1422430 - MotionMark CSS bouncing filter circles spends is faster without retained display lists

Status: NEW

(Core :: Web Painting, defect, P2)

Description

[Jeff Muizelaar [:jrmuizel]]

With WebRender on I get scores of 370-390 with retaining off and around 300 with retaining on.

About 36% of the time is in ComputeRebuildRegion
https://perfht.ml/2iAM82s

Comment 1

[Matt Woodrow (:mattwoodrow)]

This is pretty much the worst possible case for retained-dl.

Basically every display item is modified and needs rebuilding, but it's all through invalidations to leaf frames.

We process a large list of modified frames working out a minimum rebuild area, and we still end up needing to rebuild the whole page.

We could try bailing out from ComputeRebuildRegion early if the current accumulated rect covers (most of) the screen, though this won't work if the modified frames are ordered from top-left to bottom right.

I'll have a think and see if I can come up with another way to detect this sort of problem case earlier.