commit 6a0382d628649b8880a7ecd7fdc215fee14a3b34
author Robert Carr <racarr@google.com> Thu Jul 01 15:57:17 2021 -0700
committer Robert Carr <racarr@google.com> Thu Jul 01 16:09:48 2021 -0700
tree b58cb9924c452d40cea3deefda36f185dd669ec6
parent 06c3b63812ae498dbb30e3e276ce4dd1591c3f6c

Optimize mirror layer management

We currently have to traverse the whole hierarchy twice to
update mirror layer info. While a long term rearchitecture may avoid
this entirely, we can optimize the hotpath by avoiding both traversals
when there are no mirror layers in existence.

Bug: 186200583
Test: Existing tests pass
Change-Id: I63f1fb239aa51e6db4fb1f4cb3cd3a87113d35d9

services/surfaceflinger/Layer.cpp

diff --git a/services/surfaceflinger/Layer.cpp b/services/surfaceflinger/Layer.cpp
index ad31b3f..e8bdb61 100644
--- a/services/surfaceflinger/Layer.cpp
+++ b/services/surfaceflinger/Layer.cpp
@@ -177,6 +177,9 @@
     if (mDrawingState.sidebandStream != nullptr) {
         mFlinger->mTunnelModeEnabledReporter->decrementTunnelModeCount();
     }
+    if (mHadClonedChild) {
+        mFlinger->mNumClones--;
+    }
 }
 
 LayerCreationArgs::LayerCreationArgs(SurfaceFlinger* flinger, sp<Client> client, std::string name,
@@ -2535,6 +2538,12 @@
     return parent == nullptr ? false : parent->getPrimaryDisplayOnly();
 }
 
+void Layer::setClonedChild(const sp<Layer>& clonedChild) {
+    mClonedChild = clonedChild;
+    mHadClonedChild = true;
+    mFlinger->mNumClones++;
+}
+
 // ---------------------------------------------------------------------------
 
 std::ostream& operator<<(std::ostream& stream, const Layer::FrameRate& rate) {

services/surfaceflinger/Layer.h

diff --git a/services/surfaceflinger/Layer.h b/services/surfaceflinger/Layer.h
index ec9bb7c..e726d37 100644
--- a/services/surfaceflinger/Layer.h
+++ b/services/surfaceflinger/Layer.h
@@ -863,6 +863,8 @@
     // The layers in the cloned hierarchy will match the lifetime of the real layers. That is
     // if the real layer is destroyed, then the clone layer will also be destroyed.
     sp<Layer> mClonedChild;
+    bool mHadClonedChild = false;
+    void setClonedChild(const sp<Layer>& mClonedChild);
 
     mutable bool contentDirty{false};
     Region surfaceDamageRegion;

services/surfaceflinger/SurfaceFlinger.cpp

diff --git a/services/surfaceflinger/SurfaceFlinger.cpp b/services/surfaceflinger/SurfaceFlinger.cpp
index 8df0852..87965dd 100644
--- a/services/surfaceflinger/SurfaceFlinger.cpp
+++ b/services/surfaceflinger/SurfaceFlinger.cpp
@@ -3266,7 +3266,9 @@
     }
 
     commitOffscreenLayers();
-    mDrawingState.traverse([&](Layer* layer) { layer->updateMirrorInfo(); });
+    if (mNumClones > 0) {
+        mDrawingState.traverse([&](Layer* layer) { layer->updateMirrorInfo(); });
+    }
 }
 
 void SurfaceFlinger::commitOffscreenLayers() {
@@ -3372,7 +3374,9 @@
         mBootStage = BootStage::BOOTANIMATION;
     }
 
-    mDrawingState.traverse([&](Layer* layer) { layer->updateCloneBufferInfo(); });
+    if (mNumClones > 0) {
+        mDrawingState.traverse([&](Layer* layer) { layer->updateCloneBufferInfo(); });
+    }
 
     // Only continue with the refresh if there is actually new work to do
     return !mLayersWithQueuedFrames.empty() && newDataLatched;
@@ -4257,7 +4261,7 @@
             return result;
         }
 
-        mirrorLayer->mClonedChild = mirrorFrom->createClone();
+        mirrorLayer->setClonedChild(mirrorFrom->createClone());
     }
 
     *outLayerId = mirrorLayer->sequence;

services/surfaceflinger/SurfaceFlinger.h

diff --git a/services/surfaceflinger/SurfaceFlinger.h b/services/surfaceflinger/SurfaceFlinger.h
index 644f76f..b7da3b4 100644
--- a/services/surfaceflinger/SurfaceFlinger.h
+++ b/services/surfaceflinger/SurfaceFlinger.h
@@ -315,6 +315,9 @@
 
     void removeFromOffscreenLayers(Layer* layer);
 
+    // TODO: Remove atomic if move dtor to main thread CL lands
+    std::atomic<uint32_t> mNumClones;
+
     TransactionCallbackInvoker& getTransactionCallbackInvoker() {
         return mTransactionCallbackInvoker;
     }