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# Branching Perfetto for Chrome milestones
Merging a (set of) Perfetto change(s) to a Chrome milestone release requires
creation of a branch in the perfetto repo, cherry-picking of the change(s) to
the branch, and updating the `DEPS` file in Chrome's milestone branch to point
to the new perfetto branch's head.
## Creating the perfetto branch {#branch}
1. Determine the branch name: **`chromium/XXXX`**, where `XXXX` is the branch
number of the milestone (see
[Chromium Dash](https://chromiumdash.appspot.com/branches)). Example for
M87: `chromium/4280`.
1. Check if the branch already exists: if yes, skip to
[cherry-picking](#all-tables). To check, you can search for it in
[Gerrit's branch page](https://android-review.googlesource.com/admin/repos/platform/external/perfetto,branches).
1. Look up the appropriate base revision for the branch. You should use the
revision that Chromium's `DEPS` of the milestone branch points to (search
for `perfetto` in the file). The `DEPS` file for branch XXXX is at:
`https://chromium.googlesource.com/chromium/src.git/+/refs/branch-heads/XXXX/DEPS`
Example for M87:
[`DEPS`](https://chromium.googlesource.com/chromium/src.git/+/refs/branch-heads/4280/DEPS)
(at time of writing) points to `f4cf78e052c9427d8b6c49faf39ddf2a2e236069`.
1. Create the branch - the easiest way to do this is via
[Gerrit's branch page](https://android-review.googlesource.com/admin/repos/platform/external/perfetto,branches).
The `NEW BRANCH` button on the top right opens a wizard - fill in the branch
name and base revision determined above. If this fails with a permission
issue, contact the [Discord chat](https://discord.gg/35ShE3A) or
[perfetto-dev](https://groups.google.com/forum/#!forum/perfetto-dev) mailing
list.
## Cherry-picking the change(s) {#cherry-pick}
1. If there are no merge conflicts, cherry-picking via Gerrit will be easiest.
To attempt this, open your change in Gerrit and use the `Cherry pick` entry
in the overflow menu on the top right, providing the `chromium/XXXX` branch
name (see [above](#branch)).
1. Otherwise, merge the patch locally into a branch tracking
`origin/chromium/XXXX` and upload a Gerrit change as usual:
```
$ git fetch origin
$ git checkout -tb cpick origin/chromium/XXXX
$ git cherry-pick -x <commit hash> # Resolve conflicts manually.
$ tools/gen_all out/xxx # If necessary.
$ git cl upload # Remove "Change-Id:" lines from commit message.
```
1. Send the patch for review and land it. Note the commit's revision hash.
## Updating the DEPS file in Chromium
1. Create, send for review, and land a Chromium patch that edits the top-level
`DEPS` file on the Chromium's milestone branch. You can also combine this
step with cherry-picks of any chromium changes. For details, see
[Chromium's docs](https://www.chromium.org/developers/how-tos/drover). It
amounts to:
```
$ gclient sync --with_branch_heads
$ git fetch
$ git checkout -tb perfetto_uprev refs/remotes/branch-heads/XXXX
$ ... # Edit DEPS.
$ git cl upload
```