[Intel-gfx] [PATCH] Xv: free tearing on textured video
krh at bitplanet.net
Wed Feb 25 19:54:27 CET 2009
On Wed, Feb 25, 2009 at 12:24 PM, Keith Packard <keithp at keithp.com> wrote:
> On Wed, 2009-02-25 at 12:05 -0500, Kristian Høgsberg wrote:
>> I'll have to try it out - I'm not sure what the exact effect of
>> syncing everything to vblank might be. For all I know it may not be
>> noticable at all, except for cases where you do a lot of individual
>> read backs per frame... time for me to stop waving the hands and try
> We block the chip until vblank, once the command to blt the video is
> queued. So, any other rendering will back-up behind the video blt. If
> anything needs to wait for the GPU (for a fallback, or ring full,
> or...), you'll block the CPU as well.
That's the theory; what I've been saying is that we're only increasing
the latency, not the throughput. And even though the server may block
waiting to read back from a buffer, there's still a window between one
Xv copy and the next where it's not waiting for vsync and can work
though a back log of requests.
But enough speculation, I'll try it out now.
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