Life of a Chrome commit on Chrome OS

This document provides a brief overview of how Chrome changes get committed and tested on Chrome OS.

For details on non-Chrome Chrome OS changes, see Life of a Chrome OS commit.

Create a Chrome change

Make and upload changes

See the section on contributing code at for how to create a branch and make changes.

Once a change is completed and tested locally, upload it to codereview:

git cl upload

Have your change reviewed

Use codereview to review your change and prepare it for the commit queue. See contributing code for details.

The Chrome commit pipeline

The Commit Queue and Tryservers

The Chrome commit queue has a very large pool of builders that will apply individual changes to the master, build them, and test them.

Before the patch is approved

A developer can click on ‘Choose trybots’ to select specific builders to run (there are a lot of them).

Alternately they can click ‘CQ dry run’ to run all of the builders that the CQ will run in advance, without scheduling a commit.

The commit queue

Once a change has been reviewed and approved, the developer can check the ‘Commit’ checkbox. This will mark the change as ready for the CQ.

Depending on what was changed, the CQ selects a suite of tryserver builders for win, mac, linux, and android.

Note: The linux builders include linux-chromeos builders (linux builders with chromeos=1). These run browser_tests and unit_tests for Chrome on Chrome OS.

If the CQ builders succeed then the change will be committed to the master.

Otherwise the ‘Commit’ checkbox will need to be re-checked once the failure is fixed or determined to be unrelated to the change.

The chromium waterfall

Once a change is committed on the master, it is picked up by the chromium waterfall. This includes a very large number of builders that will thoroughly test the commit, including a number of linux-chromeos builders.

Note: Due to lab limitations not every builder in the waterfall is included in the Commit Queue. For Chrome OS there are a few Debug test builders that only exist on the waterfall. Failures there are infrequent but possible, so keep an eye out!

The Chrome OS commit pipeline for Chrome changes

Once a Chrome change lands in the master, it needs to get through the PFQ before it will be picked up by Chrome OS. This is to protect the Chrome OS builders, since Chrome OS depends heavily on Chrome itself.

The PFQ Informational builders

Continuous PFQ builders in the chrome_informational group apply the most recent Chrome changes to the most recent Chrome OS build. This group also has open-source Chromium builders and a builder that runs telemetry unit tests.

The PFQ builders

The PFQ builds a daily Chrome version and the most recent Chrome OS version (using the manifest from the latest CQ/paladin build). It then builds a Chrome OS image and runs several test suites against the result.

  • Once daily (currently at 8 PM PT) a Chrome release branch is created and tagged.
    • Sometimes additional tags are created for the release branch, e.g. after a revert or fix for a bad change is merged to the branch.
  • Whenever such a branch tag is created, a new master PFQ build is triggered.
  • The master triggers a series of Chrome and Chromium slave builders covering all cpu types (arm, amd64, and x86) and important variants. Coverage is ensured by chromite/cbuildbot/binhost_test.
  • PFQ Builders do the following:
    • Check out the Chrome OS source from the LKGM manifest.
    • Check out the Chrome source from the tagged Chrome release branch.
    • Build Chrome OS, including Chrome from the local source checkout.
    • Run VM tests on all non ARM builders.
    • Run HW tests on builders where HW is available, including ARC tests on boards that support it.
    • Verify the Simple Chrome environment for developers (in parallel with HW tests).
      • Download the tarball built by the respective Chrome OS “release” or “full” builder that includes necessary dependencies for building Chrome for Chrome OS.
      • Test the [Simple Chrome workflow] with this tarball.
      • If all non-experimental builders pass, the PFQ master generates a Chromium CL to update chromeos/CHROMEOS_LKGM and sends it to the CQ. This file determines which version of the tarball Simple Chrome will try to download.