1764197 - High CPU usage on high refreshrate monitor

Status: RESOLVED DUPLICATE of bug 1763451

(Core :: Performance, defect)

Description

[C Nieuweboer]

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:99.0) Gecko/20100101 Firefox/99.0

Steps to reproduce:

I've been having problems with Firefox CPU usage on a high refreshrate monitor (240Hz).

Actual results:

On some websites Firefox CPU usage stays on 10% in the task manager, which means 100% usage for a single thread on my CPU, even when not scrolling or interacting with the websites in any way.

The easiest to reproduce is a dutch hardware news website https://nl.hardware.info/, but I've seen the same on other websites like Youtube. Sometimes it starts directly after loading a website, sometimes after scrolling up and down a bit.
This doesn't always happen. And when I reload the exact same website CPU usage often goes down to around 1% after few seconds.

When I lower the monitor refreshrate to 60 I can't get CPU usage to stay above 1% for any amount of time when not interacting with a website.

I've tried refreshing Firefox, and disabled all extensions, but that didn't make any difference.

about:support
https://pastebin.com/WvajWixN

Profile of idling website at max CPU usage
https://share.firefox.dev/3jsQbK5

Comment 1

[BugBot [:suhaib / :marco/ :calixte]]

The Bugbug bot thinks this bug should belong to the 'Core::Performance' component, and is moving the bug to that component. Please correct in case you think the bot is wrong.

Comment 2

[Emilio Cobos Álvarez (:emilio)]

Thanks for filing!

Olli literally landed Changes to idle handling on high refresh rate monitors days ago I think, can you report if you see the same result on Nightly? https://nightly.mozilla.org

Comment 3

[C Nieuweboer]

Wow, that is quite the coincidence. Nightly works fine for me. CPU usage goes down to 1-2% a few seconds after loading a website or scrolling, or 0-1% while using an ad blocker.

Comment 4

[Emilio Cobos Álvarez (:emilio)]

Bug 1763451 is what I was thinking btw.

Comment 5

[Emilio Cobos Álvarez (:emilio)]

It seems somewhat related in the sense that the profiles show that a lot of time is spent posting idle callbacks and bug 1763451 is about idle callbacks not getting processed (so maybe the event queue grows too much or something?).

Olli, is it a dupe?

Comment 6

[Olli Pettay [:smaug][[e-mail]]]

This could be a dup. Let me ask beta approval.