From github: https://github.com/mozilla-mobile/fenix/issues/16319.

Scrolling is not smooth on the Web site:
https://utmagazine.ru/finansoviy-slovar-treidera

See how to reproduce here
https://youtu.be/FkzMfUfM0I8

Change performed by the Move to Bugzilla add-on.

I can reproduce this badness with WR. Profile here: https://share.firefox.dev/3ei0PQo

Unfortunately, the profile doesn't contain WR scene and frame building threads. On the Renderer side, about 17% time is spent uploading textures. Jamie, is that the issue you've been looking at?

Nope, different issue. I'm looking at Mali driver-specific upload problems. If the bulk of the upload time is in memcpy then the problem probably isn't that upload is slow, but that we're uploading waaaaay too much. Memory bandwidth could be exhausted, and the profiler screenshots are probably exacerbating that.

Snorp, can you retake the profile with screenshots disabled and with the other webrender threads? (Or use the "Firefox Graphics" preset)

232ms glMapBufferRange... I bet we're trying to upload an insane amount of texture data. My current work probably will actually help with that, as I'm making it so we used fixed size persistent PBOs. But there'll still be too much data being copied.

New profile with the "firefox graphics" preset here: https://share.firefox.dev/3849wgd

Thanks!

If I enable glyph flashing I can see that some of the glyphs are being rerasterized every frame, but not all of them. Doesn't happen with request desktop site. Still, it's surprising that it's quite this slow, I assume there's more going on.

Zooming in slightly, so the header bar is hidden, makes scrolling down very smooth. Scrolling back up again is choppy because the header bar comes back in to view

This is another case of website uses gigantic sparsely packed svg as a spritesheet: https://utmagazine.ru/img/css/svg/sprite/build/sprite.svg

This causes us to rasterize and upload 5718x5667 image. it blows the caches which means we continually rerasterize and reupload. similar to bug 1665518 which was also filed recently.

Bug 1673653 should allow us to fix this.

Kevin, do you still see this?

I forwarded the question to the GitHub issue. https://github.com/mozilla-mobile/fenix/issues/16319#issuecomment-828773267

Appears to run well now, and there is no response from the reporter.