Recompute the mNextFrameStartUnstuffed on every frame

At runtime, the intended_vsync difference is not constant value of
16.66ms.  If JankTracker repeatedly adds 16.66ms to
mNextFrameStartUnstuffed, it might be difted away after the tiny
differences being accumulated over many frames.

This Cl re-computes mNextFrameStartUnstuffed based on intended_vsync
for each triple buffering frame.

Test: existing JankTrackerTests

Change-Id: Ifa0b456be61905648f87327bddc3328e9abfef0a

1 files changed, 14 insertions, 9 deletions

diff --git a/libs/hwui/JankTracker.cpp b/libs/hwui/JankTracker.cpp
index 4b0ddd2fa2ef..c5c2d159bf03 100644
--- a/libs/hwui/JankTracker.cpp
+++ b/libs/hwui/JankTracker.cpp
@@ -206,6 +206,7 @@ void JankTracker::finishFrame(FrameInfo& frame, std::unique_ptr<FrameMetricsRepo
         frame.set(FrameInfoIndex::FrameDeadline) = deadline;
     }
 
+    bool computeNextFrameStartUnstuffed = false;
     // If we hit the deadline, cool!
     if (frame[FrameInfoIndex::GpuCompleted] < deadline) {
         if (isTripleBuffered) {
@@ -213,7 +214,8 @@ void JankTracker::finishFrame(FrameInfo& frame, std::unique_ptr<FrameMetricsRepo
             (*mGlobalData)->reportJankType(JankType::kHighInputLatency);
 
             // Buffer stuffing state gets carried over to next frame, unless there is a "pause"
-            mNextFrameStartUnstuffed += frameInterval;
+            // Instead of increase by frameInterval, recompute to catch up the drifting vsync
+            computeNextFrameStartUnstuffed = true;
         }
     } else {
         mData->reportJankType(JankType::kMissedDeadline);
@@ -222,14 +224,7 @@ void JankTracker::finishFrame(FrameInfo& frame, std::unique_ptr<FrameMetricsRepo
         (*mGlobalData)->reportJank();
 
         // Janked, store the adjust deadline to detect triple buffering in next frame correctly.
-        nsecs_t jitterNanos = frame[FrameInfoIndex::GpuCompleted]
-                - frame[FrameInfoIndex::Vsync];
-        nsecs_t lastFrameOffset = jitterNanos % frameInterval;
-
-        // Note the time when the next frame would start in an unstuffed situation. If it starts
-        // earlier, we are in a stuffed situation.
-        mNextFrameStartUnstuffed = frame[FrameInfoIndex::GpuCompleted]
-                - lastFrameOffset + frameInterval;
+        computeNextFrameStartUnstuffed = true;
 
         recomputeThresholds(frameInterval);
         for (auto& comparison : COMPARISONS) {
@@ -254,6 +249,16 @@ void JankTracker::finishFrame(FrameInfo& frame, std::unique_ptr<FrameMetricsRepo
         }
     }
 
+    if (computeNextFrameStartUnstuffed) {
+        nsecs_t jitterNanos = frame[FrameInfoIndex::GpuCompleted] - frame[FrameInfoIndex::Vsync];
+        nsecs_t lastFrameOffset = jitterNanos % frameInterval;
+
+        // Note the time when the next frame would start in an unstuffed situation. If it starts
+        // earlier, we are in a stuffed situation.
+        mNextFrameStartUnstuffed =
+                frame[FrameInfoIndex::GpuCompleted] - lastFrameOffset + frameInterval;
+    }
+
     int64_t totalGPUDrawTime = frame.gpuDrawTime();
     if (totalGPUDrawTime >= 0) {
         mData->reportGPUFrame(totalGPUDrawTime);