “core dump”.
kdump works similar to kexec (see Chapter 18, kexec and kdump (page 205)). The
capture kernel is executed after the running production kernel crashes. The difference
is that kexec replaces the production kernel with the capture kernel. With kdump, you
still have access to the memory space of the crashed production kernel. You can save
the memory snapshot of the crashed kernel in the environment of the kdump kernel.
TIP: Dumps over Network
In environments with limited local storage, you need to set up kernel dumps
over the network. kdump supports configuring the specified network interface and bringing it up via initrd. Both LAN and VLAN interfaces are supported. You have to specify the network interface and the mode (dhcp or static) either with YaST, or using the KDUMP_NETCONFIG option in the /etc/
sysconfig/kdump file. The third way is to build initrd manually, for example with
/sbin/mkinitrd -D vlan0
for a dhcp VLAN interface, or
/sbin/mkinitrd -I eth0
for a static LAN interface.
You can either configure kdump manually or with YaST.
IMPORTANT: Target Filesystem for kdump Must Be Mounted During
Configuration
When configuring kdump, you can specify a location to which the dumped
images will be saved (default: /var/crash). This location must be mounted
when configuring kdump, otherwise the configuration will fail.
kexec and kdump
209
18.6.1 Manual kdump Configuration
kdump reads its configuration from the /etc/sysconfig/kdump file. To make
sure that kdump works on your system, its default configuration is sufficient. To use
kdump with the default settings,follow these steps:
1 Append the following kernel command line option to your boot loader configuration, and reboot the system:
crashkernel=size@offset
You can find the corresponding values for size and offset in the following table:
Table 18.1: Recommended Values for Additional Kernel Command Line
Parameters
210
Architecture
Recommended value
i386 and x86-64
crashkernel=256M for 0 - 12
GB memory
crashkernel=512M for 13 - 48
GB memory
crashkernel=1G for 49 - 128
GB memory
crashkernel=2G for 129 - 256
GB memory
IA64
crashkernel=256M (small systems)
or crashkernel=512M (larger systems)
ppc64
crashkernel=128M@4M or
crashkernel=256M@4M (larger systems)
s390x
crashkernel=128M (small systems)
or crashkernel=256M (larger systems)
System Analysis and Tuning Guide
2 Enable kdump init script:
chkconfig boot.kdump on
3 You can edit the options in /etc/sysconfig/kdump. Reading the comments
will help you understand the meaning of individual options.
4 Execute the init script once with rckdump start, or reboot the system.
After configuring kdump with the default values, check if it works as expected. Make
sure that no users are currently logged in and no important services are running on
your system. Then follow these steps:
1 Switch to runlevel 1 with telinit 1
2 Unmount all the disk file systems except the root file system with umount -a
3 Remount the root file system in read-only mode: mount -o remount,ro /
4 Invoke “kernel panic” with the procfs interface to Magic SysRq keys:
echo c >/proc/sysrq-trigger
IMPORTANT: The Size of Kernel Dumps
The KDUMP_KEEP_OLD_DUMPS option controls the number of preserved
kernel dumps (default is 5). Without compression, the size of the dump can
take up to the size of the physical RAM memory. Make sure you have sufficient space on the /var partition.
The capture kernel boots and the crashed kernel memory snapshot is saved to the file
system. The save path is given by the KDUMP_SAVEDIR option and it defaults to /
var/crash. If KDUMP_IMMEDIATE_REBOOT is set to yes , the system automatically reboots the production kernel. Log in and check that the dump has been created
under /var/crash.
WARNING: Screen Freezes in X11 Session
When kdump takes control and you are logged in an X11 session, the screen
will freeze without any notice. Some kdump activity can be still visible (for example, deformed messages of a booting kernel on the screen).
kexec and kdump
211
Do not reset the computer because kdump always needs some time to complete its task.
18.6.2 YaST Configuration
In order to configure kdump with YaST, you need to install the yast2-kdump
package. Then either start the Kernel Kdump module in the System category of YaST
Control Center, or enter yast2 kdump in the command line as root.
Figure 18.1: YaST2 Kdump Module - Start-Up Page
In the Start-Up window, select Enable Kdump. The default value for kdump memory
is sufficient on most systems.
Click Dump Filtering in the left pane, and check what pages to include in the dump.
You do not need to include the following memory content to be able to debug kernel
problems:
• Pages filled with zero
• Cache pages
• User data pages
• Free pages
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System Analysis and Tuning Guide
In the Dump Target window, select the type of the dump target and the URL where
you want to save the dump. If you selected a network protocol, such as FTP or SSH,
you need to enter relevant access information as well.
Fill the Email Notification window information if you want kdump to inform you
about its events via E-mail and confirm your changes with OK after fine tuning
kdump in the Expert Settings window. kdump is now configured.
18.7 Analyzing the Crash Dump
After you obtain the dump, it is time to analyze it. There are several options.
The original tool to analyze the dumps is GDB. You can even use it in the latest environments, although it has several disadvantages and limitations:
• GDB was not specifically designed to debug kernel dumps.
• GDB does not support ELF64 binaries on 32-bit platforms.
• GDB does not understand other formats than ELF dumps (it cannot debug compressed dumps).
That is why the crash utility was implemented. It analyzes crash dumps and debugs
the running system as well. It provides functionality specific to debugging the Linux
kernel and is much more suitable for advanced debugging.
If you want to debug the Linux kernel, you need to install its debugging information
package in addition. Check if the package is installed on your system with zypper
se kernel | grep debug.
IMPORTANT: Repository for Packages with Debugging Information
If you subscribed your system for online updates, you can find “debuginfo”
packages in the *-Debuginfo-Updates online installation repository relevant for SUSE Linux Enterprise Server 11 SP3. Use YaST to enable the
repository.
To open the captured dump in crash on the machine that produced the dump, use a
command like this:
crash /boot/vmlinux-2.6.32.8-0.1-default.gz /var/
crash/2010-04-23-11\:17/vmcore
kexec and kdump
213
The first parameter represents the kernel image. The second parameter is the dump
file captured by kdump. You can find this file under /var/crash by default.
18.7.1 Kernel Binary Formats
The Linux kernel comes in Executable and Linkable Format (ELF). This file is usually called vmlinux and is directly generated in the compilation process. Not all boot
loaders, especially on x86 (i386 and x86_64) architecture, support ELF binaries. The
following solutions exist on different architectures supported by SUSE® Linux Enterprise Server.
18.7.1.1 x86 (i386 and x86_64)
Mostly for historic reasons, the Linux kernel consists of two parts: the Linux kernel itself (vmlinux) and the setup code run by the boot loader.
These two parts are linked together in a file called bzImage, which can be found in
the kernel source tree. The file is now called vmlinuz (note z vs. x) in the kernel
package.
The ELF image is never directly used on x86. Therefore, the main kernel package
contains the vmlinux file in compressed form called vmlinux.gz.
To sum it up, an x86 SUSE kernel package has two kernel files:
• vmlinuz which is executed by the boot loader.
• vmlinux.gz, the compressed ELF image that is required by crash and GDB.
18.7.1.2 IA64
The elilo boot loader, which boots the Linux kernel on the IA64 architecture, supports loading ELF images (even compressed ones) out of the box. The IA64 kernel
package contains only one file called vmlinuz. It is a compressed ELF image. vm​
linuz on IA64 is the same as vmlinux.gz on x86.
18.7.1.3 PPC and PPC64
The yaboot boot loader on PPC also supports loading ELF images, but not compressed ones. In the PPC kernel package, there is an ELF Linux kernel file vmlin​
ux. Considering crash, this is the easiest architecture.
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System Analysis and Tuning Guide
If you decide to analyze the dump on another machine, you must check both the architecture of the computer and the files necessary for debugging.
You can analyze the dump on another computer only if it runs a Linux system of the
same architecture. To check the compatibility, use the command uname -i on both
computers and compare the outputs.
If you are going to analyze the dump on another computer, you also need the appropriate files from the kernel and kernel debug packages.
1 Put the kernel dump, the kernel image from /boot, and its associated debugging
info file from /usr/lib/debug/boot into a single empty directory.
2 Additionally, copy the kernel modules from /lib/modules/$(uname -r)/
kernel/ and the associated debug info files from /usr/lib/debug/lib/
modules/$(uname -r)/kernel/ into a subdirectory named modules.
3 In the directory with the dump, the kernel image, its debug info file, and the mod​
ules subdirectory, launch the crash utility: crash vmlinux-version vmcore.
NOTE: Support for Kernel Images
Compressed kernel images (gzip, not the bzImage file) are supported by
SUSE packages of crash since SUSE® Linux Enterprise Server 11. For older versions, you have to extract the vmlinux.gz (x86) or the vmlinuz
(IA64) to vmlinux.
Regardless of the computer on which you analyze the dump, the crash utility will produce an output similar to this:
tux@mercury:~> crash /boot/vmlinux-2.6.32.8-0.1-default.gz
/var/crash/2010-04-23-11\:17/vmcore
crash 4.0-7.6
Copyright (C) 2002, 2003, 2004, 2005, 2006, 2007, 2008 Red Hat, Inc.
Copyright (C) 2004, 2005, 2006 IBM Corporation
Copyright (C) 1999-2006 Hewlett-Packard Co
Copyright (C) 2005, 2006 Fujitsu Limited
Copyright (C) 2006, 2007 VA Linux Systems Japan K.K.
Copyright (C) 2005 NEC Corporation
Copyright (C) 1999, 2002, 2007 Silicon Graphics, Inc.
Copyright (C) 1999, 2000, 2001, 2002 Mission Critical Linux, Inc.
This program is free software, covered by the GNU General Public License,
and you are welcome to change it and/or distribute copies of it under
certain conditions. Enter "help copying" to see the conditions.
kexec and kdump
215
This program has absolutely no warranty.
Enter "help warranty" for details.
GNU gdb 6.1
Copyright 2004 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain
conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB. Type "show warranty" for details.
This GDB was configured as "x86_64-unknown-linux-gnu"...
KERNEL:
DEBUGINFO:
DUMPFILE:
CPUS:
DATE:
UPTIME:
LOAD AVERAGE:
TASKS:
NODENAME:
RELEASE:
VERSION:
MACHINE:
MEMORY:
PANIC:
PID:
COMMAND:
TASK:
CPU:
STATE:
crash>
/boot/vmlinux-2.6.32.8-0.1-default.gz
/usr/lib/debug/boot/vmlinux-2.6.32.8-0.1-default.debug
/var/crash/2009-04-23-11:17/vmcore
2
Thu Apr 23 13:17:01 2010
00:10:41
0.01, 0.09, 0.09
42
eros
2.6.32.8-0.1-default
#1 SMP 2010-03-31 14:50:44 +0200
x86_64 (2999 Mhz)
1 GB
"SysRq : Trigger a crashdump"
9446
"bash"
ffff88003a57c3c0 [THREAD_INFO: ffff880037168000]
1
TASK_RUNNING (SYSRQ)
The command output prints first useful data: There were 42 tasks running at the moment of the kernel crash. The cause of the crash was a SysRq trigger invoked by the
task with PID 9446. It was a Bash process because the echo that has been used is an
internal command of the Bash shell.
The crash utility builds upon GDB and provides many useful additional commands. If
you enter bt without any parameters, the backtrace of the task running at the moment
of the crash is printed:
crash> bt
PID: 9446
TASK: ffff88003a57c3c0 CPU: 1
COMMAND: "bash"
#0 [ffff880037169db0] crash_kexec at ffffffff80268fd6
#1 [ffff880037169e80] __handle_sysrq at ffffffff803d50ed
#2 [ffff880037169ec0] write_sysrq_trigger at ffffffff802f6fc5
#3 [ffff880037169ed0] proc_reg_write at ffffffff802f068b
#4 [ffff880037169f10] vfs_write at ffffffff802b1aba
#5 [ffff880037169f40] sys_write at ffffffff802b1c1f
#6 [ffff880037169f80] system_call_fastpath at ffffffff8020bfbb
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System Analysis and Tuning Guide
RIP: 00007fa958991f60 RSP:
RAX: 0000000000000001 RBX:
RDX: 0000000000000002 RSI:
RBP: 0000000000000002
R8:
R10: 00007fa958c209c0 R11:
R13: 00007fa959284000 R14:
ORIG_RAX: 0000000000000001
crash>
00007fff61330390 RFLAGS: 00010246
ffffffff8020bfbb RCX: 0000000000000001
00007fa959284000 RDI: 0000000000000001
00007fa9592516f0
R9: 00007fa958c209c0
0000000000000246 R12: 00007fa958c1f780
0000000000000002 R15: 00000000595569d0
CS: 0033 SS: 002b
Now it is clear what happened: The internal echo command of Bash shell sent a
character to /proc/sysrq-trigger. After the corresponding handler recognized
this character, it invoked the crash_kexec() function. This function called panic() and kdump saved a dump.
In addition to the basic GDB commands and the extended version of bt, the crash
utility defines many other commands related to the structure of the Linux kernel.
These commands understand the internal data structures of the Linux kernel and
present their contents in a human readable format. For example, you can list the tasks
running at the moment of the crash with ps. With sym, you can list all the kernel
symbols with the corresponding addresses, or inquire an individual symbol for its
value. With files, you can display all the open file descriptors of a process. With
kmem, you can display details about the kernel memory usage. With vm, you can inspect the virtual memory of a process, even at the level of individual page mappings.
The list of useful commands is very long and many of these accept a wide range of
options.
The commands that we mentioned reflect the functionality of the common Linux
commands, such as ps and lsof. If you would like to find out the exact sequence of
events with the debugger, you need to know how to use GDB and to have strong debugging skills. Both of these are out of the scope of this document. In addition, you
need to understand the Linux kernel. Several useful reference information sources are
given at the end of this document.
18.8 Advanced kdump
Configuration
The configuration for kdump is stored in /etc/sysconfig/kdump. You can also use YaST to configure it. kdump configuration options are available under System
> Kernel Kdump in YaST Control Center. The following kdump options may be useful
for you:
kexec and kdump
217
You can change the directory for the kernel dumps with the KDUMP_SAVEDIR
option. Keep in mind that the size of kernel dumps can be very large. kdump will
refuse to save the dump if the free disk space, subtracted by the estimated dump
size, drops below the value specified by the KDUMP_FREE_DISK_SIZE option.
Note that KDUMP_SAVEDIR understands URL format protocol://specification, where protocol is one of file, ftp, sftp, nfs or cifs,
and specification varies for each protocol. For example, to save kernel dump on an FTP server, use the following URL as a template: ftp://
username:password@ftp.example.com:123/var/crash.
Kernel dumps are usually huge and contain many pages that are not necessary for
analysis. With KDUMP_DUMPLEVEL option, you can omit such pages. The option
understands numeric value between 0 and 31. If you specify 0, the dump size will be
largest. If you specify 31, it will produce the smallest dump. For a complete table of
possible values, see the manual page of kdump (man 7 kdump).
Sometimes it is very useful to make the size of the kernel dump smaller. For example, if you want to transfer the dump over the network, or if you need to save some
disk space in the dump directory. This can be done with KDUMP_DUMPFORMAT set
to compressed. The crash utility supports dynamic decompression of the compressed dumps.
IMPORTANT: Changes to kdump Configuration File
You always need to execute rckdump restart after you make manual
changes to /etc/sysconfig/kdump. Otherwise these changes will take
effect next time you reboot the system.
18.9 For More Information
Since there is no single comprehensive reference to kexec and kdump usage, you have
to explore several resources to get the information you need. Here are some of them:
• For the kexec utility usage, see the manual page of kexec (man 8 kexec).
• You can find general information about kexec at http://www.ibm.com/de​
veloperworks/linux/library/l-kexec.html . Might be slightly outdated.
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System Analysis and Tuning Guide
• For more details on kdump specific to SUSE Linux, see http://
ftp.suse.com/pub/people/tiwai/kdump-training/kdumptraining.pdf .
• An in-depth description of kdump internals can be found at http://
lse.sourceforge.net/kdump/documentation/ols2oo5-kdumppaper.pdf .
For more details on crash dump analysis and debugging tools, use the following resources:
• In addition to the info page of GDB (info gdb), you might want to read the
printable guides at http://sourceware.org/gdb/documentation/ .
• A white paper with a comprehensive description of the crash utility usage can be found at http://people.redhat.com/ander​
son/crash_whitepaper/.
• The crash utility also features a comprehensive online help. Just write help command to display the online help for command.
• If you have the necessary Perl skills, you can use Alicia to make the debugging
easier. This Perl-based front end to the crash utility can be found at http://
alicia.sourceforge.net/ .
• If you prefer Python instead, you may want to install Pykdump. This package helps
you control GDB through Python scripts and can be downloaded from http://
sf.net/projects/pykdump .
• A very comprehensive overview of the Linux kernel internals is given in Understanding the Linux Kernel by Daniel P. Bovet and Marco Cesati (ISBN
978-0-596-00565-8).
kexec and kdump
219
GNU Licenses
This appendix contains the GNU Free Documentation License version 1.2.
GNU Free Documentation License
Copyright (C) 2000, 2001, 2002 Free Software Foundation, Inc. 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. Everyone is permitted to
copy and distribute verbatim copies of this license document, but changing it is not allowed.
0. PREAMBLE
The purpose of this License is to make a manual, textbook, or other functional and useful document "free" in the sense of freedom: to assure everyone
the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others.
This License is a kind of "copyleft", which means that derivative works of the document must themselves be free in the same sense. It complements
the GNU General Public License, which is a copyleft license designed for free software.
We have designed this License in order to use it for manuals for free software, because free software needs free documentation: a free program should
come with manuals providing the same freedoms that the software does. But this License is not limited to software manuals; it can be used for any textual work, regardless of subject matter or whether it is published as a printed book. We recommend this License principally for works whose purpose
is instruction or reference.
1. APPLICABILITY AND DEFINITIONS
This License applies to any manual or other work, in any medium, that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License. Such a notice grants a world-wide, royalty-free license, unlimited in duration, to use that work under the conditions stated herein. The "Document", below, refers to any such manual or work. Any member of the public is a licensee, and is addressed as "you". You accept
the license if you copy, modify or distribute the work in a way requiring permission under copyright law.
A "Modified Version" of the Document means any work containing the Document or a portion of it, either copied verbatim, or with modifications
and/or translated into another language.
A "Secondary Section" is a named appendix or a front-matter section of the Document that deals exclusively with the relationship of the publishers or
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a matter of historical connection with the subject or with related matters, or of legal, commercial, philosophical, ethical or political position regarding
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The "Invariant Sections" are certain Secondary Sections whose titles are designated, as being those of Invariant Sections, in the notice that says that the
Document is released under this License. If a section does not fit the above definition of Secondary then it is not allowed to be designated as Invariant.
The Document may contain zero Invariant Sections. If the Document does not identify any Invariant Sections then there are none.
A
The "Cover Texts" are certain short passages of text that are listed, as Front-Cover Texts or Back-Cover Texts, in the notice that says that the Document is released under this License. A Front-Cover Text may be at most 5 words, and a Back-Cover Text may be at most 25 words.
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(for drawings) some widely available drawing editor, and that is suitable for input to text formatters or for automatic translation to a variety of formats
suitable for input to text formatters. A copy made in an otherwise Transparent file format whose markup, or absence of markup, has been arranged to
thwart or discourage subsequent modification by readers is not Transparent. An image format is not Transparent if used for any substantial amount of
text. A copy that is not "Transparent" is called "Opaque".
Examples of suitable formats for Transparent copies include plain ASCII without markup, Texinfo input format, LaTeX input format, SGML or XML
using a publicly available DTD, and standard-conforming simple HTML, PostScript or PDF designed for human modification. Examples of transparent image formats include PNG, XCF and JPG. Opaque formats include proprietary formats that can be read and edited only by proprietary word
processors, SGML or XML for which the DTD and/or processing tools are not generally available, and the machine-generated HTML, PostScript or
PDF produced by some word processors for output purposes only.
The "Title Page" means, for a printed book, the title page itself, plus such following pages as are needed to hold, legibly, the material this License requires to appear in the title page. For works in formats which do not have any title page as such, "Title Page" means the text near the most prominent
appearance of the work's title, preceding the beginning of the body of the text.
A section "Entitled XYZ" means a named subunit of the Document whose title either is precisely XYZ or contains XYZ in parentheses following text
that translates XYZ in another language. (Here XYZ stands for a specific section name mentioned below, such as "Acknowledgements", "Dedications",
"Endorsements", or "History".) To "Preserve the Title" of such a section when you modify the Document means that it remains a section "Entitled
XYZ" according to this definition.
The Document may include Warranty Disclaimers next to the notice which states that this License applies to the Document. These Warranty Disclaimers are considered to be included by reference in this License, but only as regards disclaiming warranties: any other implication that these Warranty Disclaimers may have is void and has no effect on the meaning of this License.
2. VERBATIM COPYING
You may copy and distribute the Document in any medium, either commercially or noncommercially, provided that this License, the copyright notices, and the license notice saying this License applies to the Document are reproduced in all copies, and that you add no other conditions whatsoever
to those of this License. You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute.
However, you may accept compensation in exchange for copies. If you distribute a large enough number of copies you must also follow the conditions
in section 3.
You may also lend copies, under the same conditions stated above, and you may publicly display copies.
3. COPYING IN QUANTITY
If you publish printed copies (or copies in media that commonly have printed covers) of the Document, numbering more than 100, and the Document's
license notice requires Cover Texts, you must enclose the copies in covers that carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on
the front cover, and Back-Cover Texts on the back cover. Both covers must also clearly and legibly identify you as the publisher of these copies. The
front cover must present the full title with all words of the title equally prominent and visible. You may add other material on the covers in addition.
Copying with changes limited to the covers, as long as they preserve the title of the Document and satisfy these conditions, can be treated as verbatim
copying in other respects.
If the required texts for either cover are too voluminous to fit legibly, you should put the first ones listed (as many as fit reasonably) on the actual cover, and continue the rest onto adjacent pages.
If you publish or distribute Opaque copies of the Document numbering more than 100, you must either include a machine-readable Transparent copy
along with each Opaque copy, or state in or with each Opaque copy a computer-network location from which the general network-using public has access to download using public-standard network protocols a complete Transparent copy of the Document, free of added material. If you use the latter
option, you must take reasonably prudent steps, when you begin distribution of Opaque copies in quantity, to ensure that this Transparent copy will remain thus accessible at the stated location until at least one year after the last time you distribute an Opaque copy (directly or through your agents or
retailers) of that edition to the public.
It is requested, but not required, that you contact the authors of the Document well before redistributing any large number of copies, to give them a
chance to provide you with an updated version of the Document.
4. MODIFICATIONS
You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above, provided that you release the Modified Version under precisely this License, with the Modified Version filling the role of the Document, thus licensing distribution and modification of
the Modified Version to whoever possesses a copy of it. In addition, you must do these things in the Modified Version:
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A.Use in the Title Page (and on the covers, if any) a title distinct from that of the Document, and from those of previous versions (which should, if
there were any, be listed in the History section of the Document). You may use the same title as a previous version if the original publisher of that
version gives permission.
B. List on the Title Page, as authors, one or more persons or entities responsible for authorship of the modifications in the Modified Version, together
with at least five of the principal authors of the Document (all of its principal authors, if it has fewer than five), unless they release you from this
requirement.
C.State on the Title page the name of the publisher of the Modified Version, as the publisher.
D.Preserve all the copyright notices of the Document.
E. Add an appropriate copyright notice for your modifications adjacent to the other copyright notices.
F. Include, immediately after the copyright notices, a license notice giving the public permission to use the Modified Version under the terms of this
License, in the form shown in the Addendum below.
G.Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document's license notice.
H.Include an unaltered copy of this License.
I. Preserve the section Entitled "History", Preserve its Title, and add to it an item stating at least the title, year, new authors, and publisher of the Modified Version as given on the Title Page. If there is no section Entitled "History" in the Document, create one stating the title, year, authors, and publisher of the Document as given on its Title Page, then add an item describing the Modified Version as stated in the previous sentence.
J. Preserve the network location, if any, given in the Document for public access to a Transparent copy of the Document, and likewise the network locations given in the Document for previous versions it was based on. These may be placed in the "History" section. You may omit a network location for a work that was published at least four years before the Document itself, or if the original publisher of the version it refers to gives permission.
K.For any section Entitled "Acknowledgements" or "Dedications", Preserve the Title of the section, and preserve in the section all the substance and
tone of each of the contributor acknowledgements and/or dedications given therein.
L. Preserve all the Invariant Sections of the Document, unaltered in their text and in their titles. Section numbers or the equivalent are not considered
part of the section titles.
M.Delete any section Entitled "Endorsements". Such a section may not be included in the Modified Version.
N.Do not retitle any existing section to be Entitled "Endorsements" or to conflict in title with any Invariant Section.
O.Preserve any Warranty Disclaimers.
If the Modified Version includes new front-matter sections or appendices that qualify as Secondary Sections and contain no material copied from the
Document, you may at your option designate some or all of these sections as invariant. To do this, add their titles to the list of Invariant Sections in the
Modified Version's license notice. These titles must be distinct from any other section titles.
You may add a section Entitled "Endorsements", provided it contains nothing but endorsements of your Modified Version by various parties--for example, statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard.
You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version. Only one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through arrangements
made by) any one entity. If the Document already includes a cover text for the same cover, previously added by you or by arrangement made by the
same entity you are acting on behalf of, you may not add another; but you may replace the old one, on explicit permission from the previous publisher
that added the old one.
The author(s) and publisher(s) of the Document do not by this License give permission to use their names for publicity for or to assert or imply endorsement of any Modified Version.
5. COMBINING DOCUMENTS
You may combine the Document with other documents released under this License, under the terms defined in section 4 above for modified versions,
provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and list them all as Invariant
Sections of your combined work in its license notice, and that you preserve all their Warranty Disclaimers.
The combined work need only contain one copy of this License, and multiple identical Invariant Sections may be replaced with a single copy. If there
are multiple Invariant Sections with the same name but different contents, make the title of each such section unique by adding at the end of it, in
parentheses, the name of the original author or publisher of that section if known, or else a unique number. Make the same adjustment to the section
titles in the list of Invariant Sections in the license notice of the combined work.
In the combination, you must combine any sections Entitled "History" in the various original documents, forming one section Entitled "History"; likewise combine any sections Entitled "Acknowledgements", and any sections Entitled "Dedications". You must delete all sections Entitled "Endorsements".
GNU Licenses
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6. COLLECTIONS OF DOCUMENTS
You may make a collection consisting of the Document and other documents released under this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License for verbatim
copying of each of the documents in all other respects.
You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License
into the extracted document, and follow this License in all other respects regarding verbatim copying of that document.
7. AGGREGATION WITH INDEPENDENT WORKS
A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, is called an "aggregate" if the copyright resulting from the compilation is not used to limit the legal rights of the compilation's users beyond what the individual works permit. When the Document is included in an aggregate, this License does not apply to the other works in the aggregate which are not themselves derivative works of the Document.
If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one half of the entire aggregate, the Document's Cover Texts may be placed on covers that bracket the Document within the aggregate, or the electronic equivalent of covers if
the Document is in electronic form. Otherwise they must appear on printed covers that bracket the whole aggregate.
8. TRANSLATION
Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant
Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections
in addition to the original versions of these Invariant Sections. You may include a translation of this License, and all the license notices in the Document, and any Warranty Disclaimers, provided that you also include the original English version of this License and the original versions of those notices and disclaimers. In case of a disagreement between the translation and the original version of this License or a notice or disclaimer, the original
version will prevail.
If a section in the Document is Entitled "Acknowledgements", "Dedications", or "History", the requirement (section 4) to Preserve its Title (section 1)
will typically require changing the actual title.
9. TERMINATION
You may not copy, modify, sublicense, or distribute the Document except as expressly provided for under this License. Any other attempt to copy,
modify, sublicense or distribute the Document is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance.
10. FUTURE REVISIONS OF THIS LICENSE
The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will
be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See http://www.gnu.org/copyleft/.
Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License "or
any later version" applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has
been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose
any version ever published (not as a draft) by the Free Software Foundation.
ADDENDUM: How to use this License for your documents
Copyright (c) YEAR YOUR NAME.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.2
or any later version published by the Free Software Foundation;
with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
A copy of the license is included in the section entitled “GNU
Free Documentation License”.
If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the “with...Texts.” line with this:
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with the Invariant Sections being LIST THEIR TITLES, with the
Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST.
If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.
If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.
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