1705478 - dom.input_events.strict_input_vsync_alignment = true with a private browsing window causes firefox to become unresponsive

Status: RESOLVED INVALID

(Core :: Performance: General, defect, P3)

Description

[[e-mail] (:bhearsum)]

Basic information

Steps to Reproduce:

1. Set dom.input_events.strict_input_vsync_alignment to true
2. open a private browser window

Expected Results: firefox should continue being responsive

Actual Results: firefox has ~1s input lag for keyboard and mouse, as well as very slow rendering, making it unusable

---

OS version: Ubuntu 21.04

GPU model: Intel

Number of cores: 8

Amount of memory (RAM): 16GB

Comment 1

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

Set release status flags based on info from the regressing bug 1697585

Comment 2

[Sean Feng [:sefeng211]]

bhearsum, I couldn't reproduce the issue. Can you reproduce the issue reliably?

Was there a specific website that you were visiting that was being unresponsive? Or it was the browser UI or something?

The page that was loaded in a private browsing window could still be located in the same process as the non-private browsing window, so it's also possible that a non-private browsing window was causing this.

Anyway, if you can reproduce this reliably and provide more information, that would be great.

Comment 3

[[e-mail] (:bhearsum)]

(In reply to Sean Feng [:sefeng] from comment #2)

bhearsum, I couldn't reproduce the issue. Can you reproduce the issue reliably?

Was there a specific website that you were visiting that was being unresponsive? Or it was the browser UI or something?

The page that was loaded in a private browsing window could still be located in the same process as the non-private browsing window, so it's also possible that a non-private browsing window was causing this.

Anyway, if you can reproduce this reliably and provide more information, that would be great.

I'm unable to repro in the latest Nightly now, but literally all I had to do was open a private browsing window (I didn't load an URLs before things got slow).

If I can repro again I'll try to grab a profile.

Comment 4

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

Has this occurred recently? dom.input_events.strict_input_vsync_alignment has been enabled in Nightly since
https://hg.mozilla.org/mozilla-central/rev/0a25bef65ce3 (26 Apr 2021)

Comment 5

[[e-mail] (:bhearsum)]

(In reply to Olli Pettay [:smaug] from comment #4)

Has this occurred recently? dom.input_events.strict_input_vsync_alignment has been enabled in Nightly since
https://hg.mozilla.org/mozilla-central/rev/0a25bef65ce3 (26 Apr 2021)

I can't repro this anymore. I do seem to be having an issue with similar symptoms, but it appears entirely unrelated to this pref. I filed that as https://bugzilla.mozilla.org/show_bug.cgi?id=1714567, with a profile.