See go/chrome-pgo-internal (Googlers only).
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_remoteexec = true
For android you need these in addition:
target_os = "android" target_cpu = "arm64"
Run representative benchmarks to produce profiles
python3 tools/pgo/generate_profile.py -C out/builddir
If collecting profiles on an android device, add a browser name like one of these:
python3 tools/pgo/generate_profile.py -C out/builddir \
--android-browser android-trichrome-bundle
You can find available browsers using:
tools/perf/run_benchmark run --browser=list
By default, some benchmark replay archives require special access permissions. For more details and to request access, please refer to Telemetry documentation. You can also choose to run generate_profile.py without these benchmarks, using the --run-public-benchmarks-only flag. However, note that doing so may produce a profile that isn't fully representative.
python3 tools/pgo/generate_profile.py -C out/builddir \ --android-browser android-trichrome-bundle \ --run-public-benchmarks-only
If generate_profile.py fails with ServiceException: 401 Anonymous caller does not have storage.objects.get access to the Google Cloud Storage object., then run download_from_google_storage --config (with your @google address; enter 0 as project-id).
This will produce out/builddir/profile.profdata
Produce the final PGO'd executable with the following gn args (and additional android args, if any):
enable_resource_allowlist_generation = false is_official_build = true symbol_level = 0 use_remoteexec = true pgo_data_path = "//out/builddir/profile.profdata"
chrome_pgo_phase is defined in build/config/compiler/pgo/pgo.gni. This GN variable can be one of 0, 1, or 2, meaning “don't use profile”, “generating profile”, and “use profile” respectively. See pgo.gni for details on platform-specific GN variables that determine which phase is used in each build.
Which file under //chrome/build/pgo_profiles/ gets used? It depends on both the platform and _pgo_target. For example, for 64-bit android, the file //chrome/build/android-arm64.pgo.txt contains the name of the *.profdata file that is used as the PGO profile by default if no other profile is specified via the GN arg pgo_data_path.
https://clang.llvm.org/docs/UsersManual.html#profile-guided-optimization