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Commit 99a0afba authored by Eric Penner's avatar Eric Penner
Browse files

BufferQueueProducer: Throttle EGL frame production. 

Throttling was previously controlled by a combination of the
driver and the number of buffers in the queue. This patch makes
a more consistent trade-off, which allows two GPU frames pending
but not three. More buffering could improve throughput in the
case of varying frame times, but this also increases latency.

Bug: 17502897
Change-Id: I4ee68019ca94c635294c5959931a555a6c4ef2df
parent 6c925ede

include/gui/BufferQueueProducer.h

+6 −0
Original line number Diff line number Diff line
@@ -197,6 +197,12 @@ private: 


    uint32_t mStickyTransform;



    // This saves the fence from the last queueBuffer, such that the

    // next queueBuffer call can throttle buffer production. The prior

    // queueBuffer's fence is not nessessarily available elsewhere,

    // since the previous buffer might have already been acquired.

    sp<Fence> mLastQueueBufferFence;



}; // class BufferQueueProducer



} // namespace android

libs/gui/BufferQueueProducer.cpp

+11 −1
Original line number Diff line number Diff line
@@ -38,7 +38,8 @@ BufferQueueProducer::BufferQueueProducer(const sp<BufferQueueCore>& core) : 
    mCore(core),

    mSlots(core->mSlots),

    mConsumerName(),

    mStickyTransform(0) {}

    mStickyTransform(0),

    mLastQueueBufferFence(Fence::NO_FENCE) {}



BufferQueueProducer::~BufferQueueProducer() {}
@@ -644,6 +645,15 @@ status_t BufferQueueProducer::queueBuffer(int slot, 
        ATRACE_INT(mCore->mConsumerName.string(), mCore->mQueue.size());

    } // Autolock scope



    // Wait without lock held

    if (mCore->mConnectedApi == NATIVE_WINDOW_API_EGL) {

        // Waiting here allows for two full buffers to be queued but not a

        // third. In the event that frames take varying time, this makes a

        // small trade-off in favor of latency rather than throughput.

        mLastQueueBufferFence->waitForever("Throttling EGL Production");

        mLastQueueBufferFence = fence;

    }



    // Call back without lock held

    if (listener != NULL) {

        listener->onFrameAvailable();