Talos has detected a Firefox performance regression from push:

https://hg.mozilla.org/integration/mozilla-inbound/pushloghtml?fromchange=5772a92c49cf6cc746fe0d22a797fe3f08a20f39&tochange=34510ca46cc61984ca775f30a7c4f288371cf329

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

Regressions:

2% displaylist_mutate linux64-shippable-qr opt e10s stylo 3,756.75 -> 3,833.60

Improvements:

3% sessionrestore linux64-shippable-qr opt e10s stylo 954.46 -> 926.17
2% startup_about_home_paint linux64-shippable-qr opt e10s stylo 1,211.38 -> 1,184.33

You can find links to graphs and comparison views for each of the above tests at: https://treeherder.mozilla.org/perf.html#/alerts?id=20873

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/Performance_sheriffing/Talos/Tests

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

These are the Gecko profiles for the regression:

before: https://perf-html.io/from-url/https%3A%2F%2Fqueue.taskcluster.net%2Fv1%2Ftask%2FQH3Vqr9xQZyfsQzgSxA_Jg%2Fruns%2F0%2Fartifacts%2Fpublic%2Ftest_info%2Fprofile_displaylist_mutate.zip

after: https://perf-html.io/from-url/https%3A%2F%2Fqueue.taskcluster.net%2Fv1%2Ftask%2FPs3WNI-IQmSzn_HQaSBuNw%2Fruns%2F0%2Fartifacts%2Fpublic%2Ftest_info%2Fprofile_displaylist_mutate.zip

The scene builder threads don't seem to have any samples, that is where most of the code I changed should be running. I'm not very concerned about this regression, I assumed there was a possibility for a small regression, given we do more calculations when building the picture tree, but that is unavoidable for correctness purposes.

(In reply to Andrew Osmond [:aosmond] from comment #2)

The scene builder threads don't seem to have any samples, that is where most of the code I changed should be running. I'm not very concerned about this regression, I assumed there was a possibility for a small regression, given we do more calculations when building the picture tree, but that is unavoidable for correctness purposes.

So we close this as WONTFIX, then?

This regression may go away with bug 1574493 given I've removed a lot of the code I added before, and we are doing overall less work to perform snapping.