1844359 - Elude the memory arena lookup lock for main thread only arenas.

Status: RESOLVED FIXED

(Core :: Memory Allocator, enhancement, P1)

Description

[Paul Bone [:pbone]]

mozjemalloc now supports main thread only arenas which avoids locking the arena itself. But looking up this arena involves taking a lock. We can avoid that by putting these arenas into a separate structure.

Comment 1

[Paul Bone [:pbone]]

I have a patch started for this, here's the result:

https://treeherder.mozilla.org/perfherder/compare?originalProject=try&originalRevision=38056748f95bc8e08a9ea438c3b42d75fd84db74&newProject=try&newRevision=5a75c05ba02e98eab3e55fceecce3bec9d1187a4&framework=13&page=1

It's not statistically significant (the confidence for all the tests & sub-tests is low) but I don't see a drawback. And when I profile it I see the proportion of time spent in GetById is reduced - so long as nothing else is increased due to some other effect.

Comment 2

[Markus Stange [:mstange]]

Good!

The difference is certainly noticeable in the focused profiles.

Before: https://share.firefox.dev/3Q71aKK
After: https://share.firefox.dev/3OiQk2W

This is evidence enough that this is worth doing. Not every improvement has to be justified by statistically significant benchmark results.

Comment 3

[Paul Bone [:pbone]]

Great! that was my thought also but it's nice to confirm. Okay I'll tidy up the patch.

Comment 4

[Paul Bone [:pbone]]

Attachment: Bug 1844359 - Lookup main thread only arenas without a lock r=glandium

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/8b494378f504
Lookup main thread only arenas without a lock r=glandium

Comment 6

[Cristian Tuns]

https://hg.mozilla.org/mozilla-central/rev/8b494378f504