Bug 232271

Summary:

REGRESSION (iOS 15): Fragment shader performance is several times worse

Product:

WebKit

Reporter:

Brian Richardson <brichardson>

Component:

WebGL

Assignee:

Nobody <webkit-unassigned>

Status:

NEW

Severity:

Normal

CC:

3dsrdlab, dino, kbr, kkinnunen, kpiddington, sebastien.videcoq, webkit-bug-importer

Priority:

Keywords:

InRadar

Version:

WebKit Nightly Build

Hardware:

All

OS:

Unspecified

Bug Depends on:

Bug Blocks:

231180

Attachments:

Description	Flags
Test case showing the issue. If you run with /?num=6 you'll see the perf cliff vs /?num=5	none
another test case	none
Workaround demonstrating how uniform data type affects performance	none

Brian Richardson

Reported 2021-10-25 14:28:16 PDT

We've noticed a performance regression when having a lot of work inside of a fragment shader. I happened to have an iPad Air (3rd gen) that was still on iOS 14 so I could do a proper test. I reproduced it with a small Three.JS testbed: iOS15, iOS14, Test 60, 60, https://depot.knowhere.net/ios15regression/?num=5 6, 55, https://depot.knowhere.net/ios15regression/?num=6 4, 33, https://depot.knowhere.net/ios15regression/?num=10 I see the same cliff at num=6 with my iPhone 12 Pro. Normally, I'd just say that's the perf cliff and call it good. But it's odd that it's changed so much between 14 and 15, maybe something can be done?

Attachments
Test case showing the issue. If you run with /?num=6 you'll see the perf cliff vs /?num=5 (3.28 KB, text/html) 2021-10-27 10:36 PDT, Brian Richardson	no flags	Details
another test case (7.26 KB, text/html) 2021-11-24 10:12 PST, Sébastien VIDECOQ	no flags	Details
Workaround demonstrating how uniform data type affects performance (3.29 KB, text/html) 2022-01-18 16:54 PST, Kyle Piddington	no flags	Details
View All Add attachment proposed patch, testcase, etc.

Kimmo Kinnunen

Comment 1 2021-10-25 23:36:03 PDT

Thank you for the report. If you have time, a test case where three.js and the payload app code is unbundled and both are not minified would be most useful. I can reproduce the issue. Reproduces also on macOS, AMD. The GPU work increases very much when using ANGLE Metal backend.

Brian Richardson

Comment 2 2021-10-26 11:21:38 PDT

Hello Kimmo: Thanks for taking the time to look into this. I've updated the example to use just vanilla HTML/JS and an external version of Three.JS. I hope that makes things easier!

Radar WebKit Bug Importer

Comment 3 2021-10-26 17:30:41 PDT

<rdar://problem/84688595>

Kimmo Kinnunen

Comment 4 2021-10-27 06:03:04 PDT

(In reply to Brian Richardson from comment #2) > Hello Kimmo: > > Thanks for taking the time to look into this. I've updated the example to > use just vanilla HTML/JS and an external version of Three.JS. I hope that > makes things easier! Thanks! The update does not seem to work on Safari? "[Error] TypeError: Module specifier, 'three' does not start with "/", "./", or "../". Referenced from https://depot.knowhere.net/ios15regression/?num=5 promiseReactionJob" (It does work on Chrome, though..)

Brian Richardson

Comment 5 2021-10-27 10:35:46 PDT

(In reply to Kimmo Kinnunen from comment #4) > The update does not seem to work on Safari? Fixed. I thought it'd be a fun time to try import maps, I guess when I tested on my phone it was using a cached version. Removed that and it works in Safari for me!

Brian Richardson

Comment 6 2021-10-27 10:36:53 PDT

Created attachment 442606 [details] Test case showing the issue. If you run with /?num=6 you'll see the perf cliff vs /?num=5

Sébastien VIDECOQ

Comment 7 2021-11-24 10:10:56 PST

Hello, any progress on this bug ? It deeply impacts our product, FPS has dropped from 60 to 2 FPS. Adding another test sample that illustrate the behavior. Thanks in advance.

Sébastien VIDECOQ

Comment 8 2021-11-24 10:12:17 PST

Created attachment 445098 [details] another test case

Brian Richardson

Comment 9 2021-11-24 11:39:08 PST

Sébastien: In our case, manually unrolling the loop seems to work around the issue. Give it a shot! Hope that helps! Brian

Sébastien VIDECOQ

Comment 10 2021-11-24 11:53:24 PST

Brian, thanks a lot for the advice, we already gave a quick try this afternoon, but we are far from getting back performances of iOS 14. Maybe we are now facing another iOS 15 regression ? We will try again tomorrow and provide feedbacks.

Kyle Piddington

Comment 11 2022-01-18 12:59:50 PST

Hi all! Some updates for you. Apologies for the delay. We've identified the main issue here. Part of our shader transformation passes tries it's best to preserve the original GLSL struct while following Metal alignment best practices. What this means for the attached shaders is that we're promoting the vec3 uniforms to vec4 for sending over as uniform data, but are then converting back to vec3 in the MSL shader. This temporary variable is able to be stored in shader registers, up until the arrays get too big. We'll have a fix in on our end, but if you need faster performance in the meantime, try changing your vec3 variables to vec4.

Kyle Piddington

Comment 12 2022-01-18 16:54:18 PST

Created attachment 449452 [details] Workaround demonstrating how uniform data type affects performance

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