From 84be783ff179fd6589bd01091f08f174f1f6a95d Mon Sep 17 00:00:00 2001
From: John Dias <joaodias@google.com>
Date: Tue, 18 Jun 2019 17:05:26 -0700
Subject: SF: delay region sampling when short on time

In a number of janky traces, particularly at high
frame rates, we've seen the surfaceflinger thread
overrunning its time slot. In some of those cases,
the surfaceflinger thread is doing region-sampling.
This change causes region-sampling to check how much
time is left until the next vsync before deciding
whether to sample this frame. If low on time,
it will defer the sampling to a later frame.

Bug: 133779857
Test: trace inspection from scrolling in various apps
Change-Id: I92c2368e80033c1ba6e27f947a456d14db02064c
---
 services/surfaceflinger/RegionSamplingThread.cpp | 23 +++++++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

(limited to 'services/surfaceflinger/RegionSamplingThread.cpp')

diff --git a/services/surfaceflinger/RegionSamplingThread.cpp b/services/surfaceflinger/RegionSamplingThread.cpp
index 66906e950c..4fca63aa96 100644
--- a/services/surfaceflinger/RegionSamplingThread.cpp
+++ b/services/surfaceflinger/RegionSamplingThread.cpp
@@ -44,11 +44,14 @@ constexpr auto lumaSamplingStepTag = "LumaSamplingStep";
 enum class samplingStep {
     noWorkNeeded,
     idleTimerWaiting,
+    waitForQuietFrame,
     waitForZeroPhase,
     waitForSamplePhase,
     sample
 };
 
+constexpr auto timeForRegionSampling = 5000000ns;
+constexpr auto maxRegionSamplingSkips = 10;
 constexpr auto defaultRegionSamplingOffset = -3ms;
 constexpr auto defaultRegionSamplingPeriod = 100ms;
 constexpr auto defaultRegionSamplingTimerTimeout = 100ms;
@@ -215,9 +218,9 @@ void RegionSamplingThread::removeListener(const sp<IRegionSamplingListener>& lis
 void RegionSamplingThread::checkForStaleLuma() {
     std::lock_guard lock(mThreadControlMutex);
 
-    if (mDiscardedFrames) {
+    if (mDiscardedFrames > 0) {
         ATRACE_INT(lumaSamplingStepTag, static_cast<int>(samplingStep::waitForZeroPhase));
-        mDiscardedFrames = false;
+        mDiscardedFrames = 0;
         mPhaseCallback->startVsyncListener();
     }
 }
@@ -235,13 +238,25 @@ void RegionSamplingThread::doSample() {
     auto now = std::chrono::nanoseconds(systemTime(SYSTEM_TIME_MONOTONIC));
     if (lastSampleTime + mTunables.mSamplingPeriod > now) {
         ATRACE_INT(lumaSamplingStepTag, static_cast<int>(samplingStep::idleTimerWaiting));
-        mDiscardedFrames = true;
+        if (mDiscardedFrames == 0) mDiscardedFrames++;
         return;
     }
+    if (mDiscardedFrames < maxRegionSamplingSkips) {
+        // If there is relatively little time left for surfaceflinger
+        // until the next vsync deadline, defer this sampling work
+        // to a later frame, when hopefully there will be more time.
+        DisplayStatInfo stats;
+        mScheduler.getDisplayStatInfo(&stats);
+        if (std::chrono::nanoseconds(stats.vsyncTime) - now < timeForRegionSampling) {
+            ATRACE_INT(lumaSamplingStepTag, static_cast<int>(samplingStep::waitForQuietFrame));
+            mDiscardedFrames++;
+            return;
+        }
+    }
 
     ATRACE_INT(lumaSamplingStepTag, static_cast<int>(samplingStep::sample));
 
-    mDiscardedFrames = false;
+    mDiscardedFrames = 0;
     lastSampleTime = now;
 
     mIdleTimer.reset();
-- 
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