1959085 - 38.06 - 9.8% twitter fcp / instagram ContentfulSpeedIndex + 2 more (Linux, OSX) regression on Wed April 2 2025

Status: RESOLVED DUPLICATE of bug 1958241

(Core :: Privacy: Anti-Tracking, defect)

Description

[Treeherder Bug Filer]

Perfherder has detected a browsertime performance regression from push 1dcb66eab4412818d5d0bbf36e8501d1b75b850d. 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)	Performance Profiles
38%	twitter fcp	macosx1470-64-shippable	bytecode-cached cold fission webrender	72.81 -> 100.52	Before/After
29%	instagram fcp	macosx1470-64-shippable	cold fission webrender	98.40 -> 126.89	Before/After
18%	google-mail LastVisualChange	linux1804-64-shippable-qr	fission warm webrender	1,130.23 -> 1,334.48	Before/After
10%	instagram ContentfulSpeedIndex	linux1804-64-shippable-qr	bytecode-cached cold fission webrender	942.78 -> 1,035.18	Before/After

Improvements:

Ratio	Test	Platform	Options	Absolute values (old vs new)	Performance Profiles
11%	paypal fcp	windows11-64-24h2-shippable	fission warm webrender	57.14 -> 50.97	Before/After
8%	paypal largestContentfulPaint	windows11-64-24h2-shippable	fission warm webrender	59.80 -> 55.12	Before/After

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 44597

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 1948288

Comment 2

[Tooru Fujisawa [:arai]]

At least this is not from bug 1948288, but something else in the patch stack.

before vs up to Bug 1902403: https://perf.compare/compare-results?baseRev=65ac3a586161069bd14f6ce4fca87d3f2f286c03&baseRepo=try&newRev=4a2acd6edac07986b695a439960cd41c76997ac0&newRepo=try&framework=13
Bug 1902403 vs Bug 1948288: https://perf.compare/compare-results?baseRev=4a2acd6edac07986b695a439960cd41c76997ac0&baseRepo=try&newRev=6af74049924fe0cbf7accf36b4fcce0dacde7102&newRepo=try&framework=13

Comment 3

[Thomas Wisniewski [:twisniewski]]

The only other patch in that stack which could presumably cause this is https://phabricator.services.mozilla.com/D243395, as it's adding a content script. But that makes no sense, as it's marked to not be run before FCP, but only on document_idle, so I have no idea what's going on here.

Comment 4

[Thomas Wisniewski [:twisniewski]]

With luck this will be fixed by the patch which just landed in bug 1960374.

Comment 5

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

:arai, since you are the author of the regressor, bug 1948288, could you take a look? Also, could you set the severity field?

For more information, please visit BugBot documentation.