Re: IOMMU and graphics cards

Dave Airlie
2009-07-06T22:05:34Z

On 07/07/2009, at 7:35, Dave Airlie <airlied@linux.ie> 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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