Re: Xvideo acceleration: GATOS for PPC?
Michel Lanners wrote:
> >> So the question is: why does X on the Dell use so little CPU,
> >
> > I guess either because it has write combining for the framebuffer or
> > because top lies.
>
> I wouldn't know for top, but I can say that mtrr definitely makes a
> difference: 45% cpu for X without mtrr, down to roughly 5% with the
> proper mtrr configured. So that was it.
>
> >> and why can't we achieve the same thing on ppc
> >
> > We might if we used bus mastering for the video data transfer. There ar
> > plans to implement that, see current discussion on dri-devel.
>
> We might be able to squeeze a few percent out of better caching for the
> framebuffer (making X's framebuffer mapping cacheable enables bursting
> from the CPU; combined with float or vector stores instead of regular
> memcpy that should give a boost that _could_ come close to what mtrr
> achieves on i386.
>
> Michel, do you know what X uses to map the framebuffer? I suppose it
> mmap()s it; but what device? /dev/mem or /dev/fb (which X both has open)
> or something else?
The latter with UseFBDev, probably the former otherwise, not sure though.
Beware that I once tried your mmap() patch, and it caused visual artifacts.
--
Earthling Michel Dänzer (MrCooper) \ Debian GNU/Linux (powerpc) developer
CS student, Free Software enthusiast \ XFree86 and DRI project member
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