Re: [PATCH] x86: avoid unnecessary low zone allocation in AMD IOMMU's alloc_coherent

From: Joerg Roedel
Date: Wed Sep 10 2008 - 10:53:27 EST

On Wed, Sep 10, 2008 at 11:39:00PM +0900, FUJITA Tomonori wrote:

> btw, in tip/x86/iommu, GART's alloc_coherent always does virtual
> mappings to allocate a size-aligned memory (as DMA-mapping.txt
> defines).
> Because someone strongly insisted, I modified GART's alloc_coherent to
> do so but as I said again and again, it's completely meaningless (only
> POWER IOMMU does it and drivers don't depend on such requirement).
> I guess that it would be better to do virtual mappings only when
> necessary as the current mainline does since GART I/O space is
> precious in some systems. But I don't care much. What's your opinion
> (as a AMD developer)?

Very true. My original rewrite did the mapping only when necessary too.
What were the reasons to do the mapping always?


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