1959641 - 10.87 - 3.15% expedia FirstVisualChange / expedia SpeedIndex + 3 more (Linux) regression on Wed April 2 2025

Status: RESOLVED WONTFIX

(Core :: Networking, defect)

Description

[Treeherder Bug Filer]

Perfherder has detected a browsertime performance regression from push 80ee470262e88e352e20fab88b4e245d936f02e4. 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
11%	expedia FirstVisualChange	linux1804-64-shippable-qr	fission warm webrender	206.03 -> 228.43	Before/After
10%	bing-search fcp	windows11-64-24h2-shippable	bytecode-cached cold fission webrender	76.27 -> 84.03	Before/After
9%	expedia largestContentfulPaint	linux1804-64-shippable-qr	fission warm webrender	143.56 -> 156.29	Before/After
8%	expedia fcp	linux1804-64-shippable-qr	fission warm webrender	184.94 -> 199.48	Before/After
5%	expedia ContentfulSpeedIndex	linux1804-64-shippable-qr	fission warm webrender	347.80 -> 366.63	Before/After
3%	expedia SpeedIndex	linux1804-64-shippable-qr	fission warm webrender	550.67 -> 568.03	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 44619

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 1957619

Comment 2

[Valentin Gosu [:valentin]]

This regression is due to Firefox no longer caching 301 and 308 redirects indefinitely, and instead revalidating them.
The change came out of a web-compat issue - bug 1934586 - where Firefox's caching of the redirect was causing a user noticeable issue.

All other browsers have the same behavior regarding cached redirects.
See HTTP cache does not reuse a redirected response with no max-age and no Last-Modified header in WPT.FYI

I am inclined to WONTFIX this one.

Comment 3

[Valentin Gosu [:valentin]]

I discussed this with the team.
This is mostly happening on expedia, because they probably have redirects without the proper caching headers. If they had Cache-Control headers for redirects this would not be an issue.
Unless someone is reporting that this made our load times significantly slower compared to other browsers (which doesn't seem to be the case), I will close the bug with WONTFIX.