Patch to avoid calling gettimeofday while busy-waiting (I830WaitLpRing)

Carl Worth cworth at cworth.org
Tue Jul 10 18:22:32 PDT 2007


I noticed that I830WaitLpRing is making a system call to gettimeofday
while otherwise busy waiting.

Here's a patch to reduce that significantly, (calling gettimeofday
only every 4096 iterations). It doesn't actually improve performance
much as it primarily just makes the driver busy-wait faster. And all
the waiting appears to be due to the way the driver is written to
re-use the same in-video-memory state buffer for every composite
operation, (so no more than one can be in flight at a time).

I've put a lot more details on this and related issues here:

	http://www.cworth.org/exa/i965/synchronous_composite/

I'd greatly appreciate any feedback or suggestions for improving
things.

Thanks,

-Carl

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