1492831 - 5.03% installer size (linux32) regression on push 303fb0953da3d720582705879415680d33270838 (Tue Sep 18 2018)

Status: RESOLVED WONTFIX

(Core :: Gecko Profiler, defect)

Description

[Joel Maher ( :jmaher ) (UTC -8)]

We have detected a build metrics regression from push:

https://hg.mozilla.org/integration/autoland/pushloghtml?changeset=303fb0953da3d720582705879415680d33270838

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

Regressions:

  5%  installer size linux32 pgo      62,213,348.42 -> 65,341,222.42


You can find links to graphs and comparison views for each of the above tests at: https://treeherder.mozilla.org/perf.html#/alerts?id=15982

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 jobs in a pushlog format.

To learn more about the regressing test(s), please see: https://developer.mozilla.org/en-US/docs/Mozilla/Performance/Automated_Performance_Testing_and_Sheriffing/Build_Metrics

Comment 1

[Joel Maher ( :jmaher ) (UTC -8)]

does your change in bug 1491236 make sense to regress the installer size?

Comment 2

[Mike Hommey [:glandium]]

Yes, it's very much expected. The low size was actually a regression. If you look at the bigger picture, it becomes clearer what happened:

https://treeherder.mozilla.org/perf.html#/graphs?series=autoland,1310061,1,2&series=autoland,1307441,1,2

On Sep 12, we switched those builds to clang. On linux64, this increased the installer size, and on linux32, this decreased it.  The latter is due to clang and GCC having different defaults wrt unwind tables on linux32 (but the same on linux64), and that was the cause of the size decrease. If clang had the same default on linux32, we would have seen a size increase like on linux64. Now, the lack of those unwind tables is causing different problems, and we actually do need them. So overall, we got back in a "normal" situation where switching to clang regressed the installer size on both platforms. With the benefit that, well, performance increased significantly (https://bugzilla.mozilla.org/show_bug.cgi?id=1481721#c9)