I tried out linux' perf 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.
What I did:
perf record -g -p $(pidof someapp)
perf report -g -n
Now I see something like this:
+ 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 ...
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.
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.
Is this possible with perf? If so - how?
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:
- 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
Could it be an issue that I'm running on 64 bit? See also: http://lists.fedoraproject.org/pipermail/devel/2010-November/144952.html (I'm not using fedora but seems to apply to all 64bit systems).
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