SurfaceFlinger: use TFD_TIMER_ABSTIME for VSP timer
Using the semantics of alarmIn in VSP timer may lead to lag
if the thread is getting preempted. For example:
Time 0: t1 calls to alarmIn(5)
-- t1 gets preempted for 2ms --
Time 2: t1 calls to timerfd_settime(5)
Time 7: timer wakes up t1, results in 2ms lag
Switching to alarmAt semantics and using TFD_TIMER_ABSTIME to
schedule the timer solves this problem:
Time 0: t1 calls to alarmAt(5)
-- t1 gets preempted for 2ms --
Time 2: t1 calls to timerfd_settime(5)
Time 5: timer wakes up t1
Bug: 159884130
Test: bouncy ball with simulated scheduling delays
Change-Id: I3d727530c2dd47c1a8d1d6a66114d654d7261d87
diff --git a/services/surfaceflinger/Scheduler/VSyncDispatchTimerQueue.cpp b/services/surfaceflinger/Scheduler/VSyncDispatchTimerQueue.cpp
index 2a6fd05..ef92680 100644
--- a/services/surfaceflinger/Scheduler/VSyncDispatchTimerQueue.cpp
+++ b/services/surfaceflinger/Scheduler/VSyncDispatchTimerQueue.cpp
@@ -180,10 +180,10 @@
mTimeKeeper->alarmCancel();
}
-void VSyncDispatchTimerQueue::setTimer(nsecs_t targetTime, nsecs_t now) {
+void VSyncDispatchTimerQueue::setTimer(nsecs_t targetTime, nsecs_t /*now*/) {
mIntendedWakeupTime = targetTime;
- mTimeKeeper->alarmIn(std::bind(&VSyncDispatchTimerQueue::timerCallback, this),
- targetTime - now);
+ mTimeKeeper->alarmAt(std::bind(&VSyncDispatchTimerQueue::timerCallback, this),
+ mIntendedWakeupTime);
mLastTimerSchedule = mTimeKeeper->now();
}