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

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=231031

--- Comment #2 from Kimmo Kinnunen <kkinnunen at apple.com> ---
Thanks for the report and good benchmark.

If you have time, please update the title and comments regarding following details:
It appears that you mention that the performance characteristics is a regression to something. Please add mention what characteristic regressed compared to which release. For macOS reports, it's important to include both Safari version as well as the OS version.


To simplify the reporting, please use only the default flags. Non-default flags are not intended for use.

For the benchmark:
WebGL calls complete asynchronously, so you cannot benchmark a call by using pattern:
 var t = time();
 gl.texImage2D(...);
 var dt = time() - dt;
This is especially true with the GPU process case, where the JS call may have returned when the GPU Process might not even have started running the command.

If you want to see how long the time took, you can employ either of following:
a) Call gl.finish();
b) Increase the amount of work done in rAF callback until rAF starts missing 60fps mark.

The option b is preferred. In this case, the test would increase the times it uploads to different textures until rAF callback would not be called at 16ms intervals. Care should be taken to not hit the optimisation or the bug discussed in bug 203148. One strategy would be to upload two different videos on alternate steps.

To compare against the SW codepath:
Currently only full texture uploads go through the GPU path, so if you do texSubImage2D with w-1 width, it will force the SW codepath.


For RGB vs RGBA difference:
There are certain quirks that force RGB be a bit slower than RGBA, especially on older hardware that uses the OpenGL and OpenGL ES backends. This difference is known and less prioritised. If you notice the same behaviour on newer HW or newer macOS, that is higher priority.

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