1977852 - 77.54 - 49.35% perf_reftest_singletons insert-subtree-not-nth-edge-has-pseudo.html / perf_reftest_singletons insert-subtree-not-nth-edge-has-pseudo.html + 2 more (Linux, OSX, Windows) regression on Fri July 4 2025

Status: RESOLVED FIXED

(Core :: CSS Parsing and Computation, defect)

Description

[Treeherder Bug Filer]

Perfherder has detected a talos performance regression from push 4224c7750c3e8853a56330819cf401423386d75b. 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)
78%	perf_reftest_singletons insert-subtree-not-nth-edge-has-pseudo.html	windows11-64-24h2-shippable	e10s fission stylo webrender	5.89 -> 10.46
60%	perf_reftest_singletons insert-subtree-not-nth-edge-has-pseudo.html	linux1804-64-shippable-qr	e10s fission stylo webrender	24.48 -> 39.25
57%	perf_reftest_singletons insert-subtree-not-nth-edge-has-pseudo.html	linux1804-64-shippable-qr	e10s fission stylo webrender	24.66 -> 38.82
49%	perf_reftest_singletons insert-subtree-not-nth-edge-has-pseudo.html	macosx1470-64-shippable	e10s fission stylo webrender	14.48 -> 21.63

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 45939

The following documentation link provides more information about this command.

Comment 1

[Alex Finder|PTO, returning August 18th]

Actual revision that caused the regression is 1c622bdca13b60ae68a7acbdd2de373dc3f30568

Comment 2

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

Set release status flags based on info from the regressing bug 1855690

Comment 3

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

The bug is marked as tracked for firefox142 (nightly). However, the bug still isn't assigned.

:fgriffith, could you please find an assignee for this tracked bug? Given that it is a regression and we know the cause, we could also simply backout the regressor. If you disagree with the tracking decision, please talk with the release managers.

For more information, please visit BugBot documentation.

Comment 4

[David Shin[:dshin]]

Attachment: Bug 1977852: Ignore presence of indexed selector in compound when considering collapsing relative dependencies. r=#style

Previously, we didn't pull out indexed selectors from the inner selector of
:has(:not(:first-child)) - now we it is like :has(:first-child:not(*)).
On any invalidation, we see that our compound contains :first-child, so
we become unable to consider the invalidation for collapsing with the impllied
* invalidation, effectively resulting in redundant invalidations.
Because in this case we're considering two different invalidations for the
same element, we can in fact ignore the presence of the indexed selector
and allow collapsing.

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/c807d67f7acf
https://hg.mozilla.org/integration/autoland/rev/1871fa2b54f1
Ignore presence of indexed selector in compound when considering collapsing relative dependencies. r=firefox-style-system-reviewers,emilio

Comment 6

[Sandor Molnar[:smolnar]]

https://hg.mozilla.org/mozilla-central/rev/1871fa2b54f1

Comment 7

[Acasandrei Beatrice (needinfo me)]

(In reply to Pulsebot from comment #5)

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/c807d67f7acf
https://hg.mozilla.org/integration/autoland/rev/1871fa2b54f1
Ignore presence of indexed selector in compound when considering collapsing
relative dependencies. r=firefox-style-system-reviewers,emilio

Perfherder has detected a talos performance change from push 1871fa2b54f186e603b03ff65a9e567cc2465d14.

If you have any questions, please reach out to a performance sheriff. Alternatively, you can find help on Slack by joining #perf-help, and on Matrix you can find help by joining #perftest.

Improvements:

Ratio	Test	Platform	Options	Absolute values (old vs new)
33%	perf_reftest_singletons insert-subtree-not-nth-edge-has-pseudo.html	macosx1470-64-shippable	e10s fission stylo webrender	22.28 -> 14.94
33%	perf_reftest_singletons insert-subtree-not-nth-edge-has-pseudo.html	linux1804-64-shippable-qr	e10s fission stylo webrender	38.28 -> 25.81
20%	perf_reftest_singletons append-nth-edge-has-pseudo.html	linux1804-64-shippable-qr	e10s fission stylo webrender	18.65 -> 14.92
19%	perf_reftest_singletons append-nth-edge-has-pseudo.html	macosx1470-64-shippable	e10s fission stylo webrender	10.87 -> 8.81
17%	perf_reftest_singletons remove-front-has-pseudo.html	linux1804-64-shippable-qr	e10s fission stylo webrender	1.85 -> 1.54
16%	perf_reftest_singletons remove-front-has-pseudo.html	macosx1470-64-shippable	e10s fission stylo webrender	1.41 -> 1.18

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 a performance sheriff to do that for you.

You can run all of these tests on try with ./mach try perf --alert 46008

The following documentation link provides more information about this command.