Add sharding to Binder Latency collection and make it configurable. The

hash code of the binder class will be used to select which apis will be
collected for based on the configured modulo.

Test: unit tests
Bug: 180584913
Change-Id: I7544135a77cf510fa9e542d98262a7211760935c

3 files changed, 112 insertions, 9 deletions

diff --git a/core/java/com/android/internal/os/BinderCallsStats.java b/core/java/com/android/internal/os/BinderCallsStats.java
index 1004e17e91e6..c297a1fc4279 100644
--- a/core/java/com/android/internal/os/BinderCallsStats.java
+++ b/core/java/com/android/internal/os/BinderCallsStats.java
@@ -1105,9 +1105,11 @@ public class BinderCallsStats implements BinderInternal.Observer {
         public static final String SETTINGS_MAX_CALL_STATS_KEY = "max_call_stats_count";
         public static final String SETTINGS_IGNORE_BATTERY_STATUS_KEY = "ignore_battery_status";
         // Settings for BinderLatencyObserver.
-        public static final String SETTINGS_COLLECT_LATENCY_DATA_KEY = "collect_Latency_data";
+        public static final String SETTINGS_COLLECT_LATENCY_DATA_KEY = "collect_latency_data";
         public static final String SETTINGS_LATENCY_OBSERVER_SAMPLING_INTERVAL_KEY =
                 "latency_observer_sampling_interval";
+        public static final String SETTINGS_LATENCY_OBSERVER_SHARDING_MODULO_KEY =
+                "latency_observer_sharding_modulo";
         public static final String SETTINGS_LATENCY_OBSERVER_PUSH_INTERVAL_MINUTES_KEY =
                 "latency_observer_push_interval_minutes";
         public static final String SETTINGS_LATENCY_HISTOGRAM_BUCKET_COUNT_KEY =
@@ -1187,6 +1189,9 @@ public class BinderCallsStats implements BinderInternal.Observer {
             binderLatencyObserver.setSamplingInterval(mParser.getInt(
                     SETTINGS_LATENCY_OBSERVER_SAMPLING_INTERVAL_KEY,
                     BinderLatencyObserver.PERIODIC_SAMPLING_INTERVAL_DEFAULT));
+            binderLatencyObserver.setShardingModulo(mParser.getInt(
+                    SETTINGS_LATENCY_OBSERVER_SHARDING_MODULO_KEY,
+                    BinderLatencyObserver.SHARDING_MODULO_DEFAULT));
             binderLatencyObserver.setHistogramBucketsParams(
                     mParser.getInt(
                             SETTINGS_LATENCY_HISTOGRAM_BUCKET_COUNT_KEY,
diff --git a/core/java/com/android/internal/os/BinderLatencyObserver.java b/core/java/com/android/internal/os/BinderLatencyObserver.java
index 5fa96bd9a152..ed7e172e8071 100644
--- a/core/java/com/android/internal/os/BinderLatencyObserver.java
+++ b/core/java/com/android/internal/os/BinderLatencyObserver.java
@@ -44,6 +44,7 @@ public class BinderLatencyObserver {
 
     // Latency observer parameters.
     public static final int PERIODIC_SAMPLING_INTERVAL_DEFAULT = 10;
+    public static final int SHARDING_MODULO_DEFAULT = 1;
     public static final int STATSD_PUSH_INTERVAL_MINUTES_DEFAULT = 360;
 
     // Histogram buckets parameters.
@@ -58,6 +59,11 @@ public class BinderLatencyObserver {
     // Sampling period to control how often to track CPU usage. 1 means all calls, 100 means ~1 out
     // of 100 requests.
     private int mPeriodicSamplingInterval = PERIODIC_SAMPLING_INTERVAL_DEFAULT;
+    // Controls how many APIs will be collected per device. 1 means all APIs, 10 means every 10th
+    // API will be collected.
+    private int mShardingModulo = SHARDING_MODULO_DEFAULT;
+    // Controls which shards will be collected on this device.
+    private int mShardingOffset;
 
     private int mBucketCount = BUCKET_COUNT_DEFAULT;
     private int mFirstBucketSize = FIRST_BUCKET_SIZE_DEFAULT;
@@ -156,7 +162,7 @@ public class BinderLatencyObserver {
                 FrameworkStatsLog.BINDER_LATENCY_REPORTED,
                 atom.getBytes(),
                 mPeriodicSamplingInterval,
-                1,
+                mShardingModulo,
                 mBucketCount,
                 mFirstBucketSize,
                 mBucketScaleFactor);
@@ -185,6 +191,7 @@ public class BinderLatencyObserver {
         mLatencyBuckets = new BinderLatencyBuckets(
             mBucketCount, mFirstBucketSize, mBucketScaleFactor);
         mProcessSource = processSource;
+        mShardingOffset = mRandom.nextInt(mShardingModulo);
         noteLatencyDelayed();
     }
 
@@ -194,7 +201,12 @@ public class BinderLatencyObserver {
             return;
         }
 
-        LatencyDims dims = new LatencyDims(s.binderClass, s.transactionCode);
+        LatencyDims dims = LatencyDims.create(s.binderClass, s.transactionCode);
+
+        if (!shouldCollect(dims)) {
+            return;
+        }
+
         long elapsedTimeMicro = getElapsedRealtimeMicro();
         long callDuration = elapsedTimeMicro - s.timeStarted;
 
@@ -220,6 +232,10 @@ public class BinderLatencyObserver {
         return SystemClock.elapsedRealtimeNanos() / 1000;
     }
 
+    protected boolean shouldCollect(LatencyDims dims) {
+        return (dims.hashCode() + mShardingOffset) % mShardingModulo == 0;
+    }
+
     protected boolean shouldKeepSample() {
         return mRandom.nextInt() % mPeriodicSamplingInterval == 0;
     }
@@ -240,6 +256,23 @@ public class BinderLatencyObserver {
         }
     }
 
+    /** Updates the sharding modulo. */
+    public void setShardingModulo(int shardingModulo) {
+        if (shardingModulo <= 0) {
+            Slog.w(TAG, "Ignored invalid sharding modulo (value must be positive): "
+                    + shardingModulo);
+            return;
+        }
+
+        synchronized (mLock) {
+            if (shardingModulo != mShardingModulo) {
+                mShardingModulo = shardingModulo;
+                mShardingOffset = mRandom.nextInt(shardingModulo);
+                reset();
+            }
+        }
+    }
+
     /** Updates the statsd push interval. */
     public void setPushInterval(int pushIntervalMinutes) {
         if (pushIntervalMinutes <= 0) {
@@ -289,7 +322,12 @@ public class BinderLatencyObserver {
         // Cached hash code, 0 if not set yet.
         private int mHashCode = 0;
 
-        public LatencyDims(Class<? extends Binder> binderClass, int transactionCode) {
+        /** Creates a new instance of LatencyDims. */
+        public static LatencyDims create(Class<? extends Binder> binderClass, int transactionCode) {
+            return new LatencyDims(binderClass, transactionCode);
+        }
+
+        private LatencyDims(Class<? extends Binder> binderClass, int transactionCode) {
             this.mBinderClass = binderClass;
             this.mTransactionCode = transactionCode;
         }
@@ -317,7 +355,7 @@ public class BinderLatencyObserver {
                 return mHashCode;
             }
             int hash = mTransactionCode;
-            hash = 31 * hash + mBinderClass.hashCode();
+            hash = 31 * hash + mBinderClass.getName().hashCode();
             mHashCode = hash;
             return hash;
         }
diff --git a/core/tests/coretests/src/com/android/internal/os/BinderLatencyObserverTest.java b/core/tests/coretests/src/com/android/internal/os/BinderLatencyObserverTest.java
index 4157f5e72871..5af7376dc132 100644
--- a/core/tests/coretests/src/com/android/internal/os/BinderLatencyObserverTest.java
+++ b/core/tests/coretests/src/com/android/internal/os/BinderLatencyObserverTest.java
@@ -41,6 +41,7 @@ import org.junit.runner.RunWith;
 
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Iterator;
 import java.util.Random;
 
 @SmallTest
@@ -71,9 +72,9 @@ public class BinderLatencyObserverTest {
 
         ArrayMap<LatencyDims, int[]> latencyHistograms = blo.getLatencyHistograms();
         assertEquals(2, latencyHistograms.keySet().size());
-        assertThat(latencyHistograms.get(new LatencyDims(binder.getClass(), 1)))
+        assertThat(latencyHistograms.get(LatencyDims.create(binder.getClass(), 1)))
             .asList().containsExactly(2, 0, 1, 0, 0).inOrder();
-        assertThat(latencyHistograms.get(new LatencyDims(binder.getClass(), 2)))
+        assertThat(latencyHistograms.get(LatencyDims.create(binder.getClass(), 2)))
             .asList().containsExactly(0, 0, 0, 0, 2).inOrder();
     }
 
@@ -115,7 +116,7 @@ public class BinderLatencyObserverTest {
 
         // The long call should be capped to maxint (to not overflow) and placed in the last bucket.
         assertThat(blo.getLatencyHistograms()
-            .get(new LatencyDims(binder.getClass(), 1)))
+            .get(LatencyDims.create(binder.getClass(), 1)))
             .asList().containsExactly(0, 0, 0, 0, 1)
             .inOrder();
     }
@@ -132,7 +133,7 @@ public class BinderLatencyObserverTest {
         blo.setElapsedTime(2);
         blo.callEnded(callSession);
 
-        LatencyDims dims = new LatencyDims(binder.getClass(), 1);
+        LatencyDims dims = LatencyDims.create(binder.getClass(), 1);
         // Fill the buckets with maxint.
         Arrays.fill(blo.getLatencyHistograms().get(dims), Integer.MAX_VALUE);
         assertThat(blo.getLatencyHistograms().get(dims))
@@ -240,6 +241,61 @@ public class BinderLatencyObserverTest {
                 .inOrder();
     }
 
+    @Test
+    public void testSharding() {
+        TestBinderLatencyObserver blo = new TestBinderLatencyObserver();
+        blo.setShardingModulo(2);
+        blo.setHistogramBucketsParams(5, 5, 1.125f);
+
+        Binder binder = new Binder();
+        CallSession callSession = new CallSession();
+        callSession.binderClass = binder.getClass();
+        callSession.transactionCode = 1;
+        blo.setElapsedTime(2);
+        blo.callEnded(callSession);
+        callSession.transactionCode = 2;
+        blo.setElapsedTime(4);
+        blo.callEnded(callSession);
+        callSession.transactionCode = 3;
+        blo.setElapsedTime(2);
+        blo.callEnded(callSession);
+        callSession.transactionCode = 4;
+        blo.setElapsedTime(4);
+        blo.callEnded(callSession);
+
+        ArrayMap<LatencyDims, int[]> latencyHistograms = blo.getLatencyHistograms();
+        Iterator<LatencyDims> iterator = latencyHistograms.keySet().iterator();
+        LatencyDims dims;
+
+        // Hash codes are not consistent per device and not mockable so the test needs to consider
+        // whether the hashCode of LatencyDims is odd or even and test accordingly.
+        if (LatencyDims.create(binder.getClass(), 0).hashCode() % 2 == 0) {
+            assertEquals(2, latencyHistograms.size());
+            dims = iterator.next();
+            assertEquals(binder.getClass(), dims.getBinderClass());
+            assertEquals(1, dims.getTransactionCode());
+            assertThat(latencyHistograms.get(dims)).asList().containsExactly(1, 0, 0, 0, 0)
+                .inOrder();
+            dims = iterator.next();
+            assertEquals(binder.getClass(), dims.getBinderClass());
+            assertEquals(3, dims.getTransactionCode());
+            assertThat(latencyHistograms.get(dims)).asList().containsExactly(1, 0, 0, 0, 0)
+                .inOrder();
+        } else {
+            assertEquals(2, latencyHistograms.size());
+            dims = iterator.next();
+            assertEquals(binder.getClass(), dims.getBinderClass());
+            assertEquals(2, dims.getTransactionCode());
+            assertThat(latencyHistograms.get(dims)).asList().containsExactly(1, 0, 0, 0, 0)
+                .inOrder();
+            dims = iterator.next();
+            assertEquals(binder.getClass(), dims.getBinderClass());
+            assertEquals(4, dims.getTransactionCode());
+            assertThat(latencyHistograms.get(dims)).asList().containsExactly(1, 0, 0, 0, 0)
+                .inOrder();
+        }
+    }
+
     public static class TestBinderLatencyObserver extends BinderLatencyObserver {
         private long mElapsedTime = 0;
         private ArrayList<String> mWrittenAtoms;
@@ -259,6 +315,10 @@ public class BinderLatencyObserverTest {
                                 public int nextInt() {
                                     return mCallCount++;
                                 }
+
+                                public int nextInt(int x) {
+                                    return 1;
+                                }
                             };
                         }
                     },