Intent to Experiment: Long Animation Frame Timing

[Noam Rosenthal]

Contact emails

nrose...@chromium.org

Explainer

https://github.com/w3c/longtasks/blob/main/loaf-explainer.md

Specification

https://github.com/w3c/longtasks/blob/main/loaf-explainer.md

Summary

This is a extension of long tasks. It measures the task together with its subsequent rendering update, adding information such as long running scripts, rendering time, and time spent in forced layout and style ("layout thrashing"). Developers can use this as a diagnostic for "sluggishness", which is measured by INP, by finding the causes for main-thread congestion which is often the cause for bad INP.

Blink component

Blink>PerformanceAPIs

TAG review

TAG review status

Pending

Risks

Interoperability and Compatibility

Gecko: Positive Not yet a formal signal but showed positive interest at WG call.

WebKit: No signal

Web developers: Positive (https://twitter.com/jebbacca/status/1653355406368952321) Wix, Taboola, and others have already experimented with this in Canary. Strong excitement from several partners at We Love Speed conference.

Other signals:

Ergonomics

It should work well with other performance timeline entries, mainly event-timing/INP.

Security

This feature exposes rendering time to iframes, which might be cross-origin (same-process). However, this is anyway observable, by using requestAnimationFrame. Note that everything in this feature is same-process.

WebView application risks

Does this intent deprecate or change behavior of existing APIs, such that it has potentially high risk for Android WebView-based applications?

Goals for experimentation

Ongoing technical constraints

None

Debuggability

Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, Chrome OS, Android, and Android WebView)?

Yes

Is this feature fully tested by web-platform-tests?

Yes

Flag name

LongAnimationFrameTiming

Requires code in //chrome?

False

Tracking bug

https://bugs.chromium.org/p/chromium/issues/detail?id=1392685

Launch bug

https://launch.corp.google.com/launch/4244858

Estimated milestones

OriginTrial desktop last	120
OriginTrial desktop first	115

OriginTrial Android last	120
OriginTrial Android first	115

OriginTrial webView last	120
OriginTrial webView first	115

Link to entry on the Chrome Platform Status

https://chromestatus.com/feature/6118675067699200

Links to previous Intent discussions

Intent to prototype: https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAJn%3DMYbX%3DEOAwkEvDQY9Ja1trSXLFtM1XNsuw1Lr2QR88%2BTnqw%40mail.gmail.com

This intent message was generated by Chrome Platform Status.

[Rick Byers]

LGTM - excited to see people experiment with this!

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