Difference between revisions of "System Tap"

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== Links ==
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* [https://events.linuxfoundation.org/events/collaboration-summit/stone SystemTap Sans Kernel: A Pure Userspace Backend]    [https://events.linuxfoundation.org/images/stories/pdf/lfcs2012_jstone.pdf Slides] [http://video.linux.com/videos/systemtap-sans-kernel-a-pure-userspace-backend Video]
  
 
[[Category:Development Tools]]
 
[[Category:Development Tools]]

Latest revision as of 01:35, 14 April 2012

This page has information about System Tap, which is of interest to embedded developers, because tracers are a useful tool for diagnosing problems during product development.

Introduction

SystemTap is a flexible and extensible system for adding trace collection and analysis to a running Linux kernel.

SystemTap is designed to be very flexible (allowing for the insertion of arbitrary C code), yet also easy-to-use (most trace statements are written in a simple scripting language, with useful data collection and aggregation routines available in (essentially) library form).

A key aspect of SystemTap is that it is intended to allow you to create a trace set (a "tapset"), and run it on a running Linux system, with no modification or re-compilation of the system required. To do this, it uses the kernel KProbes interface and loadable kernel modules to dynamically add probe points and newly generated code to the running kernel.

Open Source Projects/Mailing Lists

The main SystemTap site is at: http://sourceware.org/systemtap/

The SystemTap mail list archives are at: http://sourceware.org/ml/systemtap/

The tutorial, which gives a good overview of the system, is at: http://sourceware.org/systemtap/tutorial/

Miscellaneous notes

Probe types

There are several types of probes:

  • kprobe & kretprobe, for dynamically insterted probes
  • timers
  • static instrumentation markers
  • performance counter events

In the future, there may be:

  • user-space probes,
  • user-space return probes, and
  • watchpoint probes (kernel & user)
  • and more

See Also

Note that SystemTap is one of the major tracing systems for the Linux kernel.

There is work afoot (as of spring 2006) to try to collaborate on different parts of the tracing problem, between some of the major tracing projects. See the Tracing Collaboration Project page for more information.

ARM Support

System Tap works on ARM & OMAP platforms instructions are available here

Some Performance measurements

Jian Gui writes (in July 2006 on the System Tap mailing list):

Hi, we've tested the overhead of systemtap/LKET with some benchmarks
on a ppc64 machine.

It shows the overhead of systemtap/LKET is acceptable generally.
But it will also cause significant overhead for some benchmark of
special behavior, e.g. dbench. Dbench calls kill() in a very high
frequency to check whether a task is complete, thus leads to a high
overhead.

We categorized the event hooks into five groups in the testing:
grp1 - syscall.entry, process
grp2 - syscall.return, process
grp3 - iosyscall, ioscheduler, scsi, aio, process
grp4 - tskdispatch, pagefault, netdev, process
grp5 - syscall.entry, syscall.return, process

All the results are
   (score1 - score2)/score2 * 100%,  where:
score1: the benchmark score when probed by systemtap
score2: the benchmark score without probing

dbench (<3% is noise)
--------------------
grp1            -14.4%
grp2            -33.1%
grp3            -7.92%
grp4            -13.6%
grp5            -43.3%

specjbb (<3% is noise)
---------------------
grp 1           -0.87%
grp 2           -0.67%
grp 4           +0.47%
grp 5           +0.05%

tiobench (<3% is noise)
----------------------
grp1       sequential reads      +1.45%
           sequential writes     -6.98%
           random reads          +0.57%
           random writes         -2.11%
grp2       sequential reads      +0.11%
           sequential writes     -5.81%
           random reads          +0.03%
           random writes         -2.11%
grp3       sequential reads      +1.42%
           sequential writes     -6.98%
           random reads          +0.51%
           random writes         -2.11%
grp4       sequential reads      +1.38%
           sequential writes     -5.81%
           random reads          +0.60%
           random writes         -2.11%
grp5       sequential reads      +0.22%
           sequential writes     -8.14%
           random reads          -0.10%
           random writes         -1.05%

Rawiobench (<3% is noise)
------------------------
grp1       sequential aioread()     0%
           sequential aiowrite()    0%
           random aioread()         0%
           random aiowrite()        0%
grp2       sequential aioread()     0%
           sequential aiowrite()    0%
           random aioread()         0%
           random aiowrite()        -0.82%
grp3       sequential aioread()     0%
           sequential aiowrite()    0%
           random aioread()         0%
           random aiowrite()        0%
grp4       sequential aioread()     0%
           sequential aiowrite()    0%
           random aioread()         +0.79%
           random aiowrite()        -0.82%
grp5       sequential aioread()     0%
           sequential aiowrite()    -6.41%
           random aioread()         +0.79%
           random aiowrite()        0%

Test environment:
Machine:  Open Power 720/ 8 cpus/ 2 cores/ 6GB RAM (tiobench use 1G)
Software: RHEL4-U3GA/ 2.6.17.2/ systemtap-20060718/ elfutils-0.122-0.4

Links