1628327 - 4.7 - 5.33% tabswitch (linux64-shippable, linux64-shippable-qr) regression on push 2018df8cdb6fab6b7d19fc4df6b1c1f7b0292273 (Tue April 7 2020)

Status: NEW

(Core :: DOM: Core & HTML, defect, P5)

Description

[Marian Raiciof [:marauder]]

Talos has detected a Firefox performance regression from push:

https://hg.mozilla.org/integration/autoland/pushloghtml?changeset=2018df8cdb6fab6b7d19fc4df6b1c1f7b0292273

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

Regressions:

5% tabswitch linux64-shippable opt e10s stylo 9.25 -> 9.75
5% tabswitch linux64-shippable opt e10s stylo 9.13 -> 9.60
5% tabswitch linux64-shippable-qr opt e10s stylo 7.33 -> 7.68

Improvements:

12% tp5o responsiveness windows10-64-shippable-qr opt e10s stylo 1.35 -> 1.19
11% tp5o_webext responsiveness windows10-64-shippable-qr opt e10s stylo 2.15 -> 1.91
11% tp5o responsiveness windows7-32-shippable opt e10s stylo 1.11 -> 0.99
11% tp5o responsiveness linux64-shippable-qr opt e10s stylo 1.84 -> 1.64
10% tp5o_webext responsiveness windows7-32-shippable opt e10s stylo 1.79 -> 1.61
9% tp5o_webext responsiveness windows10-64-shippable opt e10s stylo 2.11 -> 1.91
8% tp5o_webext responsiveness linux64-shippable-qr opt e10s stylo 2.86 -> 2.63
8% about_newtab_with_snippets responsiveness linux64-shippable opt e10s stylo 0.18 -> 0.17
7% about_newtab_with_snippets responsiveness linux64-shippable opt e10s stylo 0.18 -> 0.17
3% tabswitch windows10-64-shippable opt e10s stylo 9.78 -> 9.49

You can find links to graphs and comparison views for each of the above tests at: https://treeherder.mozilla.org/perf.html#/alerts?id=25566

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

[Marian Raiciof [:marauder]]

There are a few regressions but mostly improvements on the generated alerts.
Please let me know if these are expected.
Thanks!

Comment 2

[Olli Pettay [:smaug][[e-mail]]]

That tabswitch case is very surprising. The patch makes us do less work.
Though, I'm a bit surprised how much improvements it shows too.

As of now I wouldn't do anything here, since the key thing which might show more interesting data is to check telemetry in couple of days.

Comment 3

[Tim Spurway [:tspurway]]

smaug, could you take this bug and prioritize, please?

Comment 4

[Andrew McCreight [:mccr8]]

Traversing the custom elements does add some overhead, though it would be surprising if it was really taking so long that it would show up. I don't think I've seen CC changes show up on perf tests, either positive or negative.

Comment 5

[Olli Pettay [:smaug][[e-mail]]]

I'm not going to take this since I'm not planning to do anything here atm :)
(I am looking into other similar CC optimizations atm)

The patch makes use do black marking on things which otherwise would use gray marking. So ok, that might mean a tiny overhead, but there aren't that many custom element definitions. The issue was more that the definitions are keeping lots of js alive.

And yes, I am surprised to see any perf changes here.

Comment 6

[Ryan VanderMeulen [:RyanVM]]

Doesn't sound like we're expecting a timely fix for this.