1991429 - 5.53 - 5.32% perf_reftest_singletons nth-index-1.html / perf_reftest_singletons nth-index-2.html (Linux) regression on Tue September 16 2025

Status: NEW

(Core :: CSS Parsing and Computation, defect)

Description

[Treeherder Bug Filer]

Perfherder has detected a talos performance regression from push a64a76eb1c924032342bf1c200c6de6b2c77023d. As author of one of the patches included in that push, we need your help to address this regression.

Please acknowledge, and begin investigating this alert within 3 business days, or the patch(es) may be backed out in accordance with our regression policy. Our guide to handling regression bugs has information about how you can proceed with this investigation.

If you have any questions or need any help with the investigation, please reach out to [e-mail]. Alternatively, you can find help on Slack by joining #perf-help, and on Matrix you can find help by joining #perftest.

Regressions:

Ratio	Test	Platform	Options	Absolute values (old vs new)
6%	perf_reftest_singletons nth-index-1.html	linux1804-64-shippable-qr	e10s fission stylo webrender	1.24 -> 1.31
5%	perf_reftest_singletons nth-index-2.html	linux1804-64-shippable-qr	e10s fission stylo webrender	1.24 -> 1.30

Details of the alert can be found in the alert summary, including links to graphs and comparisons for each of the affected tests.

If you need the profiling jobs you can trigger them yourself from treeherder job view or ask [e-mail] to do that for you.

You can run all of these tests on try with ./mach try perf --alert 46934

The following documentation link provides more information about this command.

Comment 1

[BugBot [:suhaib / :marco/ :calixte]]

Set release status flags based on info from the regressing bug 1986738

Comment 2

[Diego Ciudad Real Escalante [:descalante]]

Hello, currently we are monitoring performance improvements that could come from fixing Bug 1991007.

Comment 3

[Pascal Chevrel:pascalc]

(In reply to Diego Ciudad Real Escalante [:descalante] from comment #2)

Hello, currently we are monitoring performance improvements that could come from fixing Bug 1991007.

Diego, has the performance returned to normal after landing Bug 1991007? Thanks

Comment 4

[Diego Ciudad Real Escalante [:descalante]]

Hello. The performance doesn't seem to have returned to normal. After some discussion we would like to keep this bug open. This is because the push does introduce some (required) complexity to invalidation and there have not been any other perf-alerts associated with the push to date. Adding the fact that the slowdown amount is small and the test in question tests for exponential slowdowns of pathological scenarios in terms of invalidation, we would like to investigate further but don't think this requires immediate attention.

Comment 5

[BugBot [:suhaib / :marco/ :calixte]]

Set release status flags based on info from the regressing bug 1986738