1917833 - Re-assess the number of multiple processes (threads) used for xpcshell-tests (reduce developer time/CI time)

Status: RESOLVED FIXED

(Testing :: XPCShell Harness, task)

Description

[Mark Banner (:standard8)]

On my Mac M1 Max machine, I experience quite heavy hanging running the search xpcshell-tests, so much so that it makes it pretty much unusable whilst the tests are running. I have therefore been using the --threads option to run a lower number of processes at the same time. I have realised that using a lower number of threads has been around the same speed or faster. So I did some investigations.

My processor has 8 performance cores & 2 efficiency cores. By default this means that xpcshell runs 15 processes (1.5 * cores). Approximate times (min:sec):

Directory	15 threads	10 threads	8 threads
toolkit/components/search	0:45	0:35	0:31
toolkit/components/places	1:20	0:45	0:20

Note: later in the day, I'm seeing worse times overall, however the ratio of improvement is still approximately the same.

Bug 1321026 last looked at this 8 years ago, and set it at 1.5 * cores when running on the local machine and 4 * cores when running on CI. I think given these results it might be worth looking into the multipliers again and see if they still make sense - especially on Macs. It may also be that we can generally improve times on CI, given architecture changes etc.

Comment 1

[Mark Banner (:standard8)]

This was a try push, effectively replacing 4 * cores with 1 * cores (windows ended up not changing): https://treeherder.mozilla.org/jobs?repo=try&revision=d1aafaa2a387e7b545cfae38a2d2af7a929798e3

This was based off of this mozilla-central revision: https://treeherder.mozilla.org/jobs?repo=mozilla-central&revision=ebf0e33ba93e6be120a2c9d1b257b840b467c235

Comment 2

[Mark Banner (:standard8)]

Attachment: Bug 1917833 - Use the number of performance cores when running multiple xpcshell-tests on Mac. r?jmaher!

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/9738f8b16441
Use the number of performance cores when running multiple xpcshell-tests on Mac. r=jmaher

Comment 4

[Sandor Molnar[:smolnar]]

https://hg.mozilla.org/mozilla-central/rev/9738f8b16441