Talos has detected a Firefox performance regression from push: https://hg.mozilla.org/releases/mozilla-beta/pushloghtml?fromchange=2638feb177dd9104a3887fae2ce05931a6b41d6c&tochange=f7e05dffb1ab4e0b9ed46fa2350c3b5fd4b9efe4 As author of one of the patches included in that push, we need your help to address this regression. Regressions: 3% sessionrestore_many_windows linux64 opt e10s 1,554.50 -> 1,606.33 You can find links to graphs and comparison views for each of the above tests at: https://treeherder.mozilla.org/perf.html#/alerts?id=8764 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/Buildbot/Talos/Tests For information on reproducing and debugging the regression, either on try or locally, see: https://wiki.mozilla.org/Buildbot/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/Buildbot/Talos/RegressionBugsHandling

::dao, this landed recently and I see you authored the patch. This is on mozilla-beta and I don't see a matching regression on m-c.- is this expected to regression mozilla-beta?

oddly enough, both of these regressions have gone away after seeing this multi-patch commit land on beta: https://hg.mozilla.org/releases/mozilla-beta/pushloghtml?fromchange=7f3005046367008a49b33c00b53eb077451ccca4&tochange=6ea7b3eb8990bb0f7a16119f8545bcf429d88131

Some sessionstore perf impact wouldn't be too surprising and unavoidable for the time being since we had to disable a feature. But I also think sessionrestore_many_windows isn't very reliable.