Android Start-up Performance

Stages of Start-up

Every Android component (activities, broadcast receivers, etc) can be a start-up entry point for Chrome. The main start-up scenarios we optimize for are:

• Launching from the home screen
• Handling a View intent
• Showing a Chrome Custom Tab

For a home screen launch, we consider start-up to be complete once the Activity is rendered. For the latter two, we care both about:

• The first Navigation Commit in the app lifetime
• The initial First Contentful Paint

UMA

Here are some UMA metrics that measure start-up (UMA's UI has descriptions):

• Startup.Android.Cold.TimeToFirstVisibleContent4
• Startup.Android.Cold.TimeToFirstNavigationCommit3.Tabbed
• Browser.PaintPreview.TabbedPlayer.TimeToFirstBitmap
• Startup.Android.Cold.TimeToFirstContentfulPaint3.Tabbed

This one can be useful for measuring dex optimization changes:

• Startup.LoadTime.ProcessCreateToApplicationStart

For Googlers, there's more background in this doc.

ChromePerf

Here are some chromeperf metrics that measure start-up in a lab environment:

• ChromiumPerf/android-pixel4-perf/startup.mobile / messageloop_start_time
• ChromiumPerf/android-pixel4-perf/startup.mobile / navigation_commit_time
• ChromiumPerf/android-pixel4-perf/startup.mobile / first_contentful_paint_time

Pinpoint

When using Pinpoint to test start-up changes, make sure to:

• Use bundles rather than APKs.
  • For 32-bit: --browser=android-trichrome-chrome-google-bundle
  • For 64-bit: --browser=android-trichrome-chrome-google-64-32-bundle
• Compile DEX: --compile-apk=speed

Some start-up changes can improve start-up for high-end devices but degrade it for low-end ones (or vice versa). It is important to test both.

For small regressions (e.g. ~1%), it can help to add --pageset-repeat 10 or --pageset-repeat 20 in order to increase the number of samples collected. A single repeat produces 8 samples, then Pinpoint normally runs it 10 times (total 80). With --pageset-repeat=20 the total number of samples is 1600.

• Use android-go-* devices to test low-end.
• Use android-pixel6-* to test high-end. They set is_high_end_android=true.
• The full list of bots is here.