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
