1435648 - Reduce the cost of allocating the ClippedDisplayItems array

Status: RESOLVED FIXED

(Core :: Web Painting, enhancement, P3)

Description

[Matt Woodrow (:mattwoodrow)]

This shows up a fair bit in profiles when the display list is long (like the displaylist_mutate talos test)

Comment 1

[Matt Woodrow (:mattwoodrow)]

Attachment: Part 1: Share storage with mAssignedDisplayItems

These two arrays are more or less identical, so let's share storage for them.

Comment 2

[Matt Woodrow (:mattwoodrow)]

Attachment: Part 2: SetCapacity to the length we had last time

Growing the array and moving the elements can be slow sometimes, let's use the size we had last paint to size the array upfront.

Comment 3

[Markus Stange [:mstange]]

Comment on attachment 8948295 [details] [diff] [review]
Part 1: Share storage with mAssignedDisplayItems

Review of attachment 8948295 [details] [diff] [review]:
-----------------------------------------------------------------

Would be nice to rename the cdi variables at some point in the future.

Comment 4

[Markus Stange [:mstange]]

Comment on attachment 8948296 [details] [diff] [review]
Part 2: SetCapacity to the length we had last time

Review of attachment 8948296 [details] [diff] [review]:
-----------------------------------------------------------------

::: layout/painting/FrameLayerBuilder.cpp
@@ +1527,5 @@
>    // DrawPaintedLayer, for example when progressive paint is enabled.
>    nsIntRegion mVisibilityComputedRegion;
>  
> +  // The number of items assigned to this layer on the previous paint.
> +  uint32_t mLastItemCount;

size_t

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/mozilla-inbound/rev/c95aade68024
Part 1: Share storage between mClippedDisplayItems and mAssignedDisplayItems. r=mstange
https://hg.mozilla.org/integration/mozilla-inbound/rev/102c8a3bbaf6
Part 2: Preallocate the mAssignedDisplayItems array to the size it was last time. r=mstange

Comment 6

[Raul Gurzau (:RaulG)]

https://hg.mozilla.org/mozilla-central/rev/c95aade68024
https://hg.mozilla.org/mozilla-central/rev/102c8a3bbaf6

Comment 7

[Joel Maher ( :jmaher ) (UTC -8)]

this landed with a few other patches from other bugs:
https://hg.mozilla.org/integration/mozilla-inbound/pushloghtml?fromchange=66c1c1596bea7cfb2316e78c940e52679b595efa&tochange=32bf2817fb7a4b35dc1cbb66ffac8e1f0658c68f

here are some improvements:
== Change summary for alert #11672 (as of Wed, 21 Feb 2018 07:45:26 GMT) ==

Improvements:

 13%  displaylist_mutate osx-10-10 opt e10s stylo     6,656.25 -> 5,807.67
  8%  displaylist_mutate windows10-64 opt e10s stylo  5,103.33 -> 4,672.75
  7%  displaylist_mutate windows10-64 pgo e10s stylo  4,516.71 -> 4,186.25
  7%  displaylist_mutate linux64 opt e10s stylo       2,781.08 -> 2,585.08
  6%  displaylist_mutate linux64 pgo e10s stylo       2,439.21 -> 2,281.83

For up to date results, see: https://treeherder.mozilla.org/perf.html#/alerts?id=11672