1433848 - Severe scrolling performance regression after Skia 59 update when <textarea> visible in document containing border-radius styling

Status: RESOLVED FIXED

(Core :: Graphics, defect, P3)

Description

[Kestrel]

Attachment: skia59-scrolling-regression.png

STR:
1. Install Reddit Enhancement Suite (RES) extension.
2. Go to reddit.com, login and open reply box to a comment.
3. Fill reply box with text so that it overflows and scrollbar is visible. 
4. Make sure reply box is focused.
5. Scroll page.

Scrolling is very slow with large stutters while the reply box is visible. See attached performance recording and screenshot.

RES puts a border around every .comment with border-radius: 3px by default, disabling this border radius makes the problem go away. Changing gfx.content.azure.backends to cairo also fixes the problem.

Regression window:
https://hg.mozilla.org/integration/mozilla-inbound/pushloghtml?fromchange=58f6e99c9a83dd85e44d435037dabdf7a0afdd83&tochange=e06077091df1f2577a052b43e86135cc12e87a4c

Regressed by: Bug 1340627

Ubuntu 17.10 (Xorg)
AMD integrated GPU

Comment 1

[Kestrel]

Attachment: skia59-scrolling-regression.json

Comment 2

[Milan Sreckovic [:milan] (needinfo for best results)]

Updating Skia in 60, let's see what that does do this test case.

Comment 3

[Kestrel]

Attachment: example.html

New STR with simpler test case:
1. Load attached example.html.
2. Focus text box.
3. Scroll page.

Note bad scrolling performance when a focused overflowing <textarea> is visible inside an element with border-radius > 1px and overflow:hidden. Scrolling improves after a while but degrades every time the <textarea> is refocused.

Comment 4

[Kestrel]

Enabling WebRender on latest Nightly 62.0a1 fixes this performance problem for me on Ubuntu 18.04 with AMD BARTS.