cc: Always try to fill the upload queue.

cc/CCTextureUpdateController.cpp

Index: cc/CCTextureUpdateController.cpp
diff --git a/cc/CCTextureUpdateController.cpp b/cc/CCTextureUpdateController.cpp
index 200948da6b8522c1320df3e4d1e538c152389bca..7e0800142eca6416a082319984661bcc1f64969f 100644
--- a/cc/CCTextureUpdateController.cpp
+++ b/cc/CCTextureUpdateController.cpp
@@ -16,7 +16,7 @@
 namespace {
 
 // Number of partial updates we allow.
-static const size_t partialTextureUpdatesMax = 12;
+static const int partialTextureUpdatesMax = 12;
 
 // Measured in seconds.
 static const double textureUpdateTickRate = 0.004;
@@ -28,31 +28,28 @@ static const double uploaderBusyTickRate = 0.001;
 static const int textureUploadFlushPeriod = 4;
 
 // Number of blocking update intervals to allow.
-static const size_t maxBlockingUpdateIntervals = 4;
+static const double maxBlockingUpdateIntervals = 4;
+
+// We will upload this many intervals worth of textures initially
+// then attempt to keep at least this many intervals queued.
+static const double targetBlockingUpdateIntervals = 2;
 
 } // anonymous namespace
 
 namespace cc {
 
-size_t CCTextureUpdateController::maxPartialTextureUpdates()
+int CCTextureUpdateController::maxPartialTextureUpdates()
 {
     return partialTextureUpdatesMax;
 }
 
-size_t CCTextureUpdateController::maxFullUpdatesPerTick(TextureUploader* uploader)
-{
-    double texturesPerSecond = uploader->estimatedTexturesPerSecond();
-    size_t texturesPerTick = floor(textureUpdateTickRate * texturesPerSecond);
-    return texturesPerTick ? texturesPerTick : 1;
-}
-
 CCTextureUpdateController::CCTextureUpdateController(CCTextureUpdateControllerClient* client, CCThread* thread, PassOwnPtr<CCTextureUpdateQueue> queue, CCResourceProvider* resourceProvider, TextureUploader* uploader)
     : m_client(client)
     , m_timer(adoptPtr(new CCTimer(thread, this)))
     , m_queue(queue)
     , m_resourceProvider(resourceProvider)
     , m_uploader(uploader)
-    , m_textureUpdatesPerTick(maxFullUpdatesPerTick(uploader))
+    , m_estimatedTexturesPerSecond(uploader->estimatedTexturesPerSecond())
     , m_firstUpdateAttempt(true)
 {
 }
@@ -81,7 +78,7 @@ void CCTextureUpdateController::performMoreUpdates(
 
         m_firstUpdateAttempt = false;
     } else
-        updateMoreTexturesNow();
+        updateMoreTexturesNow(updateMoreTexturesSize());
 }
 
 void CCTextureUpdateController::discardUploadsToEvictedResources()
@@ -91,7 +88,7 @@ void CCTextureUpdateController::discardUploadsToEvictedResources()
 
 void CCTextureUpdateController::finalize()
 {
-    size_t uploadCount = 0;
+    int uploadCount = 0;
     while (m_queue->fullUploadSize()) {
         if (!(uploadCount % textureUploadFlushPeriod) && uploadCount)
             m_resourceProvider->shallowFlushIfSupported();
@@ -142,49 +139,80 @@ base::TimeDelta CCTextureUpdateController::updateMoreTexturesTime() const
     return base::TimeDelta::FromMilliseconds(textureUpdateTickRate * 1000);
 }
 
-size_t CCTextureUpdateController::updateMoreTexturesSize() const
+int CCTextureUpdateController::updateMoreTexturesSize() const
 {
-    return m_textureUpdatesPerTick;
+    return m_estimatedTexturesPerSecond * textureUpdateTickRate;
 }
 
-size_t CCTextureUpdateController::maxBlockingUpdates() const
+int CCTextureUpdateController::maxBlockingUploads() const
 {
     return updateMoreTexturesSize() * maxBlockingUpdateIntervals;
 }
 
+int CCTextureUpdateController::targetBlockingUploads() const
+{
+    return updateMoreTexturesSize() * targetBlockingUpdateIntervals;
+}
+
+int CCTextureUpdateController::maxTexturesBeforeTimeLimit()
+{
+    if (m_timeLimit.is_null())
+        return std::numeric_limits<int>::max();
+
+    return m_estimatedTexturesPerSecond *
+           (m_timeLimit - this->now()).InSecondsF();
+}
+
 bool CCTextureUpdateController::updateMoreTexturesIfEnoughTimeRemaining()
 {
+    if (!m_queue->fullUploadSize())
+        return false;
+
     // Blocking uploads will increase when we're too aggressive in our upload
     // time estimate. We use a different timeout here to prevent unnecessary
     // amounts of idle time when blocking uploads have reached the max.
-    if (m_uploader->numBlockingUploads() >= maxBlockingUpdates()) {
+    int numBlockingUploads = m_uploader->numBlockingUploads();
+    if (numBlockingUploads >= maxBlockingUploads()) {
         m_timer->startOneShot(uploaderBusyTickRate);
         return true;
     }
 
-    if (!m_queue->fullUploadSize())
-        return false;
+    int maxTextures = 0;
+    bool highLatencyMode = numBlockingUploads >= targetBlockingUploads();
+    if (highLatencyMode) {
+        // If we are in a high latency mode, we do not have enough feedback
+        // so we blindly upload the estimated number of textures.
+        maxTextures = updateMoreTexturesSize();
+    } else {
+        // If we are in a low latency mode, we can throttle our uploads
+        // to a well defined target.
+        maxTextures = targetBlockingUploads() - numBlockingUploads;
+    }
 
-    bool hasTimeRemaining = m_timeLimit.is_null() ||
-        this->now() < m_timeLimit - updateMoreTexturesTime();
-    if (hasTimeRemaining)
-        updateMoreTexturesNow();
+    // Make sure our texture uploads don't block drawing.
+    maxTextures = std::min(maxTextures, maxTexturesBeforeTimeLimit());
 
-    return true;
+    updateMoreTexturesNow(maxTextures);
+    return m_queue->fullUploadSize();
 }
 
-void CCTextureUpdateController::updateMoreTexturesNow()
+void CCTextureUpdateController::updateMoreTexturesNow(int maxTextures)
 {
-    size_t uploads = std::min(
-        m_queue->fullUploadSize(), updateMoreTexturesSize());
-    m_timer->startOneShot(
-        updateMoreTexturesTime().InSecondsF() / updateMoreTexturesSize() *
-        uploads);
+    int uploads = std::min((int)m_queue->fullUploadSize(), maxTextures);
+    ASSERT(uploads >= 0);
 
-    if (!uploads)
+    if (uploads <= 0) {
+        m_timer->startOneShot(uploaderBusyTickRate);
         return;
+    } else if (uploads == m_queue->fullUploadSize()) {
+        m_timer->startOneShot(
+            updateMoreTexturesTime().InSecondsF() / updateMoreTexturesSize() *
+            uploads);
+    } else {
+        m_timer->startOneShot(updateMoreTexturesTime().InSecondsF());
+    }
 
-    size_t uploadCount = 0;
+    int uploadCount = 0;
     while (m_queue->fullUploadSize() && uploadCount < uploads) {
         if (!(uploadCount % textureUploadFlushPeriod) && uploadCount)
             m_resourceProvider->shallowFlushIfSupported();