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<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>4.3. Profiling</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css" /><meta name="generator" content="publican 1.6" /><meta name="package" content="Systemtap-SystemTap_Beginners_Guide-1.0-en-US-2.0-2" /><link rel="home" href="index.html" title="SystemTap Beginners Guide" /><link rel="up" href="useful-systemtap-scripts.html" title="Chapter 4. Useful SystemTap Scripts" /><link rel="prev" href="ioblktimesect.html" title="4.2.7. Periodically Print I/O Block Time" /><link rel="next" href="paracallgraph.html" title="4.3.2. Call Graph Tracing" /></head><body class=""><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site" /></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site" /></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="ioblktimesect.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="paracallgraph.html"><strong>Next</strong></a></li></ul><div class="section" title="4.3. Profiling"><div class="titlepage"><div><div><h2 class="title" id="mainsect-profiling">4.3. Profiling</h2></div></div></div><div class="para">
The following sections showcase scripts that profile kernel activity by monitoring function calls.
</div><div xml:lang="en-US" class="section" title="4.3.1. Counting Function Calls Made" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="countcallssect">4.3.1. Counting Function Calls Made</h3></div></div></div><a id="id3053051" class="indexterm"></a><a id="id2915322" class="indexterm"></a><a id="id2843285" class="indexterm"></a><a id="id2872162" class="indexterm"></a><a id="id2786730" class="indexterm"></a><div class="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.
</div><div class="formalpara"><h5 class="formalpara" id="countcalls">functioncallcount.stp</h5>
<pre class="programlisting">
#! /usr/bin/env stap
# The following line command will probe all the functions
# in kernel's memory management code:
#
# stap functioncallcount.stp "*@mm/*.c"
probe kernel.function(@1).call { # probe functions listed on commandline
called[probefunc()] <<< 1 # add a count efficiently
}
global called
probe end {
foreach (fn in called-) # Sort by call count (in decreasing order)
# (fn+ in called) # Sort by function name
printf("%s %d\n", fn, @count(called[fn]))
exit()
}
</pre>
</div><div class="para">
<a class="xref" href="mainsect-profiling.html#countcalls" title="functioncallcount.stp">functioncallcount.stp</a> 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.
</div><a id="id2868754" class="indexterm"></a><a id="id2803374" class="indexterm"></a><a id="id3008935" class="indexterm"></a><div class="para">
You can increase the sample time by editing the timer in the second probe (<code class="command">timer.ms()</code>). The output of <a class="xref" href="mainsect-profiling.html#countcalls" title="functioncallcount.stp">functioncallcount.stp</a> contains the name of the function called and how many times it was called during the sample time (in alphabetical order). <a class="xref" href="mainsect-profiling.html#countcallsoutput" title="Example 4.13. functioncallcount.stp Sample Output">Example 4.13, “functioncallcount.stp Sample Output”</a> contains an excerpt from the output of <code class="command">stap countcalls.stp "*@mm/*.c"</code>:
</div><div class="example" id="countcallsoutput"><div class="example-contents"><pre class="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
[...]
</pre></div><h6>Example 4.13. <a class="xref" href="mainsect-profiling.html#countcalls" title="functioncallcount.stp">functioncallcount.stp</a> Sample Output</h6></div><br class="example-break" /></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="ioblktimesect.html"><strong>Prev</strong>4.2.7. Periodically Print I/O Block Time</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="paracallgraph.html"><strong>Next</strong>4.3.2. Call Graph Tracing</a></li></ul></body></html>
