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/TimeKeeper.h b/services/surfaceflinger/Scheduler/TimeKeeper.h
index da2195c..40dd841 100644
--- a/services/surfaceflinger/Scheduler/TimeKeeper.h
+++ b/services/surfaceflinger/Scheduler/TimeKeeper.h
@@ -43,10 +43,10 @@
virtual ~TimeKeeper();
/*
- * Arms callback to fired in time nanoseconds.
+ * Arms callback to fired when time is current based on CLOCK_MONOTONIC
* There is only one timer, and subsequent calls will reset the callback function and the time.
*/
- virtual void alarmIn(std::function<void()> const& callback, nsecs_t time) = 0;
+ virtual void alarmAt(std::function<void()> const& callback, nsecs_t time) = 0;
/*
* Cancels an existing pending callback