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
Merged-In: 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
diff --git a/services/surfaceflinger/Scheduler/Timer.cpp b/services/surfaceflinger/Scheduler/Timer.cpp
index 7c5058e..59c336a 100644
--- a/services/surfaceflinger/Scheduler/Timer.cpp
+++ b/services/surfaceflinger/Scheduler/Timer.cpp
@@ -88,7 +88,7 @@
return systemTime(SYSTEM_TIME_MONOTONIC);
}
-void Timer::alarmIn(std::function<void()> const& cb, nsecs_t fireIn) {
+void Timer::alarmAt(std::function<void()> const& cb, nsecs_t time) {
std::lock_guard<decltype(mMutex)> lk(mMutex);
using namespace std::literals;
static constexpr int ns_per_s =
@@ -99,11 +99,11 @@
struct itimerspec old_timer;
struct itimerspec new_timer {
.it_interval = {.tv_sec = 0, .tv_nsec = 0},
- .it_value = {.tv_sec = static_cast<long>(fireIn / ns_per_s),
- .tv_nsec = static_cast<long>(fireIn % ns_per_s)},
+ .it_value = {.tv_sec = static_cast<long>(time / ns_per_s),
+ .tv_nsec = static_cast<long>(time % ns_per_s)},
};
- if (timerfd_settime(mTimerFd, 0, &new_timer, &old_timer)) {
+ if (timerfd_settime(mTimerFd, TFD_TIMER_ABSTIME, &new_timer, &old_timer)) {
ALOGW("Failed to set timerfd %s (%i)", strerror(errno), errno);
}
}
diff --git a/services/surfaceflinger/Scheduler/Timer.h b/services/surfaceflinger/Scheduler/Timer.h
index a8e2d5a..69ce079 100644
--- a/services/surfaceflinger/Scheduler/Timer.h
+++ b/services/surfaceflinger/Scheduler/Timer.h
@@ -30,9 +30,9 @@
~Timer();
nsecs_t now() const final;
- // NB: alarmIn and alarmCancel are threadsafe; with the last-returning function being effectual
+ // NB: alarmAt and alarmCancel are threadsafe; with the last-returning function being effectual
// Most users will want to serialize thes calls so as to be aware of the timer state.
- void alarmIn(std::function<void()> const& cb, nsecs_t fireIn) final;
+ void alarmAt(std::function<void()> const& cb, nsecs_t time) final;
void alarmCancel() final;
void dump(std::string& result) const final;
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();
}