1875117 - Ship parallel marking

Status: RESOLVED FIXED

(Core :: JavaScript: GC, task)

Description

[Jon Coppeard (:jonco)]

The most recent nightly experiment to enable parallel marking show some clear improvements so let's ship this to our users:

https://docs.google.com/spreadsheets/d/1NkTLDfDf-Gf30nwN-U1pIsSvHQpu33eb3Mq98C6b4bw/edit#gid=0

Summary:

• 20-30% reduction in GC time across desktop platforms
• 10% reduction in GC max pause time
• 10% fewer GC slices
• Slices that overran their budget were worse but these remain rare
• Parallel marking performs significantly better macOS than other platforms

Caveats:

• This will not be enabled for mobile which requires further work
• Only two threads will be used to start with

The plan is to enable this in version 124. If there are problems we can hold this as nightly only or disable it again.

Comment 1

[Jon Coppeard (:jonco)]

Attachment: Bug 1875117 - Ship GC parallel marking r?sfink

Comment 2

[Jon Coppeard (:jonco)]

Benchmark comparison: https://treeherder.mozilla.org/perfherder/compare?originalProject=try&originalRevision=8da4e37b0d4e1fd7ee6dbe3c738077c77eabb192&newProject=try&newRevision=0fae179fb4f223adf2ae3ede7f93d2907febdba5&framework=13&page=1

Summary:

• Jetstream2: high-confidence 28% improvements splay-Worst and 8% on splay-Average subtests on Windows
• matrix-react-bench: high-confidence 1.3% overall improvement on macOS
• Speedometer3: overall unaffected, with several low-confidence changes in both directions

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/1051cef25fba
Ship GC parallel marking r=sfink

Comment 4

[Atila Butkovits]

https://hg.mozilla.org/mozilla-central/rev/1051cef25fba

Comment 5

[Jon Coppeard (:jonco)]

Telemetry indicates this is working well.

Mark rate increased by 50-60%, median total GC time decreased by 35% (and by more for longer collections) and median max pause time decreased by 20%.

Summary of telemetry changes: https://docs.google.com/spreadsheets/d/1eWcQGeXnfhu0nUHUj1wj7VZ3SMMilump8h19w5s1bXc/edit?usp=sharing