Merge "Writing battery history tags into the history buffer"

5 files changed, 133 insertions, 122 deletions

diff --git a/core/java/android/os/BatteryStats.java b/core/java/android/os/BatteryStats.java
index fb9911811da9..dd387dadd4dd 100644
--- a/core/java/android/os/BatteryStats.java
+++ b/core/java/android/os/BatteryStats.java
@@ -1908,6 +1908,10 @@ public abstract class BatteryStats implements Parcelable {
         public final HistoryTag localWakeReasonTag = new HistoryTag();
         public final HistoryTag localEventTag = new HistoryTag();
 
+        // Includes a tag's first occurrence in the parcel, so the value of the tag is written
+        // rather than just its index in the history tag pool.
+        public boolean tagsFirstOccurrence;
+
         @UnsupportedAppUsage
         public HistoryItem() {
         }
@@ -2014,6 +2018,7 @@ public abstract class BatteryStats implements Parcelable {
             wakeReasonTag = null;
             eventCode = EVENT_NONE;
             eventTag = null;
+            tagsFirstOccurrence = false;
         }
 
         @UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.P)
@@ -2061,6 +2066,7 @@ public abstract class BatteryStats implements Parcelable {
             } else {
                 eventTag = null;
             }
+            tagsFirstOccurrence = o.tagsFirstOccurrence;
             currentTime = o.currentTime;
         }
 
diff --git a/core/java/android/os/BatteryUsageStats.java b/core/java/android/os/BatteryUsageStats.java
index 591b665f97a2..d37c0eb5f1d2 100644
--- a/core/java/android/os/BatteryUsageStats.java
+++ b/core/java/android/os/BatteryUsageStats.java
@@ -133,7 +133,6 @@ public final class BatteryUsageStats implements Parcelable, Closeable {
     private final List<UserBatteryConsumer> mUserBatteryConsumers;
     private final AggregateBatteryConsumer[] mAggregateBatteryConsumers;
     private final Parcel mHistoryBuffer;
-    private final List<BatteryStats.HistoryTag> mHistoryTagPool;
     private CursorWindow mBatteryConsumersCursorWindow;
 
     private BatteryUsageStats(@NonNull Builder builder) {
@@ -145,7 +144,6 @@ public final class BatteryUsageStats implements Parcelable, Closeable {
         mDischargedPowerLowerBound = builder.mDischargedPowerLowerBoundMah;
         mDischargedPowerUpperBound = builder.mDischargedPowerUpperBoundMah;
         mHistoryBuffer = builder.mHistoryBuffer;
-        mHistoryTagPool = builder.mHistoryTagPool;
         mBatteryTimeRemainingMs = builder.mBatteryTimeRemainingMs;
         mChargeTimeRemainingMs = builder.mChargeTimeRemainingMs;
         mCustomPowerComponentNames = builder.mCustomPowerComponentNames;
@@ -283,7 +281,7 @@ public final class BatteryUsageStats implements Parcelable, Closeable {
     /**
      * Returns the names of custom power components in order, so the first name in the array
      * corresponds to the custom componentId
-     * {@link BatteryConsumer.FIRST_CUSTOM_POWER_COMPONENT_ID}.
+     * {@link BatteryConsumer#FIRST_CUSTOM_POWER_COMPONENT_ID}.
      */
     @NonNull
     public String[] getCustomPowerComponentNames() {
@@ -299,8 +297,7 @@ public final class BatteryUsageStats implements Parcelable, Closeable {
             throw new IllegalStateException(
                     "Battery history was not requested in the BatteryUsageStatsQuery");
         }
-        return new BatteryStatsHistoryIterator(new BatteryStatsHistory(mHistoryBuffer),
-                mHistoryTagPool);
+        return new BatteryStatsHistoryIterator(new BatteryStatsHistory(mHistoryBuffer));
     }
 
     @Override
@@ -361,19 +358,8 @@ public final class BatteryUsageStats implements Parcelable, Closeable {
 
             mHistoryBuffer = Parcel.obtain();
             mHistoryBuffer.unmarshall(historyBlob, 0, historyBlob.length);
-
-            int historyTagCount = source.readInt();
-            mHistoryTagPool = new ArrayList<>(historyTagCount);
-            for (int i = 0; i < historyTagCount; i++) {
-                BatteryStats.HistoryTag tag = new BatteryStats.HistoryTag();
-                tag.string = source.readString();
-                tag.uid = source.readInt();
-                tag.poolIdx = source.readInt();
-                mHistoryTagPool.add(tag);
-            }
         } else {
             mHistoryBuffer = null;
-            mHistoryTagPool = null;
         }
     }
 
@@ -395,13 +381,6 @@ public final class BatteryUsageStats implements Parcelable, Closeable {
         if (mHistoryBuffer != null) {
             dest.writeBoolean(true);
             dest.writeBlob(mHistoryBuffer.marshall());
-            dest.writeInt(mHistoryTagPool.size());
-            for (int i = mHistoryTagPool.size() - 1; i >= 0; i--) {
-                final BatteryStats.HistoryTag tag = mHistoryTagPool.get(i);
-                dest.writeString(tag.string);
-                dest.writeInt(tag.uid);
-                dest.writeInt(tag.poolIdx);
-            }
         } else {
             dest.writeBoolean(false);
         }
@@ -769,7 +748,6 @@ public final class BatteryUsageStats implements Parcelable, Closeable {
         private final SparseArray<UserBatteryConsumer.Builder> mUserBatteryConsumerBuilders =
                 new SparseArray<>();
         private Parcel mHistoryBuffer;
-        private List<BatteryStats.HistoryTag> mHistoryTagPool;
 
         public Builder(@NonNull String[] customPowerComponentNames) {
             this(customPowerComponentNames, false);
@@ -888,10 +866,8 @@ public final class BatteryUsageStats implements Parcelable, Closeable {
          * Sets the parceled recent history.
          */
         @NonNull
-        public Builder setBatteryHistory(Parcel historyBuffer,
-                List<BatteryStats.HistoryTag> historyTagPool) {
+        public Builder setBatteryHistory(Parcel historyBuffer) {
             mHistoryBuffer = historyBuffer;
-            mHistoryTagPool = historyTagPool;
             return this;
         }
 
diff --git a/core/java/com/android/internal/os/BatteryStatsHistoryIterator.java b/core/java/com/android/internal/os/BatteryStatsHistoryIterator.java
index 1871ac5074c9..c5f18487ac74 100644
--- a/core/java/com/android/internal/os/BatteryStatsHistoryIterator.java
+++ b/core/java/com/android/internal/os/BatteryStatsHistoryIterator.java
@@ -21,8 +21,7 @@ import android.os.BatteryManager;
 import android.os.BatteryStats;
 import android.os.Parcel;
 import android.util.Slog;
-
-import java.util.List;
+import android.util.SparseArray;
 
 /**
  * An iterator for {@link BatteryStats.HistoryItem}'s.
@@ -33,23 +32,11 @@ public class BatteryStatsHistoryIterator {
     private final BatteryStatsHistory mBatteryStatsHistory;
     private final BatteryStats.HistoryStepDetails mReadHistoryStepDetails =
             new BatteryStats.HistoryStepDetails();
-    private final String[] mReadHistoryStrings;
-    private final int[] mReadHistoryUids;
+    private final SparseArray<BatteryStats.HistoryTag> mHistoryTags = new SparseArray<>();
 
-    public BatteryStatsHistoryIterator(@NonNull BatteryStatsHistory history,
-            @NonNull List<BatteryStats.HistoryTag> historyTagPool) {
+    public BatteryStatsHistoryIterator(@NonNull BatteryStatsHistory history) {
         mBatteryStatsHistory = history;
-
         mBatteryStatsHistory.startIteratingHistory();
-
-        mReadHistoryStrings = new String[historyTagPool.size()];
-        mReadHistoryUids = new int[historyTagPool.size()];
-        for (int i = historyTagPool.size() - 1; i >= 0; i--) {
-            BatteryStats.HistoryTag tag = historyTagPool.get(i);
-            final int idx = tag.poolIdx;
-            mReadHistoryStrings[idx] = tag.string;
-            mReadHistoryUids[idx] = tag.uid;
-        }
     }
 
     /**
@@ -161,26 +148,16 @@ public class BatteryStatsHistoryIterator {
         }
 
         if ((firstToken & BatteryStatsImpl.DELTA_WAKELOCK_FLAG) != 0) {
-            int indexes = src.readInt();
-            int wakeLockIndex = indexes & 0xffff;
-            int wakeReasonIndex = (indexes >> 16) & 0xffff;
-            if (wakeLockIndex != 0xffff) {
+            final int indexes = src.readInt();
+            final int wakeLockIndex = indexes & 0xffff;
+            final int wakeReasonIndex = (indexes >> 16) & 0xffff;
+            if (readHistoryTag(src, wakeLockIndex, cur.localWakelockTag)) {
                 cur.wakelockTag = cur.localWakelockTag;
-                readHistoryTag(wakeLockIndex, cur.wakelockTag);
-                if (DEBUG) {
-                    Slog.i(TAG, "READ DELTA: wakelockTag=#" + cur.wakelockTag.poolIdx
-                            + " " + cur.wakelockTag.uid + ":" + cur.wakelockTag.string);
-                }
             } else {
                 cur.wakelockTag = null;
             }
-            if (wakeReasonIndex != 0xffff) {
+            if (readHistoryTag(src, wakeReasonIndex, cur.localWakeReasonTag)) {
                 cur.wakeReasonTag = cur.localWakeReasonTag;
-                readHistoryTag(wakeReasonIndex, cur.wakeReasonTag);
-                if (DEBUG) {
-                    Slog.i(TAG, "READ DELTA: wakeReasonTag=#" + cur.wakeReasonTag.poolIdx
-                            + " " + cur.wakeReasonTag.uid + ":" + cur.wakeReasonTag.string);
-                }
             } else {
                 cur.wakeReasonTag = null;
             }
@@ -195,7 +172,11 @@ public class BatteryStatsHistoryIterator {
             final int codeAndIndex = src.readInt();
             cur.eventCode = (codeAndIndex & 0xffff);
             final int index = ((codeAndIndex >> 16) & 0xffff);
-            readHistoryTag(index, cur.eventTag);
+            if (readHistoryTag(src, index, cur.localEventTag)) {
+                cur.eventTag = cur.localEventTag;
+            } else {
+                cur.eventTag = null;
+            }
             cur.numReadInts += 1;
             if (DEBUG) {
                 Slog.i(TAG, "READ DELTA: event=" + cur.eventCode + " tag=#"
@@ -220,40 +201,29 @@ public class BatteryStatsHistoryIterator {
         cur.wifiRailChargeMah = src.readDouble();
     }
 
-    int getHistoryStringPoolSize() {
-        return mReadHistoryStrings.length;
-    }
-
-    int getHistoryStringPoolBytes() {
-        int totalChars = 0;
-        for (int i = mReadHistoryStrings.length - 1; i >= 0; i--) {
-            if (mReadHistoryStrings[i] != null) {
-                totalChars += mReadHistoryStrings[i].length() + 1;
-            }
+    private boolean readHistoryTag(Parcel src, int index, BatteryStats.HistoryTag outTag) {
+        if (index == 0xffff) {
+            return false;
         }
 
-        // Each entry is a fixed 12 bytes: 4 for index, 4 for uid, 4 for string size
-        // Each string character is 2 bytes.
-        return (mReadHistoryStrings.length * 12) + (totalChars * 2);
-    }
+        if ((index & BatteryStatsImpl.TAG_FIRST_OCCURRENCE_FLAG) != 0) {
+            BatteryStats.HistoryTag tag = new BatteryStats.HistoryTag();
+            tag.readFromParcel(src);
+            tag.poolIdx = index & ~BatteryStatsImpl.TAG_FIRST_OCCURRENCE_FLAG;
+            mHistoryTags.put(tag.poolIdx, tag);
 
-    String getHistoryTagPoolString(int index) {
-        return mReadHistoryStrings[index];
-    }
-
-    int getHistoryTagPoolUid(int index) {
-        return mReadHistoryUids[index];
-    }
-
-    private void readHistoryTag(int index, BatteryStats.HistoryTag tag) {
-        if (index < mReadHistoryStrings.length) {
-            tag.string = mReadHistoryStrings[index];
-            tag.uid = mReadHistoryUids[index];
+            outTag.setTo(tag);
         } else {
-            tag.string = null;
-            tag.uid = 0;
+            BatteryStats.HistoryTag historyTag = mHistoryTags.get(index);
+            if (historyTag != null) {
+                outTag.setTo(historyTag);
+            } else {
+                outTag.string = null;
+                outTag.uid = 0;
+            }
+            outTag.poolIdx = index;
         }
-        tag.poolIdx = index;
+        return true;
     }
 
     private static void readBatteryLevelInt(int batteryLevelInt, BatteryStats.HistoryItem out) {
diff --git a/core/java/com/android/internal/os/BatteryStatsImpl.java b/core/java/com/android/internal/os/BatteryStatsImpl.java
index 94a1efec80d9..63cce0a94052 100644
--- a/core/java/com/android/internal/os/BatteryStatsImpl.java
+++ b/core/java/com/android/internal/os/BatteryStatsImpl.java
@@ -160,7 +160,7 @@ public class BatteryStatsImpl extends BatteryStats {
     private static final int MAGIC = 0xBA757475; // 'BATSTATS'
 
     // Current on-disk Parcel version
-    static final int VERSION = 201;
+    static final int VERSION = 202;
 
     // The maximum number of names wakelocks we will keep track of
     // per uid; once the limit is reached, we batch the remaining wakelocks
@@ -757,7 +757,11 @@ public class BatteryStatsImpl extends BatteryStats {
     protected boolean mRecordingHistory = false;
     int mNumHistoryItems;
 
+    private static final int HISTORY_TAG_INDEX_LIMIT = 0x7ffe;
+    private static final int MAX_HISTORY_TAG_STRING_LENGTH = 256;
+
     final HashMap<HistoryTag, Integer> mHistoryTagPool = new HashMap<>();
+    private SparseArray<HistoryTag> mHistoryTags;
     final Parcel mHistoryBuffer = Parcel.obtain();
     final HistoryItem mHistoryLastWritten = new HistoryItem();
     final HistoryItem mHistoryLastLastWritten = new HistoryItem();
@@ -816,7 +820,6 @@ public class BatteryStatsImpl extends BatteryStats {
 
     private BatteryStatsHistoryIterator mBatteryStatsHistoryIterator;
     private HistoryItem mHistoryIterator;
-    private boolean mReadOverflow;
 
     int mStartCount;
 
@@ -1191,12 +1194,21 @@ public class BatteryStatsImpl extends BatteryStats {
     }
 
     public BatteryStatsImpl(Clock clock) {
+        this(clock, (File) null);
+    }
+
+    public BatteryStatsImpl(Clock clock, File historyDirectory) {
         init(clock);
         mStartClockTimeMs = clock.currentTimeMillis();
-        mStatsFile = null;
         mCheckinFile = null;
         mDailyFile = null;
-        mBatteryStatsHistory = new BatteryStatsHistory(mHistoryBuffer);
+        if (historyDirectory == null) {
+            mStatsFile = null;
+            mBatteryStatsHistory = new BatteryStatsHistory(mHistoryBuffer);
+        } else {
+            mStatsFile = new AtomicFile(new File(historyDirectory, "batterystats.bin"));
+            mBatteryStatsHistory = new BatteryStatsHistory(this, historyDirectory, mHistoryBuffer);
+        }
         mHandler = null;
         mPlatformIdleStateCallback = null;
         mMeasuredEnergyRetriever = null;
@@ -3321,21 +3333,43 @@ public class BatteryStatsImpl extends BatteryStats {
         return kmt;
     }
 
+    /**
+     * Returns the index for the specified tag. If this is the first time the tag is encountered
+     * while writing the current history buffer, the method returns
+     * <code>(index | TAG_FIRST_OCCURRENCE_FLAG)</code>
+     */
     private int writeHistoryTag(HistoryTag tag) {
         Integer idxObj = mHistoryTagPool.get(tag);
         int idx;
         if (idxObj != null) {
             idx = idxObj;
-        } else {
+            if ((idx & TAG_FIRST_OCCURRENCE_FLAG) != 0) {
+                idx &= ~TAG_FIRST_OCCURRENCE_FLAG;
+                mHistoryTagPool.put(tag, idx);
+            }
+            return idx;
+        } else if (mNextHistoryTagIdx < HISTORY_TAG_INDEX_LIMIT) {
             idx = mNextHistoryTagIdx;
             HistoryTag key = new HistoryTag();
             key.setTo(tag);
             tag.poolIdx = idx;
             mHistoryTagPool.put(key, idx);
             mNextHistoryTagIdx++;
-            mNumHistoryTagChars += key.string.length() + 1;
+            final int stringLength = key.string.length();
+
+            if (stringLength > MAX_HISTORY_TAG_STRING_LENGTH) {
+                Slog.wtf(TAG, "Long battery history tag: " + key.string);
+            }
+
+            mNumHistoryTagChars += stringLength + 1;
+            if (mHistoryTags != null) {
+                mHistoryTags.put(idx, key);
+            }
+            return idx | TAG_FIRST_OCCURRENCE_FLAG;
+        } else {
+            // Tag pool overflow: include the tag itself in the parcel
+            return HISTORY_TAG_INDEX_LIMIT | TAG_FIRST_OCCURRENCE_FLAG;
         }
-        return idx;
     }
 
     /*
@@ -3439,6 +3473,10 @@ public class BatteryStatsImpl extends BatteryStats {
     // These upper bits are the frequently changing state bits.
     static final int DELTA_STATE_MASK                       = 0xfe000000;
 
+    // Flag in history tag index: indicates that this is the first occurrence of this tag,
+    // therefore the tag value is written in the parcel
+    static final int TAG_FIRST_OCCURRENCE_FLAG = 0x8000;
+
     // These are the pieces of battery state that are packed in to the upper bits of
     // the state int that have been packed in to the first delta int.  They must fit
     // in STATE_BATTERY_MASK.
@@ -3556,11 +3594,23 @@ public class BatteryStatsImpl extends BatteryStats {
                 wakeReasonIndex = 0xffff;
             }
             dest.writeInt((wakeReasonIndex<<16) | wakeLockIndex);
+            if (cur.wakelockTag != null && (wakeLockIndex & TAG_FIRST_OCCURRENCE_FLAG) != 0) {
+                cur.wakelockTag.writeToParcel(dest, 0);
+                cur.tagsFirstOccurrence = true;
+            }
+            if (cur.wakeReasonTag != null && (wakeReasonIndex & TAG_FIRST_OCCURRENCE_FLAG) != 0) {
+                cur.wakeReasonTag.writeToParcel(dest, 0);
+                cur.tagsFirstOccurrence = true;
+            }
         }
         if (cur.eventCode != HistoryItem.EVENT_NONE) {
-            int index = writeHistoryTag(cur.eventTag);
-            int codeAndIndex = (cur.eventCode&0xffff) | (index<<16);
+            final int index = writeHistoryTag(cur.eventTag);
+            final int codeAndIndex = (cur.eventCode & 0xffff) | (index << 16);
             dest.writeInt(codeAndIndex);
+            if ((index & TAG_FIRST_OCCURRENCE_FLAG) != 0) {
+                cur.eventTag.writeToParcel(dest, 0);
+                cur.tagsFirstOccurrence = true;
+            }
             if (DEBUG) Slog.i(TAG, "WRITE DELTA: event=" + cur.eventCode + " tag=#"
                     + cur.eventTag.poolIdx + " " + cur.eventTag.uid + ":"
                     + cur.eventTag.string);
@@ -3750,6 +3800,7 @@ public class BatteryStatsImpl extends BatteryStats {
         if (mHistoryBufferLastPos >= 0 && mHistoryLastWritten.cmd == HistoryItem.CMD_UPDATE
                 && timeDiffMs < 1000 && (diffStates & lastDiffStates) == 0
                 && (diffStates2&lastDiffStates2) == 0
+                && (!mHistoryLastWritten.tagsFirstOccurrence && !cur.tagsFirstOccurrence)
                 && (mHistoryLastWritten.wakelockTag == null || cur.wakelockTag == null)
                 && (mHistoryLastWritten.wakeReasonTag == null || cur.wakeReasonTag == null)
                 && mHistoryLastWritten.stepDetails == null
@@ -3809,9 +3860,17 @@ public class BatteryStatsImpl extends BatteryStats {
             mHistoryBuffer.setDataPosition(0);
             mHistoryBuffer.setDataCapacity(mConstants.MAX_HISTORY_BUFFER / 2);
             mHistoryBufferLastPos = -1;
+            mHistoryLastWritten.clear();
+            mHistoryLastLastWritten.clear();
+
+            // Mark every entry in the pool with a flag indicating that the tag
+            // has not yet been encountered while writing the current history buffer.
+            for (Map.Entry<HistoryTag, Integer> entry: mHistoryTagPool.entrySet()) {
+                entry.setValue(entry.getValue() | TAG_FIRST_OCCURRENCE_FLAG);
+            }
+            startRecordingHistory(elapsedRealtimeMs, uptimeMs, false);
             HistoryItem newItem = new HistoryItem();
             newItem.setTo(cur);
-            startRecordingHistory(elapsedRealtimeMs, uptimeMs, false);
             addHistoryBufferLocked(elapsedRealtimeMs, HistoryItem.CMD_UPDATE, newItem);
             return;
         }
@@ -3830,7 +3889,9 @@ public class BatteryStatsImpl extends BatteryStats {
         }
         mHistoryBufferLastPos = mHistoryBuffer.dataPosition();
         mHistoryLastLastWritten.setTo(mHistoryLastWritten);
+        final boolean hasTags = mHistoryLastWritten.tagsFirstOccurrence || cur.tagsFirstOccurrence;
         mHistoryLastWritten.setTo(mHistoryBaseTimeMs + elapsedRealtimeMs, cmd, cur);
+        mHistoryLastWritten.tagsFirstOccurrence = hasTags;
         mHistoryLastWritten.states &= mActiveHistoryStates;
         mHistoryLastWritten.states2 &= mActiveHistoryStates2;
         writeHistoryDelta(mHistoryBuffer, mHistoryLastWritten, mHistoryLastLastWritten);
@@ -3839,6 +3900,7 @@ public class BatteryStatsImpl extends BatteryStats {
         cur.wakeReasonTag = null;
         cur.eventCode = HistoryItem.EVENT_NONE;
         cur.eventTag = null;
+        cur.tagsFirstOccurrence = false;
         if (DEBUG_HISTORY) Slog.i(TAG, "Writing history buffer: was " + mHistoryBufferLastPos
                 + " now " + mHistoryBuffer.dataPosition()
                 + " size is now " + mHistoryBuffer.dataSize());
@@ -11281,7 +11343,6 @@ public class BatteryStatsImpl extends BatteryStats {
     @Override
     @UnsupportedAppUsage
     public boolean startIteratingHistoryLocked() {
-        mReadOverflow = false;
         mBatteryStatsHistoryIterator = createBatteryStatsHistoryIterator();
         return true;
     }
@@ -11291,34 +11352,42 @@ public class BatteryStatsImpl extends BatteryStats {
      */
     @VisibleForTesting
     public BatteryStatsHistoryIterator createBatteryStatsHistoryIterator() {
-        ArrayList<HistoryTag> tags = new ArrayList<>(mHistoryTagPool.size());
-        for (Map.Entry<HistoryTag, Integer> entry: mHistoryTagPool.entrySet()) {
-            final HistoryTag tag = entry.getKey();
-            tag.poolIdx = entry.getValue();
-            tags.add(tag);
-        }
-
-        return new BatteryStatsHistoryIterator(mBatteryStatsHistory, tags);
+        return new BatteryStatsHistoryIterator(mBatteryStatsHistory);
     }
 
     @Override
     public int getHistoryStringPoolSize() {
-        return mBatteryStatsHistoryIterator.getHistoryStringPoolSize();
+        return mHistoryTagPool.size();
     }
 
     @Override
     public int getHistoryStringPoolBytes() {
-        return mBatteryStatsHistoryIterator.getHistoryStringPoolBytes();
+        return mNumHistoryTagChars;
     }
 
     @Override
     public String getHistoryTagPoolString(int index) {
-        return mBatteryStatsHistoryIterator.getHistoryTagPoolString(index);
+        ensureHistoryTagArray();
+        HistoryTag historyTag = mHistoryTags.get(index);
+        return historyTag != null ? historyTag.string : null;
     }
 
     @Override
     public int getHistoryTagPoolUid(int index) {
-        return mBatteryStatsHistoryIterator.getHistoryTagPoolUid(index);
+        ensureHistoryTagArray();
+        HistoryTag historyTag = mHistoryTags.get(index);
+        return historyTag != null ? historyTag.uid : Process.INVALID_UID;
+    }
+
+    private void ensureHistoryTagArray() {
+        if (mHistoryTags != null) {
+            return;
+        }
+
+        mHistoryTags = new SparseArray<>(mHistoryTagPool.size());
+        for (Map.Entry<HistoryTag, Integer> entry: mHistoryTagPool.entrySet()) {
+            mHistoryTags.put(entry.getValue(), entry.getKey());
+        }
     }
 
     @Override
diff --git a/core/java/com/android/internal/os/BatteryUsageStatsProvider.java b/core/java/com/android/internal/os/BatteryUsageStatsProvider.java
index e9e489d9ddb7..615ab6367c30 100644
--- a/core/java/com/android/internal/os/BatteryUsageStatsProvider.java
+++ b/core/java/com/android/internal/os/BatteryUsageStatsProvider.java
@@ -31,7 +31,6 @@ import com.android.internal.annotations.VisibleForTesting;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
-import java.util.Map;
 
 /**
  * Uses accumulated battery stats data and PowerCalculators to produce power
@@ -186,16 +185,7 @@ public class BatteryUsageStatsProvider {
             }
 
             BatteryStatsImpl batteryStatsImpl = (BatteryStatsImpl) mStats;
-            ArrayList<BatteryStats.HistoryTag> tags = new ArrayList<>(
-                    batteryStatsImpl.mHistoryTagPool.size());
-            for (Map.Entry<BatteryStats.HistoryTag, Integer> entry :
-                    batteryStatsImpl.mHistoryTagPool.entrySet()) {
-                final BatteryStats.HistoryTag tag = entry.getKey();
-                tag.poolIdx = entry.getValue();
-                tags.add(tag);
-            }
-
-            batteryUsageStatsBuilder.setBatteryHistory(batteryStatsImpl.mHistoryBuffer, tags);
+            batteryUsageStatsBuilder.setBatteryHistory(batteryStatsImpl.mHistoryBuffer);
         }
 
         return batteryUsageStatsBuilder.build();