2005825 - Consider disabling the "app image" for child processes ("_disable_art_image_")

Status: RESOLVED FIXED

(Firefox for Android :: Performance, task)

Description

[Markus Stange [:mstange]]

The profile from bug 1985895 shows a lot of time spent in ImageSpace::Loader::InitAppImage: https://share.firefox.dev/3KRsrR7

The app image contains data that accelerates the execution of Java / Kotlin code; it's basically a dump of ART's internal C++ structures. A lot of its size is based on the number of Java / Kotlin classes that are used during startup.

Fenix has a lot of classes.

The app image is useful in our main process and speeds up Fenix main process startup.

But we don't need any of this in child processes. Our child process don't actually execute any appreciable amount of Java code; they pretty much only exist to run Gecko.

As of August 2023, Android has a super hacky way to opt out of the app image: You can include the string _disable_art_image_ in the process name, and then Android will skip the InitAppImage work for that process, at the cost of slower Java / Kotlin execution.

It's worth checking if this makes an appreciable difference for Fenix startup. We are bottlenecked on the CPU during startup, and we launch 4 child process in the first second of startup, so any reduction in CPU work for child process startup will help.

Comment 1

[Markus Stange [:mstange]]

Attachment: Bug 2005825 - Rename all child processes to include the substring "_disable_art_image_", to reduce child process startup time. r=tcampbell

Comment 2

[Jonathan Almeida [:jonalmeida]]

Triage: adding the whiteboard label for tracking.

Comment 3

[Polly [:polly]]

NB this flag doesn't seem to be documented anywhere in the Android APIs, so there is a worry that using it would couple us to internals of the platform which are not guaranteed to be stable and could be suddenly removed without any deprecation warnings.

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/2b3484fbdfb0
https://hg.mozilla.org/integration/autoland/rev/2079b68dcfd8
Rename all child processes to include the substring "_disable_art_image_", to reduce child process startup time. r=tcampbell,geckoview-reviewers

Comment 5

[Serban Stanca [:SerbanS]]

https://hg.mozilla.org/mozilla-central/rev/2079b68dcfd8

Comment 6

[Andra Esanu (needinfo me)]

(In reply to Pulsebot from comment #4)

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/2b3484fbdfb0
https://hg.mozilla.org/integration/autoland/rev/2079b68dcfd8
Rename all child processes to include the substring "disable_art_image",
to reduce child process startup time. r=tcampbell,geckoview-reviewers

Perfherder has detected a mozperftest performance change from push 2079b68dcfd811ac86545de31746eab52dc0a19a.

No action is required from the author; this comment is provided for informational purposes only.

Improvements	Test	Platform	Options	Absolute values [old vs new]
49%	shopify-applink-startup org.mozilla.fenix:crashhelper-cpu-time	android-hw-a55-14-0-aarch64-shippable		124.50 ms -> 63.83 ms
46%	newssite-applink-startup org.mozilla.fenix:crashhelper-cpu-time	android-hw-a55-14-0-aarch64-shippable		124.17 ms -> 66.67 ms
45%	tab-restore-shopify org.mozilla.fenix:crashhelper-cpu-time	android-hw-a55-14-0-aarch64-shippable		124.17 ms -> 68.67 ms
41%	homeview-startup org.mozilla.fenix:crashhelper-cpu-time	android-hw-a55-14-0-aarch64-shippable		111.67 ms -> 65.67 ms
8%	browser_translations_perf_tiny.js engine-init-time	linux1804-64-shippable		316.56 ms -> 291.85 ms
...	...	...	...	...
5%	newssite-applink-startup org.mozilla.fenix:tab-cpu-time	android-hw-a55-14-0-aarch64-shippable		1,347.92 ms -> 1,282.17 ms

Need Help or Information?

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