[browser] scrolling uneven and queues up

[Bill Filler]

I've noticed this on a bunch of websites, mainly on Arale but also on krillin, both running latest rc-proposed with and without oxide 1.15

The scenario is I'm on page A, navigate to page B, press back button, then try to scroll page A (flicking up). The page doesn't move for a short time then scrolls super fast almost to the bottom. Seems like the scroll events are getting queued up and then all applied at once.

This site reproduces it pretty easy for me:

1) goto boston.craigslist.org
2) type "kayak" in the search field
3) you'll get a page full of results
4) click on one of the results
5) wait till page fully loads, flick quickly a few times, first flicks ignored. then press back button
6) wait till page fully loads and then start scrolling (flicking up, multiple times), first flicks ignored/queued then scrolling happens fast

Expected results:
the page should start scrolling immediately and keep up with action of finger

Actual results:
the page is not responsive for a few seconds then scrolls super fast toward the bottom

[Bill Filler (bfiller)]

Here is a video that shows it:
https://www.dropbox.com/s/4lpom34glkud238/File%20May%2023%2C%205%2009%2020%20PM.mov?dl=0

[Olivier Tilloy (osomon)]

I can easily observe the same kind of issue with slashdot.org on my krillin running rc-proposed:
 - browse to slashdot.org, wait for the main page to be loaded
 - tap on an article headline to open it
 - wait for the page to be fully loaded, tap the back button
 - flick the page once

It seems that if I wait long enough after the main page has been loaded back (a few seconds), then the issue cannot be reproduced, so I’m guessing this is linked to loading/rendering not being fully complete by the time the flick gesture is delivered.

[Robin Heroldich (robinheroldich)]

This is one of the most annoying issues with the browsing experience. Could you figure out a solution for OTA-14? I'd really appreciate it. Thanks. :)

[Santosh (santoshbit2007)]

Initial investigation: There seems to be a blocking of task by blink scheduler because of prioritization of other task. So this may be result of side effect of blink scheduler policy.
Need to check more before any conclusion.
I get this log on console thrown by blink scheduler while scrolling on slashdot.org

qml: [JS] (https://slashdot.org/:0) Blink deferred a task in order to make scrolling smoother. Your timer and network tasks should take less than 50ms to run to avoid this. Please see https://developers.google.com/web/tools/chrome-devtools/profile/evaluate-performance/rail and https://crbug.com/574343#c40 for more information.

[Santosh (santoshbit2007)]

I tried to reproduce the same bug on Arale but to me it looks somewhat ok. I am using lastest oxide. There has been some changes in upstream chromium which might resolved this issue(https://crbug.com/574343#c40).

I can see similar janked scrolling when I use --disable-features=SchedulerExpensiveTaskBlocking
Which was default in chromium sometime before.

I feel bug should not occur in latest oxide. Could you confirm that this bug is happening with latest trunk oxide also

[Santosh (santoshbit2007)]

Bill confirmed that scrolling is quite improved with latest oxide1.17 and the same issue
is not observable.

[Santosh (santoshbit2007)]

Some part of bug may be related https://bugs.launchpad.net/oxide/+bug/1643428 (May be)