SurfaceFlinger: Do less work when using PTS

Currently, SurfaceFlinger is very dumb about how it handles buffer
updates at less than 60fps. If there is a new frame pending, but its
timestamp says not to present it until later SurfaceFlinger will wake
up every vsync until it is time to present it. Even worse, if
SurfaceFlinger has woken up but nothing has changed, it still goes
through the entire composition process.

This change (mostly) fixes that inefficiency. SurfaceFlinger will
still wake up every refresh period while there is a new frame
pending, but if there is no work to do, it will almost immediately go
back to sleep.

Bug: 18111837
Change-Id: I7825bacd37f40bf26edcc6a5e0f051dce45291fb

services/surfaceflinger/Layer.cpp

@@ -34,6 +34,7 @@
 #include <ui/GraphicBuffer.h>
 #include <ui/PixelFormat.h>
 
+#include <gui/BufferItem.h>
 #include <gui/Surface.h>
 
 #include "clz.h"
@@ -159,11 +160,26 @@ void Layer::onLayerDisplayed(const sp<const DisplayDevice>& /* hw */,
     }
 }
 
-void Layer::onFrameAvailable(const BufferItem& /* item */) {
+void Layer::onFrameAvailable(const BufferItem& item) {
+    // Add this buffer from our internal queue tracker
+    { // Autolock scope
+        Mutex::Autolock lock(mQueueItemLock);
+        mQueueItems.push_back(item);
+    }
+
     android_atomic_inc(&mQueuedFrames);
     mFlinger->signalLayerUpdate();
 }
 
+void Layer::onFrameReplaced(const BufferItem& item) {
+    Mutex::Autolock lock(mQueueItemLock);
+    if (mQueueItems.empty()) {
+        ALOGE("Can't replace a frame on an empty queue");
+        return;
+    }
+    mQueueItems.editItemAt(0) = item;
+}
+
 void Layer::onSidebandStreamChanged() {
     if (android_atomic_release_cas(false, true, &mSidebandStreamChanged) == 0) {
         // mSidebandStreamChanged was false
@@ -1014,6 +1030,14 @@ bool Layer::setLayerStack(uint32_t layerStack) {
 // pageflip handling...
 // ----------------------------------------------------------------------------
 
+bool Layer::shouldPresentNow(const DispSync& dispSync) const {
+    Mutex::Autolock lock(mQueueItemLock);
+    nsecs_t expectedPresent =
+            mSurfaceFlingerConsumer->computeExpectedPresent(dispSync);
+    return mQueueItems.empty() ?
+            false : mQueueItems[0].mTimestamp < expectedPresent;
+}
+
 bool Layer::onPreComposition() {
     mRefreshPending = false;
     return mQueuedFrames > 0 || mSidebandStreamChanged;
@@ -1203,6 +1227,12 @@ Region Layer::latchBuffer(bool& recomputeVisibleRegions)
             return outDirtyRegion;
         }
 
+        // Remove this buffer from our internal queue tracker
+        { // Autolock scope
+            Mutex::Autolock lock(mQueueItemLock);
+            mQueueItems.removeAt(0);
+        }
+
         // Decrement the queued-frames count.  Signal another event if we
         // have more frames pending.
         if (android_atomic_dec(&mQueuedFrames) > 1) {

services/surfaceflinger/Layer.h

@@ -210,6 +210,8 @@ public:
     void onLayerDisplayed(const sp<const DisplayDevice>& hw,
             HWComposer::HWCLayerInterface* layer);
 
+    bool shouldPresentNow(const DispSync& dispSync) const;
+
     /*
      * called before composition.
      * returns true if the layer has pending updates.
@@ -331,6 +333,7 @@ protected:
 private:
     // Interface implementation for SurfaceFlingerConsumer::ContentsChangedListener
     virtual void onFrameAvailable(const BufferItem& item);
+    virtual void onFrameReplaced(const BufferItem& item);
     virtual void onSidebandStreamChanged();
 
     void commitTransaction();
@@ -404,6 +407,10 @@ private:
 
     // This layer can be a cursor on some displays.
     bool mPotentialCursor;
+
+    // Local copy of the queued contents of the incoming BufferQueue
+    mutable Mutex mQueueItemLock;
+    Vector<BufferItem> mQueueItems;
 };
 
 // ---------------------------------------------------------------------------

services/surfaceflinger/SurfaceFlinger.cpp

@@ -829,30 +829,39 @@ void SurfaceFlinger::eventControl(int disp, int event, int enabled) {
 void SurfaceFlinger::onMessageReceived(int32_t what) {
     ATRACE_CALL();
     switch (what) {
-    case MessageQueue::TRANSACTION:
-        handleMessageTransaction();
-        break;
-    case MessageQueue::INVALIDATE:
-        handleMessageTransaction();
-        handleMessageInvalidate();
-        signalRefresh();
-        break;
-    case MessageQueue::REFRESH:
-        handleMessageRefresh();
-        break;
+        case MessageQueue::TRANSACTION: {
+            handleMessageTransaction();
+            break;
+        }
+        case MessageQueue::INVALIDATE: {
+            bool refreshNeeded = handleMessageTransaction();
+            refreshNeeded |= handleMessageInvalidate();
+            if (refreshNeeded) {
+                // Signal a refresh if a transaction modified the window state or if
+                // a new buffer was latched
+                signalRefresh();
+            }
+            break;
+        }
+        case MessageQueue::REFRESH: {
+            handleMessageRefresh();
+            break;
+        }
     }
 }
 
-void SurfaceFlinger::handleMessageTransaction() {
+bool SurfaceFlinger::handleMessageTransaction() {
     uint32_t transactionFlags = peekTransactionFlags(eTransactionMask);
     if (transactionFlags) {
         handleTransaction(transactionFlags);
+        return true;
     }
+    return false;
 }
 
-void SurfaceFlinger::handleMessageInvalidate() {
+bool SurfaceFlinger::handleMessageInvalidate() {
     ATRACE_CALL();
-    handlePageFlip();
+    return handlePageFlip();
 }
 
 void SurfaceFlinger::handleMessageRefresh() {
@@ -1685,12 +1694,13 @@ void SurfaceFlinger::invalidateLayerStack(uint32_t layerStack,
     }
 }
 
-void SurfaceFlinger::handlePageFlip()
+bool SurfaceFlinger::handlePageFlip()
 {
     Region dirtyRegion;
 
     bool visibleRegions = false;
     const LayerVector& layers(mDrawingState.layersSortedByZ);
+    bool frameQueued = false;
 
     // Store the set of layers that need updates. This set must not change as
     // buffers are being latched, as this could result in a deadlock.
@@ -1704,8 +1714,12 @@ void SurfaceFlinger::handlePageFlip()
     Vector<Layer*> layersWithQueuedFrames;
     for (size_t i = 0, count = layers.size(); i<count ; i++) {
         const sp<Layer>& layer(layers[i]);
-        if (layer->hasQueuedFrame())
-            layersWithQueuedFrames.push_back(layer.get());
+        if (layer->hasQueuedFrame()) {
+            frameQueued = true;
+            if (layer->shouldPresentNow(mPrimaryDispSync)) {
+                layersWithQueuedFrames.push_back(layer.get());
+            }
+        }
     }
     for (size_t i = 0, count = layersWithQueuedFrames.size() ; i<count ; i++) {
         Layer* layer = layersWithQueuedFrames[i];
@@ -1715,6 +1729,16 @@ void SurfaceFlinger::handlePageFlip()
     }
 
     mVisibleRegionsDirty |= visibleRegions;
+
+    // If we will need to wake up at some time in the future to deal with a
+    // queued frame that shouldn't be displayed during this vsync period, wake
+    // up during the next vsync period to check again.
+    if (frameQueued && layersWithQueuedFrames.empty()) {
+        signalLayerUpdate();
+    }
+
+    // Only continue with the refresh if there is actually new work to do
+    return !layersWithQueuedFrames.empty();
 }
 
 void SurfaceFlinger::invalidateHwcGeometry()

services/surfaceflinger/SurfaceFlinger.h

@@ -247,8 +247,12 @@ private:
     // called on the main thread in response to setPowerMode()
     void setPowerModeInternal(const sp<DisplayDevice>& hw, int mode);
 
-    void handleMessageTransaction();
-    void handleMessageInvalidate();
+    // Returns whether the transaction actually modified any state
+    bool handleMessageTransaction();
+
+    // Returns whether a new buffer has been latched (see handlePageFlip())
+    bool handleMessageInvalidate();
+
     void handleMessageRefresh();
 
     void handleTransaction(uint32_t transactionFlags);
@@ -256,10 +260,11 @@ private:
 
     void updateCursorAsync();
 
-    /* handlePageFilp: this is were we latch a new buffer
-     * if available and compute the dirty region.
+    /* handlePageFlip - latch a new buffer if available and compute the dirty
+     * region. Returns whether a new buffer has been latched, i.e., whether it
+     * is necessary to perform a refresh during this vsync.
      */
-    void handlePageFlip();
+    bool handlePageFlip();
 
     /* ------------------------------------------------------------------------
      * Transactions

services/surfaceflinger/SurfaceFlingerConsumer.h

@@ -67,9 +67,9 @@ public:
 
     sp<NativeHandle> getSidebandStream() const;
 
-private:
     nsecs_t computeExpectedPresent(const DispSync& dispSync);
 
+private:
     virtual void onSidebandStreamChanged();
 
     wp<ContentsChangedListener> mContentsChangedListener;