[sf] only update the last latch time if the layer has a buffer

If we apply a transaction that does not latch a buffer, we
incorrectly updated the last latch time. In the next vsync,
if we presented a buffer late, we would misclassify the
jank as buffer stuffing.

Fix this by only updating the latch time if the layer has
a buffer.

Test: verify in perfetto traces
Fixes: 270041584
Change-Id: I423a28803a2660ada80ef554469f3977c389fbfa

1 files changed, 4 insertions, 0 deletions

diff --git a/services/surfaceflinger/Layer.cpp b/services/surfaceflinger/Layer.cpp
index 433606a732..ded607eb49 100644
--- a/services/surfaceflinger/Layer.cpp
+++ b/services/surfaceflinger/Layer.cpp
@@ -3037,6 +3037,10 @@ bool Layer::setBuffer(std::shared_ptr<renderengine::ExternalTexture>& buffer,
                                       mLastClientCompositionFence);
             mLastClientCompositionFence = nullptr;
         }
+    } else {
+        // if we are latching a buffer for the first time then clear the mLastLatchTime since
+        // we don't want to incorrectly classify a frame if we miss the desired present time.
+        updateLastLatchTime(0);
     }
 
     mDrawingState.producerId = bufferData.producerId;