VSR: dispatch cbs skipped due to timer lag.

If the timer has a lot of lag relative to the intended wakeup time,
there could be two callbacks that should be dispatched during this
wakeup, not just one, with the additional callback being woken up being
the one that was skipped because of the timer lag.

Fixes: 159884130
Test: 1 new unit test
Test: uibench a/b

Change-Id: Ia17bc5a09a085fcb334226849214e5247e010b37
(cherry picked from commit f947783f66ddbc2275379fc1e45f991245c62967)

2 files changed, 34 insertions, 3 deletions

diff --git a/services/surfaceflinger/Scheduler/VSyncDispatchTimerQueue.cpp b/services/surfaceflinger/Scheduler/VSyncDispatchTimerQueue.cpp
index a596bce002..2a6fd0521f 100644
--- a/services/surfaceflinger/Scheduler/VSyncDispatchTimerQueue.cpp
+++ b/services/surfaceflinger/Scheduler/VSyncDispatchTimerQueue.cpp
@@ -243,7 +243,8 @@ void VSyncDispatchTimerQueue::timerCallback() {
     std::vector<Invocation> invocations;
     {
         std::lock_guard<decltype(mMutex)> lk(mMutex);
-        mLastTimerCallback = mTimeKeeper->now();
+        auto const now = mTimeKeeper->now();
+        mLastTimerCallback = now;
         for (auto it = mCallbacks.begin(); it != mCallbacks.end(); it++) {
             auto& callback = it->second;
             auto const wakeupTime = callback->wakeupTime();
@@ -251,7 +252,8 @@ void VSyncDispatchTimerQueue::timerCallback() {
                 continue;
             }
 
-            if (*wakeupTime < mIntendedWakeupTime + mTimerSlack) {
+            auto const lagAllowance = std::max(now - mIntendedWakeupTime, static_cast<nsecs_t>(0));
+            if (*wakeupTime < mIntendedWakeupTime + mTimerSlack + lagAllowance) {
                 callback->executing();
                 invocations.emplace_back(
                         Invocation{callback, *callback->lastExecutedVsyncTarget(), *wakeupTime});
diff --git a/services/surfaceflinger/tests/unittests/VSyncDispatchTimerQueueTest.cpp b/services/surfaceflinger/tests/unittests/VSyncDispatchTimerQueueTest.cpp
index d940dc5870..db5d6af611 100644
--- a/services/surfaceflinger/tests/unittests/VSyncDispatchTimerQueueTest.cpp
+++ b/services/surfaceflinger/tests/unittests/VSyncDispatchTimerQueueTest.cpp
@@ -115,11 +115,15 @@ public:
 
     operator VSyncDispatch::CallbackToken() const { return mToken; }
 
-    void counter(nsecs_t time, nsecs_t) { mCalls.push_back(time); }
+    void counter(nsecs_t time, nsecs_t wakeup_time) {
+        mCalls.push_back(time);
+        mWakeupTime.push_back(wakeup_time);
+    }
 
     VSyncDispatch& mDispatch;
     VSyncDispatch::CallbackToken mToken;
     std::vector<nsecs_t> mCalls;
+    std::vector<nsecs_t> mWakeupTime;
 };
 
 class PausingCallback {
@@ -747,6 +751,31 @@ TEST_F(VSyncDispatchTimerQueueTest, rearmsWhenCancelledAndIsNextScheduled) {
     EXPECT_THAT(cb2.mCalls.size(), Eq(1));
 }
 
+TEST_F(VSyncDispatchTimerQueueTest, laggedTimerGroupsCallbacksWithinLag) {
+    CountingCallback cb1(mDispatch);
+    CountingCallback cb2(mDispatch);
+
+    Sequence seq;
+    EXPECT_CALL(mStubTracker, nextAnticipatedVSyncTimeFrom(1000))
+            .InSequence(seq)
+            .WillOnce(Return(1000));
+    EXPECT_CALL(mMockClock, alarmIn(_, 600)).InSequence(seq);
+    EXPECT_CALL(mStubTracker, nextAnticipatedVSyncTimeFrom(1000))
+            .InSequence(seq)
+            .WillOnce(Return(1000));
+
+    EXPECT_EQ(mDispatch.schedule(cb1, 400, 1000), ScheduleResult::Scheduled);
+    EXPECT_EQ(mDispatch.schedule(cb2, 390, 1000), ScheduleResult::Scheduled);
+
+    mMockClock.setLag(100);
+    mMockClock.advanceBy(700);
+
+    ASSERT_THAT(cb1.mWakeupTime.size(), Eq(1));
+    EXPECT_THAT(cb1.mWakeupTime[0], Eq(600));
+    ASSERT_THAT(cb2.mWakeupTime.size(), Eq(1));
+    EXPECT_THAT(cb2.mWakeupTime[0], Eq(610));
+}
+
 class VSyncDispatchTimerQueueEntryTest : public testing::Test {
 protected:
     nsecs_t const mPeriod = 1000;