|Version 4 (modified by simonmar, 6 years ago) (diff)|
OProfile does a system-wide profile using performance counters. It can also generate annotated source/assembly just like VTune. Unfortunately, because GHC can't export source-level debugging symbols, OProfile cannot do source-level annotation of GHC programs.
It can be installed from a package on Ubuntu, which is cool. But beware: Ubuntu bug 172495: https://bugs.launchpad.net/ubuntu/+source/oprofile/+bug/172495/ : change the /bin/sh to /bin/bash at the top of /usr/bin/opcontrol.
There seems to be a problem with the counters just stopping arbitrarily, requiring a restart of the daemon.
Recipe for profiling something:
$ sudo opcontrol --init $ sudo opcontrol --reset $ sudo opcontrol --setup --event=<event> $ sudo opcontrol --start $ ... run program... $ sudo opcontrol --stop $ sudo opreport
check that the program you ran is at the top of the profile somewhere. Sometimes for me it doesn't appear, and have to run it again. To see a list of possible <event>s, use $ opcontrol --list-events.
It may be necessary to use opcontrol --dump; opcontrol --shutdown prior to sudo opreport above. We are not sure.
Then to annotate the source:
$ sudo opannotate --source <program> >&! log
lists the contents of source files in order of importance. Alternatively use --output-dir to put the source files in a directory, but then you don't get to find out which are the important ones.
Things to be aware of
- You might think that you could use the -fvia-C -optc-g options to force GHC to export C-source-level debugging symbols. The Evil Mangler script that post-processes the .s file output by gcc does not understand the debug annotations added by gcc's -g flag, and so -optc-g will not work. You can, however, get GHC to output assembly-level debugging symbols by using -opta-g. You'll probably also want to use the -keep-s-files option so that opannotate can get at the relevant .s files.
- Suppose that you do
$ sudo opcontrol --setup --event=<eventname>:<count>and receive an error message that "Count <count> for event <eventname> is below the minimum." If you check the minimum value for <eventname> using the --list-events option and see that <count> is in fact not below the purported minimum count, then you may have passed in a non-zero value for --callgraph option. When doing callgraph profiling, OProfile requires that the sample count be at least 15 times the minimum.
opcontrol --status will show you if callgraph is currently set. To reset it, make sure the oprofile daemon is stopped and reset the callgraph value:
$ sudo opcontrol --shutdown $ sudo opcontrol --callgraph=0Now you can re-run your profiling and the original <count> should work.