Talos has detected a Firefox performance regression from push 7acb1edc3f91. As author of one of the patches included in that push, we need your help to address this regression. This is a list of all known regressions and improvements related to the push: https://treeherder.allizom.org/perf.html#/alerts?id=122 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#tpaint Reproducing and debugging the regression: If you would like to re-run this Talos test on a potential fix, use try with the following syntax: try: -b o -p win64 -u none -t other-e10s[Windows XP,Windows 8] --rebuild 5 # add "mozharness: --spsProfile" to generate profile data (we suggest --rebuild 5 to be more confident in the results) To run the test locally and do a more in-depth investigation, first set up a local Talos environment: https://wiki.mozilla.lorg/Buildbot/Talos/Running#Running_locally_-_Source_Code Then run the following command from the directory where you set up Talos: talos --develop -e <path>/firefox -a tpaint --e10s Making a decision: As the patch author we need your feedback to help us handle this regression. *** Please let us know your plans by Friday, 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

this is a hard bug to pinpoint: https://treeherder.allizom.org/perf.html#/graphs?series=[mozilla-inbound,c6caad67b3eb993652e0e986c372d016af4d6c8b,1]&series=[mozilla-central,c6caad67b3eb993652e0e986c372d016af4d6c8b,1]&highlightedRevisions=5bf10cf78faf&highlightedRevisions=7acb1edc3f91&zoom=1454717288946.7788,1455147369691.8767,246.35687732342006,261.04089219330854 you can see we have a lot of retriggers showing a big range of data, but I determined that 7acb1edc3f91 is the one where we didn't post in the ~250 range. This is pgo only which makes it odd. I have lower confidence in this bug, but we do have a real regression. Hopefully there is a simple explanation by just looking at the code. :terrence, can you take a stab at this to see if anything in your code would cause tpaint (window resizing) to regression on windows 8 in e10s and pgo?

I've checked in a backout. I'll run Tpaint before I reland.

Thanks! Let me know if I can help at all or if you have questions on how best to use try/talos/perfherder.