Messages in this thread | | | Date | Tue, 7 Jul 2009 10:59:04 +0200 | From | Joerg Roedel <> | Subject | Re: IOMMU and graphics cards |
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On Mon, Jul 06, 2009 at 10:35:59PM +0100, Dave Airlie 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.
Are you sure that using the dma-api has such an performance impact? I've heard from other people that switching to dma-api with amd iommu had no significant performance impact.
> 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.
You just need to switch to dma-api. You don't need an iommu to test. Most bugs in such code can also be found and eliminated using the dma-api debugging interface.
Joerg
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