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

[Rene Herman <rene.herman@keyaccess.nl>]

On 20-08-08 12:50, Rene Herman wrote:

> On 20-08-08 12:04, Ingo Molnar wrote:
> 
>> * Venki Pallipadi <venkatesh.pallipadi@intel.com> 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.
> 
> Do note also that this means that Venki's change would not constitite a 
> correct/final fix. Sure, caching the last entry speeds up traversing a 
> 16K entry list but the issue is that there shouldn't be a 16K entry 
> list. Through AGP, or maybe even by coalescing entries in the PAT list 
> if that's at all possible (I guess it's not really).
> 
> Even if such a more fundamental fix isn't (easily) available, the PAT 
> code already comments that the list, which is sorted by ->start value, 
> is expected to be short, and should be turned into an rbtree if it isn't 
> which might be slightly less of a bandaid.
> 
> Dave Airlie (as the MAINTAINERS entry) can't be arsed to answer email it 
> seems so I've added Dave Jones for a possible comment from the AGP side.
> If I'm reading this right upto now, still many AGP driver (among which 
> my amd-k7-agp) are affected.

This was based on a wrong reading; I was looking at the GATT allocation.

I'm giving up looking until someone can tell me whether or not those 16K 
entries are expected though. I have just one AGP card in a PAT capable 
machine.

How many entries in /debug/x86/pat_memtype_list are there on other AGP 
systems with Option "AGPSize" "64" in their xorg.conf:"Device" section 
(and their AGP aperture set to 64M or bigger in the BIOS)?

Rene.