[Webkit-unassigned] [Bug 231031] REGRESSION (Safari 15): WebGL Video Texture Performance Regression - Looks GPU-process related

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Thu Oct 7 07:46:36 PDT 2021


--- Comment #4 from Simon Taylor <simontaylor1 at ntlworld.com> ---
Thanks Kimmo,

The regression on iOS is with respect to the test cases in Bug 216250 - my baseline case was some iOS 13 numbers which gave around 2ms for the texUpload2d call.

I take your point about timing around the texUpload2d call not necessarily capturing the full GPU workload. However as the main JS thread is the only one that can make WebGL calls, and the game loop logic also needs to be running in 16ms to maintain 60 FPS, the amount of time individual WebGL functions take on the main JS thread is also critical to performance. [Aside - on Chrome for example there were some glGet calls that involved a GPU process round trip with a horrible performance penalty].

I usually try out Bug 203148 on each iOS update, and noticed it was no longer reproducible on iOS 15. I then also noticed the upload timings looked higher than I remembered with previous iOS versions. A short comment in Bug 216250 wondering whether iOS 15 changes had potentially regressed video upload performance received a response requesting I add a new bug, hence this one.

Performance with default settings is all I personally care about, but I noticed those seemingly new GPU Process settings that sounded potentially relevant and they do appear to have an impact on the timings. It sounds from your latest comments that it’s more likely a Metal backend change rather than the GPU Process stuff though.

Default iOS 15 settings have "GPU Process: Media" turned on, and "GPU Process: WebGL" turned off. I wondered whether the HW GPU upload path was still expected to be useable in that case? I guess there is some XPC overhead still involved, so perhaps that overhead explains the difference between the timings and that's just the price to pay for the improved security (?) of moving Media decoding to a separate process.

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