So far we did nothing on EndScene, but the API
doc says it flushes the GPU command queue.
The doc implies one can optimize CPU usage
by calling EndScene long before Present() is called.
Implementing the flush behaviour gives me +15-20%
on the CPU limited Halo. On the other hand, do limit
the flush to only once per frame.
3DMark03/3Mark05 get a 2% perf hit with the patch,
but 5% if I allow more flushes.
Signed-off-by: Axel Davy <davyaxel0@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9451>
634adfa253