Kernel configuration options

[Jordan Crouse]

On 02/01/08 08:18 -0500, Bernardo Innocenti wrote:
> Tom Sylla wrote:
> 
> > http://openbios.org/viewvc/cpu/x86/pc/olpc/lxmsrs.fth?view=markup&revision=739&root=OpenFirmware
> > has:
> >   msr: 0000.1810 fdfff000.fd000111.  \ Video (write through), fbsize
> > 
> > which is setting the framebuffer as write-combining. (the "write
> > through" comment is incorrect)
> 
> This takes care of the physical mapping, but how would userspace
> be able to mmap the framebuffer into virtual memory without
> additional MMU programming?
> 
> I was under the impression that we also need to cover the whole
> region with small 4KB MMU pages.  This degrades performance
> somewhat due to TLB misses when the CPU accesses the framebuffer.

Well, in an ideal world, we wouldn't need to read framebuffer so much
that any performance hit would be small, especially with as big a 
offscreen buffer as we have.

I know that this is not an ideal world, and there is some X breakage
that reads and writes a lot from the framebuffer, but quite frankly,
thats the least of our speed worries right now.

But out of curiosity, what you would you have us do differently?  Are you
advocating that we move to 4Mb pages?

Jordan

-- 
Jordan Crouse
Systems Software Development Engineer 
Advanced Micro Devices, Inc.