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POlinux perf: how to interpret and find hotspots
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  1. POlinux perf: how to interpret and find hotspots
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    copied!<p>I tried out linux' <a href="https://perf.wiki.kernel.org/index.php/Main_Page">perf</a> utility today and am having trouble in interpreting its results. I'm used to valgrind's callgrind which is of course a totally different approach to the sampling based method of perf.</p> <p>What I did:</p> <pre><code>perf record -g -p $(pidof someapp) perf report -g -n </code></pre> <p>Now I see something like this:</p> <pre> + 16.92% kdevelop libsqlite3.so.0.8.6 [.] 0x3fe57 ↑ + 10.61% kdevelop libQtGui.so.4.7.3 [.] 0x81e344 ▮ + 7.09% kdevelop libc-2.14.so [.] 0x85804 ▒ + 4.96% kdevelop libQtGui.so.4.7.3 [.] 0x265b69 ▒ + 3.50% kdevelop libQtCore.so.4.7.3 [.] 0x18608d ▒ + 2.68% kdevelop libc-2.14.so [.] memcpy ▒ + 1.15% kdevelop [kernel.kallsyms] [k] copy_user_generic_string ▒ + 0.90% kdevelop libQtGui.so.4.7.3 [.] QTransform::translate(double, double) ▒ + 0.88% kdevelop libc-2.14.so [.] __libc_malloc ▒ + 0.85% kdevelop libc-2.14.so [.] memcpy ... </pre> <p>Ok, these functions might be slow, but how do I find out where they are getting called from? As all these hotspots lie in external libraries I see no way to optimize my code. </p> <p>Basically I am looking for some kind of callgraph annotated with accumulated cost, where my functions have a higher inclusive sampling cost than the library functions I call.</p> <p>Is this possible with perf? If so - how?</p> <p>Note: I found out that "E" unwraps the callgraph and gives somewhat more information. But the callgraph is often not deep enough and/or terminates randomly without giving information about how much info was spent where. Example:</p> <pre> - 10.26% kate libkatepartinterfaces.so.4.6.0 [.] Kate::TextLoader::readLine(int&... Kate::TextLoader::readLine(int&, int&) Kate::TextBuffer::load(QString const&, bool&, bool&) KateBuffer::openFile(QString const&) KateDocument::openFile() 0x7fe37a81121c </pre> <p>Could it be an issue that I'm running on 64 bit? See also: <a href="http://lists.fedoraproject.org/pipermail/devel/2010-November/144952.html">http://lists.fedoraproject.org/pipermail/devel/2010-November/144952.html</a> (I'm not using fedora but seems to apply to all 64bit systems).</p>
 

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