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SubjectRe: [PATCH] x86: fix gart iommu using for amd 64 bit system

* FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp> wrote:

> On Tue, 24 Nov 2009 16:26:45 +0100
> Ingo Molnar <mingo@elte.hu> wrote:
>
> >
> > * FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp> wrote:
> >
> > > > don't think user will like to use SWIOTLB instead of swiotlb.
> > >
> > > I doubt that users care about a way to fix their problems.
> >
> > As far as swiotlb vs. GART goes, arguably a non-bouncing hw based
> > solution (GART) is superior to a bouncing one (swiotlb), right?
>
> Yeah, but GART is not a real IOMMU that always does address
> translation. If users want performance, they need 64bit DMA capable
> devices to skip GART. With such devices, GART and SWIOTLB are same.
>
> So this hacky GART workaround is useful for only people who use non
> 64bit DMA devices and broken BIOS with GART. IMO, it's not worth
> having the workaround.

Well, what Yinghai is saying that for that (nonzero) subset of people
this change is a regression, and his patch fixes that. We dont do
regressions so this needs to be addressed.

Thanks,

Ingo


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