1601924 - 6.61 - 12.07% tscrollx / tsvg_static (linux64-shippable-qr, windows10-64-shippable-qr) regression on push a9cafeb45d28191e63199da9f228284004648618 (Thu December 5 2019)

Status: RESOLVED FIXED

(Core :: Graphics: WebRender, defect)

Description

[Florin Strugariu [:Bebe]]

Talos has detected a Firefox performance regression from push:

https://hg.mozilla.org/integration/autoland/pushloghtml?changeset=a9cafeb45d28191e63199da9f228284004648618

As author of one of the patches included in that push, we need your help to address this regression.

Regressions:

12% tscrollx windows10-64-shippable-qr opt e10s stylo 0.76 -> 0.86
11% tscrollx windows10-64-shippable-qr opt e10s stylo 0.77 -> 0.85
7% tsvg_static linux64-shippable-qr opt e10s stylo 44.64 -> 47.95
7% tscrollx linux64-shippable-qr opt e10s stylo 1.12 -> 1.19

You can find links to graphs and comparison views for each of the above tests at: https://treeherder.mozilla.org/perf.html#/alerts?id=24290

On the page above you can see an alert for each affected platform as well as a link to a graph showing the history of scores for this test. There is also a link to a treeherder page showing the Talos jobs in a pushlog format.

To learn more about the regressing test(s), please see: https://wiki.mozilla.org/TestEngineering/Performance/Talos

For information on reproducing and debugging the regression, either on try or locally, see: https://wiki.mozilla.org/TestEngineering/Performance/Talos/Running

*** Please let us know your plans within 3 business days, or the offending patch(es) will be backed out! ***

Our wiki page outlines the common responses and expectations: https://wiki.mozilla.org/TestEngineering/Performance/Talos/RegressionBugsHandling

Comment 1

[Emilio Cobos Álvarez (:emilio)]

That regression range is wrong. This was a build-system-only change, didn't change any code. The patch before it though (bug 1599327), sounds much more likely to cause that regression.

Comment 2

[Bert Peers [:bpeers]]

Thanks for catching this. The regression seems to be caused by scrollbar-like tiling on areas that are not scrollbars (see also: Bug 1601865). I'm investigating if the scrollbar flags are being mangled on the WebRender side, or if there is a larger problem with layout/display-lists tagging items as scrollbar when they are not, in which case we may need to back this out. I will keep you posted.

Comment 3

[Bert Peers [:bpeers]]

Backed out:
https://hg.mozilla.org/integration/autoland/rev/f47661feecce9b319848f7d77202cfa67334be8f

Comment 4

[Marian Raiciof [:marauder]]

The backout from
https://bugzilla.mozilla.org/show_bug.cgi?id=1599327#c10

fixed the regression
https://treeherder.mozilla.org/perf.html#/graphs?highlightAlerts=1&selected=1928327,608820,1229.3943338101517,203.58606831667012,997381844&series=autoland,1928327,1,1&series=mozilla-inbound,1946657,1,1&timerange=1209600&zoom=1575461951504,1575949664107,39.08747761179259,51.32734569053295

Improvement:
https://treeherder.mozilla.org/perf.html#/alerts?id=24442&hideDwnToInv=0

Comment 5

[Bert Peers [:bpeers]]

As confirmed by Marian.