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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:

Attach gdb to the process: $ gdb -p 12345
Cause it to dump a profile: (gdb) p HeapProfilerDump("foobar")
The filename will be printed on the console, e.g. "Dumping heap profile to heap.0001.heap (foobar)"

Reference

Linux Profiling in Chromium

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