1778399 - Terrible input lag on twitch.tv chat

Status: REOPENED

(Core :: JavaScript Engine, defect, P2)

Description

[Hinatori]

Attachment: Firefox 2022-07-06 23.07 profile.json.gz

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:104.0) Gecko/20100101 Firefox/104.0

Steps to reproduce:

Occasionally experience terrible input lag when using twitch.tv chat. I managed to capture a performance profile which shows the issue.

Actual results:

Chat become unusable due to bad input lag.

Expected results:

Users expect to have zero input lag when typing something.

Comment 1

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

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

Comment 2

[Mayank Bansal]

Looks to be lots of time spent in JS

Comment 3

[Hinatori]

Attachment: Firefox 2022-07-10 21.03 profile.json.gz

Here is another capture that shows the issue. Notice the DomEvent Keypress duration on marker chart.

Comment 4

[Nicolas B. Pierron [:nbp]]

In the second profile the problem seems to be magnified by the GC major which is happening concurrently, which requires that we use write barrier.
Making key-presses go from ~300ms to ~520ms.

Then the code seems to spend a lot of time in Proxy related code, as well as js::Call and js::MaybeEnterJit, which suggests that we should optimize the code and start JIT-ing code path for making these calls instead of jumping into C++ to return back in the JIT.

Iain, would you know who might be looking at this issue?