SurfaceFlinger: calculate expected present once

Calculate the expected present time in the beginning of the frame
and use the same value across the frame composition.

Bug: 137873466
Test: App transitions
Change-Id: I0b41c62796f6150702e8d50ec7d28838d3a5aa87

2 files changed, 12 insertions, 5 deletions

diff --git a/services/surfaceflinger/SurfaceFlinger.cpp b/services/surfaceflinger/SurfaceFlinger.cpp
index 0c9263b408..56cccfbce5 100644
--- a/services/surfaceflinger/SurfaceFlinger.cpp
+++ b/services/surfaceflinger/SurfaceFlinger.cpp
@@ -1686,22 +1686,26 @@ bool SurfaceFlinger::previousFrameMissed() NO_THREAD_SAFETY_ANALYSIS {
     return fence != Fence::NO_FENCE && (fence->getStatus() == Fence::Status::Unsignaled);
 }
 
-nsecs_t SurfaceFlinger::getExpectedPresentTime() NO_THREAD_SAFETY_ANALYSIS {
+void SurfaceFlinger::populateExpectedPresentTime() NO_THREAD_SAFETY_ANALYSIS {
     DisplayStatInfo stats;
     mScheduler->getDisplayStatInfo(&stats);
     const nsecs_t presentTime = mScheduler->getDispSyncExpectedPresentTime();
     // Inflate the expected present time if we're targetting the next vsync.
-    const nsecs_t correctedTime =
+    mExpectedPresentTime =
             mVsyncModulator.getOffsets().sf < mPhaseOffsets->getOffsetThresholdForNextVsync()
             ? presentTime
             : presentTime + stats.vsyncPeriod;
-    return correctedTime;
 }
 
 void SurfaceFlinger::onMessageReceived(int32_t what) NO_THREAD_SAFETY_ANALYSIS {
     ATRACE_CALL();
     switch (what) {
         case MessageQueue::INVALIDATE: {
+            // calculate the expected present time once and use the cached
+            // value throughout this frame to make sure all layers are
+            // seeing this same value.
+            populateExpectedPresentTime();
+
             bool frameMissed = previousFrameMissed();
             bool hwcFrameMissed = mHadDeviceComposition && frameMissed;
             bool gpuFrameMissed = mHadClientComposition && frameMissed;
diff --git a/services/surfaceflinger/SurfaceFlinger.h b/services/surfaceflinger/SurfaceFlinger.h
index 556a4b9be5..d836795e99 100644
--- a/services/surfaceflinger/SurfaceFlinger.h
+++ b/services/surfaceflinger/SurfaceFlinger.h
@@ -301,10 +301,11 @@ public:
     // TODO: this should be made accessible only to MessageQueue
     void onMessageReceived(int32_t what);
 
-    // Returns the expected present time for this frame.
+    // populates the expected present time for this frame.
     // When we are in negative offsets, we perform a correction so that the
     // predicted vsync for the *next* frame is used instead.
-    nsecs_t getExpectedPresentTime();
+    void populateExpectedPresentTime();
+    nsecs_t getExpectedPresentTime() const { return mExpectedPresentTime; }
 
     // for debugging only
     // TODO: this should be made accessible only to HWComposer
@@ -1184,6 +1185,8 @@ private:
     // Flags to capture the state of Vsync in HWC
     HWC2::Vsync mHWCVsyncState = HWC2::Vsync::Disable;
     HWC2::Vsync mHWCVsyncPendingState = HWC2::Vsync::Disable;
+
+    nsecs_t mExpectedPresentTime;
 };
 
 } // namespace android