I see some frame skipping when scrolling on youtube.com. It's not at all clear what the cause is. More profiling to come...

The frame skips are caused by texture upload. https://perfht.ml/2okzO92

kvark and Jeff to discuss this bug

The profile Jeff used definitely shows us waiting on texture updates, caused by the slow path in Angle as a workaround for Intel Broadwell/Skylake. See https://bugzilla.mozilla.org/show_bug.cgi?id=1562462 for the history of why we use this slow path.

Testing a try with this workaround disabled shows close to be ideal scrolling. There are still smallest hitches, but it's hard to pinpoint the cause - might simply be the fact that the memory bandwidth is consumed by other threads/processes, and that slows the renderer momentarily.

The first step I suggest to do is restricting the workaround to only affect specific texture formats, e.g. 128-bit formats we use for vertex textures. Adding ni? for Glenn to check if that would be sufficient with respect to bug 1562462. I'm working on this in https://github.com/mozilla/angle/pull/21

The next step could be extending the GPU scattering code path (that we have optionally supported for GPU cache specifically) to support textures. This would allow us to avoid the slow path on the affected platforms entirely.

It's hard to say conclusively, but yes, I think restricting the workaround in the way you've suggested should be sufficient.

We believe the change should land and bake a bit in Nightly before
we'd consider upstreaming it to Angle proper.

https://hg.mozilla.org/mozilla-central/rev/165b21fe5674

Are we ready to upstream this?

Since we haven't gotten any feedback on the patch, sounds like indeed that would be a useful thing to upstream, assuming that wouldn't be too difficult. Having this to bake a bit more is a good option as well.

Upstreaming: https://chromium-review.googlesource.com/c/angle/angle/+/2029517