Tweak RT-animator scheduling

Bug: 18226391

The issue occurs as a result of a dispatchFrame itself
taking longer than 12ms, the alloted budget. The result
is that a vsync request (which occured at the end) would
miss the vsync that occured 1ms prior to the end of the frame.
As a result it would end up waiting for the following vsync,
essentially dropping to 30fps even though 60 could have been
sustained.

Fix this with a few tweaks.
First, adjust the UI thread's delay bias from (now + 4ms) to
(vsync + 4ms), this prevents RT animators from slowly drifting
if the vsync occurs mid-task.
Second, request a vsync preemptively prior to running callbacks.
This way if any callbacks needs the next vsync and it takes
"too long", we will catch that vsync.
Finally, fix an issue where the display event queue was always
drained & rejected at the end of a task loop. Instead, drain
and reject all stale vsyncs. This still prevents the issue of
both UI thread & RT thread trying to drive 2 frames in a single
pulse, but also allows RT to notice that it missed a vsync
pulse it needed and that it should speed-up a bit in response

Change-Id: I9d6be037737e9283297898cac2e3563453e797cd

4 files changed, 22 insertions, 15 deletions

diff --git a/libs/hwui/renderthread/RenderThread.cpp b/libs/hwui/renderthread/RenderThread.cpp
index 38cb4cde6bc2..3e4e9653518c 100644
--- a/libs/hwui/renderthread/RenderThread.cpp
+++ b/libs/hwui/renderthread/RenderThread.cpp
@@ -40,7 +40,7 @@ namespace renderthread {
 static const size_t EVENT_BUFFER_SIZE = 100;
 
 // Slight delay to give the UI time to push us a new frame before we replay
-static const int DISPATCH_FRAME_CALLBACKS_DELAY = 4;
+static const nsecs_t DISPATCH_FRAME_CALLBACKS_DELAY = milliseconds_to_nanoseconds(4);
 
 TaskQueue::TaskQueue() : mHead(0), mTail(0) {}
 
@@ -209,16 +209,16 @@ static nsecs_t latestVsyncEvent(DisplayEventReceiver* receiver) {
     return latest;
 }
 
-void RenderThread::drainDisplayEventQueue(bool skipCallbacks) {
+void RenderThread::drainDisplayEventQueue() {
     ATRACE_CALL();
     nsecs_t vsyncEvent = latestVsyncEvent(mDisplayEventReceiver);
     if (vsyncEvent > 0) {
         mVsyncRequested = false;
-        mTimeLord.vsyncReceived(vsyncEvent);
-        if (!skipCallbacks && !mFrameCallbackTaskPending) {
+        if (mTimeLord.vsyncReceived(vsyncEvent) && !mFrameCallbackTaskPending) {
             ATRACE_NAME("queue mFrameCallbackTask");
             mFrameCallbackTaskPending = true;
-            queueDelayed(mFrameCallbackTask, DISPATCH_FRAME_CALLBACKS_DELAY);
+            nsecs_t runAt = (vsyncEvent + DISPATCH_FRAME_CALLBACKS_DELAY);
+            queueAt(mFrameCallbackTask, runAt);
         }
     }
 }
@@ -230,8 +230,13 @@ void RenderThread::dispatchFrameCallbacks() {
     std::set<IFrameCallback*> callbacks;
     mFrameCallbacks.swap(callbacks);
 
-    for (std::set<IFrameCallback*>::iterator it = callbacks.begin(); it != callbacks.end(); it++) {
-        (*it)->doFrame();
+    if (callbacks.size()) {
+        // Assume one of them will probably animate again so preemptively
+        // request the next vsync in case it occurs mid-frame
+        requestVsync();
+        for (std::set<IFrameCallback*>::iterator it = callbacks.begin(); it != callbacks.end(); it++) {
+            (*it)->doFrame();
+        }
     }
 }
 
@@ -273,7 +278,7 @@ bool RenderThread::threadLoop() {
         }
 
         if (mPendingRegistrationFrameCallbacks.size() && !mFrameCallbackTaskPending) {
-            drainDisplayEventQueue(true);
+            drainDisplayEventQueue();
             mFrameCallbacks.insert(
                     mPendingRegistrationFrameCallbacks.begin(), mPendingRegistrationFrameCallbacks.end());
             mPendingRegistrationFrameCallbacks.clear();
@@ -299,9 +304,8 @@ void RenderThread::queueAtFront(RenderTask* task) {
     mLooper->wake();
 }
 
-void RenderThread::queueDelayed(RenderTask* task, int delayMs) {
-    nsecs_t now = systemTime(SYSTEM_TIME_MONOTONIC);
-    task->mRunAt = now + milliseconds_to_nanoseconds(delayMs);
+void RenderThread::queueAt(RenderTask* task, nsecs_t runAtNs) {
+    task->mRunAt = runAtNs;
     queue(task);
 }
 
diff --git a/libs/hwui/renderthread/RenderThread.h b/libs/hwui/renderthread/RenderThread.h
index 4126d021a281..99c2e1527ea2 100644
--- a/libs/hwui/renderthread/RenderThread.h
+++ b/libs/hwui/renderthread/RenderThread.h
@@ -75,7 +75,7 @@ public:
     // and will delete them after they are run
     ANDROID_API void queue(RenderTask* task);
     ANDROID_API void queueAtFront(RenderTask* task);
-    void queueDelayed(RenderTask* task, int delayMs);
+    void queueAt(RenderTask* task, nsecs_t runAtNs);
     void remove(RenderTask* task);
 
     // Mimics android.view.Choreographer
@@ -103,7 +103,7 @@ private:
     void initThreadLocals();
     void initializeDisplayEventReceiver();
     static int displayEventReceiverCallback(int fd, int events, void* data);
-    void drainDisplayEventQueue(bool skipCallbacks = false);
+    void drainDisplayEventQueue();
     void dispatchFrameCallbacks();
     void requestVsync();
 
diff --git a/libs/hwui/renderthread/TimeLord.cpp b/libs/hwui/renderthread/TimeLord.cpp
index 9bd4eae1ea7c..f18749317ab6 100644
--- a/libs/hwui/renderthread/TimeLord.cpp
+++ b/libs/hwui/renderthread/TimeLord.cpp
@@ -24,10 +24,12 @@ TimeLord::TimeLord()
         , mFrameTimeNanos(0) {
 }
 
-void TimeLord::vsyncReceived(nsecs_t vsync) {
+bool TimeLord::vsyncReceived(nsecs_t vsync) {
     if (vsync > mFrameTimeNanos) {
         mFrameTimeNanos = vsync;
+        return true;
     }
+    return false;
 }
 
 nsecs_t TimeLord::computeFrameTimeMs() {
diff --git a/libs/hwui/renderthread/TimeLord.h b/libs/hwui/renderthread/TimeLord.h
index 8b0372cc2baa..7c155d28feef 100644
--- a/libs/hwui/renderthread/TimeLord.h
+++ b/libs/hwui/renderthread/TimeLord.h
@@ -29,7 +29,8 @@ class RenderThread;
 class TimeLord {
 public:
     void setFrameInterval(nsecs_t intervalNanos) { mFrameIntervalNanos = intervalNanos; }
-    void vsyncReceived(nsecs_t vsync);
+    // returns true if the vsync is newer, false if it was rejected for staleness
+    bool vsyncReceived(nsecs_t vsync);
     nsecs_t computeFrameTimeMs();
 
 private: