Re: AGP and PAT (induced?) problem (on AMD family 6)

[Rene Herman]

On 20-08-08 23:02, Dave Airlie wrote:

> On Wed, Aug 20, 2008 at 8:50 PM, Rene Herman
> <rene.herman@xxxxxxxxxxxx> wrote:
> > On 20-08-08 12:04, Ingo Molnar wrote:
> >
> > > * Venki Pallipadi <venkatesh.pallipadi@xxxxxxxxx> wrote:
> > >
> > > > > I'd really like a reply from the AGP or PAT side right about
> > > > > now.
> > > > Hmm. Looks like there are more than 16000 entries in the PAT
> > > > list!
> > > hm, btw., why is that?
> > Because 64M of AGP memory divided by 4K pages is 16K. That is, the 
> > underlying problem seems to be AGP drivers using order 0
> > allocations. I'm looking.

[ ... ]

> I haven't anything to add, I'm the maintainer not the author, all the
> people who wrote the offending code were already involved.

The underlying problem is the order 0 allocations (agp_allocate_memory 
--> agp_generic_allocate_page) where each single page is set uncached 
individually, creating a PAT entry.

Non order 0 allocations generally would ofcourse help. That's very much 
AGP internal -- do you feel that's the way to go?

All the current AGP drivers except sgi-agp use agp_generic_alloc_page().

Doing a quick local hack to collect pages in agp_allocate_memory() into 
regions and set the regions (generally 1) UC in one fell swoop, but I 
don't know if that's safe (and it feels like a rather poor hack anyway).

(not to mention that it's time for bed again).

Rene.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/