1372665 - Github scrolling is janky if you're hovering over the "add-comment" buttons.

Status: RESOLVED WONTFIX

(Core :: Graphics, defect, P3)

Description

[Emilio Cobos Álvarez (:emilio)]

STR:

 * Open a GitHub PR where you can scroll, such as the URL attached to the bug.
 * Hover over any "Add comment" button (the blue "plus" sign, near the line count), and scroll.

Curiously, if I scroll not hovering over the button makes scrolling smooth again.

I'm filling under graphics potentially, because I took a profile and it seemed mostly paint code.

Curiously enough, if I disable the following rule:

.add-line-comment:hover {
  -webkit-transform: scale(1, 1);
  transform: scale(1, 1);
}

Scroll stops being janky (layerization issue?).

I'll attach a profile ASAP.

I can add graphics card info if needed, though it's a pretty standard intel card in Linux, with up-to-date Mesa drivers.

Comment 1

[Emilio Cobos Álvarez (:emilio)]

Profile url scrolling while hovering those buttons: https://perfht.ml/2rs6Vnv
Without doing that: https://perfht.ml/2rsfFK6

Paint flashing didn't go particularly crazy, FWIW, but the profile definitely shows a lot of time in painting code.

So at first glance the pauses that are on the first profile but not on the second are huge calls (~600ms) under do_futex_wait, inside mozilla::layers::TextureClient::TryReadLock()...

But I have no idea about why can that happen or not :)

Comment 2

[Kartikaya Gupta (email:[e-mail])]

The profile shows we're spending a lot of time rendering layers in BasicCompositor. This is likely specific to Linux. On OS X I could only see janks when the blue plus button appeared or disappeared while I was scrolling. It wasn't continuous janking.

Comment 3

[Darkspirit]

bug 1727876