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<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>5.3.4. Monitoring Polling Applications</title><link rel="stylesheet" type="text/css" href="Common_Content/css/default.css" /><link rel="stylesheet" media="print" href="Common_Content/css/print.css" type="text/css" /><meta name="generator" content="publican 2.8" /><meta name="package" content="Systemtap-SystemTap_Beginners_Guide-2.1-en-US-2.1-2" /><link rel="home" href="index.html" title="SystemTap Beginners Guide" /><link rel="up" href="mainsect-profiling.html" title="5.3. Profiling" /><link rel="prev" href="threadtimessect.html" title="5.3.3. Determining Time Spent in Kernel and User Space" /><link rel="next" href="topsyssect.html" title="5.3.5. Tracking Most Frequently Used System Calls" /></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site" /></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site" /></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="threadtimessect.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="topsyssect.html"><strong>Next</strong></a></li></ul><div xml:lang="en-US" class="section" id="timeoutssect" lang="en-US"><div class="titlepage"><div><div keep-together.within-column="always"><h3 class="title" id="timeoutssect">5.3.4. Monitoring Polling Applications</h3></div></div></div><a id="idm2005256" class="indexterm"></a><a id="idm8527848" class="indexterm"></a><a id="idp5851968" class="indexterm"></a><a id="idp6061832" class="indexterm"></a><div class="para">
This section describes how to identify and monitor which applications are polling. Doing so allows you to track unnecessary or excessive polling, which can help you pinpoint areas for improvement in terms of CPU usage and power savings.
</div><div class="formalpara" id="timeouts"><h5 class="formalpara">timeout.stp</h5>
<pre class="programlisting">#! /usr/bin/env stap
# Copyright (C) 2009 Red Hat, Inc.
# Written by Ulrich Drepper <drepper@redhat.com>
# Modified by William Cohen <wcohen@redhat.com>
global process, timeout_count, to
global poll_timeout, epoll_timeout, select_timeout, itimer_timeout
global nanosleep_timeout, futex_timeout, signal_timeout
probe syscall.poll, syscall.epoll_wait {
if (timeout) to[pid()]=timeout
}
probe syscall.poll.return {
p = pid()
if ($return == 0 && to[p] > 0 ) {
poll_timeout[p]++
timeout_count[p]++
process[p] = execname()
delete to[p]
}
}
probe syscall.epoll_wait.return {
p = pid()
if ($return == 0 && to[p] > 0 ) {
epoll_timeout[p]++
timeout_count[p]++
process[p] = execname()
delete to[p]
}
}
probe syscall.select.return {
if ($return == 0) {
p = pid()
select_timeout[p]++
timeout_count[p]++
process[p] = execname()
}
}
probe syscall.futex.return {
if (errno_str($return) == "ETIMEDOUT") {
p = pid()
futex_timeout[p]++
timeout_count[p]++
process[p] = execname()
}
}
probe syscall.nanosleep.return {
if ($return == 0) {
p = pid()
nanosleep_timeout[p]++
timeout_count[p]++
process[p] = execname()
}
}
probe kernel.function("it_real_fn") {
p = pid()
itimer_timeout[p]++
timeout_count[p]++
process[p] = execname()
}
probe syscall.rt_sigtimedwait.return {
if (errno_str($return) == "EAGAIN") {
p = pid()
signal_timeout[p]++
timeout_count[p]++
process[p] = execname()
}
}
probe syscall.exit {
p = pid()
if (p in process) {
delete process[p]
delete timeout_count[p]
delete poll_timeout[p]
delete epoll_timeout[p]
delete select_timeout[p]
delete itimer_timeout[p]
delete futex_timeout[p]
delete nanosleep_timeout[p]
delete signal_timeout[p]
}
}
probe timer.s(1) {
ansi_clear_screen()
printf (" pid | poll select epoll itimer futex nanosle signal| process\n")
foreach (p in timeout_count- limit 20) {
printf ("%5d |%7d %7d %7d %7d %7d %7d %7d| %-.38s\n", p,
poll_timeout[p], select_timeout[p],
epoll_timeout[p], itimer_timeout[p],
futex_timeout[p], nanosleep_timeout[p],
signal_timeout[p], process[p])
}
}
</pre>
</div><div class="para">
<a class="xref" href="timeoutssect.html#timeouts">timeout.stp</a> tracks how many times each of the following system calls completed due to time expiring rather than due to an actual event occurring:
</div><div class="itemizedlist"><ul><li class="listitem"><div class="para">
<code class="command">poll</code>
</div></li><li class="listitem"><div class="para">
<code class="command">select</code>
</div></li><li class="listitem"><div class="para">
<code class="command">epoll</code>
</div></li><li class="listitem"><div class="para">
<code class="command">itimer</code>
</div></li><li class="listitem"><div class="para">
<code class="command">futex</code>
</div></li><li class="listitem"><div class="para">
<code class="command">nanosleep</code>
</div></li><li class="listitem"><div class="para">
<code class="command">signal</code>
</div></li></ul></div><a id="idp6532648" class="indexterm"></a><a id="idp9344600" class="indexterm"></a><a id="idm9537632" class="indexterm"></a><div class="example" id="timeoutsoutput"><h6>Example 5.16. <a class="xref" href="timeoutssect.html#timeouts">timeout.stp</a> Sample Output</h6><div class="example-contents"><pre class="screen"> uid | poll select epoll itimer futex nanosle signal| process
28937 | 148793 0 0 4727 37288 0 0| firefox
22945 | 0 56949 0 1 0 0 0| scim-bridge
0 | 0 0 0 36414 0 0 0| swapper
4275 | 23140 0 0 1 0 0 0| mixer_applet2
4191 | 0 14405 0 0 0 0 0| scim-launcher
22941 | 7908 1 0 62 0 0 0| gnome-terminal
4261 | 0 0 0 2 0 7622 0| escd
3695 | 0 0 0 0 0 7622 0| gdm-binary
3483 | 0 7206 0 0 0 0 0| dhcdbd
4189 | 6916 0 0 2 0 0 0| scim-panel-gtk
1863 | 5767 0 0 0 0 0 0| iscsid
2562 | 0 2881 0 1 0 1438 0| pcscd
4257 | 4255 0 0 1 0 0 0| gnome-power-man
4278 | 3876 0 0 60 0 0 0| multiload-apple
4083 | 0 1331 0 1728 0 0 0| Xorg
3921 | 1603 0 0 0 0 0 0| gam_server
4248 | 1591 0 0 0 0 0 0| nm-applet
3165 | 0 1441 0 0 0 0 0| xterm
29548 | 0 1440 0 0 0 0 0| httpd
1862 | 0 0 0 0 0 1438 0| iscsid</pre></div></div><br class="example-break" /><div class="para">
You can increase the sample time by editing the second probe (<code class="command">timer.s(1)</code>). The output of <a class="xref" href="timeoutssect.html#timeouts">timeout.stp</a> contains the name and UID of the top 20 polling applications, along with how many times each application performed each polling system call (over time). <a class="xref" href="timeoutssect.html#timeoutsoutput">Example 5.16, “timeout.stp Sample Output”</a> contains an excerpt of the script. In this particular example firefox is doing an excessive amount of polling due to a plugin module.
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