SF: dont shift vsync timeline unless missed a frame

Bug: 329036771
Test: presubmit
Test: com.android.uibench.microbenchmark.UiBenchInflatingHanListViewFlingMicrobenchmark
Change-Id: Id0acfd4aff9b002df09fe79f175e07814f46c5a8
diff --git a/services/surfaceflinger/Scheduler/VSyncPredictor.cpp b/services/surfaceflinger/Scheduler/VSyncPredictor.cpp
index acb3760..b3c1f6b 100644
--- a/services/surfaceflinger/Scheduler/VSyncPredictor.cpp
+++ b/services/surfaceflinger/Scheduler/VSyncPredictor.cpp
@@ -635,33 +635,30 @@
     const auto threshold = model.slope / 2;
     const auto lastFrameMissed =
             lastVsyncOpt && std::abs(*lastVsyncOpt - missedVsync.vsync.ns()) < threshold;
-    nsecs_t vsyncFixupTime = 0;
     if (FlagManager::getInstance().vrr_config() && lastFrameMissed) {
         // If the last frame missed is the last vsync, we already shifted the timeline. Depends on
         // whether we skipped the frame (onFrameMissed) or not (onFrameBegin) we apply a different
         // fixup. There is no need to to shift the vsync timeline again.
         vsyncTime += missedVsync.fixup.ns();
         ATRACE_FORMAT_INSTANT("lastFrameMissed");
-    } else if (minFramePeriodOpt) {
-        if (FlagManager::getInstance().vrr_config() && lastVsyncOpt) {
-            // lastVsyncOpt is based on the old timeline before we shifted it. we should correct it
-            // first before trying to use it.
-            if (mLastVsyncSequence->seq > 0) {
-                lastVsyncOpt = snapToVsyncAlignedWithRenderRate(model, *lastVsyncOpt);
-            }
-            const auto vsyncDiff = vsyncTime - *lastVsyncOpt;
-            if (vsyncDiff <= minFramePeriodOpt->ns() - threshold) {
-                vsyncFixupTime = *lastVsyncOpt + minFramePeriodOpt->ns() - vsyncTime;
-                ATRACE_FORMAT_INSTANT("minFramePeriod violation. next in %.2f which is %.2f "
-                                      "from "
-                                      "prev. "
-                                      "adjust by %.2f",
-                                      static_cast<float>(vsyncTime - TimePoint::now().ns()) / 1e6f,
-                                      static_cast<float>(vsyncTime - *lastVsyncOpt) / 1e6f,
-                                      static_cast<float>(vsyncFixupTime) / 1e6f);
-            }
+    } else if (FlagManager::getInstance().vrr_config() && minFramePeriodOpt && mRenderRateOpt &&
+               lastVsyncOpt) {
+        // lastVsyncOpt is based on the old timeline before we shifted it. we should correct it
+        // first before trying to use it.
+        lastVsyncOpt = snapToVsyncAlignedWithRenderRate(model, *lastVsyncOpt);
+        const auto vsyncDiff = vsyncTime - *lastVsyncOpt;
+        if (vsyncDiff <= minFramePeriodOpt->ns() - threshold) {
+            // avoid a duplicate vsync
+            ATRACE_FORMAT_INSTANT("skipping a vsync to avoid duplicate frame. next in %.2f which "
+                                  "is %.2f "
+                                  "from "
+                                  "prev. "
+                                  "adjust by %.2f",
+                                  static_cast<float>(vsyncTime - TimePoint::now().ns()) / 1e6f,
+                                  static_cast<float>(vsyncDiff) / 1e6f,
+                                  static_cast<float>(mRenderRateOpt->getPeriodNsecs()) / 1e6f);
+            vsyncTime += mRenderRateOpt->getPeriodNsecs();
         }
-        vsyncTime += vsyncFixupTime;
     }
 
     ATRACE_FORMAT_INSTANT("vsync in %.2fms", float(vsyncTime - TimePoint::now().ns()) / 1e6f);
@@ -671,12 +668,6 @@
         return std::nullopt;
     }
 
-    // If we needed a fixup, it means that we changed the render rate and the chosen vsync would
-    // cross minFramePeriod. In that case we need to shift the entire vsync timeline.
-    if (vsyncFixupTime > 0) {
-        shiftVsyncSequence(Duration::fromNs(vsyncFixupTime));
-    }
-
     return TimePoint::fromNs(vsyncTime);
 }
 
diff --git a/services/surfaceflinger/tests/unittests/SchedulerTest.cpp b/services/surfaceflinger/tests/unittests/SchedulerTest.cpp
index d4735c7..e6bae90 100644
--- a/services/surfaceflinger/tests/unittests/SchedulerTest.cpp
+++ b/services/surfaceflinger/tests/unittests/SchedulerTest.cpp
@@ -607,10 +607,10 @@
 
     EXPECT_EQ(Fps::fromPeriodNsecs(2000),
               scheduler.getNextFrameInterval(kMode->getPhysicalDisplayId(),
-                                             TimePoint::fromNs(4500)));
+                                             TimePoint::fromNs(5500)));
     EXPECT_EQ(Fps::fromPeriodNsecs(2000),
               scheduler.getNextFrameInterval(kMode->getPhysicalDisplayId(),
-                                             TimePoint::fromNs(6500)));
+                                             TimePoint::fromNs(7500)));
 }
 
 TEST_F(SchedulerTest, resyncAllToHardwareVsync) FTL_FAKE_GUARD(kMainThreadContext) {
diff --git a/services/surfaceflinger/tests/unittests/VSyncPredictorTest.cpp b/services/surfaceflinger/tests/unittests/VSyncPredictorTest.cpp
index aac1cac..eafba0a 100644
--- a/services/surfaceflinger/tests/unittests/VSyncPredictorTest.cpp
+++ b/services/surfaceflinger/tests/unittests/VSyncPredictorTest.cpp
@@ -704,14 +704,17 @@
     EXPECT_EQ(21500, vrrTracker.nextAnticipatedVSyncTimeFrom(19000, 19000));
 
     vrrTracker.setRenderRate(Fps::fromPeriodNsecs(1000), /*applyImmediately*/ false);
-    EXPECT_EQ(5000, vrrTracker.nextAnticipatedVSyncTimeFrom(4000, 4000));
-    EXPECT_EQ(6000, vrrTracker.nextAnticipatedVSyncTimeFrom(5000, 5000));
-    EXPECT_EQ(7000, vrrTracker.nextAnticipatedVSyncTimeFrom(6000, 6000));
-    EXPECT_EQ(9000, vrrTracker.nextAnticipatedVSyncTimeFrom(8000, 8000));
-    EXPECT_EQ(11000, vrrTracker.nextAnticipatedVSyncTimeFrom(10000, 10000));
-    EXPECT_EQ(13000, vrrTracker.nextAnticipatedVSyncTimeFrom(12000, 12000));
-    EXPECT_EQ(17000, vrrTracker.nextAnticipatedVSyncTimeFrom(15500, 15500));
-    EXPECT_EQ(20000, vrrTracker.nextAnticipatedVSyncTimeFrom(19000, 19000));
+    EXPECT_EQ(5500, vrrTracker.nextAnticipatedVSyncTimeFrom(4000, 4000));
+    EXPECT_EQ(6500, vrrTracker.nextAnticipatedVSyncTimeFrom(5000, 5000));
+    EXPECT_EQ(7500, vrrTracker.nextAnticipatedVSyncTimeFrom(6000, 6000));
+    EXPECT_EQ(9500, vrrTracker.nextAnticipatedVSyncTimeFrom(8000, 8000));
+    EXPECT_EQ(11500, vrrTracker.nextAnticipatedVSyncTimeFrom(10000, 10000));
+    EXPECT_EQ(13500, vrrTracker.nextAnticipatedVSyncTimeFrom(12000, 12000));
+    EXPECT_EQ(16500, vrrTracker.nextAnticipatedVSyncTimeFrom(15500, 15500));
+    EXPECT_EQ(20500, vrrTracker.nextAnticipatedVSyncTimeFrom(19000, 19000));
+
+    // matches the previous cadence
+    EXPECT_EQ(21500, vrrTracker.nextAnticipatedVSyncTimeFrom(20500, 20500));
 }
 
 TEST_F(VSyncPredictorTest, minFramePeriodDoesntApplyWhenSameWithRefreshRate) {
@@ -820,7 +823,7 @@
 
     vrrTracker.setRenderRate(Fps::fromPeriodNsecs(1000), /*applyImmediately*/ false);
     vrrTracker.addVsyncTimestamp(0);
-    EXPECT_EQ(2000, vrrTracker.nextAnticipatedVSyncTimeFrom(1234, 1234));
+    EXPECT_EQ(2500, vrrTracker.nextAnticipatedVSyncTimeFrom(1234, 1234));
 }
 
 TEST_F(VSyncPredictorTest, adjustsVrrTimeline) {