Dedicate a special caching slot for the layer override buffer
By using a special caching slot, this avoids import/freeBuffer churn in
the composer process which can occur when a layer is no longer using an
override buffer. Previously the layer's buffer would have been cached by
a previous setBuffer call, but since the override buffer was clobbering
a caching slot, replacing the override buffer requires re-importing the
buffer.
To resolve this, increase the size of the hwc buffer cache so it's ever
so slightly less tied to buffer queue sizes, which allows for room for
the override buffer which improves caching hit rate. On devices that
don't have layer caching turned on, this is a functional no-op because
those devices will never use the additional caching slot.
Bug: 185570241
Test: libcompositionengine_test
Test: Perfetto trace of opening and closing calculator app shows fewer
import/free buffers in the composer process
Change-Id: I219b1a1f6a31c5405736cb06d4921f300fe4a3ee
diff --git a/services/surfaceflinger/DisplayHardware/ComposerHal.h b/services/surfaceflinger/DisplayHardware/ComposerHal.h
index c756d65..0619b8c 100644
--- a/services/surfaceflinger/DisplayHardware/ComposerHal.h
+++ b/services/surfaceflinger/DisplayHardware/ComposerHal.h
@@ -32,6 +32,7 @@
#include <android/hardware/graphics/composer/2.4/IComposer.h>
#include <android/hardware/graphics/composer/2.4/IComposerClient.h>
#include <composer-command-buffer/2.4/ComposerCommandBuffer.h>
+#include <gui/BufferQueue.h>
#include <gui/HdrMetadata.h>
#include <math/mat4.h>
#include <ui/DisplayedFrameStats.h>
@@ -491,6 +492,11 @@
// 64KiB minus a small space for metadata such as read/write pointers
static constexpr size_t kWriterInitialSize =
64 * 1024 / sizeof(uint32_t) - 16;
+ // Max number of buffers that may be cached for a given layer
+ // We obtain this number by:
+ // 1. Tightly coupling this cache to the max size of BufferQueue
+ // 2. Adding an additional slot for the layer caching feature in SurfaceFlinger (see: Planner.h)
+ static const constexpr uint32_t kMaxLayerBufferCount = BufferQueue::NUM_BUFFER_SLOTS + 1;
CommandWriter mWriter;
CommandReader mReader;
};