User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:72.0) Gecko/20100101 Firefox/72.0

Steps to reproduce:

1. Go to a page like reddit.com
2. Hit page down a few times

On OSX Mojave 10.14.6 (18G1012) with Firefox Nightly version 72.0a1 (2019-11-18) (64-bit).

Actual results:

Frame rate drops to single digits. See the attached profile. It looks "paint" takes a long time.

Expected results:

Frame rate should not have dropped this much.

suresh.lalith, thanks for the report! Can you take a profiling as to include Compositor thread by using gecko profiler add-on? Default setting of gecko profiler addon capture Compositor thread.

• https://developer.mozilla.org/en-US/docs/Mozilla/Performance/Profiling_with_the_Built-in_Profiler

From Attachment 9109399 [details], I got the following timeline view. But it did not have Compositor thread.

• https://perfht.ml/2qo1OKC

And can you upload about:support info?

Sorry for the delay. I've attached a trace using the built-in profiler.

To reproduce:

1. Go to the following page: https://github.com/vmware/hillview/pull/610/files
2. Hit page down a few times.
3. The fps should be low

I'm on 79.0a1 (2020-06-06) (64-bit) now.

Interestingly, scrolling down using the mouse wheel works smoothly!

And here's the about:support info as requested:

Application Basics

Name: Firefox
Version: 79.0a1
Build ID: 20200606214744
Distribution ID:
Update Channel: nightly
User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:79.0) Gecko/20100101 Firefox/79.0
OS: Darwin 19.5.0 Darwin Kernel Version 19.5.0: Tue May 26 20:41:44 PDT 2020; root:xnu-6153.121.2~2/RELEASE_X86_64
Multiprocess Windows: 1/1 Enabled by default
Remote Processes: 10
Enterprise Policies: Inactive
Google Location Service Key: Found
Google Safebrowsing Key: Found
Mozilla Location Service Key: Found
Safe Mode: false

Crash Reports for the Last 3 Days

Report ID: bp-463561da-5273-4f3d-bf1d-775fc0200608
Submitted: 2 hours ago

Nightly Features

Name: DoH Roll-Out
Version: 1.3.0
ID: doh-rollout@mozilla.org

Name: Firefox Screenshots
Version: 39.0.0
ID: screenshots@mozilla.org

Name: Form Autofill
Version: 1.0
ID: formautofill@mozilla.org

Name: Web Compat
Version: 11.0.0
ID: webcompat@mozilla.org

Name: WebCompat Reporter
Version: 1.3.0
ID: webcompat-reporter@mozilla.org

Remote Processes

Type: Web Content
Count: 6 / 8

Type: Extension
Count: 1

Type: Privileged About
Count: 1

Type: Preallocated
Count: 1

Type: Socket
Count: 1

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ID: amazondotcom@search.mozilla.org

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ID: bing@search.mozilla.org

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ID: ddg@search.mozilla.org

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Enabled: true
ID: ebay@search.mozilla.org

Name: Google
Version: 1.0
Enabled: true
ID: google@search.mozilla.org

Name: LastPass: Free Password Manager
Version: 4.47.0.3
Enabled: true
ID: support@lastpass.com

Name: uBlock Origin
Version: 1.27.10
Enabled: true
ID: uBlock0@raymondhill.net

Name: Wikipedia (en)
Version: 1.0
Enabled: true
ID: wikipedia@search.mozilla.org

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Features
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Asynchronous Pan/Zoom: wheel input enabled; scrollbar drag enabled; keyboard enabled; autoscroll enabled
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WebGL 2 Driver Renderer: ATI Technologies Inc. -- AMD Radeon Pro 555X OpenGL Engine
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Uses Tiling: true
Uses Tiling (Content): true
Off Main Thread Painting Enabled: true
Off Main Thread Painting Worker Count: 4
Target Frame Rate: 60
GPU #1
Active: Yes
Vendor ID: 0x1002
Device ID: 0x67ef
RAM: 0

Diagnostics
AzureCanvasBackend: skia
AzureContentBackend: skia
AzureFallbackCanvasBackend: none
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Decision Log
HW_COMPOSITING:
available by default
OPENGL_COMPOSITING:
available by default
WEBRENDER:
opt-in by default: WebRender is an opt-in feature
WEBRENDER_QUALIFIED:
available by default
blacklisted by env: No qualified hardware
WEBRENDER_COMPOSITOR:
disabled by default: Disabled by default
WEBRENDER_ANGLE:
opt-in by default: WebRender ANGLE is an opt-in feature
WEBRENDER_DCOMP_PRESENT:
opt-in by default: WebRender DirectComposition is an opt-in feature
OMTP:
available by default
WEBGPU:
disabled by default: Disabled by default

Media

Audio Backend: audiounit-rust
Max Channels: 2
Preferred Sample Rate: 48000
Roundtrip latency (standard deviation): 58.06ms (0.01)
Output Devices
Name: Group
ZoomAudioDevice: zoom.us.zoomaudiodevice
MacBook Pro Speakers: builtin-internal-mic|spk
Input Devices
Name: Group
ZoomAudioDevice: zoom.us.zoomaudiodevice
MacBook Pro Microphone: builtin-internal-mic|spk
Media Capabilities
Enumerate database

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browser.cache.disk.telemetry_report_ID: 138
browser.contentblocking.category: custom
browser.download.useDownloadDir: false
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Library Versions

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Remote Debugging (Chromium Protocol)

Accepting Connections: false
URL:

:mstange, do you know if there is already a similar bug?

The smooth scroll animation which is initiated by the page down key is not running on the compositor. Kats, can you find out why?
Furthermore, the page down key event itself could be processed by APZ, but it's processed by the main thread.

Another data point: scrolling by holding the arrow key is also slow.

Both github and reddit have non-passive key listeners registered on their root elements. Having that means we can't do APZ scrolling for keyboard inputs, unfortunately.

(In reply to Markus Stange [:mstange] from comment #5)

Furthermore, the page down key event itself could be processed by APZ, but it's processed by the main thread.

My comment explains this.

The smooth scroll animation which is initiated by the page down key is not running on the compositor. Kats, can you find out why?

This is still an open question, I can take a closer look.

Initial backtrace of spacebar scrolling shows that here the code is passing in ScrollMode::Smooth instead of ScrollMode::SmoothMsd. The latter will drive APZ scrolling while the former does not. So changing that should help. Markus, do you have cycles to try and that see if it breaks anything? Right now my focus is pretty much entirely on desktop zooming so I won't be able to look at this more in the near future.

Thanks! So maybe all that's needed here is to make Smooth behave like SmoothMsd (in the sense of handing it off to the compositor), just with a different scroll animation type. I'll try to find some time to look into this some more.

We could also just change the animations to use SmoothMsd. It would feel a little different but I doubt most people would notice the difference.

True.

Any update on this bug? I'd be happy to help test.

(In reply to Kartikaya Gupta (email:kats@mozilla.com) from comment #9)

Initial backtrace of spacebar scrolling shows that here the code is passing in ScrollMode::Smooth instead of ScrollMode::SmoothMsd. The latter will drive APZ scrolling while the former does not. So changing that should help.

It sounds like bug 1658169 should have fixed this?

With these conditions true, yes, I believe the spacebar scrolls should now be going through APZ and using the same scroll physics as the main thread used to. Same with up/down arrow keys. We're still going to have the problem where the key can't be handled directly by APZ because of the key listener. So the net result is that the scroll animation may be delayed, but once it starts, it should be smooth at 60fps.

The conditions linked above require both apz.allow_zooming=true (which is the case on Nightly but not on Beta or Release) and also apz.force_disable_desktop_zooming_scrollbars=false (which is not true anywhere yet).

suresh, if you have some time, you can try a recent Nightly build - go to about:config, ensure apz.allow_zooming is true, and change apz.force_disable_desktop_zooming_scrollbars to false. Then restart the browser and try keyboard scrolling. I expect the actual scroll animations to be smooth, even though there might be a bit of lag between pressing the key and the scroll animation starting.

Tried setting apz.force_disable_desktop_zooming_scrollbars=false, and keeping apz.allow_zooming=true on Nightly 83.0a1 (2020-09-30) (64-bit): the keyboard scroll is indeed smooth now! I'll run Nightly like this for a while and report if anything comes up.

Thanks!

Great to hear, thanks!