Generating PGO Profiles

Normally devs don't need to worry about this and can use the default profile for official builds. The default profile can be fetched by adding "checkout_pgo_profiles": True to custom_vars in the gclient config and running gclient runhooks.

To produce an executable built with a custom PGO profile:

• Produce the instrumented executable using the following gn args:

  chrome_pgo_phase = 1
  enable_resource_allowlist_generation = false
  is_official_build = true
  symbol_level = 0
  use_goma = true
  

• Run representative benchmarks to produce profiles

  • vpython tools/perf/run_benchmark system_health.common_desktop --assert-gpu-compositing --run-abridged-story-set --browser=exact --browser-executable=out/path/to/chrome
  • vpython tools/perf/run_benchmark speedometer2 --assert-gpu-compositing --browser=exact --browser-executable=out/path/to/chrome
  • This will produce *.profraw files in the current working directory

• Merge the profiling data

  • Get the llvm-profdata tool by adding "checkout_clang_coverage_tools": True, to custom_vars in the gclient config and running gclient runhooks.
  • Run third_party/llvm-build/Release+Asserts/bin/llvm-profdata merge *.profraw -o chrome.profdata

• Produce the final PGO'd executable with the following gn args:

  enable_resource_allowlist_generation = false
  is_official_build = true
  symbol_level = 0
  use_goma = true
  pgo_data_path = {path-to-the-profile}