SurfaceFlinger: add grace time for present fence to signal

To avoid racing with HWVsync when SF wakeup at a small offset from vsync,
we want to give a small grace period for the present fence to fire
instead of just giving up on this frame.

Bug: 141312250
Test: Set SF offset to 0 and observe systrace
Change-Id: I713fad164fa2f4e0f00a2b4efaae063ac8f4a2b7
Merged-In: I713fad164fa2f4e0f00a2b4efaae063ac8f4a2b7

2 files changed, 21 insertions, 4 deletions

diff --git a/services/surfaceflinger/SurfaceFlinger.cpp b/services/surfaceflinger/SurfaceFlinger.cpp
index d91b0e7db7..fe09c9c3d2 100644
--- a/services/surfaceflinger/SurfaceFlinger.cpp
+++ b/services/surfaceflinger/SurfaceFlinger.cpp
@@ -1676,7 +1676,8 @@ void SurfaceFlinger::updateVrFlinger() {
     setTransactionFlags(eDisplayTransactionNeeded);
 }
 
-bool SurfaceFlinger::previousFrameMissed() NO_THREAD_SAFETY_ANALYSIS {
+bool SurfaceFlinger::previousFrameMissed(int graceTimeMs) NO_THREAD_SAFETY_ANALYSIS {
+    ATRACE_CALL();
     // We are storing the last 2 present fences. If sf's phase offset is to be
     // woken up before the actual vsync but targeting the next vsync, we need to check
     // fence N-2
@@ -1685,7 +1686,15 @@ bool SurfaceFlinger::previousFrameMissed() NO_THREAD_SAFETY_ANALYSIS {
             ? mPreviousPresentFences[0]
             : mPreviousPresentFences[1];
 
-    return fence != Fence::NO_FENCE && (fence->getStatus() == Fence::Status::Unsignaled);
+    if (fence == Fence::NO_FENCE) {
+        return false;
+    }
+
+    if (graceTimeMs > 0 && fence->getStatus() == Fence::Status::Unsignaled) {
+        fence->wait(graceTimeMs);
+    }
+
+    return (fence->getStatus() == Fence::Status::Unsignaled);
 }
 
 void SurfaceFlinger::populateExpectedPresentTime() NO_THREAD_SAFETY_ANALYSIS {
@@ -1708,7 +1717,15 @@ void SurfaceFlinger::onMessageReceived(int32_t what) NO_THREAD_SAFETY_ANALYSIS {
             // seeing this same value.
             populateExpectedPresentTime();
 
-            bool frameMissed = previousFrameMissed();
+            // When Backpressure propagation is enabled we want to give a small grace period
+            // for the present fence to fire instead of just giving up on this frame to handle cases
+            // where present fence is just about to get signaled.
+            const int graceTimeForPresentFenceMs =
+                    (mPropagateBackpressure &&
+                     (mPropagateBackpressureClientComposition || !mHadClientComposition))
+                    ? 1
+                    : 0;
+            bool frameMissed = previousFrameMissed(graceTimeForPresentFenceMs);
             bool hwcFrameMissed = mHadDeviceComposition && frameMissed;
             bool gpuFrameMissed = mHadClientComposition && frameMissed;
             ATRACE_INT("FrameMissed", static_cast<int>(frameMissed));
diff --git a/services/surfaceflinger/SurfaceFlinger.h b/services/surfaceflinger/SurfaceFlinger.h
index 74882f3909..484b719f22 100644
--- a/services/surfaceflinger/SurfaceFlinger.h
+++ b/services/surfaceflinger/SurfaceFlinger.h
@@ -851,7 +851,7 @@ private:
         return hwcDisplayId ? getHwComposer().toPhysicalDisplayId(*hwcDisplayId) : std::nullopt;
     }
 
-    bool previousFrameMissed();
+    bool previousFrameMissed(int graceTimeMs = 0);
     void setVsyncEnabledInHWC(DisplayId displayId, HWC2::Vsync enabled);
 
     /*