Don't send override buffer down to HWC if the layer would be skipped

Consider a set of five cached layers. Because ComposerResources' caches
are scoped per-layer and does not globally track buffers, the override
buffer for each layer needs to be re-imported, and a previous override
buffer needs to be freed, if the new override buffer changed between
frames. This causes a lot of churn in validate(), up to double CPU time
in the hot path.

Instead, we shouldn't override the buffer if a layer would be skipped.
In the aforementioned example, this would cause 1 buffers-worth of chrun
when importing, rather than 5.

Bug: 190654391
Test: Perfetto trace
Change-Id: I907b0c4c340fd99a0023429a8ad740ecc9208815
diff --git a/services/surfaceflinger/CompositionEngine/include/compositionengine/impl/OutputLayer.h b/services/surfaceflinger/CompositionEngine/include/compositionengine/impl/OutputLayer.h
index 2ffd472..244f8ab 100644
--- a/services/surfaceflinger/CompositionEngine/include/compositionengine/impl/OutputLayer.h
+++ b/services/surfaceflinger/CompositionEngine/include/compositionengine/impl/OutputLayer.h
@@ -73,10 +73,11 @@
     void writeOutputIndependentGeometryStateToHWC(HWC2::Layer*, const LayerFECompositionState&,
                                                   bool skipLayer);
     void writeOutputDependentPerFrameStateToHWC(HWC2::Layer*);
-    void writeOutputIndependentPerFrameStateToHWC(HWC2::Layer*, const LayerFECompositionState&);
+    void writeOutputIndependentPerFrameStateToHWC(HWC2::Layer*, const LayerFECompositionState&,
+                                                  bool skipLayer);
     void writeSolidColorStateToHWC(HWC2::Layer*, const LayerFECompositionState&);
     void writeSidebandStateToHWC(HWC2::Layer*, const LayerFECompositionState&);
-    void writeBufferStateToHWC(HWC2::Layer*, const LayerFECompositionState&);
+    void writeBufferStateToHWC(HWC2::Layer*, const LayerFECompositionState&, bool skipLayer);
     void writeCompositionTypeToHWC(HWC2::Layer*, Hwc2::IComposerClient::Composition,
                                    bool isPeekingThrough, bool skipLayer);
     void detectDisallowedCompositionTypeChange(Hwc2::IComposerClient::Composition from,
diff --git a/services/surfaceflinger/CompositionEngine/src/OutputLayer.cpp b/services/surfaceflinger/CompositionEngine/src/OutputLayer.cpp
index cd14327..e4e46a7 100644
--- a/services/surfaceflinger/CompositionEngine/src/OutputLayer.cpp
+++ b/services/surfaceflinger/CompositionEngine/src/OutputLayer.cpp
@@ -349,7 +349,7 @@
     }
 
     writeOutputDependentPerFrameStateToHWC(hwcLayer.get());
-    writeOutputIndependentPerFrameStateToHWC(hwcLayer.get(), *outputIndependentState);
+    writeOutputIndependentPerFrameStateToHWC(hwcLayer.get(), *outputIndependentState, skipLayer);
 
     writeCompositionTypeToHWC(hwcLayer.get(), requestedCompositionType, isPeekingThrough,
                               skipLayer);
@@ -471,7 +471,8 @@
 }
 
 void OutputLayer::writeOutputIndependentPerFrameStateToHWC(
-        HWC2::Layer* hwcLayer, const LayerFECompositionState& outputIndependentState) {
+        HWC2::Layer* hwcLayer, const LayerFECompositionState& outputIndependentState,
+        bool skipLayer) {
     switch (auto error = hwcLayer->setColorTransform(outputIndependentState.colorTransform)) {
         case hal::Error::NONE:
             break;
@@ -504,7 +505,7 @@
             break;
         case hal::Composition::CURSOR:
         case hal::Composition::DEVICE:
-            writeBufferStateToHWC(hwcLayer, outputIndependentState);
+            writeBufferStateToHWC(hwcLayer, outputIndependentState, skipLayer);
             break;
         case hal::Composition::INVALID:
         case hal::Composition::CLIENT:
@@ -541,7 +542,8 @@
 }
 
 void OutputLayer::writeBufferStateToHWC(HWC2::Layer* hwcLayer,
-                                        const LayerFECompositionState& outputIndependentState) {
+                                        const LayerFECompositionState& outputIndependentState,
+                                        bool skipLayer) {
     auto supportedPerFrameMetadata =
             getOutput().getDisplayColorProfile()->getSupportedPerFrameMetadata();
     if (auto error = hwcLayer->setPerFrameMetadata(supportedPerFrameMetadata,
@@ -554,7 +556,7 @@
     sp<GraphicBuffer> buffer = outputIndependentState.buffer;
     sp<Fence> acquireFence = outputIndependentState.acquireFence;
     int slot = outputIndependentState.bufferSlot;
-    if (getState().overrideInfo.buffer != nullptr) {
+    if (getState().overrideInfo.buffer != nullptr && !skipLayer) {
         buffer = getState().overrideInfo.buffer->getBuffer();
         acquireFence = getState().overrideInfo.acquireFence;
         slot = HwcBufferCache::FLATTENER_CACHING_SLOT;
diff --git a/services/surfaceflinger/CompositionEngine/tests/OutputLayerTest.cpp b/services/surfaceflinger/CompositionEngine/tests/OutputLayerTest.cpp
index 5bd1216..e9ecf3e 100644
--- a/services/surfaceflinger/CompositionEngine/tests/OutputLayerTest.cpp
+++ b/services/surfaceflinger/CompositionEngine/tests/OutputLayerTest.cpp
@@ -699,6 +699,7 @@
             Hwc2::IComposerClient::BlendMode::PREMULTIPLIED;
     static constexpr float kAlpha = 51.f;
     static constexpr float kOverrideAlpha = 1.f;
+    static constexpr float kSkipAlpha = 0.f;
     static constexpr ui::Dataspace kDataspace = static_cast<ui::Dataspace>(71);
     static constexpr ui::Dataspace kOverrideDataspace = static_cast<ui::Dataspace>(72);
     static constexpr int kSupportedPerFrameMetadata = 101;
@@ -1055,6 +1056,22 @@
                                  /*zIsOverridden*/ false, /*isPeekingThrough*/ false);
 }
 
+TEST_F(OutputLayerWriteStateToHWCTest, overriddenSkipLayerDoesNotSendBuffer) {
+    mLayerFEState.compositionType = Hwc2::IComposerClient::Composition::DEVICE;
+    includeOverrideInfo();
+
+    expectGeometryCommonCalls(kOverrideDisplayFrame, kOverrideSourceCrop, kOverrideBufferTransform,
+                              kOverrideBlendMode, kSkipAlpha);
+    expectPerFrameCommonCalls(SimulateUnsupported::None, kOverrideDataspace, kOverrideVisibleRegion,
+                              kOverrideSurfaceDamage);
+    expectSetHdrMetadataAndBufferCalls();
+    expectSetCompositionTypeCall(Hwc2::IComposerClient::Composition::DEVICE);
+    EXPECT_CALL(*mLayerFE, hasRoundedCorners()).WillRepeatedly(Return(false));
+
+    mOutputLayer.writeStateToHWC(/*includeGeometry*/ true, /*skipLayer*/ true, 0,
+                                 /*zIsOverridden*/ false, /*isPeekingThrough*/ false);
+}
+
 TEST_F(OutputLayerWriteStateToHWCTest, includesOverrideInfoIfPresent) {
     mLayerFEState.compositionType = Hwc2::IComposerClient::Composition::DEVICE;
     includeOverrideInfo();