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generating-baseline-profiles

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Use this skill to generate and measure Jetpack Compose Baseline Profiles end-to-end with the AGP 8.2+ Baseline Profile Generator module and the Macrobenchmark harness. Covers writing the `BaselineProfileRule` journey for cold startup plus first-scroll, generating `baseline-prof.txt`, verifying it shipped at `assets/dexopt/baseline.prof`, measuring with `MacrobenchmarkRule` under `CompilationMode.Partial(BaselineProfileMode.Require)`, and emitting accurate time-to-fully-drawn via `ReportDrawn` / `ReportDrawnWhen` / `ReportDrawnAfter` from `androidx.activity.compose`. Compose ships unbundled, so every Compose UI app benefits — cited gains around 30% faster startup and 40% smoother first-scroll. Use when the user mentions "baseline profile", "macrobenchmark", "slow cold startup", "first-scroll jank", "StartupTimingMetric", "FrameTimingMetric", "ReportDrawn", "TTFD", or preparing a release build for performance measurement.

measurement/generating-baseline-profiles/SKILL.md

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Jun 16, 2026
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# Generating Baseline Profiles — ship the AOT compilation hint list and prove it moved the needle

Baseline Profiles ship an AOT compilation hint list inside the APK so ART pre-compiles hot Compose code paths on install instead of relying on JIT during the first runs. Cited gains: roughly 30% faster cold startup and 40% smoother first-scroll on the journeys that were profiled. Compose ships **unbundled** from the platform, so every Compose UI app benefits — there is no version of Android where Compose is already AOT-compiled by the system image.

This skill is the measurement spine for the rest of the performance work. Profiles are generated with `BaselineProfileRule` from `androidx.benchmark:benchmark-macro-junit4` and measured with `MacrobenchmarkRule` from the same artifact. Generation and measurement are two distinct `@Test` files in a separate `:baselineprofile` module that AGP 8.2+ scaffolds via **New Module → Baseline Profile Generator**.

## When to use this skill

- Cold startup is slow and the developer wants AOT-compiled hot paths on first launch.
- First-scroll on a `LazyColumn` / `LazyVerticalGrid` is janky on real devices even after stability fixes.
- Preparing a release build and the developer needs a perf baseline before shipping.
- Verifying that a stability or strong-skipping fix actually moved cold-startup or frame-timing numbers — Macrobenchmark is the ground truth.
- The user mentions "baseline profile", "macrobenchmark", "TTFD", "time-to-fully-drawn", "StartupTimingMetric", "FrameTimingMetric", "CompilationMode", `aosp_cf_x86_64_phone-userdebug`, or "ReportDrawn".
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