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<?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="topsyssect">
<title>Tracking Most Frequently Used System Calls</title>
<indexterm>
<primary>script examples</primary>
<secondary>monitoring system calls</secondary>
</indexterm>
<indexterm>
<primary>examples of SystemTap scripts</primary>
<secondary>monitoring system calls</secondary>
</indexterm>
<indexterm>
<primary>monitoring system calls</primary>
<secondary>examples of SystemTap scripts</secondary>
</indexterm>
<!--
<indexterm>
<primary>counting function calls</primary>
<secondary>examples of SystemTap scripts</secondary>
</indexterm>
-->
<indexterm>
<primary>system calls, monitoring</primary>
<secondary>examples of SystemTap scripts</secondary>
</indexterm>
<remark>
uses systemtap/testsuite/systemtap.examples/profiling/topsys.stp
</remark>
<para>
<xref linkend="timeouts"/> from <xref linkend="timeoutssect"/> helps you identify which applications
are polling by pointing out which ones used the following system calls most frequently:
</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>
However, in some systems, a different system call might be responsible for excessive polling. If you suspect
that a polling application might is using a different system call to poll, you need to identify first the top
system calls used by the system. To do this, use <xref linkend="topsys"/>.
</para>
<formalpara id="topsys">
<title>topsys.stp</title>
<para>
<programlisting>
<xi:include parse="text" href="../testsuite/systemtap.examples/profiling/topsys.stp" xmlns:xi="http://www.w3.org/2001/XInclude" />
</programlisting>
</para>
</formalpara>
<para>
<xref linkend="topsys"/> lists the top 20 system calls used by the system per 5-second interval. It also lists
how many times each system call was used during that period. Refer to <xref linkend="topsysoutput"/> for a sample output.
</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="topsysoutput">
<title><xref linkend="topsys"/> Sample Output</title>
<screen>
--------------------------------------------------------------
SYSCALL COUNT
gettimeofday 1857
read 1821
ioctl 1568
poll 1033
close 638
open 503
select 455
write 391
writev 335
futex 303
recvmsg 251
socket 137
clock_gettime 124
rt_sigprocmask 121
sendto 120
setitimer 106
stat 90
time 81
sigreturn 72
fstat 66
--------------------------------------------------------------
</screen>
</example>
<!--probe kernel.function(@1) { # probe function passed as argument from stdin
called[probefunc()] <<< 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()
}-->
</section>
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