Re: IOMMU and graphics cards

[Dave Airlie]

On 07/07/2009, at 7:35, Dave Airlie <airlied@xxxxxxxx> wrote:

> On Mon, 6 Jul 2009, David Woodhouse wrote:
>
> > On Mon, 2009-07-06 at 15:11 +0200, Joerg Roedel wrote:
> > > Ok, cool, that sounds good. Which in-kernel DRM drivers break with  
> > > IOMMU
> > > for you? I'll may probably add a similar temporary workaround for  
> > > AMD
> > > IOMMU too...
> >
> > The Intel one definitely broke -- I don't know about the others.  
> > There
> > are some old patches at http://people.freedesktop.org/~zhen/agp-mm-*
> > which make it look like _all_ AGP drivers are broken.
> >
> > I wouldn't bother adding the workaround -- as I said, I'm planning to
> > rip it out of 2.6.32 (and in linux-next as soon as it's reasonable  
> > to do
> > so). Let's just let them fix it.
>
> cc'ing Eric,
>
> My memory of this is graphics becomes totally useless and can be  
> 10x-50x
> slower. I think ripping this out without the person doing the ripping
> taking responsiblity for doing speed regression testing is totally  
> insane.
>
> I personally have no IOMMU hw from Intel or AMD and nobody has seen  
> it fit
> to supply me with any at any point in time, I'm not on the correct  
> gravy
> train. So I suspect the people with the hw will have to do the work  
> and
> the regression testing.

Could you also enumerate any limitations of the IOMMUs on the amount  
of memory they can remap per device if any.

Dave

> Dave.
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