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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>
<para>
<xref linkend="timeouts"/> from <xref linkend="timeoutssect"/>
helps you identify which applications
are polling by examining a small subset of system calls (
<command>poll</command>,
<command>select</command>,
<command>epoll</command>,
<command>itimer</command>,
<command>futex</command>,
<command>nanosleep</command>, and
<command>signal</command>).
However, in some systems, an excessive number of system calls
outside that small subset
might be responsible for time spent in the
kernel. If you suspect that an application is using
system calls excessively, you need to
identify the most frequently used system calls on 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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