Intensive throttling of Javascript timer wake ups

Category: Performance
Type: New or changed feature
Status: Enabled by default (Chrome 86)
Intent stage: Shipped

Summary

In a Window whose top Window has been hidden for 5 minutes and which is not opted out from intensive wake up throttling, a timer task with non-zero timeout can run: - on a 1-second aligned wake up if: - the timer task's nesting level is < 5, or, -the Window is same-origin with the top Window and at least 1 minute has elapsed since the last timer task with nesting level >= 5 has run in any Window in the tree that is same-origin with the top Window - on a 1-minute aligned wake up, otherwise.

Motivation

Local experiments demonstrate that this intervention extends battery life.

Standards & signals

Specification: https://html.spec.whatwg.org/multipage/timers-and-user-prompts.html
Firefox: No signal — In Firefox 77.0.1, a recursive setTimeout with a 10 ms timeout runs every 10 ms.
Safari: Shipped/Shipping — In Safari 13.1.1, a recursive setTimeout with a 10 ms timeout runs: < 2.5 minutes in background: Every 250 ms - 30 seconds > 2.5 minutes in background: Every 40 seconds
Web developers: No signals — There were strong negative signals for page freezing on desktop https://groups.google.com/a/chromium.org/g/blink-dev/c/sotCDcI-E7Y/m/boghpXElDAAJ. This intervention provides similar performance benefits, but addresses breakages raised by Web developers. We will update this section when we get signals from Web developers specifically on this improved intervention.
Tracking bug: https://crbug.com/1075553

Docs: https://docs.google.com/document/d/11FhKHRcABGS4SWPFGwoL6g0ALMqrFKapCk5ZTKKupEk/edit?usp=sharing

Explainers: https://docs.google.com/document/d/105Hlbcb1mTV06bT9aDpwBotY13eZiKV5Hl4PW5LlyeE/edit?usp=sharing

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