[TimeStats] Add callback for layer stats

Bug: 119885568
Test: adb shell cmd stats pull-source 10063
Change-Id: I385c9a49e2c7f98d4dacba6ac399e927c5b0e192
diff --git a/services/surfaceflinger/TimeStats/Android.bp b/services/surfaceflinger/TimeStats/Android.bp
index 7ff2594..d27fbb4 100644
--- a/services/surfaceflinger/TimeStats/Android.bp
+++ b/services/surfaceflinger/TimeStats/Android.bp
@@ -8,6 +8,7 @@
         "libcutils",
         "liblog",
         "libprotobuf-cpp-lite",
+        "libprotoutil",
         "libstatslog",
         "libstatspull",
         "libstatssocket",
@@ -17,6 +18,7 @@
     ],
     export_include_dirs: ["."],
     export_shared_lib_headers: [
+        "libprotoutil",
         "libstatslog",
         "libstatspull",
         "libstatssocket",
diff --git a/services/surfaceflinger/TimeStats/TimeStats.cpp b/services/surfaceflinger/TimeStats/TimeStats.cpp
index 44a59fd..7c824ec 100644
--- a/services/surfaceflinger/TimeStats/TimeStats.cpp
+++ b/services/surfaceflinger/TimeStats/TimeStats.cpp
@@ -24,6 +24,7 @@
 #include "TimeStats.h"
 
 #include <android-base/stringprintf.h>
+#include <android/util/ProtoOutputStream.h>
 #include <log/log.h>
 #include <utils/String8.h>
 #include <utils/Timers.h>
@@ -36,42 +37,134 @@
 
 namespace impl {
 
-status_pull_atom_return_t TimeStats::pullGlobalAtomCallback(int32_t atom_tag,
-                                                            pulled_stats_event_list* data,
-                                                            void* cookie) {
+status_pull_atom_return_t TimeStats::pullAtomCallback(int32_t atom_tag,
+                                                      pulled_stats_event_list* data, void* cookie) {
     impl::TimeStats* timeStats = reinterpret_cast<impl::TimeStats*>(cookie);
-    if (atom_tag != android::util::SURFACEFLINGER_STATS_GLOBAL_INFO) {
-        return STATS_PULL_SKIP;
+    if (atom_tag == android::util::SURFACEFLINGER_STATS_GLOBAL_INFO) {
+        return timeStats->populateGlobalAtom(data);
+    } else if (atom_tag == android::util::SURFACEFLINGER_STATS_LAYER_INFO) {
+        return timeStats->populateLayerAtom(data);
     }
 
-    std::lock_guard<std::mutex> lock(timeStats->mMutex);
+    return STATS_PULL_SKIP;
+}
 
-    const auto& stats = timeStats->mTimeStats;
-    if (stats.statsStart == 0) {
+status_pull_atom_return_t TimeStats::populateGlobalAtom(pulled_stats_event_list* data) {
+    std::lock_guard<std::mutex> lock(mMutex);
+
+    if (mTimeStats.statsStart == 0) {
         return STATS_PULL_SKIP;
     }
-    timeStats->flushPowerTimeLocked();
+    flushPowerTimeLocked();
 
-    struct stats_event* event = timeStats->mStatsDelegate->addStatsEventToPullData(data);
-    timeStats->mStatsDelegate->statsEventSetAtomId(event,
-                                                   android::util::SURFACEFLINGER_STATS_GLOBAL_INFO);
-    timeStats->mStatsDelegate->statsEventWriteInt64(event, stats.totalFrames);
-    timeStats->mStatsDelegate->statsEventWriteInt64(event, stats.missedFrames);
-    timeStats->mStatsDelegate->statsEventWriteInt64(event, stats.clientCompositionFrames);
-    timeStats->mStatsDelegate->statsEventWriteInt64(event, stats.displayOnTime);
-    timeStats->mStatsDelegate->statsEventWriteInt64(event, stats.presentToPresent.totalTime());
-    timeStats->mStatsDelegate->statsEventBuild(event);
-    timeStats->clearGlobalLocked();
+    struct stats_event* event = mStatsDelegate->addStatsEventToPullData(data);
+    mStatsDelegate->statsEventSetAtomId(event, android::util::SURFACEFLINGER_STATS_GLOBAL_INFO);
+    mStatsDelegate->statsEventWriteInt64(event, mTimeStats.totalFrames);
+    mStatsDelegate->statsEventWriteInt64(event, mTimeStats.missedFrames);
+    mStatsDelegate->statsEventWriteInt64(event, mTimeStats.clientCompositionFrames);
+    mStatsDelegate->statsEventWriteInt64(event, mTimeStats.displayOnTime);
+    mStatsDelegate->statsEventWriteInt64(event, mTimeStats.presentToPresent.totalTime());
+    mStatsDelegate->statsEventBuild(event);
+    clearGlobalLocked();
 
     return STATS_PULL_SUCCESS;
 }
 
-TimeStats::TimeStats() : TimeStats(nullptr) {}
+namespace {
+// Histograms align with the order of fields in SurfaceflingerStatsLayerInfo.
+const std::array<std::string, 6> kHistogramNames = {
+        "present2present", "post2present",    "acquire2present",
+        "latch2present",   "desired2present", "post2acquire",
+};
 
-TimeStats::TimeStats(std::unique_ptr<StatsEventDelegate> statsDelegate) {
+std::string histogramToProtoByteString(const std::unordered_map<int32_t, int32_t>& histogram,
+                                       size_t maxPulledHistogramBuckets) {
+    auto buckets = std::vector<std::pair<int32_t, int32_t>>(histogram.begin(), histogram.end());
+    std::sort(buckets.begin(), buckets.end(),
+              [](std::pair<int32_t, int32_t>& left, std::pair<int32_t, int32_t>& right) {
+                  return left.second > right.second;
+              });
+
+    util::ProtoOutputStream proto;
+    int histogramSize = 0;
+    for (const auto& bucket : buckets) {
+        if (++histogramSize > maxPulledHistogramBuckets) {
+            break;
+        }
+        proto.write(android::util::FIELD_TYPE_INT32 | android::util::FIELD_COUNT_REPEATED |
+                            1 /* field id */,
+                    (int32_t)bucket.first);
+        proto.write(android::util::FIELD_TYPE_INT64 | android::util::FIELD_COUNT_REPEATED |
+                            2 /* field id */,
+                    (int64_t)bucket.second);
+    }
+
+    std::string byteString;
+    proto.serializeToString(&byteString);
+    return byteString;
+}
+} // namespace
+
+status_pull_atom_return_t TimeStats::populateLayerAtom(pulled_stats_event_list* data) {
+    std::lock_guard<std::mutex> lock(mMutex);
+
+    std::vector<TimeStatsHelper::TimeStatsLayer const*> dumpStats;
+    for (const auto& ele : mTimeStats.stats) {
+        dumpStats.push_back(&ele.second);
+    }
+
+    std::sort(dumpStats.begin(), dumpStats.end(),
+              [](TimeStatsHelper::TimeStatsLayer const* l,
+                 TimeStatsHelper::TimeStatsLayer const* r) {
+                  return l->totalFrames > r->totalFrames;
+              });
+
+    if (mMaxPulledLayers < dumpStats.size()) {
+        dumpStats.resize(mMaxPulledLayers);
+    }
+
+    for (const auto& layer : dumpStats) {
+        struct stats_event* event = mStatsDelegate->addStatsEventToPullData(data);
+        mStatsDelegate->statsEventSetAtomId(event, android::util::SURFACEFLINGER_STATS_LAYER_INFO);
+        mStatsDelegate->statsEventWriteString8(event, layer->layerName.c_str());
+        mStatsDelegate->statsEventWriteInt64(event, layer->totalFrames);
+        mStatsDelegate->statsEventWriteInt64(event, layer->droppedFrames);
+
+        for (const auto& name : kHistogramNames) {
+            const auto& histogram = layer->deltas.find(name);
+            if (histogram == layer->deltas.cend()) {
+                mStatsDelegate->statsEventWriteByteArray(event, nullptr, 0);
+            } else {
+                std::string bytes = histogramToProtoByteString(histogram->second.hist,
+                                                               mMaxPulledHistogramBuckets);
+                mStatsDelegate->statsEventWriteByteArray(event, (const uint8_t*)bytes.c_str(),
+                                                         bytes.size());
+            }
+        }
+
+        mStatsDelegate->statsEventBuild(event);
+    }
+    clearLayersLocked();
+
+    return STATS_PULL_SUCCESS;
+}
+
+TimeStats::TimeStats() : TimeStats(nullptr, std::nullopt, std::nullopt) {}
+
+TimeStats::TimeStats(std::unique_ptr<StatsEventDelegate> statsDelegate,
+                     std::optional<size_t> maxPulledLayers,
+                     std::optional<size_t> maxPulledHistogramBuckets) {
     if (statsDelegate != nullptr) {
         mStatsDelegate = std::move(statsDelegate);
     }
+
+    if (maxPulledLayers) {
+        mMaxPulledLayers = *maxPulledLayers;
+    }
+
+    if (maxPulledHistogramBuckets) {
+        mMaxPulledHistogramBuckets = *maxPulledHistogramBuckets;
+    }
 }
 
 void TimeStats::onBootFinished() {
@@ -634,7 +727,9 @@
     mTimeStats.statsStart = static_cast<int64_t>(std::time(0));
     mPowerTime.prevTime = systemTime();
     mStatsDelegate->registerStatsPullAtomCallback(android::util::SURFACEFLINGER_STATS_GLOBAL_INFO,
-                                                  TimeStats::pullGlobalAtomCallback, nullptr, this);
+                                                  TimeStats::pullAtomCallback, nullptr, this);
+    mStatsDelegate->registerStatsPullAtomCallback(android::util::SURFACEFLINGER_STATS_LAYER_INFO,
+                                                  TimeStats::pullAtomCallback, nullptr, this);
     ALOGD("Enabled");
 }
 
@@ -649,6 +744,7 @@
     mTimeStats.statsEnd = static_cast<int64_t>(std::time(0));
     mStatsDelegate->unregisterStatsPullAtomCallback(
             android::util::SURFACEFLINGER_STATS_GLOBAL_INFO);
+    mStatsDelegate->unregisterStatsPullAtomCallback(android::util::SURFACEFLINGER_STATS_LAYER_INFO);
     ALOGD("Disabled");
 }
 
diff --git a/services/surfaceflinger/TimeStats/TimeStats.h b/services/surfaceflinger/TimeStats/TimeStats.h
index 5cd421c..cf1c3c6 100644
--- a/services/surfaceflinger/TimeStats/TimeStats.h
+++ b/services/surfaceflinger/TimeStats/TimeStats.h
@@ -165,10 +165,21 @@
             return stats_event_write_int64(event, field);
         }
 
+        virtual void statsEventWriteString8(struct stats_event* event, const char* field) {
+            return stats_event_write_string8(event, field);
+        }
+
+        virtual void statsEventWriteByteArray(struct stats_event* event, const uint8_t* buf,
+                                              size_t numBytes) {
+            return stats_event_write_byte_array(event, buf, numBytes);
+        }
+
         virtual void statsEventBuild(struct stats_event* event) { return stats_event_build(event); }
     };
     // For testing only for injecting custom dependencies.
-    TimeStats(std::unique_ptr<StatsEventDelegate> statsDelegate);
+    TimeStats(std::unique_ptr<StatsEventDelegate> statsDelegate,
+              std::optional<size_t> maxPulledLayers,
+              std::optional<size_t> maxPulledHistogramBuckets);
 
     void onBootFinished() override;
     void parseArgs(bool asProto, const Vector<String16>& args, std::string& result) override;
@@ -207,9 +218,10 @@
     static const size_t MAX_NUM_TIME_RECORDS = 64;
 
 private:
-    static status_pull_atom_return_t pullGlobalAtomCallback(int32_t atom_tag,
-                                                            pulled_stats_event_list* data,
-                                                            void* cookie);
+    static status_pull_atom_return_t pullAtomCallback(int32_t atom_tag,
+                                                      pulled_stats_event_list* data, void* cookie);
+    status_pull_atom_return_t populateGlobalAtom(pulled_stats_event_list* data);
+    status_pull_atom_return_t populateLayerAtom(pulled_stats_event_list* data);
     bool recordReadyLocked(int32_t layerId, TimeRecord* timeRecord);
     void flushAvailableRecordsToStatsLocked(int32_t layerId);
     void flushPowerTimeLocked();
@@ -233,6 +245,8 @@
     static const size_t MAX_NUM_LAYER_RECORDS = 200;
     static const size_t MAX_NUM_LAYER_STATS = 200;
     std::unique_ptr<StatsEventDelegate> mStatsDelegate = std::make_unique<StatsEventDelegate>();
+    size_t mMaxPulledLayers = 8;
+    size_t mMaxPulledHistogramBuckets = 6;
 };
 
 } // namespace impl
diff --git a/services/surfaceflinger/tests/unittests/Android.bp b/services/surfaceflinger/tests/unittests/Android.bp
index e500672..1eaf2dd 100644
--- a/services/surfaceflinger/tests/unittests/Android.bp
+++ b/services/surfaceflinger/tests/unittests/Android.bp
@@ -83,6 +83,7 @@
         "perfetto_trace_protos",
     ],
     shared_libs: [
+        "libprotoutil",
         "libstatssocket",
         "libsurfaceflinger",
         "libtimestats",
diff --git a/services/surfaceflinger/tests/unittests/TimeStatsTest.cpp b/services/surfaceflinger/tests/unittests/TimeStatsTest.cpp
index c667080..5044626 100644
--- a/services/surfaceflinger/tests/unittests/TimeStatsTest.cpp
+++ b/services/surfaceflinger/tests/unittests/TimeStatsTest.cpp
@@ -22,6 +22,7 @@
 #define LOG_TAG "LibSurfaceFlingerUnittests"
 
 #include <TimeStats/TimeStats.h>
+#include <android/util/ProtoOutputStream.h>
 #include <gmock/gmock.h>
 #include <gtest/gtest.h>
 #include <log/log.h>
@@ -41,9 +42,11 @@
 namespace {
 
 using testing::_;
+using testing::AnyNumber;
 using testing::Contains;
 using testing::InSequence;
 using testing::SizeIs;
+using testing::StrEq;
 using testing::UnorderedElementsAre;
 
 // clang-format off
@@ -149,7 +152,7 @@
         }
         void registerStatsPullAtomCallback(int32_t atom_tag, stats_pull_atom_callback_t callback,
                                            pull_atom_metadata*, void* cookie) override {
-            mAtomTag = atom_tag;
+            mAtomTags.push_back(atom_tag);
             mCallback = callback;
             mCookie = cookie;
         }
@@ -161,17 +164,19 @@
         MOCK_METHOD1(unregisterStatsPullAtomCallback, void(int32_t));
         MOCK_METHOD2(statsEventSetAtomId, void(struct stats_event*, uint32_t));
         MOCK_METHOD2(statsEventWriteInt64, void(struct stats_event*, int64_t));
+        MOCK_METHOD2(statsEventWriteString8, void(struct stats_event*, const char*));
+        MOCK_METHOD3(statsEventWriteByteArray, void(struct stats_event*, const uint8_t*, size_t));
         MOCK_METHOD1(statsEventBuild, void(struct stats_event*));
 
         struct stats_event* mEvent = stats_event_obtain();
-        int32_t mAtomTag = 0;
+        std::vector<int32_t> mAtomTags;
         stats_pull_atom_callback_t mCallback = nullptr;
         void* mCookie = nullptr;
     };
-
     FakeStatsEventDelegate* mDelegate = new FakeStatsEventDelegate;
     std::unique_ptr<TimeStats> mTimeStats =
-            std::make_unique<impl::TimeStats>(std::unique_ptr<FakeStatsEventDelegate>(mDelegate));
+            std::make_unique<impl::TimeStats>(std::unique_ptr<FakeStatsEventDelegate>(mDelegate),
+                                              std::nullopt, std::nullopt);
 };
 
 std::string TimeStatsTest::inputCommand(InputCommand cmd, bool useProto) {
@@ -260,10 +265,14 @@
 TEST_F(TimeStatsTest, canEnableAndDisableTimeStats) {
     EXPECT_TRUE(inputCommand(InputCommand::ENABLE, FMT_STRING).empty());
     ASSERT_TRUE(mTimeStats->isEnabled());
-    EXPECT_EQ(android::util::SURFACEFLINGER_STATS_GLOBAL_INFO, mDelegate->mAtomTag);
+    EXPECT_THAT(mDelegate->mAtomTags,
+                UnorderedElementsAre(android::util::SURFACEFLINGER_STATS_GLOBAL_INFO,
+                                     android::util::SURFACEFLINGER_STATS_LAYER_INFO));
 
     EXPECT_CALL(*mDelegate,
                 unregisterStatsPullAtomCallback(android::util::SURFACEFLINGER_STATS_GLOBAL_INFO));
+    EXPECT_CALL(*mDelegate,
+                unregisterStatsPullAtomCallback(android::util::SURFACEFLINGER_STATS_LAYER_INFO));
     EXPECT_TRUE(inputCommand(InputCommand::DISABLE, FMT_STRING).empty());
     ASSERT_FALSE(mTimeStats->isEnabled());
 }
@@ -696,7 +705,9 @@
     mTimeStats->setPresentFenceGlobal(std::make_shared<FenceTime>(3000000));
     mTimeStats->setPresentFenceGlobal(std::make_shared<FenceTime>(5000000));
 
-    EXPECT_EQ(android::util::SURFACEFLINGER_STATS_GLOBAL_INFO, mDelegate->mAtomTag);
+    EXPECT_THAT(mDelegate->mAtomTags,
+                UnorderedElementsAre(android::util::SURFACEFLINGER_STATS_GLOBAL_INFO,
+                                     android::util::SURFACEFLINGER_STATS_LAYER_INFO));
     EXPECT_NE(nullptr, mDelegate->mCallback);
     EXPECT_EQ(mTimeStats.get(), mDelegate->mCookie);
 
@@ -713,7 +724,8 @@
         EXPECT_CALL(*mDelegate, statsEventBuild(mDelegate->mEvent));
     }
     EXPECT_EQ(STATS_PULL_SUCCESS,
-              mDelegate->makePullAtomCallback(mDelegate->mAtomTag, mDelegate->mCookie));
+              mDelegate->makePullAtomCallback(android::util::SURFACEFLINGER_STATS_GLOBAL_INFO,
+                                              mDelegate->mCookie));
 
     SFTimeStatsGlobalProto globalProto;
     ASSERT_TRUE(globalProto.ParseFromString(inputCommand(InputCommand::DUMP_ALL, FMT_PROTO)));
@@ -724,6 +736,266 @@
     EXPECT_EQ(0, globalProto.present_to_present_size());
 }
 
+namespace {
+std::string buildExpectedHistogramBytestring(const std::vector<int32_t>& times,
+                                             const std::vector<int32_t>& frameCounts) {
+    util::ProtoOutputStream proto;
+    for (int i = 0; i < times.size(); i++) {
+        ALOGE("Writing time: %d", times[i]);
+        proto.write(util::FIELD_TYPE_INT32 | util::FIELD_COUNT_REPEATED | 1 /* field id */,
+                    (int32_t)times[i]);
+        ALOGE("Writing count: %d", frameCounts[i]);
+        proto.write(util::FIELD_TYPE_INT64 | util::FIELD_COUNT_REPEATED | 2 /* field id */,
+                    (int64_t)frameCounts[i]);
+    }
+    std::string byteString;
+    proto.serializeToString(&byteString);
+    return byteString;
+}
+
+std::string dumpByteStringHex(const std::string& str) {
+    std::stringstream ss;
+    ss << std::hex;
+    for (const char& c : str) {
+        ss << (int)c << " ";
+    }
+
+    return ss.str();
+}
+
+} // namespace
+
+MATCHER_P2(BytesEq, bytes, size, "") {
+    std::string expected;
+    expected.append((const char*)bytes, size);
+    std::string actual;
+    actual.append((const char*)arg, size);
+
+    *result_listener << "Bytes are not equal! \n";
+    *result_listener << "size: " << size << "\n";
+    *result_listener << "expected: " << dumpByteStringHex(expected).c_str() << "\n";
+    *result_listener << "actual: " << dumpByteStringHex(actual).c_str() << "\n";
+
+    return expected == actual;
+}
+
+TEST_F(TimeStatsTest, layerStatsCallback_pullsAllHistogramsAndClears) {
+    EXPECT_TRUE(inputCommand(InputCommand::ENABLE, FMT_STRING).empty());
+
+    mTimeStats->onBootFinished();
+
+    insertTimeRecord(NORMAL_SEQUENCE, LAYER_ID_0, 1, 1000000);
+    insertTimeRecord(NORMAL_SEQUENCE, LAYER_ID_0, 2, 2000000);
+
+    EXPECT_THAT(mDelegate->mAtomTags,
+                UnorderedElementsAre(android::util::SURFACEFLINGER_STATS_GLOBAL_INFO,
+                                     android::util::SURFACEFLINGER_STATS_LAYER_INFO));
+    EXPECT_NE(nullptr, mDelegate->mCallback);
+    EXPECT_EQ(mTimeStats.get(), mDelegate->mCookie);
+
+    std::string expectedPresentToPresent = buildExpectedHistogramBytestring({1}, {1});
+    std::string expectedPostToPresent = buildExpectedHistogramBytestring({4}, {1});
+    std::string expectedAcquireToPresent = buildExpectedHistogramBytestring({3}, {1});
+    std::string expectedLatchToPresent = buildExpectedHistogramBytestring({2}, {1});
+    std::string expectedDesiredToPresent = buildExpectedHistogramBytestring({1}, {1});
+    std::string expectedPostToAcquire = buildExpectedHistogramBytestring({1}, {1});
+    {
+        InSequence seq;
+        EXPECT_CALL(*mDelegate,
+                    statsEventSetAtomId(mDelegate->mEvent,
+                                        android::util::SURFACEFLINGER_STATS_LAYER_INFO));
+        EXPECT_CALL(*mDelegate,
+                    statsEventWriteString8(mDelegate->mEvent,
+                                           StrEq(genLayerName(LAYER_ID_0).c_str())));
+        EXPECT_CALL(*mDelegate, statsEventWriteInt64(mDelegate->mEvent, 1));
+        EXPECT_CALL(*mDelegate, statsEventWriteInt64(mDelegate->mEvent, 0));
+        EXPECT_CALL(*mDelegate,
+                    statsEventWriteByteArray(mDelegate->mEvent,
+                                             BytesEq((const uint8_t*)
+                                                             expectedPresentToPresent.c_str(),
+                                                     expectedPresentToPresent.size()),
+                                             expectedPresentToPresent.size()));
+        EXPECT_CALL(*mDelegate,
+                    statsEventWriteByteArray(mDelegate->mEvent,
+                                             BytesEq((const uint8_t*)expectedPostToPresent.c_str(),
+                                                     expectedPostToPresent.size()),
+                                             expectedPostToPresent.size()));
+        EXPECT_CALL(*mDelegate,
+                    statsEventWriteByteArray(mDelegate->mEvent,
+                                             BytesEq((const uint8_t*)
+                                                             expectedAcquireToPresent.c_str(),
+                                                     expectedAcquireToPresent.size()),
+                                             expectedAcquireToPresent.size()));
+        EXPECT_CALL(*mDelegate,
+                    statsEventWriteByteArray(mDelegate->mEvent,
+                                             BytesEq((const uint8_t*)expectedLatchToPresent.c_str(),
+                                                     expectedLatchToPresent.size()),
+                                             expectedLatchToPresent.size()));
+        EXPECT_CALL(*mDelegate,
+                    statsEventWriteByteArray(mDelegate->mEvent,
+                                             BytesEq((const uint8_t*)
+                                                             expectedDesiredToPresent.c_str(),
+                                                     expectedDesiredToPresent.size()),
+                                             expectedDesiredToPresent.size()));
+        EXPECT_CALL(*mDelegate,
+                    statsEventWriteByteArray(mDelegate->mEvent,
+                                             BytesEq((const uint8_t*)expectedPostToAcquire.c_str(),
+                                                     expectedPostToAcquire.size()),
+                                             expectedPostToAcquire.size()));
+        EXPECT_CALL(*mDelegate, statsEventBuild(mDelegate->mEvent));
+    }
+    EXPECT_EQ(STATS_PULL_SUCCESS,
+              mDelegate->makePullAtomCallback(android::util::SURFACEFLINGER_STATS_LAYER_INFO,
+                                              mDelegate->mCookie));
+
+    SFTimeStatsGlobalProto globalProto;
+    ASSERT_TRUE(globalProto.ParseFromString(inputCommand(InputCommand::DUMP_ALL, FMT_PROTO)));
+
+    EXPECT_EQ(0, globalProto.stats_size());
+}
+
+TEST_F(TimeStatsTest, layerStatsCallback_pullsMultipleLayers) {
+    EXPECT_TRUE(inputCommand(InputCommand::ENABLE, FMT_STRING).empty());
+
+    mTimeStats->onBootFinished();
+
+    insertTimeRecord(NORMAL_SEQUENCE, LAYER_ID_0, 1, 1000000);
+    insertTimeRecord(NORMAL_SEQUENCE, LAYER_ID_0, 2, 2000000);
+    insertTimeRecord(NORMAL_SEQUENCE, LAYER_ID_1, 1, 2000000);
+    insertTimeRecord(NORMAL_SEQUENCE, LAYER_ID_1, 2, 3000000);
+
+    EXPECT_THAT(mDelegate->mAtomTags,
+                UnorderedElementsAre(android::util::SURFACEFLINGER_STATS_GLOBAL_INFO,
+                                     android::util::SURFACEFLINGER_STATS_LAYER_INFO));
+    EXPECT_NE(nullptr, mDelegate->mCallback);
+    EXPECT_EQ(mTimeStats.get(), mDelegate->mCookie);
+
+    EXPECT_CALL(*mDelegate,
+                statsEventSetAtomId(mDelegate->mEvent,
+                                    android::util::SURFACEFLINGER_STATS_LAYER_INFO))
+            .Times(2);
+    EXPECT_CALL(*mDelegate,
+                statsEventWriteString8(mDelegate->mEvent, StrEq(genLayerName(LAYER_ID_0).c_str())));
+    EXPECT_CALL(*mDelegate,
+                statsEventWriteString8(mDelegate->mEvent, StrEq(genLayerName(LAYER_ID_1).c_str())));
+    EXPECT_EQ(STATS_PULL_SUCCESS,
+              mDelegate->makePullAtomCallback(android::util::SURFACEFLINGER_STATS_LAYER_INFO,
+                                              mDelegate->mCookie));
+}
+
+TEST_F(TimeStatsTest, layerStatsCallback_pullsMultipleBuckets) {
+    EXPECT_TRUE(inputCommand(InputCommand::ENABLE, FMT_STRING).empty());
+
+    mTimeStats->onBootFinished();
+
+    insertTimeRecord(NORMAL_SEQUENCE, LAYER_ID_0, 1, 1000000);
+    insertTimeRecord(NORMAL_SEQUENCE, LAYER_ID_0, 2, 2000000);
+    insertTimeRecord(NORMAL_SEQUENCE, LAYER_ID_0, 3, 4000000);
+    insertTimeRecord(NORMAL_SEQUENCE, LAYER_ID_0, 4, 5000000);
+
+    // Now make sure that TimeStats flushes global stats to register the
+    // callback.
+    mTimeStats->setPowerMode(HWC_POWER_MODE_NORMAL);
+    mTimeStats->setPresentFenceGlobal(std::make_shared<FenceTime>(3000000));
+    mTimeStats->setPresentFenceGlobal(std::make_shared<FenceTime>(5000000));
+    EXPECT_THAT(mDelegate->mAtomTags,
+                UnorderedElementsAre(android::util::SURFACEFLINGER_STATS_GLOBAL_INFO,
+                                     android::util::SURFACEFLINGER_STATS_LAYER_INFO));
+    EXPECT_NE(nullptr, mDelegate->mCallback);
+    EXPECT_EQ(mTimeStats.get(), mDelegate->mCookie);
+
+    EXPECT_THAT(mDelegate->mAtomTags,
+                UnorderedElementsAre(android::util::SURFACEFLINGER_STATS_GLOBAL_INFO,
+                                     android::util::SURFACEFLINGER_STATS_LAYER_INFO));
+    std::string expectedPresentToPresent = buildExpectedHistogramBytestring({1, 2}, {2, 1});
+    {
+        InSequence seq;
+        EXPECT_CALL(*mDelegate,
+                    statsEventWriteByteArray(mDelegate->mEvent,
+                                             BytesEq((const uint8_t*)
+                                                             expectedPresentToPresent.c_str(),
+                                                     expectedPresentToPresent.size()),
+                                             expectedPresentToPresent.size()));
+        EXPECT_CALL(*mDelegate, statsEventWriteByteArray(mDelegate->mEvent, _, _))
+                .Times(AnyNumber());
+    }
+    EXPECT_EQ(STATS_PULL_SUCCESS,
+              mDelegate->makePullAtomCallback(android::util::SURFACEFLINGER_STATS_LAYER_INFO,
+                                              mDelegate->mCookie));
+}
+
+TEST_F(TimeStatsTest, layerStatsCallback_limitsHistogramBuckets) {
+    mDelegate = new FakeStatsEventDelegate;
+    mTimeStats =
+            std::make_unique<impl::TimeStats>(std::unique_ptr<FakeStatsEventDelegate>(mDelegate),
+                                              std::nullopt, 1);
+    EXPECT_TRUE(inputCommand(InputCommand::ENABLE, FMT_STRING).empty());
+
+    mTimeStats->onBootFinished();
+
+    insertTimeRecord(NORMAL_SEQUENCE, LAYER_ID_0, 1, 1000000);
+    insertTimeRecord(NORMAL_SEQUENCE, LAYER_ID_0, 2, 2000000);
+    insertTimeRecord(NORMAL_SEQUENCE, LAYER_ID_0, 3, 4000000);
+    insertTimeRecord(NORMAL_SEQUENCE, LAYER_ID_0, 4, 5000000);
+
+    EXPECT_THAT(mDelegate->mAtomTags,
+                UnorderedElementsAre(android::util::SURFACEFLINGER_STATS_GLOBAL_INFO,
+                                     android::util::SURFACEFLINGER_STATS_LAYER_INFO));
+    EXPECT_NE(nullptr, mDelegate->mCallback);
+    EXPECT_EQ(mTimeStats.get(), mDelegate->mCookie);
+
+    EXPECT_THAT(mDelegate->mAtomTags,
+                UnorderedElementsAre(android::util::SURFACEFLINGER_STATS_GLOBAL_INFO,
+                                     android::util::SURFACEFLINGER_STATS_LAYER_INFO));
+    std::string expectedPresentToPresent = buildExpectedHistogramBytestring({1}, {2});
+    {
+        InSequence seq;
+        EXPECT_CALL(*mDelegate,
+                    statsEventWriteByteArray(mDelegate->mEvent,
+                                             BytesEq((const uint8_t*)
+                                                             expectedPresentToPresent.c_str(),
+                                                     expectedPresentToPresent.size()),
+                                             expectedPresentToPresent.size()));
+        EXPECT_CALL(*mDelegate, statsEventWriteByteArray(mDelegate->mEvent, _, _))
+                .Times(AnyNumber());
+    }
+    EXPECT_EQ(STATS_PULL_SUCCESS,
+              mDelegate->makePullAtomCallback(android::util::SURFACEFLINGER_STATS_LAYER_INFO,
+                                              mDelegate->mCookie));
+}
+
+TEST_F(TimeStatsTest, layerStatsCallback_limitsLayers) {
+    mDelegate = new FakeStatsEventDelegate;
+    mTimeStats =
+            std::make_unique<impl::TimeStats>(std::unique_ptr<FakeStatsEventDelegate>(mDelegate), 1,
+                                              std::nullopt);
+    EXPECT_TRUE(inputCommand(InputCommand::ENABLE, FMT_STRING).empty());
+
+    mTimeStats->onBootFinished();
+
+    insertTimeRecord(NORMAL_SEQUENCE, LAYER_ID_0, 1, 1000000);
+    insertTimeRecord(NORMAL_SEQUENCE, LAYER_ID_0, 2, 2000000);
+    insertTimeRecord(NORMAL_SEQUENCE, LAYER_ID_1, 1, 2000000);
+    insertTimeRecord(NORMAL_SEQUENCE, LAYER_ID_1, 2, 3000000);
+    insertTimeRecord(NORMAL_SEQUENCE, LAYER_ID_1, 4, 5000000);
+
+    EXPECT_THAT(mDelegate->mAtomTags,
+                UnorderedElementsAre(android::util::SURFACEFLINGER_STATS_GLOBAL_INFO,
+                                     android::util::SURFACEFLINGER_STATS_LAYER_INFO));
+    EXPECT_NE(nullptr, mDelegate->mCallback);
+    EXPECT_EQ(mTimeStats.get(), mDelegate->mCookie);
+
+    EXPECT_CALL(*mDelegate,
+                statsEventSetAtomId(mDelegate->mEvent,
+                                    android::util::SURFACEFLINGER_STATS_LAYER_INFO))
+            .Times(1);
+    EXPECT_CALL(*mDelegate,
+                statsEventWriteString8(mDelegate->mEvent, StrEq(genLayerName(LAYER_ID_1).c_str())));
+    EXPECT_EQ(STATS_PULL_SUCCESS,
+              mDelegate->makePullAtomCallback(android::util::SURFACEFLINGER_STATS_LAYER_INFO,
+                                              mDelegate->mCookie));
+}
+
 TEST_F(TimeStatsTest, canSurviveMonkey) {
     if (g_noSlowTests) {
         GTEST_SKIP();