2052260 - 11.56 - 4.12% damp custom.inspector.manyrules.deselectnode + 1 more (Linux) regression on Fri June 26 2026

Status: RESOLVED FIXED

(DevTools :: Inspector: Rules, defect, P2)

Description

[Performance Sheriff Bot]

Perfherder has detected a devtools performance regression from push ffc641da40ab675b27056db29233c3b9763d9b37. 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.

Regression	Test	Platform	Options	Absolute values [old vs new]
12%	damp custom.inspector.manyrules.deselectnode (doc)	linux1804-64-shippable-qr	e10s fission stylo webrender	111.26 ms -> 124.12 ms
4%	damp custom.inspector.manyrules.selectnode (doc)	linux1804-64-shippable-qr	e10s fission stylo webrender	775.60 ms -> 807.53 ms

Support & Actionable Steps

For questions, please contact [e-mail]. You can also find help on Slack (#perf-help) or Matrix (#perftest).

Action guide details:

• See the guide to handling regression bugs for investigation steps.
• Review the alert summary for affected tests, graphs, and comparisons.
• Check the PerfCompare results.
• Tests on Try: Run all tests using ./mach try perf --alert 51186 (See documentation link for details).
• Profiling jobs: Trigger jobs from Treeherder job view or request them from [e-mail].

Comment 1

[BugBot [:suhaib / :marco]]

Set release status flags based on info from the regressing bug 2047874

Comment 2

[Nicolas Chevobbe [:nchevobbe]]

Looks like this could be caused by the new access to currentlySelectedElement in https://searchfox.org/firefox-main/rev/4b550c17bb6c2c7bac7e8842c6b76f17debf643f/devtools/server/actors/page-style.js#833-838

#getRuleItem(
  rule,
  rawNode = null,
  { inherited, isSystem, pseudoElement, keyframes } = {}
) {
  let element = inherited?.rawNode || rule.currentlySelectedElement;

See: https://share.firefox.dev/44TpEgE

It seems like we could avoid calling this getter and use the rawNode arg instead, but maybe it's worth optimizing currentlySelectedElement too

Comment 3

[Nicolas Chevobbe [:nchevobbe]]

Attachment: Bug 2052260 - [devtools] Avoid using currentlySelectedElement in #getRuleItem. r=#devtools

The getter is potentially slow (it was picked up by DAMP), and in this case,
it can be replaced with the rawNode arg.

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/9b755d659904
https://hg.mozilla.org/integration/autoland/rev/a6aa6ef257a4
[devtools] Avoid using currentlySelectedElement in #getRuleItem. r=devtools-reviewers,bomsy

Comment 5

[Sandor Molnar[:smolnar]]

https://hg.mozilla.org/mozilla-central/rev/a6aa6ef257a4

Comment 6

[BugBot [:suhaib / :marco]]

Set release status flags based on info from the regressing bug 2047874