<?xml version='1.0'?>
<!DOCTYPE section PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
]>


<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 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 application used the following system calls over time:
	</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>	

	<para>
		In some applications, these system calls are used excessively. As such, they are normally identified as "likely
		culprits" for polling applications. Note, however, that an application may be using a different system
		call to poll excessively; sometimes, it is useful to find out the top system calls used by the system (refer to 
		<xref linkend="topsyssect"/> for instructions). Doing so can help you identify any additional suspects, which you 
		can add to <xref linkend="timeouts"/> for tracking.
	</para>
		
	
<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>
<!--probe kernel.function(@1) {  # probe function passed as argument from stdin
called[probefunc()] &lt;&lt;&lt; 1  # add a count efficiently
}
global called          
probe end,timer.ms(30000) {
foreach (fn+ in called)  # Sort by function name
#       (fn in called-)  # Sort by call count (in decreasing order)
printf("%s %d\n", fn, @count(called[fn]))
exit()
}-->
<para>
	You can increase the sample time by editing the timer in the second probe (<command>timer.s()</command>). 
	The output of <xref linkend="countcalls"/> 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:
</para>
	</section>

