1981540 - 0.32% Base Content Explicit (Windows) regression on Fri August 1 2025

Status: RESOLVED FIXED

(Core :: CSS Parsing and Computation, defect, P3)

Description

[Treeherder Bug Filer]

Perfherder has detected a awsy performance regression from push f5b95b5c2423739ee543a846a43fe47549a54a05. 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)
0.32%	Base Content Explicit	windows11-64-24h2-shippable	fission	8,205,269.67 -> 8,231,492.36

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 46138

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 1954142

Comment 3

[Keith Cirkel [:keithamus]]

Investigating how we can reduce this.

Comment 4

[Keith Cirkel [:keithamus]]

Attachment: Bug 1981540 - Use Vec<T>+[Option<u8>; 91] over [Option<Box<T>>; 91] for PseudoMap r?emilio

This shrinks PseudoMap down from a 91usize (for each Box) to 91u8.
This slight memory saving in each PseudoMap should add up to some
reasonable savings overall, without significantly impacting performance
(see
https://perf.compare/compare-lando-results?baseLando=146687&newLando=147253&baseRepo=try&newRepo=try&framewor=&framework=13)

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/4d0c110c3366
https://hg.mozilla.org/integration/autoland/rev/c7f54313b6b4
Use Vec<T>+[Option<u8>; 91] over [Option<Box<T>>; 91] for PseudoMap r=emilio,firefox-style-system-reviewers

Comment 6

[Norisz Fay [:noriszfay]]

https://hg.mozilla.org/mozilla-central/rev/c7f54313b6b4

Comment 7

[Mayank Bansal]

somewhat less than 52KB improvement on Base content Explicit. \o/

But also a corresponding 11KB regression on Heap-unclassified.
So maybe consider adding memory reporter for this?