1688788 - Migrate Gecko ScriptPreloader to Stencil-XDR bytecode format

Status: RESOLVED FIXED

(Core :: JavaScript Engine, task, P1)

Description

[Ted Campbell [:tcampbell]]

The legacy-XDR format is deprecated and slated for removal. Using Stencil will be less error prone going forward and opens up a lot of new performance optimizations.

The ScriptPreloader currently uses non-incremental XDR mode which is not supported by Stencil-XDR, but also always uses full-parsing when encoding so capturing XDR on the original stencil has the same data as capturing legacy-XDR data after execution.

Comment 1

[Matthew Gaudet (he/him) [:mgaudet]]

Attachment: Bug 1688788 - Improve ScriptPreloader comments around IPC r?kmag! DONTBUILD

Comment 2

[Matthew Gaudet (he/him) [:mgaudet]]

Attachment: Bug 1688788 - Add DecodeScriptMaybeStencil that operates on a TranscodeRange r?arai

Depends on D103708

Comment 3

[Matthew Gaudet (he/him) [:mgaudet]]

Attachment: Bug 1688788 - Teach MultiScriptDecoder to offthread decode stencils r?arai

Depends on D103709

Comment 4

[Matthew Gaudet (he/him) [:mgaudet]]

Attachment: Bug 1688788 - Change ScriptPreloader XDR format to XDR Stencil r?kmag!,arai!

Depends on D103710

Comment 5

[Matthew Gaudet (he/him) [:mgaudet]]

Side note: On Ted's advice I did some Talos-other runs to spot any improvements or degradations: nothing stands out

Comment 6

[Ted Campbell [:tcampbell]]

Two more tips:

• Use MOZ_PROFILER_STARTUP=1 env var to capture early startup trace and see if you can see any change in compiles.
• Run the awsy / awsy-base tests for good measure.

Comment 7

[Matthew Gaudet (he/him) [:mgaudet]]

Attachment: Bug 1688788 - Only start incremental XDR encoding of scripts that may be cached r?arai!,kmag!

Depends on D103711

Comment 8

[Matthew Gaudet (he/him) [:mgaudet]]

Attachment: Bug 1688788 - Convert ScriptPreloader to manage Stencils, not Scripts. r?kmag!

Depends on D113012

Comment 9

[Nicolas B. Pierron [:nbp]]

Marking this bug as stalled based on review comments from Ted:

Current status is that this is stalled for potential performance issues of moving gc-atomization calls to main thread. Our strategy here will likely need to be modified.

Comment 10

[Tooru Fujisawa [:arai]]

basically depends on bug 1721120, but it needs to be addressed after this patch, due to dependency around XDR

Comment 11

[Tooru Fujisawa [:arai]]

The performance regression is going to be addressed by https://bugzilla.mozilla.org/show_bug.cgi?id=1721413 ,
but it depends on several bugs after this bug.

The plan the following:

1. Land StartupCache patches (bug 1688790)
2. Land ScriptPreloader patches (bug 1688788 = this bug)
3. Remove remaining usage of legacy XDR (bug 1718194 and bug 1718481)
4. Remove remaining usage of script cloning (bug 1718623 and bug 1718536)
5. Remove script cloning bug 1718529 and bug 1662152
6. Remove legacy XDR (bug 1718711 and bug 1688791)
7. Address the performance regression (bug 1721413)

Comment 12

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/e660e2c3c3d1
Improve ScriptPreloader comments around IPC r=kmag DONTBUILD
https://hg.mozilla.org/integration/autoland/rev/2bc5949902ac
Convert ScriptPreloader to manage Stencils, not Scripts. r=kmag,tcampbell

Comment 13

[Atila Butkovits]

https://hg.mozilla.org/mozilla-central/rev/e660e2c3c3d1
https://hg.mozilla.org/mozilla-central/rev/2bc5949902ac

Comment 14

[BugBot [:suhaib / :marco/ :calixte]]

Since the bug is closed, the stalled keyword is now meaningless.
For more information, please visit auto_nag documentation.

Comment 15

[Andra Esanu (needinfo me)]

== Change summary for alert #31417 (as of Tue, 21 Sep 2021 10:32:20 GMT) ==

Improvements:

Ratio	Test	Platform	Options	Absolute values (old vs new)
18%	tp5o responsiveness	windows10-64-shippable-qr	e10s stylo webrender	0.90 -> 0.73
16%	tp5o responsiveness	windows10-64-shippable-qr	e10s stylo webrender	0.89 -> 0.75
8%	tp5o responsiveness	linux1804-64-shippable-qr	e10s fission stylo webrender	6.37 -> 5.87

For up to date results, see: https://treeherder.mozilla.org/perfherder/alerts?id=31417