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<section id="timeoutssect">
<title>Monitoring Polling Applications</title>
<indexterm>
<primary>script examples</primary>
<secondary>monitoring polling applications</secondary>
</indexterm>

<indexterm>
<primary>examples of SystemTap scripts</primary>
<secondary>monitoring polling applications</secondary>
</indexterm>

<indexterm>
<primary>monitoring polling applications</primary>
<secondary>examples of SystemTap scripts</secondary>
</indexterm>

<!--
<indexterm>
<primary>counting function calls</primary>
<secondary>examples of SystemTap scripts</secondary>
</indexterm>
-->

<indexterm>
<primary>polling applications, monitoring</primary>
<secondary>examples of SystemTap scripts</secondary>
</indexterm>

<remark>
uses systemtap/testsuite/systemtap.examples/profiling/timeout.stp
</remark>


	<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.
	</para>

<formalpara id="timeouts">
	<title>timeout.stp</title>
<para>
<programlisting><xi:include parse="text" href="../testsuite/systemtap.examples/profiling/timeout.stp" xmlns:xi="http://www.w3.org/2001/XInclude" /></programlisting>
</para>
</formalpara>

	<para>
		<xref linkend="timeouts"/> tracks how many times each
		of the following system calls completed 
		due to time expiring rather than due to an actual event
		occurring:
	</para>

	<itemizedlist>
		<listitem><para><command>poll</command></para></listitem>
		<listitem><para><command>select</command></para></listitem>
		<listitem><para><command>epoll</command></para></listitem>
		<listitem><para><command>itimer</command></para></listitem>
		<listitem><para><command>futex</command></para></listitem>
		<listitem><para><command>nanosleep</command></para></listitem>
		<listitem><para><command>signal</command></para></listitem>
	</itemizedlist>


<indexterm>
<primary>script examples</primary>
<secondary>timer.s(), sample usage</secondary>
</indexterm>

<indexterm>
<primary>examples of SystemTap scripts</primary>
<secondary>timer.s(), sample usage</secondary>
</indexterm>

<indexterm>
<primary>timer.s(), sample usage</primary>
<secondary>examples of SystemTap scripts</secondary>
</indexterm>

<example id="timeoutsoutput">
	<title><xref linkend="timeouts"/> Sample Output</title>
<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</screen>
</example>
<para>
	You can increase the sample time by editing the second probe (<command>timer.s(1)</command>).
	The output of <xref linkend="timeouts"/> 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).
	<xref linkend="timeoutsoutput"/> contains an excerpt of the script.
	In this particular example firefox is doing an excessive amount of
	polling due to a plugin module.
</para>
	</section>

