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Benchmarking and analyzing scripts for Instant Start


In order to understand the performance implication of a CL, we can do a local benchmark to compare the before/after metrics.


Build two APKs for before and after a CL, on gn target monochrome_apk, and make sure they are on different Chrome channels, like Canary (gn args android_channel = "canary") and default (unspecified) because they will be installed side by side. Depending on your preferred workflow, you can use two separate workspaces like ~/code/clankium/src and ~/code/clankium2/src, or use the same workspace but two different output directories like ./out/Release and ./out/Release2, or simply use the same output directory but rename the APK like out/Release/bin/monochrome_before_apk and out/Release/bin/monochrome_after_apk.

On the device, uninstall Chrome of these two channels to make sure the environment is clean. Otherwise, chrome://flags changes and Finch trials could introduce undesirable differences. You can use the --reinstall option to automate this. When running, first-run experience (FRE) would be skipped, but you'll need to manually create one tab, make sure Feed is loaded, and swipe away the login prompt in the dry-run step. Follow the instructions of the script.

The command line looks like this:

./tools/android/instant_start/ --control-apk out/Release/bin/monochrome_before_apk --experiment-apk out/Release/bin/monochrome_after_apk -v --repeat 100 --reinstall

The metrics are persisted to runs.pickle by default, and the filename can be specified by --data-output option. This can later be analyzed like this:

./tools/android/instant_start/ runs.pickle

The output looks like:

Reading runs-pixel3xl.pickle with {'model': 'Pixel 3 XL', 'start_time': datetime.datetime(2020, 9, 19, 14, 55, 34, 596731)}
100 samples on Pixel 3 XL
                               Median  Diff with control   p-value
FirstDrawCompletedTime        155.0ms   -13.5ms (-8.71%)  0.000000
SingleTabTitleAvailableTime   117.0ms  -13.0ms (-11.11%)  0.000000
FeedStreamCreatedTime         356.0ms   -35.5ms (-9.97%)  0.000001
FeedsLoadingPlaceholderShown   94.5ms    -2.0ms (-2.12%)  0.007312
FeedContentFirstLoadedTime    924.0ms    -6.5ms (-0.70%)  0.034100