commit fbc80aef0ba1b11982cf4ca88d218b65b6eca0f3
author Brian Anderson <brianderson@google.com> Fri May 26 16:23:54 2017 -0700
committer Brian Anderson <brianderson@google.com> Tue Jun 20 12:50:50 2017 -0700
tree 888752f235709f9a484baded6d1ff199cd66fab2
parent 771666079bbec3753ae114d41712f008f24e5590

Reduce number of Fence syscalls made.

This patch saves 6 or more Fence syscalls per frame.

* Timelines are updated just before adding a new fence
  since the newly added fence is unlikely to have signaled.
* Layer::latch uses a FenceTime now, so the signal time is
  automatically shared with other owners of the FenceTime.
* DispSync uses FenceTime now, only using cached values of
  the signal time that have been populated by a Timeline.

Test: SurfaceFlinger boots and dumps still work.
Change-Id: Ie0cfc1af2aca143dd8d5f08f08dbe1e597376f2f

services/surfaceflinger/DispSync.h

diff --git a/services/surfaceflinger/DispSync.h b/services/surfaceflinger/DispSync.h
index 82ae795..c9f3b04 100644
--- a/services/surfaceflinger/DispSync.h
+++ b/services/surfaceflinger/DispSync.h
@@ -23,10 +23,14 @@
 #include <utils/Timers.h>
 #include <utils/RefBase.h>
 
+#include <ui/FenceTime.h>
+
+#include <memory>
+
 namespace android {
 
 class String8;
-class Fence;
+class FenceTime;
 class DispSyncThread;
 
 // DispSync maintains a model of the periodic hardware-based vsync events of a
@@ -67,7 +71,7 @@
     //
     // This method should be called with the retire fence from each HWComposer
     // set call that affects the display.
-    bool addPresentFence(const sp<Fence>& fence);
+    bool addPresentFence(const std::shared_ptr<FenceTime>& fenceTime);
 
     // The beginResync, addResyncSample, and endResync methods are used to re-
     // synchronize the DispSync's model to the hardware vsync events.  The re-
@@ -129,6 +133,7 @@
     enum { MIN_RESYNC_SAMPLES_FOR_UPDATE = 6 };
     enum { NUM_PRESENT_SAMPLES = 8 };
     enum { MAX_RESYNC_SAMPLES_WITHOUT_PRESENT = 4 };
+    enum { ACCEPTABLE_ZERO_ERR_SAMPLES_COUNT = 64 };
 
     const char* const mName;
 
@@ -146,9 +151,14 @@
 
     // mError is the computed model error.  It is based on the difference
     // between the estimated vsync event times and those observed in the
-    // mPresentTimes array.
+    // mPresentFences array.
     nsecs_t mError;
 
+    // mZeroErrSamplesCount keeps track of how many times in a row there were
+    // zero timestamps available in the mPresentFences array.
+    // Used to sanity check that we are able to calculate the model error.
+    size_t mZeroErrSamplesCount;
+
     // Whether we have updated the vsync event model since the last resync.
     bool mModelUpdated;
 
@@ -162,8 +172,8 @@
 
     // These member variables store information about the present fences used
     // to validate the currently computed model.
-    sp<Fence> mPresentFences[NUM_PRESENT_SAMPLES];
-    nsecs_t mPresentTimes[NUM_PRESENT_SAMPLES];
+    std::shared_ptr<FenceTime>
+            mPresentFences[NUM_PRESENT_SAMPLES] {FenceTime::NO_FENCE};
     size_t mPresentSampleOffset;
 
     int mRefreshSkipCount;