Reduce AccelerateHeavyScreenBenchmark variance

- Increased iterations from 1 to 10 for more realistic results, in line with the spirit of the performance codelab.
- Updated the measure block to only include frames from scrolling, removing: 1) frames from the cold startup of the activity and 2) frames from the initial faked load delay of 500 ms.
- Added a warmup iteration that triggers loading of images.
- The 500 ms wait wasn't enough for the drag to settle, so we were potentially starting the second drag before the first had settled, and then ending the measure too early. Bumped the wait to 1000 ms, traces now show a clear ~200 ms gaps with no frames.

Author: pyricau

PerformanceCodelab/measure/src/main/java/com/compose/performance/measure/AbstractBenchmark.kt

@@ -23,11 +23,11 @@ import androidx.benchmark.macro.junit4.MacrobenchmarkRule
 import org.junit.Rule
 
 abstract class AbstractBenchmark(
-    protected val startupMode: StartupMode = StartupMode.WARM,
-    // For the purpose of this workshop, we have iterations set to low number.
-    // For more accurate measurements, you should increase the iterations to at least 10
-    // based on how much variance occurs in the results. In general more iterations = more stable
-    // results, but longer execution time.
+    protected val startupMode: StartupMode? = StartupMode.WARM,
+    // For accurate measurements, you should set the iterations to at least 10, based on how much
+    // variance occurs in the results. In general more iterations = more stable
+    // results, but longer execution time. For exploration purposes you could set
+    // iterations to 1.
     protected val iterations: Int = 1
 ) {
     @get:Rule

PerformanceCodelab/measure/src/main/java/com/compose/performance/measure/AccelerateHeavyScreenBenchmark.kt

@@ -21,42 +21,67 @@ import androidx.benchmark.macro.ExperimentalMetricApi
 import androidx.benchmark.macro.FrameTimingMetric
 import androidx.benchmark.macro.MacrobenchmarkScope
 import androidx.benchmark.macro.Metric
-import androidx.benchmark.macro.StartupMode
 import androidx.benchmark.macro.TraceSectionMetric
 import androidx.test.ext.junit.runners.AndroidJUnit4
 import androidx.test.filters.LargeTest
 import androidx.test.uiautomator.By
+import androidx.test.uiautomator.BySelector
 import androidx.test.uiautomator.Until
 import org.junit.Test
 import org.junit.runner.RunWith
 
 @LargeTest
 @RunWith(AndroidJUnit4::class)
 @OptIn(ExperimentalMetricApi::class)
-class AccelerateHeavyScreenBenchmark : AbstractBenchmark(StartupMode.COLD) {
-
-    @Test
-    fun accelerateHeavyScreenCompilationFull() = benchmark(CompilationMode.Full())
-
-    override val metrics: List<Metric> =
-        listOf(
-            FrameTimingMetric(),
-            TraceSectionMetric("ImagePlaceholder", TraceSectionMetric.Mode.Sum),
-            TraceSectionMetric("PublishDate.registerReceiver", TraceSectionMetric.Mode.Sum),
-            TraceSectionMetric("ItemTag", TraceSectionMetric.Mode.Sum)
-        )
-
-    override fun MacrobenchmarkScope.measureBlock() {
-        pressHome()
-        startTaskActivity("accelerate_heavy")
-
-        device.wait(Until.hasObject(By.res("list_of_items")), 5_000)
-        val feed = device.findObject(By.res("list_of_items"))
-        feed.setGestureMargin(device.displayWidth / 5)
-
-        repeat(2) {
-            feed.drag(Point(feed.visibleCenter.x, feed.visibleBounds.top))
-            Thread.sleep(500)
-        }
+class AccelerateHeavyScreenBenchmark : AbstractBenchmark(
+  // This benchmark tests scrolling from an already started activity in the setup phase, we don't
+  // want the activity to be started in the measure phase.
+  startupMode = null,
+  iterations = 10
+) {
+
+  @Test
+  fun accelerateHeavyScreenCompilationFull() = benchmark(CompilationMode.Full())
+
+  override val metrics: List<Metric> =
+    listOf(
+      FrameTimingMetric(),
+      TraceSectionMetric("ImagePlaceholder", TraceSectionMetric.Mode.Sum),
+      TraceSectionMetric("PublishDate.registerReceiver", TraceSectionMetric.Mode.Sum),
+      TraceSectionMetric("ItemTag", TraceSectionMetric.Mode.Sum)
+    )
+
+  private var isFirstSetup = true
+
+  override fun MacrobenchmarkScope.setupBlock() {
+    if (isFirstSetup) {
+      isFirstSetup = false
+      startActivity()
+      // Perform a warmup round that will trigger the initial loading of images to avoid having
+      // a first iteration that's significantly slower than other iterations
+      measureBlock()
+    }
+    finishActivity()
+    startActivity()
+  }
+
+  private fun MacrobenchmarkScope.startActivity() {
+    startTaskActivity("accelerate_heavy")
+    device.wait(Until.hasObject(By.res("list_of_items")), 5_000)
+  }
+
+  private fun MacrobenchmarkScope.finishActivity() {
+    device.pressBack()
+    device.wait(Until.gone(By.res("list_of_items")), 2_000)
+  }
+
+  override fun MacrobenchmarkScope.measureBlock() {
+    val feed = device.findObject(By.res("list_of_items"))
+
+    repeat(2) {
+      feed.drag(Point(feed.visibleCenter.x, feed.visibleBounds.top))
+      // Enough time for scroll to settle.
+      Thread.sleep(1000)
     }
+  }
 }