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Date: Wed, 10 Sep 2008 15:53:47 +0200 From: Joerg Roedel <joerg.roedel@....com> To: FUJITA Tomonori <fujita.tomonori@....ntt.co.jp> CC: linux-kernel@...r.kernel.org, mingo@...e.hu Subject: Re: [PATCH] x86: avoid unnecessary low zone allocation in AMD IOMMU's alloc_coherent On Wed, Sep 10, 2008 at 10:37:45PM +0900, FUJITA Tomonori wrote: > On Wed, 10 Sep 2008 15:10:32 +0200 > Joerg Roedel <joerg.roedel@....com> wrote: > > Can't we simply make the gfp hacks depend on > > dma_ops->is_phys and avoid further gfp hacks in the hardware iommu > > implementations? > > I thought about it but adding a new dma_ops->we_don't_want_gfp_flag > hook doesn't make the code simpler much. Currently, we have the gfp > setting hack in just one place. It's not bad. Adding such new hook > means adding more lines than we can remove. The is_phys flas is already in place and its meaning is "the dma_ops return bus addresses equal to physical addresses". This is exactly the case when we need the gfp hacks. So I don't see a problem in just skipping the gfp rewrite if is_phys is zero. I don't see a point in adding gfp flags in dma_alloc_coherent and remove them again dma_ops->alloc_coherent code. Specially in this case where we already know in dma_alloc_coherent if we really need the flag rewrite. > Yeah, I was against your patch to adding the gfp setting hack to > swiotlb but it's because gfp is kinda architecture specific stuff and > swiotlb should not. It's the bad design IMO. It's ok for me that > architecture specific IOMMUs can do the architecture specific stuff > (and it's about just clearing the gfp flag). The generic swiotlb code already contained a gfp hack for IA64 and I added another one for x86 which is ok in my opinion. But the #ifdef was ugly, I agree with that now :-) Your solution of removing the flag hacks from the generic code completly was the other possible way. Joerg -- | AMD Saxony Limited Liability Company & Co. KG Operating | Wilschdorfer Landstr. 101, 01109 Dresden, Germany System | Register Court Dresden: HRA 4896 Research | General Partner authorized to represent: Center | AMD Saxony LLC (Wilmington, Delaware, US) | General Manager of AMD Saxony LLC: Dr. Hans-R. Deppe, Thomas McCoy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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