Baseline Profiles

Baseline Profiles

Generating a Baseline Profile with Macrobenchmark

A profile is recorded, not written: a test drives the app through its critical journeys while the runtime logs every class and method it touches. Jetpack 234 's Macrobenchmark 234 library runs such tests from a separate com.android.test module that installs the app, controls it through UI Automator 234 , and reads the results back. Three pieces make it work (versions from Google's Maven 129 , 25 September 2026):

a :benchmark module with the com.android.test and androidx.baselineprofile plugins (1.5.0), targetProjectPath = ":app", and benchmark-macro-junit4 1.5.0 plus uiautomator 2.4.0;
in :app, the same androidx.baselineprofile plugin, baselineProfile(project(":benchmark")), and profileinstaller 1.4.1, which installs the profile even when the APK isn't installed by Play;
a generator test:

benchmark/.../BaselineProfileGenerator.kt: startup, then the big catalogKotlin

@RunWith(AndroidJUnit4::class)
class BaselineProfileGenerator {
  @get:Rule val rule = BaselineProfileRule()
  @Test fun startupAndCatalog() = rule.collect(packageName = PACKAGE) {
    pressHome()
    startActivityAndWait()                                   // the cold-start path
    device.wait(Until.hasObject(By.text("BookNest")), 10_000)
    pressHome()
    startActivityAndWait { it.putExtra("stage", "lazy") }    // the 600-book catalog
    val list = device.findObject(By.scrollable(true))
    list.setGestureMargin(device.displayWidth / 5)
    repeat(3) { list.fling(Direction.DOWN) }                 // the scroll path
  }
}

./gradlew :app:generateBaselineProfile builds a nonMinifiedRelease variant, which the plugin adds so method names in the profile are not obfuscated, runs the test on the connected device (an emulator needs androidx.benchmark.suppressErrors=EMULATOR, since emulator timings aren't trusted for benchmarks) and copies the result into the source tree. The first attempt produced a profile full of names like SPLc71;-><init>(Lf71;...): with AGP 9.4.0's new optimization { enable = true } block, the plugin's nonMinifiedRelease variant was still minified (a 4.4 MB APK with a mapping file). Switching release to the classic isMinifyEnabled = true form (How R8 Works) fixed it, and the second run took 6 minutes:

Output of 200

A baseline profile was generated for the variant `release`:
file:///home/dev/lane-ch5/booknest/app/src/release/generated/baselineProfiles/baseline-prof.txt
Comparison with previous baseline profile:
  10704 Old rules
  28289 New rules
...
BUILD SUCCESSFUL in 6m

The file is plain text in ART's rule format: L marks a class to load at startup, and on a method H, S and P mean hot, used during startup, and used after startup. Of its 28,288 lines, 860 name BookNest's own code, for example SPLcom/example/booknest/ui/BookScreensKt;->CatalogList(...)V; the rest cover libraries. Commit the file and regenerate it when the journeys change.

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