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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="countcallssect">
<title>Counting Function Calls Made</title>
<indexterm>
<primary>script examples</primary>
<secondary>tallying function calls</secondary>
</indexterm>
<indexterm>
<primary>examples of SystemTap scripts</primary>
<secondary>tallying function calls</secondary>
</indexterm>
<indexterm>
<primary>tallying function calls</primary>
<secondary>examples of SystemTap scripts</secondary>
</indexterm>
<indexterm>
<primary>counting function calls</primary>
<secondary>examples of SystemTap scripts</secondary>
</indexterm>
<indexterm>
<primary>function calls, tallying</primary>
<secondary>examples of SystemTap scripts</secondary>
</indexterm>
<remark>
WAR STORY: Function call count http://sourceware.org/systemtap/wiki/WSFunctionCallCount?highlight=((WarStories))
</remark>
<remark>
no script in examples
</remark>
<para>This section describes how to identify how many times the system called a specific kernel function in a 30-second sample. Depending on your use of wildcards, you can also use this script to target multiple kernel functions.</para>
<formalpara id="countcalls">
<title>functioncallcount.stp</title>
<para>
<programlisting>
<xi:include parse="text" href="../testsuite/systemtap.examples/profiling/functioncallcount.stp" xmlns:xi="http://www.w3.org/2001/XInclude" />
</programlisting>
</para>
</formalpara>
<para><xref linkend="countcalls"/> takes the targeted kernel function as an argument. The argument supports wildcards, which enables you to target multiple kernel functions up to a certain extent.</para>
<indexterm>
<primary>script examples</primary>
<secondary>timer.ms(), sample usage</secondary>
</indexterm>
<indexterm>
<primary>examples of SystemTap scripts</primary>
<secondary>timer.ms(), sample usage</secondary>
</indexterm>
<indexterm>
<primary>timer.ms(), sample usage</primary>
<secondary>examples of SystemTap scripts</secondary>
</indexterm>
<para>You can increase the sample time by editing the timer in the second probe (<command>timer.ms()</command>). The output of <xref linkend="countcalls"/> contains the name of the function called and how many times it was called during the sample time (in alphabetical order). <xref linkend="countcallsoutput"/> contains an excerpt from the output of <command>stap countcalls.stp "*@mm/*.c"</command>:</para>
<example id="countcallsoutput">
<title><xref linkend="countcalls"/> Sample Output</title>
<screen>
[...]
__vma_link 97
__vma_link_file 66
__vma_link_list 97
__vma_link_rb 97
__xchg 103
add_page_to_active_list 102
add_page_to_inactive_list 19
add_to_page_cache 19
add_to_page_cache_lru 7
all_vm_events 6
alloc_pages_node 4630
alloc_slabmgmt 67
anon_vma_alloc 62
anon_vma_free 62
anon_vma_lock 66
anon_vma_prepare 98
anon_vma_unlink 97
anon_vma_unlock 66
arch_get_unmapped_area_topdown 94
arch_get_unmapped_exec_area 3
arch_unmap_area_topdown 97
atomic_add 2
atomic_add_negative 97
atomic_dec_and_test 5153
atomic_inc 470
atomic_inc_and_test 1
[...]
</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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