Measure change in performance of a single commits

[joemcgill]

Automated performance metrics were added in [55459]. Currently, each time this automated workflow runs, it records two sets of metrics: one for the current change, and one used as a baseline for normalizing results between changes. Currently the baseline measurement is always taken against the 6.1.1 tag in WordPress (the most recent stable release when the workflow was created). In order to better understand the performance impact of a single change, it would be useful to compare directly against the previous commit hash (e.g., trunk) as part of the same workflow, using the same GitHub worker infrastructure to reduce variability between separate runs of the workflow.

Goals of this ticket

1. Collect a set of performance metrics for trunk prior to a commit in addition to the two that are being tested now.
2. Calculate the percentage change between trunk before and after the current change that is being tested
3. Include the percentage change in the workflow summary logs

Trac ticket:

See:

• https://core.trac.wordpress.org/ticket/58358
• https://core.trac.wordpress.org/ticket/58358
• https://core.trac.wordpress.org/ticket/58359

PR against my repo for testing: ​https://github.com/swissspidy/wordpress-develop/pull/33

Just realized that this is PR number 5000 :D That's _alot_ of PRs.

Since #4999 has been committed, could you please incorporate the metrics TTFB, LCP, and LCP - TTFB?

That should already be the case now that I merged the latest changes from trunk. You can see the results here: ​https://github.com/swissspidy/wordpress-develop/pull/33#issuecomment-1679084103

Leave a comment on the PR with the results (​https://github.com/swissspidy/wordpress-develop/pull/33#issuecomment-1679084103)

Would you be open to leave this for a follow-up, so we can merge the rest of it ASAP. This PR provides an enormous value, so the faster we merge, the better.

Yes, definitely open to that.

Removed the PR comment part now.

I think it looks good, but I'll wait for a final review from @desrosj

Links are now fixed: ​https://github.com/WordPress/wordpress-develop/actions/runs/6051491344?pr=5000

[swissspidy]

In 56506:

Build/Test Tools: Compare results in performance measurement workflow.

This extends the performance test workflow added in [55459] to also run tests against the target branch (if running on a pull request) or the previous commit (if running on trunk).

Those results are then compared with the ones from the current commit, and the difference is displayed as a GitHub Actions workflow summary for convenience.

Props mukesh27, flixos90, desrosj, joemcgill, swissspidy.
Fixes #58358, #58359.
See #56150.

Committed in https://core.trac.wordpress.org/changeset/56506