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

On 20-08-08 12:04, Ingo Molnar wrote:

> * Venki Pallipadi <[email protected]> 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.

In the short run and if I'm not just mistaken, the best fix might be to 
make PAT dependent on not having a dumb AGP driver (but as said, still 
looking).

Note that my chipset is capable of a 2G AGP aperture. That's 512K pages 
if fully used, 256K for 1G, 128K for 512M, ...

Rene.

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