Re: [RFC] Hacky MTRR support

[Colin Watson <cjwatson@ubuntu.com>]

On Mon, Jun 28, 2010 at 09:40:21AM -0700, Colin D Bennett wrote:
> On Fri, 25 Jun 2010 09:58:34 +0100
> Colin Watson <cjwatson@ubuntu.com> wrote:
> > I recently posted ("Subject: [PATCH] Optimise memset on i386" -
> > sorry, I don't seem to have a route to lists.gnu.org at the moment so
> > I can't post an archive link) about optimising GRUB's video
> > initialisation, and hinted that it might be possible to do better by
> > implementing MTRRs as well in order to allow the system to combine
> > writes to video memory rather than taking a cache stall for every
> > single write.  I can report that, at least on the hardware I was
> > using, it does make a significant difference: filling the screen with
> > solid colour now takes 10 milliseconds rather than 160!  This ended
> > up shaving about a second off the boot time of the project I'm
> > working on.
> 
> In addition to the improved startup speed, I see the potential for a
> huge increase in graphical menu responsiveness if caching is enabled.
> Would framebuffer draw and image blitting performance be improved by
> using write-combining with MTRRs?

I didn't benchmark that, but I'd be pretty surprised if it weren't
improved.

-- 
Colin Watson                                       [cjwatson@ubuntu.com]