1640087 - Create experiment for read ahead DLL prefetches

Status: RESOLVED FIXED

(Core :: Widget: Win32, task)

Description

[Emma Malysz]

In Bug 1628903, we changed the prefetched DLLs in order to improve startup time. We need to examine how impactful these changes are on retention. To do so:

1. We should first enable these prefetches only on Nightly and maintain the previous prefetches on other builds.
2. Place this behind a pref that can be toggled to run an official experiment.

These reads happen before preferences are loaded, so we will have to place within an ifdef (similar to browser.launcherProcess.enabled). Note, this can potentially expose a problem, as the registry is not per profile and a user can have multiple profiles.

Comment 1

[Emma Malysz]

Attachment: Bug 1640087: Part 1: optimize read ahead DLL prefetches for nightly users

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/281d0e910225
Part 1: optimize read ahead DLL prefetches for nightly users r=dthayer

Comment 3

[Cristian Brindusan [:cbrindusan]]

https://hg.mozilla.org/mozilla-central/rev/281d0e910225

Comment 4

[Emma Malysz]

Attachment: Bug 1640087: Part 2: tuck optimized prefetches behind a preference.

PrefetchRegistryInfo is intended to be a temporary file in order to conduct
this experiment on startup times vs. retention.
Most of the implementation is similar to LauncherRegistryInfo.
If we startup and the registry is different than the preference,
we will want to use the preference for the purpose of this experiment.

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/5066e3d136dc
Part 2: tuck optimized prefetches behind a preference. r=dthayer,aklotz

Comment 6

[Narcis Beleuzu [:NarcisB]]

https://hg.mozilla.org/mozilla-central/rev/5066e3d136dc

Comment 7

[Alexandru Ionescu (needinfo me) [:alexandrui]]

== Change summary for alert #26330 (as of Thu, 25 Jun 2020 06:14:04 GMT) ==

Improvements:

60% tp5n nonmain_startup_fileio windows7-32-shippable opt e10s stylo 7,045,170.17 -> 2,811,533.58
60% tp5n nonmain_startup_fileio windows7-32-shippable opt e10s stylo 7,042,398.92 -> 2,825,468.33

For up to date results, see: https://treeherder.mozilla.org/perf.html#/alerts?id=26330