Coalesce input events that arrive faster than 333Hz.

Some drivers report individual finger updates one at a time
instead of all at once.  When 10 fingers are down, this can
cause the framework to have to handle 10 times as many events
each with 10 times as much data.  Applications like
PointerLocation would get significantly bogged down by all
of the redundant samples.

This change coalesces samples that are closely spaced in time,
before they are dispatched, as part of the motion event batching
protocol.

Increased the size of the InputChannel shared memory buffer so
that applications can catch up faster if they accumulate a
backlog of samples.

Added logging code to help measure input dispatch and drawing
latency issues in the view hierarchy.  See ViewDebug.DEBUG_LATENCY.

Change-Id: Ia5898f781f19901d2225c529a910c32bdf4f504f

3 files changed, 101 insertions, 21 deletions

diff --git a/services/input/EventHub.cpp b/services/input/EventHub.cpp
index 9a9d9e5..ff4b11a 100644
--- a/services/input/EventHub.cpp
+++ b/services/input/EventHub.cpp
@@ -539,7 +539,24 @@ size_t EventHub::getEvents(int timeoutMillis, RawEvent* buffer, size_t bufferSiz
                                 (int) iev.time.tv_sec, (int) iev.time.tv_usec,
                                 iev.type, iev.code, iev.value);
 
+#ifdef HAVE_POSIX_CLOCKS
+                        // Use the time specified in the event instead of the current time
+                        // so that downstream code can get more accurate estimates of
+                        // event dispatch latency from the time the event is enqueued onto
+                        // the evdev client buffer.
+                        //
+                        // The event's timestamp fortuitously uses the same monotonic clock
+                        // time base as the rest of Android.  The kernel event device driver
+                        // (drivers/input/evdev.c) obtains timestamps using ktime_get_ts().
+                        // The systemTime(SYSTEM_TIME_MONOTONIC) function we use everywhere
+                        // calls clock_gettime(CLOCK_MONOTONIC) which is implemented as a
+                        // system call that also queries ktime_get_ts().
+                        event->when = nsecs_t(iev.time.tv_sec) * 1000000000LL
+                                + nsecs_t(iev.time.tv_usec) * 1000LL;
+                        LOGV("event time %lld, now %lld", event->when, now);
+#else
                         event->when = now;
+#endif
                         event->deviceId = deviceId;
                         event->type = iev.type;
                         event->scanCode = iev.code;
diff --git a/services/input/InputDispatcher.cpp b/services/input/InputDispatcher.cpp
index 810b709..46de933 100644
--- a/services/input/InputDispatcher.cpp
+++ b/services/input/InputDispatcher.cpp
@@ -79,6 +79,22 @@ const nsecs_t APP_SWITCH_TIMEOUT = 500 * 1000000LL; // 0.5sec
 // before considering it stale and dropping it.
 const nsecs_t STALE_EVENT_TIMEOUT = 10000 * 1000000LL; // 10sec
 
+// Motion samples that are received within this amount of time are simply coalesced
+// when batched instead of being appended.  This is done because some drivers update
+// the location of pointers one at a time instead of all at once.
+// For example, when there are 10 fingers down, the input dispatcher may receive 10
+// samples in quick succession with only one finger's location changed in each sample.
+//
+// This value effectively imposes an upper bound on the touch sampling rate.
+// Touch sensors typically have a 50Hz - 200Hz sampling rate, so we expect distinct
+// samples to become available 5-20ms apart but individual finger reports can trickle
+// in over a period of 2-4ms or so.
+//
+// Empirical testing shows that a 2ms coalescing interval (500Hz) is not enough,
+// a 3ms coalescing interval (333Hz) works well most of the time and doesn't introduce
+// significant quantization noise on current hardware.
+const nsecs_t MOTION_SAMPLE_COALESCE_INTERVAL = 3 * 1000000LL; // 3ms, 333Hz
+
 
 static inline nsecs_t now() {
     return systemTime(SYSTEM_TIME_MONOTONIC);
@@ -2505,21 +2521,15 @@ void InputDispatcher::notifyMotion(nsecs_t eventTime, int32_t deviceId, uint32_t
                     continue;
                 }
 
-                if (motionEntry->action != action
-                        || motionEntry->pointerCount != pointerCount
-                        || motionEntry->isInjected()) {
+                if (!motionEntry->canAppendSamples(action, pointerCount, pointerIds)) {
                     // Last motion event in the queue for this device and source is
                     // not compatible for appending new samples.  Stop here.
                     goto NoBatchingOrStreaming;
                 }
 
-                // The last motion event is a move and is compatible for appending.
                 // Do the batching magic.
-                mAllocator.appendMotionSample(motionEntry, eventTime, pointerCoords);
-#if DEBUG_BATCHING
-                LOGD("Appended motion sample onto batch for most recent "
-                        "motion event for this device in the inbound queue.");
-#endif
+                batchMotionLocked(motionEntry, eventTime, metaState, pointerCoords,
+                        "most recent motion event for this device and source in the inbound queue");
                 mLock.unlock();
                 return; // done!
             }
@@ -2534,19 +2544,15 @@ void InputDispatcher::notifyMotion(nsecs_t eventTime, int32_t deviceId, uint32_t
                     && mPendingEvent->type == EventEntry::TYPE_MOTION) {
                 MotionEntry* motionEntry = static_cast<MotionEntry*>(mPendingEvent);
                 if (motionEntry->deviceId == deviceId && motionEntry->source == source) {
-                    if (motionEntry->action != action
-                            || motionEntry->pointerCount != pointerCount
-                            || motionEntry->isInjected()) {
-                        // Pending event is not compatible for appending new samples.  Stop here.
+                    if (!motionEntry->canAppendSamples(action, pointerCount, pointerIds)) {
+                        // Pending motion event is for this device and source but it is
+                        // not compatible for appending new samples.  Stop here.
                         goto NoBatchingOrStreaming;
                     }
 
-                    // The pending motion event is a move and is compatible for appending.
                     // Do the batching magic.
-                    mAllocator.appendMotionSample(motionEntry, eventTime, pointerCoords);
-#if DEBUG_BATCHING
-                    LOGD("Appended motion sample onto batch for the pending motion event.");
-#endif
+                    batchMotionLocked(motionEntry, eventTime, metaState, pointerCoords,
+                            "pending motion event");
                     mLock.unlock();
                     return; // done!
                 }
@@ -2629,7 +2635,7 @@ void InputDispatcher::notifyMotion(nsecs_t eventTime, int32_t deviceId, uint32_t
                     mAllocator.appendMotionSample(motionEntry, eventTime, pointerCoords);
 #if DEBUG_BATCHING
                     LOGD("Appended motion sample onto batch for most recently dispatched "
-                            "motion event for this device in the outbound queues.  "
+                            "motion event for this device and source in the outbound queues.  "
                             "Attempting to stream the motion sample.");
 #endif
                     nsecs_t currentTime = now();
@@ -2660,6 +2666,36 @@ NoBatchingOrStreaming:;
     }
 }
 
+void InputDispatcher::batchMotionLocked(MotionEntry* entry, nsecs_t eventTime,
+        int32_t metaState, const PointerCoords* pointerCoords, const char* eventDescription) {
+    // Combine meta states.
+    entry->metaState |= metaState;
+
+    // Coalesce this sample if not enough time has elapsed since the last sample was
+    // initially appended to the batch.
+    MotionSample* lastSample = entry->lastSample;
+    long interval = eventTime - lastSample->eventTimeBeforeCoalescing;
+    if (interval <= MOTION_SAMPLE_COALESCE_INTERVAL) {
+        uint32_t pointerCount = entry->pointerCount;
+        for (uint32_t i = 0; i < pointerCount; i++) {
+            lastSample->pointerCoords[i].copyFrom(pointerCoords[i]);
+        }
+        lastSample->eventTime = eventTime;
+#if DEBUG_BATCHING
+        LOGD("Coalesced motion into last sample of batch for %s, events were %0.3f ms apart",
+                eventDescription, interval * 0.000001f);
+#endif
+        return;
+    }
+
+    // Append the sample.
+    mAllocator.appendMotionSample(entry, eventTime, pointerCoords);
+#if DEBUG_BATCHING
+    LOGD("Appended motion sample onto batch for %s, events were %0.3f ms apart",
+            eventDescription, interval * 0.000001f);
+#endif
+}
+
 void InputDispatcher::notifySwitch(nsecs_t when, int32_t switchCode, int32_t switchValue,
         uint32_t policyFlags) {
 #if DEBUG_INBOUND_EVENT_DETAILS
@@ -3755,6 +3791,7 @@ InputDispatcher::MotionEntry* InputDispatcher::Allocator::obtainMotionEntry(nsec
     entry->downTime = downTime;
     entry->pointerCount = pointerCount;
     entry->firstSample.eventTime = eventTime;
+    entry->firstSample.eventTimeBeforeCoalescing = eventTime;
     entry->firstSample.next = NULL;
     entry->lastSample = & entry->firstSample;
     for (uint32_t i = 0; i < pointerCount; i++) {
@@ -3864,6 +3901,7 @@ void InputDispatcher::Allocator::appendMotionSample(MotionEntry* motionEntry,
         nsecs_t eventTime, const PointerCoords* pointerCoords) {
     MotionSample* sample = mMotionSamplePool.alloc();
     sample->eventTime = eventTime;
+    sample->eventTimeBeforeCoalescing = eventTime;
     uint32_t pointerCount = motionEntry->pointerCount;
     for (uint32_t i = 0; i < pointerCount; i++) {
         sample->pointerCoords[i].copyFrom(pointerCoords[i]);
@@ -3893,6 +3931,21 @@ uint32_t InputDispatcher::MotionEntry::countSamples() const {
     return count;
 }
 
+bool InputDispatcher::MotionEntry::canAppendSamples(int32_t action, uint32_t pointerCount,
+        const int32_t* pointerIds) const {
+    if (this->action != action
+            || this->pointerCount != pointerCount
+            || this->isInjected()) {
+        return false;
+    }
+    for (uint32_t i = 0; i < pointerCount; i++) {
+        if (this->pointerIds[i] != pointerIds[i]) {
+            return false;
+        }
+    }
+    return true;
+}
+
 
 // --- InputDispatcher::InputState ---
 
diff --git a/services/input/InputDispatcher.h b/services/input/InputDispatcher.h
index 162e606..af0153b 100644
--- a/services/input/InputDispatcher.h
+++ b/services/input/InputDispatcher.h
@@ -409,7 +409,7 @@ private:
 
         bool dispatchInProgress; // initially false, set to true while dispatching
 
-        inline bool isInjected() { return injectionState != NULL; }
+        inline bool isInjected() const { return injectionState != NULL; }
     };
 
     struct ConfigurationChangedEntry : EventEntry {
@@ -439,7 +439,8 @@ private:
     struct MotionSample {
         MotionSample* next;
 
-        nsecs_t eventTime;
+        nsecs_t eventTime; // may be updated during coalescing
+        nsecs_t eventTimeBeforeCoalescing; // not updated during coalescing
         PointerCoords pointerCoords[MAX_POINTERS];
     };
 
@@ -461,6 +462,10 @@ private:
         MotionSample* lastSample;
 
         uint32_t countSamples() const;
+
+        // Checks whether we can append samples, assuming the device id and source are the same.
+        bool canAppendSamples(int32_t action, uint32_t pointerCount,
+                const int32_t* pointerIds) const;
     };
 
     // Tracks the progress of dispatching a particular event to a particular connection.
@@ -802,6 +807,11 @@ private:
     void dispatchOnceInnerLocked(nsecs_t keyRepeatTimeout, nsecs_t keyRepeatDelay,
             nsecs_t* nextWakeupTime);
 
+    // Batches a new sample onto a motion entry.
+    // Assumes that the we have already checked that we can append samples.
+    void batchMotionLocked(MotionEntry* entry, nsecs_t eventTime, int32_t metaState,
+            const PointerCoords* pointerCoords, const char* eventDescription);
+
     // Enqueues an inbound event.  Returns true if mLooper->wake() should be called.
     bool enqueueInboundEventLocked(EventEntry* entry);