Subject: Re: Generic IOMMU pooled allocator

From: Arnd Bergmann <[email-masked]>
Date: Mon, 23 Mar 2015 19:45:13 +0100

On Monday 23 March 2015, Benjamin Herrenschmidt wrote:
> On Mon, 2015-03-23 at 07:04 +0100, Arnd Bergmann wrote:
> > 
> > My guess is that the ARM code so far has been concerned mainly with
> > getting things to work in the first place, but scalability problems
> > will only be seen when there are faster CPU cores become available.
> 
> In any case, I think this is mostly a non-issue. The complexity of the
> ARM code is in various areas related to making shit work (handling
> coherent allocations mostly) but only remotely related to the actual
> iommu DMA space allocator (iova in ARM as far as I understand the code)
> which is pretty standard.

Ok, got it. Thanks for explaining tht part.

> The work Sowmini is doing is about specifically the allocator. Making
> our (powerpc) allocator generic since it has some nice scalability
> features.
> 
> In fact, what Aik and I have been pushing and Sowmini is close to
> achieving is to mostly disconnect that allocator from the rest of the
> iommu management (the caller).
> 
> So in the end, the allocator itself should be splitable into something
> separate that resides in lib/ or similar, which ARM can chose to use as
> well.

Yes, this sounds like a good idea. I'm currently at ELC and will bring this
up with the people working on ARM IOMMU support.

	Arnd