1814344 - Re-evaluate on which platforms to use scissor clear optimisation

Status: RESOLVED FIXED

(Core :: Graphics: WebRender, task)

Description

[Jamie Nicol [:jnicol]]

For a long time we have had an optimisation where we apply a scissor rect when clearing render targets, rather than clearing the entire target. The comment states that at the time this was measured to be a win on some Intel and nvidia GPUs.

In bug 1809738, however, we realised this optimisation actively hurts performance on Mali, so disabled it there. This may be the case on other GPUs too, so we should do a bunch of measuring to determine which devices to enable it on. Glenn even suspects i may no longer be as big a win on the platforms he originally tested on.

Comment 1

[Jamie Nicol [:jnicol]]

I've done some testing on a variety of Android devices. Here are the average frame times when scrolling on twitter:

Phone	GPU	scissored clear	non-scissored clear
Pixel 7	Mali G710	22ms	8ms
Pixel 6a	Mali G78	9ms	9ms
Samsung S20 Ultra	Mali G77	15ms	14ms
Samsung S10	Mali G76	10ms	10ms
Samsung S9	Mali G72	10ms	10ms
Samsung S6	Mali T760	50ms	25ms
Samsung S22	Xclipse 920	8ms	8ms
OnePlus 8	Adreno 650	6ms	6ms
Pixel 3	Adreno 630	6ms	7ms
Pixel 2	Adreno 540	10ms	10ms
Moto G6	Adreno 506	50ms	33ms
Nexus 5	Adreno 330	90ms	90ms
Pixel 6a	Software Webrender	38ms	50ms

Disabling the scissor appears to make no difference on most devices, but is a clear win on Mali-G710, Adreno 506, and a clear loss on software webrender.

I'm going to land a patch to disable the scissor on all Android devices except SWGL. I'll leave this bug open for further investigations on Desktop GPUs.

Comment 2

[Jamie Nicol [:jnicol]]

Attachment: Bug 1814344 - Disable scissored clear optimization on all Android except SWGL. r?#gfx-reviewers

In bug 1809738 we found that our scissored render target clear
optimization actively hurt performance on some Mali GPUs. From testing
on a variety of Android devices, we have found that it mostly makes no
difference either way, but hurts performance on some other GPUs
too. On software webrender, however, it is still a performance win.

This patch therefore disables the optimization on all Android, apart
from when using software webrender.

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/4b9269d9e6be
Disable scissored clear optimization on all Android except SWGL. r=gfx-reviewers,jrmuizel

Comment 4

[Natalia Csoregi [:nataliaCs]]

https://hg.mozilla.org/mozilla-central/rev/4b9269d9e6be

Comment 5

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

The leave-open keyword is there and there is no activity for 6 months.
:jnicol, maybe it's time to close this bug?
For more information, please visit BugBot documentation.

Comment 6

[Jamie Nicol [:jnicol]]

We can always file a new bug if we decide to change anything on other platforms