1489732 - Make tscrollx/tp5_scroll use MozAfterPaint

Status: RESOLVED FIXED

(Testing :: Talos, enhancement)

Description

[Matt Woodrow (:mattwoodrow)]

I've been investigating the tscroll results a bit, and it looks like we'd be better off using MozAfterPaint to record tscrollx results (instead of rAF).

The current main-thread scrolling code is hitting a fast path where we detect that APZ can scroll the page, and we just forward the event details to APZ instead of doing a main thread scroll.

Because of this, our main-thread and async scroll code are both testing almost the exact same thing (and get almost identical scores).

There's also an issue where multiple rAF calls can get coalesced into a single composite, and we're not detecting this.

The WebRender configuration does this a lot, so we're recording twice as many frames as were actually presented to the screen. The main-thread scores end up being twice as fast as the async ones for this reason (but are currently all 0s until bug 1488980 lands).

If we switch to using MozAfterPaint, and make sure we avoid the fast path, then we should get much more relevant results. We'd expect all numbers to increase though, since the measurement would now be of round-trip time to draw a scroll change, instead of interval between frames.

Comment 1

[Matt Woodrow (:mattwoodrow)]

Attachment: Bug 1489732 - Make tscrollx/tp5_scroll use MozAfterPaint for determining when a frame is finished. r?jmaher,mstange

MozReview-Commit-ID: 1OfCZxTZotA

Comment 2

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

Comment on attachment 9007409 [details]
Bug 1489732 - Make tscrollx/tp5_scroll use MozAfterPaint for determining when a frame is finished. r?jmaher,mstange

Joel Maher ( :jmaher ) (UTC-4) has approved the revision.

Comment 3

[Markus Stange [:mstange]]

Comment on attachment 9007409 [details]
Bug 1489732 - Make tscrollx/tp5_scroll use MozAfterPaint for determining when a frame is finished. r?jmaher,mstange

Markus Stange [:mstange] has approved the revision.

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/5ee161a4e12d
Make tscrollx/tp5_scroll use MozAfterPaint for determining when a frame is finished. r=mstange,jmaher

Comment 5

[Cristian Brindusan [:cbrindusan]]

https://hg.mozilla.org/mozilla-central/rev/5ee161a4e12d

Comment 6

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

and the related performance regressions:
== Change summary for alert #15886 (as of Fri, 14 Sep 2018 05:39:03 GMT) ==

Regressions:

 48%  tscrollx windows7-32 opt e10s stylo      0.70 -> 1.04
 38%  tscrollx windows10-64 opt e10s stylo     0.63 -> 0.87
 31%  tscrollx linux64 opt e10s stylo          0.66 -> 0.87

For up to date results, see: https://treeherder.mozilla.org/perf.html#/alerts?id=15886

Comment 7

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

sorry, that didn't get them all, here is the list we have which should be closer to a full list:
== Change summary for alert #15886 (as of Fri, 14 Sep 2018 05:39:03 GMT) ==

Regressions:

 90%  tp5o_scroll windows10-64 opt e10s stylo     0.72 -> 1.36
 88%  tp5o_scroll windows7-32 pgo e10s stylo      0.72 -> 1.34
 88%  tp5o_scroll linux64 pgo e10s stylo          0.57 -> 1.07
 48%  tscrollx windows7-32 opt e10s stylo         0.70 -> 1.04
 38%  tscrollx windows10-64 opt e10s stylo        0.63 -> 0.87
 31%  tscrollx linux64 opt e10s stylo             0.66 -> 0.87

For up to date results, see: https://treeherder.mozilla.org/perf.html#/alerts?id=15886