linux-kernel - Re: IOMMU and graphics cards

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Message-Id: <0DDD3FAD-969A-421B-A36A-77AB645E8BCA@gmail.com>
Date:	Tue, 7 Jul 2009 08:00:01 +1000
From:	Dave Airlie <airlied@...il.com>
To:	Dave Airlie <airlied@...ux.ie>
Cc:	David Woodhouse <dwmw2@...radead.org>,
	Joerg Roedel <joerg.roedel@....com>,
	Joerg Roedel <joro@...tes.org>,
	Zhenyu Wang <zhenyu.z.wang@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"fujita.tomonori@....ntt.co.jp" <fujita.tomonori@....ntt.co.jp>,
	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"mingo@...hat.com" <mingo@...hat.com>,
	David Miller <davem@...emloft.net>,
	"eric@...olt.net" <eric@...olt.net>
Subject: Re: IOMMU and graphics cards


On 07/07/2009, at 7:35, Dave Airlie <airlied@...ux.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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