(inactive) Jim Chen [:jchen] [:darchons] Reporter
	Description • 8 years ago

It can take some time to trigger, but once it appears, the entire UI becomes very stuttery/janky, including scrolling, hovering, text input, etc. Everything would be smooth for a few seconds, but then suddenly becomes unresponsive for upwards of several seconds, and then go back to being smooth again; then the process repeats.

I can almost always trigger it by opening a few Reddit threads and a few YouTube videos, and then try to scroll a page around.

Initial bisection points to bug 1278408. Running under a profiler, Fx doesn't appear to be busy during an unresponsive period, so I think that's consistent with bad vsync timing. This happens for me on Windows 10 with an Intel GPU.

	Mason Chang [Inactive] [:mchang] Assignee
	Comment 1 • 8 years ago

How long does the jitter happen? Windows 10 and Intel GPUs have some pretty bad vsync timestamps, which we try to correct for but can't always do it well. Is this happening on release for you?

	(inactive) Jim Chen [:jchen] [:darchons] Reporter
	Comment 2 • 8 years ago

(In reply to Mason Chang [:mchang] from comment #1)
> How long does the jitter happen? Windows 10 and Intel GPUs have some pretty
> bad vsync timestamps, which we try to correct for but can't always do it
> well. Is this happening on release for you?

It varies. Each jank can happen for a few hundred milliseconds (i.e. short but noticeable) to a few seconds. And each episode comes and goes seemingly randomly (but seems to be more likely when opening/closing tabs). Also, I'm fairly sure this is a regression because I can reproduce on the m-i build with bug 1278408, but wasn't able to reproduce on the build before it.

	Mason Chang [Inactive] [:mchang] Assignee
	Comment 3 • 8 years ago

In about an hour, these builds should be ready. Could you try this build and see if it's better for you? If it isn't, can you run the debug build and get a log and attach that?

Thanks!

	Mason Chang [Inactive] [:mchang] Assignee
	Comment 4 • 8 years ago

https://archive.mozilla.org/pub/firefox/try-builds/mchang@mozilla.com-bb418a130e1345d9a2c0bb8a2731e63470ffc964/

	(inactive) Jim Chen [:jchen] [:darchons] Reporter
	Comment 5 • 8 years ago

Much better! Now the jank is barely noticeable, if at all. I attached a sample log; looks like there's a lot of "Bad round trip duration" and "Vsync time is very far in the past".

	Mason Chang [Inactive] [:mchang] Assignee
	Comment 6 • 8 years ago

We were mostly forgetting to compensate for negative vsync timestamps from intel HD drivers as mentioned here - http://searchfox.org/mozilla-central/source/gfx/thebes/gfxWindowsPlatform.cpp#1868

	timbugzilla
	Comment 7 • 8 years ago

This is happening for me on 64bit Nightly and Developer builds (haven't tested win32). Seems to have started about two weeks ago. I have refreshed my profile, disabled all addons etc, but it still happens. Playing videos at youtube seems to bring it on particularly quickly. 

Am on Win 10 x64 (anniversary edition), AMD HD7790 GPU (latest drivers).

There is a report of this on Mozillazine's forum too:

http://forums.mozillazine.org/viewtopic.php?f=23&t=3018125

The three addons I normally use are ublock origin, classic theme restorer, and close tab by double click.

	Mike Conley (:mconley) (:⚙️)
	Comment 9 • 8 years ago

[Tracking Requested - why for this release]:

This seems like a pretty brutal (perceived) performance regression that shouldn't slip to release.

	Mason Chang [Inactive] [:mchang] Assignee
	Comment 10 • 8 years ago

Try push - https://treeherder.mozilla.org/#/jobs?repo=try&revision=8d3daa52f423

	Pulsebot
	Comment 11 • 8 years ago

Pushed by mchang@mozilla.com:
https://hg.mozilla.org/integration/mozilla-inbound/rev/3b7441bc1ada
Correct for negative vsync timestamps on windows. r=jrmuizel

	Ryan VanderMeulen [:RyanVM]
	Comment 12 • 8 years ago
bugherder

https://hg.mozilla.org/mozilla-central/rev/3b7441bc1ada

	Lily Kim
	Comment 13 • 8 years ago

Played a long house mix on Youtube earlier today before the patch landed, and my entire browser almost hung when doing anything, but now it's still as smooth as before the video playback whenever I play long videos.

So this patch seems to work for me! 

Thank you!

	Virtual_ManPL [:Virtual] 🇵🇱 - (please needinfo? me - so I will see your comment/reply/question/etc.)
	Comment 15 • 8 years ago

Requesting an uplift request, because Firefox 50 is also affected.
Marking as P1 from duplicated bug #1296482

	Eugene Savitsky
	Comment 19 • 8 years ago

I still see the slowdown in Aurora 20160829 build. My bug was 1294653.

	Marcia Knous [:marcia]
	Comment 20 • 8 years ago

Tracking 50/51+ for this visible regression, for all the reasons in Comment 9.

	Mason Chang [Inactive] [:mchang] Assignee
	Comment 22 • 8 years ago

Comment on attachment 8781597 [details] [diff] [review]
Correct for negative vsync timestamps

Approval Request Comment
[Feature/regressing bug #]: Bug 1278408
[User impact if declined]: The entire UI can become janky and usable for a couple of frames.
[Describe test coverage new/current, TreeHerder]: Treeherder, gtests
[Risks and why]: Low, fixes negative vsync timestamps that are reported by the OS on Intel HD GPUs. We had a fix for thsi before 1278408, but forgot to put it back in.
[String/UUID change made/needed]: None

	Ritu Kothari (:ritu) (Inactive, please n-i to RyanVM, jcristau, or pascal)
	Comment 23 • 8 years ago

Comment on attachment 8781597 [details] [diff] [review]
Correct for negative vsync timestamps

I use win10 and have run into this issue a few times too. Seems like a severe regression, let's uplift to Aurora50.

	Kacper Michajłow [:kasper93]
	Comment 24 • 8 years ago

(In reply to Mason Chang [:mchang] from comment #22)
> fixes negative vsync timestamps that are reported by the OS on Intel HD GPUs.

FYI not only Intel GPU. There were dozen reports about the same issue on AMD GPUs. Including mine system which is far form Intel GPU. And I also think it should be uplifted to Aurora because regression makes Firefox basically unusable on some systems.

	Wes Kocher (:KWierso) (Not reading bugmail; email directly if needed)
	Comment 25 • 8 years ago
bugherder uplift

https://hg.mozilla.org/releases/mozilla-aurora/rev/d46712bc4455