diff --git a/Linux-Profiling.md b/Linux-Profiling.md new file mode 100644 index 0000000..a95032d --- /dev/null +++ b/Linux-Profiling.md @@ -0,0 +1,80 @@ +# Linux Profiling + +Profiling code is enabled when the `use_allocator` variable in gyp is set to +`tcmalloc` (currently the default) and `profiling` variable in gyp is set to +`1`. That will build the tcmalloc library, including the cpu profiling and heap +profiling code into edash-packager, e.g. + + GYP_DEFINES='profiling=1 use_allocator="tcmalloc"' gclient runhooks + +If the stack traces in your profiles are incomplete, this may be due to missing +frame pointers in some of the libraries. A workaround is to use the +`linux_keep_shadow_stacks=1` gyp option. This will keep a shadow stack using the +`-finstrument-functions` option of gcc and consult the stack when unwinding. + +## CPU Profiling + +In order to enable cpu profiling, run edash-packager with the environment +variable `CPUPROFILE` set to a filename. For example: + + CPUPROFILE=/tmp/cpuprofile out/Release/packager + +The cpu profile will be dumped periodically to the filename specified in the +CPUPROFILE environment variable. You can then analyze the dumps using the pprof +script (packager/third_party/tcmalloc/chromium/src/pprof). For example, + + pprof --gv out/Release/packager /tmp/cpuprofile + +This will generate a visual representation of the cpu profile as a postscript +file and load it up using `gv`. For more powerful commands, please refer to the +pprof help output and the google-perftools documentation. + +For further information, please refer to +http://google-perftools.googlecode.com/svn/trunk/doc/cpuprofile.html. + +## Heap Profiling + +To turn on the heap profiler on edash-packager, use the `HEAPPROFILE` +environment variable to specify a filename for the heap profile. For example: + + HEAPPROFILE=/tmp/heapprofile out/Release/packager + +The heap profile will be dumped periodically to the filename specified in the +`HEAPPROFILE` environment variable. The dumps can be analyzed using the same +command as cpu profiling above. + +For further information, please refer to +http://google-perftools.googlecode.com/svn/trunk/doc/heapprofile.html. + +Some tests fork short-living processes which have a small memory footprint. To +catch those, use the `HEAP_PROFILE_ALLOCATION_INTERVAL` environment variable. + +#### Dumping a profile of a running process + +To programmatically generate a heap profile before exit, use code like: + + #include "packager/third_party/tcmalloc/chromium/src/gperftools/heap-profiler.h" + + // "foobar" will be included in the message printed to the console + HeapProfilerDump("foobar"); + +Then add allocator.gyp dependency to the target with the above change: + + 'conditions': [ + ['profiling==1', { + 'dependencies': [ + 'base/allocator/allocator.gyp:allocator', + ], + }], + ], + +Or you can use gdb to attach at any point: + +1. Attach gdb to the process: `$ gdb -p 12345` +2. Cause it to dump a profile: `(gdb) p HeapProfilerDump("foobar")` +3. The filename will be printed on the console, e.g. + "`Dumping heap profile to heap.0001.heap (foobar)`" + +## Reference + +[Linux Profiling in Chromium](https://chromium.googlesource.com/chromium/src/+/master/docs/linux_profiling.md) \ No newline at end of file