2005806 - StaticPresData::GetFontPrefsForLang spends time in ICU during Fenix startup

Status: RESOLVED FIXED

(Core :: Graphics: Text, defect)

Description

[Markus Stange [:mstange]]

Profile: https://share.firefox.dev/4rOkjS5

StaticPresData::GetFontPrefsForLang spends time in uloc_addLikelySubtags_78 to figure out that we need to read the prefs ending in .x-western for geckoview.xhtml.

That document doesn't have a language set on it - will it always use en-US? Can we add a fast path to map en-US to x-western so that we don't have to engage ICU here?

Comment 1

[Markus Stange [:mstange]]

Also, the font prefs don't really matter for this document anyway because it's just a <window> with a <browser> in it and no actual text in the parent process.

Comment 2

[Markus Stange [:mstange]]

Attachment: Bug 2005806 - Add fast path for English in GetUncachedLanguageGroup to avoid ICU initialization. r=jfkthame,emilio

During startup, when geckoview.xhtml's style is initialized, we call
GetLanguageGroup("en-US") to determine font preferences. This currently
triggers expensive ICU likely subtags data loading.

Add a fast path that directly maps "en" and "en-*" to x_western without
calling AddLikelySubtags(), since all English variants use Latin script.

This defers ICU initialization until it's actually needed for non-English
languages, improving startup performance.

Comment 3

[Markus Stange [:mstange]]

Before: https://share.firefox.dev/3XOt9Sj (34 samples in nsPresContext::FlushPendingMediaFeatureValuesChanged)
After: https://share.firefox.dev/3KWh8Y0 (0 samples in nsPresContext::FlushPendingMediaFeatureValuesChanged)
(After + bug 2004948: https://share.firefox.dev/3XOkX4r )

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/7af4ff603851
https://hg.mozilla.org/integration/autoland/rev/f439d65a5473
Add fast path for English in GetUncachedLanguageGroup to avoid ICU initialization. r=jfkthame

Comment 5

[Cristian Tuns]

https://hg.mozilla.org/mozilla-central/rev/f439d65a5473

Comment 6

[Mayank Bansal]

Pretty large AWFY wins on Windows.
5.3%/440KB on Base content Explicit
3.8%/436KB on Base Content Redident Unique.

Comment 7

[Acasandrei Beatrice (needinfo me)]

(In reply to Pulsebot from comment #4)

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/7af4ff603851
https://hg.mozilla.org/integration/autoland/rev/f439d65a5473
Add fast path for English in GetUncachedLanguageGroup to avoid ICU
initialization. r=jfkthame

Perfherder has detected a awsy performance change from push f439d65a5473dd295c79803225fd2ee1ea19a909.

No action is required from the author; this comment is provided for informational purposes only.

Improvements:

Ratio	Test	Platform	Options	Absolute values (old vs new)
5%	Base Content Explicit	windows11-64-24h2-shippable	fission	8,230,420.67 -> 7,798,659.33
4%	Base Content Resident Unique Memory	windows11-64-24h2-shippable	fission	11,391,317.33 -> 10,958,506.67

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Details of the alert can be found in the alert summary, including links to graphs and comparisons for each of the affected tests.