sf: reuse luma sampling buffer when available

Reuse the luma sampling buffer when available, saving a frequent buffer
reallocation. Depending on driver refcounting behavior, this could have
resulted in the buffer free on the SF main thread (and typically did on
referenced device, costing about ~500us @10hz).

Test: verify luma sampling work reduces from ~2ms -> 1.5ms
Test: RegionSamplingTest in libgui
Fixes: 131416627

Change-Id: I8e6d57ae25bd37ceec828c82796f0f4f8f45636e

1 files changed, 3 insertions, 1 deletions

diff --git a/services/surfaceflinger/RegionSamplingThread.h b/services/surfaceflinger/RegionSamplingThread.h
index 979642912b..72b20420ef 100644
--- a/services/surfaceflinger/RegionSamplingThread.h
+++ b/services/surfaceflinger/RegionSamplingThread.h
@@ -24,13 +24,13 @@
 
 #include <android-base/thread_annotations.h>
 #include <binder/IBinder.h>
+#include <ui/GraphicBuffer.h>
 #include <ui/Rect.h>
 #include <utils/StrongPointer.h>
 #include "Scheduler/IdleTimer.h"
 
 namespace android {
 
-class GraphicBuffer;
 class IRegionSamplingListener;
 class Layer;
 class Scheduler;
@@ -121,6 +121,8 @@ private:
     std::unordered_map<wp<IBinder>, Descriptor, WpHash> mDescriptors GUARDED_BY(mMutex);
     std::chrono::nanoseconds lastSampleTime GUARDED_BY(mMutex);
     bool mDiscardedFrames GUARDED_BY(mMutex) = false;
+
+    sp<GraphicBuffer> mCachedBuffer GUARDED_BY(mMutex) = nullptr;
 };
 
 } // namespace android