1985015 - Do not activate full lto on libxul-gtest

Status: RESOLVED FIXED

(Firefox Build System :: General, task)

Description

[[:sergesanspaille]]

When compiling libxul in full lto mode, we use the same flag for libxul-gtest. This is very costly (single threaded), it's on the critical path and does not bring any clear benefit.

Comment 1

[[:sergesanspaille]]

Attachment: Bug 1985015 - Enable fat lto so that libxul-gtest can skip full lto r=glandium!

fat lto (see https://llvm.org/docs/FatLTO.html) makes it possible to
build object file once and use them for regular linking and full lto
linking, which is exactly what we need for libxul-gtest.

Comment 2

[Sylvestre Ledru [:Sylvestre]]

thanks!

Comment 3

[[:sergesanspaille]]

Considering this profile (patch applied) :
https://profiler.firefox.com/public/wgwq9r5w8g30h69gw9kqmper4ydswchgs8aaq08/marker-chart/?globalTrackOrder=0&thread=0&timelineType=category&v=11

compared to this one (not directly a parent, but should be similar, without the patch):
https://profiler.firefox.com/public/q1eqhm9nytfasvcxdjyhhnh4xd035p3twem51g8/marker-chart/?globalTrackOrder=0&thread=0&timelineType=category&v=11

We gain ~7min over a run of ~52min \o/

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/26ef9db224ff
https://hg.mozilla.org/integration/autoland/rev/67398ec9cd05
Enable fat lto so that libxul-gtest can skip full lto r=glandium

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/6e56f729dfae
https://hg.mozilla.org/integration/autoland/rev/0e91bb7a6ea1
Revert "Bug 1985015 - Enable fat lto so that libxul-gtest can skip full lto r=glandium" for causing build bustages ffat-lto-objects related

Comment 6

[Cristina Horotan [:chorotan]]

Backed out for causing build bustages ffat-lto-objects related

Backout link

Push with failures

Failure log

Comment 7

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/ec73ec60148c
https://hg.mozilla.org/integration/autoland/rev/9adcb573d71b
Enable fat lto so that libxul-gtest can skip full lto r=glandium

Comment 8

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/3a42fdaa9462
https://hg.mozilla.org/integration/autoland/rev/9a0867e72c42
Revert "Bug 1985015 - Enable fat lto so that libxul-gtest can skip full lto r=glandium" for causing py mozbuild failures

Comment 9

[Sandor Molnar[:smolnar]]

Backed out for causing py mozbuild failures

Backout link: https://hg.mozilla.org/integration/autoland/rev/9a0867e72c4266cf848050e4403eb2fbee242128

Push with failures

Failure log -> python/mozbuild/mozbuild/test/configure/lint.py::Lint::test_browser TEST-UNEXPECTED-FAIL

Comment 10

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/b6beecfa0045
https://hg.mozilla.org/integration/autoland/rev/9cea492e94a5
Enable fat lto so that libxul-gtest can skip full lto r=glandium

Comment 11

[Cristian Tuns]

https://hg.mozilla.org/mozilla-central/rev/9cea492e94a5

Comment 12

[Acasandrei Beatrice (needinfo me)]

(In reply to Pulsebot from comment #10)

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/b6beecfa0045
https://hg.mozilla.org/integration/autoland/rev/9cea492e94a5
Enable fat lto so that libxul-gtest can skip full lto r=glandium

Perfherder has detected a build_metrics performance change from push 9cea492e94a57932e3525ed5b9c4a3843bdcf038.

If you have any questions, please reach out to a performance sheriff. Alternatively, you can find help on Slack by joining #perf-help, and on Matrix you can find help by joining #perftest.

Improvements:

Ratio	Test	Platform	Options	Absolute values (old vs new)
14%	build times	linux64-shippable	nightly taskcluster-projects/970387039909/machineTypes/c3d-standard-60-lssd	3,161.19 -> 2,717.29
13%	build times	linux64-nightlyasrelease	nightly nightly-as-release taskcluster-projects/970387039909/machineTypes/c3d-standard-60-lssd	3,080.97 -> 2,693.21

Details of the alert can be found in the alert summary, including links to graphs and comparisons for each of the affected tests.

If you need the profiling jobs you can trigger them yourself from treeherder job view or ask a performance sheriff to do that for you.

You can run all of these tests on try with ./mach try perf --alert 46865

The following documentation link provides more information about this command.

Comment 13

[[:sergesanspaille]]

That's... very good news \o/