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
diff --git a/include/gui/BufferQueueProducer.h b/include/gui/BufferQueueProducer.h
index 3fc5de2..c619a11 100644
--- a/include/gui/BufferQueueProducer.h
+++ b/include/gui/BufferQueueProducer.h
@@ -197,6 +197,12 @@
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
diff --git a/libs/gui/BufferQueueProducer.cpp b/libs/gui/BufferQueueProducer.cpp
index a53775f..03bd4fd 100644
--- a/libs/gui/BufferQueueProducer.cpp
+++ b/libs/gui/BufferQueueProducer.cpp
@@ -38,7 +38,8 @@
mCore(core),
mSlots(core->mSlots),
mConsumerName(),
- mStickyTransform(0) {}
+ mStickyTransform(0),
+ mLastQueueBufferFence(Fence::NO_FENCE) {}
BufferQueueProducer::~BufferQueueProducer() {}
@@ -644,6 +645,15 @@
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();