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Commit 6db6d622 authored by Alec Mouri's avatar Alec Mouri
Browse files

When adding event listener, use fuzzy window for last event time. 

* We track the last callback time anyways, so there's no risk of
double-firing
* Without this we might risk missing a dispsync event. E.g., if vsyncs
are at T and T+11, and we're considering SF events with +1 offset, then
SF will fire at T+1. If we immediately deregister the SF listener, then
re-register later at T+13, we miss the event at T+12. But we would
probably be ok to fire at T+13 anyways.

Note that the old last event time inference did allow for this.
See change I742b30a8d28780a44592c4d3077f33d23cf65789...

listener.mLastEventTime = systemTime() - mPeriod / 2 + mPhase - mWakeupLatency;

...with +2/+6 offsets and 16.6ms period, then if SF registers at +7ms
after vsync, then last event time is inferred to be T-1.3ms, and with
reference time T-16.6ms, then the next computed event time ends up being
(floor(((T-1.3) - (T-16.6) - 6)/16.6) + 1)* 16.6 + 6 + T-16.6, which ends up
being T+6ms, which would immediately cause a wakeup. So this change
reintroduces that behavior while keeping the math right.

Bug: 128918820
Test: systrace
Change-Id: If45be5a579628045ba3d9bfe282bf8831fdb5275
parent 5e1371af

services/surfaceflinger/Scheduler/DispSync.cpp

+11 −10
Original line number Diff line number Diff line
@@ -211,13 +211,14 @@ public: 
            const nsecs_t numPeriodsSinceReference = baseTime / mPeriod;

            const nsecs_t predictedReference = mReferenceTime + numPeriodsSinceReference * mPeriod;

            const nsecs_t phaseCorrection = mPhase + listener.mPhase;

            const nsecs_t predictedLastEventTime = predictedReference + phaseCorrection;

            if (predictedLastEventTime >= now) {

                // Make sure that the last event time does not exceed the current time.

                // If it would, then back the last event time by a period.

                listener.mLastEventTime = predictedLastEventTime - mPeriod;

            } else {

                listener.mLastEventTime = predictedLastEventTime;

            listener.mLastEventTime = predictedReference + phaseCorrection;

            // If we're very close in time to the predicted last event time,

            // then we need to back up the last event time so that we can

            // attempt to fire an event immediately.

            //

            // Otherwise, keep the last event time that we predicted.

            if (isShorterThanPeriod(now - listener.mLastEventTime)) {

                listener.mLastEventTime -= mPeriod;

            }

        } else {

            listener.mLastEventTime = now + mPhase - mWakeupLatency;
@@ -314,7 +315,7 @@ private: 


    // Sanity check that the duration is close enough in length to a period without

    // falling into double-rate vsyncs.

    bool isCloseToPeriod(nsecs_t duration) {

    bool isShorterThanPeriod(nsecs_t duration) {

        // Ratio of 3/5 is arbitrary, but it must be greater than 1/2.

        return duration < (3 * mPeriod) / 5;

    }
@@ -330,7 +331,7 @@ private: 
            nsecs_t t = computeListenerNextEventTimeLocked(eventListener, onePeriodAgo);



            if (t < now) {

                if (isCloseToPeriod(now - eventListener.mLastCallbackTime)) {

                if (isShorterThanPeriod(now - eventListener.mLastCallbackTime)) {

                    eventListener.mLastEventTime = t;

                    eventListener.mLastCallbackTime = now;

                    ALOGV("[%s] [%s] Skipping event due to model error", mName,
@@ -391,7 +392,7 @@ private: 


        // Check that it's been slightly more than half a period since the last

        // event so that we don't accidentally fall into double-rate vsyncs

        if (isCloseToPeriod(t - listener.mLastEventTime)) {

        if (isShorterThanPeriod(t - listener.mLastEventTime)) {

            t += mPeriod;

            ALOGV("[%s] Modifying t -> %" PRId64, mName, ns2us(t));

        }