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SubjectRe: specific optimizations for unaccelerated framebuffers
 --- Paul [private mail] wrote:
> You might like to do some performance measurements on
> X with a shadow framebuffer - see
>
> http://www.xfree86.org/4.1.0/apm5.html

This seems to still use the processor to copy the shadow buffer
to the video memory, you will still have the PCI write stall...

> I have a machine with an SiS 630 where the video memory _is_
> main memory - the impact of the graphics processor continually
> DMAing data for display is huge.

I am not speaking of DMA'ing at the refresh frequency (approx 70 times
per second the complete video memory), just the modified 64Kb blocks,
"once upon a while": if a single pixel is written twice, you will just
see the latter written value on the screen - but who cares.
Been able to DMA the complete video memory image around 5-10 times/second
should be over the human eye sensitivity.
Moreover this pixel will stay on the processor memory cache a lot
longer, even without MTRR processors.

Etienne.



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