SF: fix vsync shift repeatedly when HWC miss a frame

Bug: 328085852
Change-Id: I17df8ae1fcf5e21662e582e795d00a3d800640f3
Test: presubmit
diff --git a/services/surfaceflinger/Scheduler/VSyncPredictor.cpp b/services/surfaceflinger/Scheduler/VSyncPredictor.cpp
index 2f9dfea..45b2961 100644
--- a/services/surfaceflinger/Scheduler/VSyncPredictor.cpp
+++ b/services/surfaceflinger/Scheduler/VSyncPredictor.cpp
@@ -45,28 +45,6 @@
 
 static auto constexpr kMaxPercent = 100u;
 
-namespace {
-nsecs_t getVsyncFixup(VSyncPredictor::Model model, Period minFramePeriod, nsecs_t vsyncTime,
-                      std::optional<nsecs_t> lastVsyncOpt) {
-    const auto threshold = model.slope / 2;
-
-    if (FlagManager::getInstance().vrr_config() && lastVsyncOpt) {
-        const auto vsyncDiff = vsyncTime - *lastVsyncOpt;
-        if (vsyncDiff >= threshold && vsyncDiff <= minFramePeriod.ns() - threshold) {
-            const auto vsyncFixup = *lastVsyncOpt + minFramePeriod.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>(vsyncFixup) / 1e6f);
-            return vsyncFixup;
-        }
-    }
-
-    return 0;
-}
-} // namespace
-
 VSyncPredictor::~VSyncPredictor() = default;
 
 VSyncPredictor::VSyncPredictor(std::unique_ptr<Clock> clock, ftl::NonNull<DisplayModePtr> modePtr,
@@ -585,16 +563,33 @@
         std::optional<nsecs_t> lastVsyncOpt) {
     ATRACE_FORMAT("renderRate %s", mRenderRateOpt ? to_string(*mRenderRateOpt).c_str() : "NA");
 
+    nsecs_t vsyncTime = snapToVsyncAlignedWithRenderRate(model, vsync);
     const auto threshold = model.slope / 2;
     const auto lastFrameMissed =
             lastVsyncOpt && std::abs(*lastVsyncOpt - missedVsync.vsync.ns()) < threshold;
-    nsecs_t vsyncTime = snapToVsyncAlignedWithRenderRate(model, vsync);
     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 {
-        vsyncFixupTime = getVsyncFixup(model, minFramePeriod, vsyncTime, lastVsyncOpt);
+        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.
+            lastVsyncOpt = snapToVsyncAlignedWithRenderRate(model, *lastVsyncOpt);
+            const auto vsyncDiff = vsyncTime - *lastVsyncOpt;
+            if (vsyncDiff <= minFramePeriod.ns() - threshold) {
+                vsyncFixupTime = *lastVsyncOpt + minFramePeriod.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);
+            }
+        }
         vsyncTime += vsyncFixupTime;
     }
 
@@ -605,6 +600,8 @@
         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));
     }
diff --git a/services/surfaceflinger/tests/unittests/SchedulerTest.cpp b/services/surfaceflinger/tests/unittests/SchedulerTest.cpp
index 049b092..e69410b 100644
--- a/services/surfaceflinger/tests/unittests/SchedulerTest.cpp
+++ b/services/surfaceflinger/tests/unittests/SchedulerTest.cpp
@@ -591,6 +591,7 @@
                                              TimePoint::fromNs(2000)));
 
     // Not crossing the min frame period
+    vrrTracker->onFrameBegin(TimePoint::fromNs(2000), TimePoint::fromNs(1500));
     EXPECT_EQ(Fps::fromPeriodNsecs(1000),
               scheduler.getNextFrameInterval(kMode->getPhysicalDisplayId(),
                                              TimePoint::fromNs(2500)));
@@ -599,15 +600,15 @@
     vrrSelectorPtr->setActiveMode(kMode->getId(), frameRate);
     scheduler.setRenderRate(kMode->getPhysicalDisplayId(), frameRate);
 
-    // Set 2000 as vsync seq #0
-    vrrTracker->nextAnticipatedVSyncTimeFrom(1700);
+    // Set 4000 as vsync seq #0
+    vrrTracker->nextAnticipatedVSyncTimeFrom(3700);
 
     EXPECT_EQ(Fps::fromPeriodNsecs(2000),
               scheduler.getNextFrameInterval(kMode->getPhysicalDisplayId(),
-                                             TimePoint::fromNs(2000)));
+                                             TimePoint::fromNs(4000)));
     EXPECT_EQ(Fps::fromPeriodNsecs(2000),
               scheduler.getNextFrameInterval(kMode->getPhysicalDisplayId(),
-                                             TimePoint::fromNs(4000)));
+                                             TimePoint::fromNs(6000)));
 }
 
 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 6b9ea56..1394c55 100644
--- a/services/surfaceflinger/tests/unittests/VSyncPredictorTest.cpp
+++ b/services/surfaceflinger/tests/unittests/VSyncPredictorTest.cpp
@@ -688,6 +688,50 @@
     EXPECT_EQ(10500, vrrTracker.nextAnticipatedVSyncTimeFrom(9000, 7000));
 }
 
+TEST_F(VSyncPredictorTest, adjustsVrrTimelineTwoClients) {
+    SET_FLAG_FOR_TEST(flags::vrr_config, true);
+
+    const int32_t kGroup = 0;
+    const auto kResolution = ui::Size(1920, 1080);
+    const auto refreshRate = Fps::fromPeriodNsecs(500);
+    const auto minFrameRate = Fps::fromPeriodNsecs(1000);
+    hal::VrrConfig vrrConfig;
+    vrrConfig.minFrameIntervalNs = minFrameRate.getPeriodNsecs();
+    const ftl::NonNull<DisplayModePtr> kMode =
+            ftl::as_non_null(createDisplayModeBuilder(DisplayModeId(0), refreshRate, kGroup,
+                                                      kResolution, DEFAULT_DISPLAY_ID)
+                                     .setVrrConfig(std::move(vrrConfig))
+                                     .build());
+
+    VSyncPredictor vrrTracker{std::make_unique<ClockWrapper>(mClock), kMode, kHistorySize,
+                              kMinimumSamplesForPrediction, kOutlierTolerancePercent};
+
+    vrrTracker.setRenderRate(minFrameRate);
+    vrrTracker.addVsyncTimestamp(0);
+    EXPECT_EQ(3000, vrrTracker.nextAnticipatedVSyncTimeFrom(2700));
+
+    EXPECT_EQ(4000, vrrTracker.nextAnticipatedVSyncTimeFrom(3000, 3000));
+
+    EXPECT_EQ(5000, vrrTracker.nextAnticipatedVSyncTimeFrom(4000, 4000));
+    EXPECT_EQ(3000, vrrTracker.nextAnticipatedVSyncTimeFrom(2700));
+    vrrTracker.onFrameBegin(TimePoint::fromNs(3000), TimePoint::fromNs(0));
+
+    EXPECT_EQ(6000, vrrTracker.nextAnticipatedVSyncTimeFrom(5000, 5000));
+    EXPECT_EQ(4000, vrrTracker.nextAnticipatedVSyncTimeFrom(3700));
+    vrrTracker.onFrameMissed(TimePoint::fromNs(4000));
+
+    EXPECT_EQ(4500, vrrTracker.nextAnticipatedVSyncTimeFrom(4000, 4000));
+    vrrTracker.onFrameBegin(TimePoint::fromNs(4500), TimePoint::fromNs(4500));
+
+    EXPECT_EQ(7500, vrrTracker.nextAnticipatedVSyncTimeFrom(6000, 6000));
+    EXPECT_EQ(5500, vrrTracker.nextAnticipatedVSyncTimeFrom(4500, 4500));
+    vrrTracker.onFrameBegin(TimePoint::fromNs(5500), TimePoint::fromNs(4500));
+
+    EXPECT_EQ(8500, vrrTracker.nextAnticipatedVSyncTimeFrom(7500, 7500));
+    EXPECT_EQ(6500, vrrTracker.nextAnticipatedVSyncTimeFrom(5500, 5500));
+    vrrTracker.onFrameBegin(TimePoint::fromNs(6500), TimePoint::fromNs(5500));
+}
+
 TEST_F(VSyncPredictorTest, renderRateIsPreservedForCommittedVsyncs) {
     tracker.addVsyncTimestamp(1000);