1293497 - Keyboard scrolling sluggish with HWA disabled

Status: RESOLVED INCOMPLETE

(Core :: Web Painting, defect)

Description

[Marty]

User Agent: Mozilla/5.0 (Windows NT 6.1; rv:48.0) Gecko/20100101 Firefox/48.0
Build ID: 20160808030442

Steps to reproduce:

With HWA disabled, multiprocess disabled, and OMTC enabled keyboard scrolling using the up and down arrow keys is very laggy. Additionally, when letting up on the key the scrolling will often continue, sometimes all the way down to the end of the page.

With HWA enabled or OMTC disabled the issue is resolved however for overall performance reasons HWA needs to be disabled on my system and OMTC now must be enabled for HTML5 videos to run properly. 

Note this is only occurring on Windows 7 with a fresh profile and no addons. Tested with Windows XP and it is not an issue with HWA disabled.

Comment 1

[Emil Pasca [:emilpasca]]

User Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:51.0) Gecko/20100101 Firefox/51.0

I have tested this issue on Windows 7 x64 with the latest Firefox release (48.0) and the latest Nightly (51.0a1-20160812030200) and could not reproduce it.
After disabling HWA, multiprocess and enabling OMTC, when scrolling using the keyboard up and down arrows the webpage (e.g. 9gag.com) has scrolled as expected without any issues.
Also tried holding the keys down for a longer time and then letting up.


Can you please retest using the latest Nightly build (https://nightly.mozilla.org/) and report back the results ? When doing this, please use a new clean Firefox profile, maybe even safe mode, to eliminate custom settings as a possible cause (https://goo.gl/PNe90E).

Comment 2

[Marty]

Currently testing with today's latest win32 inbound on Windows 7 using a new profile with default settings except for these three changes:

HWA - disabled
OMTC - enabled
Multi-process - disabled

The keyboard scrolling is laggy and will continue to scroll even after letting up on either key. 

If HWA is enabled, OMTC disabled, or multi-process enabled the issue is resolved. I'm only experiencing the problem when the settings are exactly as above. Could it be related to display drivers?

Comment 3

[Marty]

Not sure if this matters but on Windows 7 I use the classic theme, not aero. Tried running Firefox in XP compatibility mode without any difference. 

The easiest workaround is to disable OMTC but now HTML5 videos run unbearably sluggish in that setting due to some recent change in the last few weeks, which is when this problem began. Enabling HWA slows the browser down on my system considerably, especially the UI when for example clicking on bookmarks or toolbar buttons or right clicking the menu it's laggy but changing "layers.prefer-d3d9" to true seems to help a little. 

Again these problems exist only on Windows 7 and not XP.

Comment 4

[Marty]

Found a workaround by setting "general.smoothScroll" to false. Keyboard scrolling is back to normal with HWA disabled and OMTC enabled. 

The downside is that I'm losing the smooth scrolling with the mouse, which I prefer but it'll have to do for now. Hopefully someone can reproduce it.

Comment 5

[Emil Pasca [:emilpasca]]

Mozilla/5.0 (Windows NT 6.1; WOW64; rv:51.0) Gecko/20100101 Firefox/51.0

I've tried again to reproduce the issue using the Windows 7 classic theme,HWA - disabled, OMTC - enabled
and Multi-process - disabled, anyhow, when scrolling, I haven't encountered any issues.
However in order to enable OMTC, I have changed the flags to true for the following variables:
webgl.force-enabled
layers.acceleration.force-enabled
layers.offmainthreadcomposition.enabled
Could you tell us which variables have you modified in order to enable OMTC?

Comment 6

[Marty]

Isn't OMTC on by default in a new profile? When creating one I did nothing with that and no variables, e.g. "webgl.force-enabled" or 
"layers.acceleration.force-enabled" were changed. Only HWA and multi-process were disabled to experience the effect. 

This is occurring with the 51 branch, I have not tested it in 48 so to disable OMTC now you need to manually add 
"layers.offmainthreadcomposition.force-disabled" and set to true. Doing that however makes HTML5 videos run so slow that it must be enabled.

Another better workaround I have found is to leave smooth scrolling enabled but instead set "general.smoothScroll.lines" to false. With that change keyboard scrolling is normal in Windows 7.

Comment 7

[Emil Pasca [:emilpasca]]

I am assigning a component to this issue in order to involve the development team and get an opinion on this.

Comment 8

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

A needinfo is requested from the reporter, however, the reporter is inactive on Bugzilla. Closing the bug as incomplete.

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