Message-ID: <476ADD05.5090801@opengridcomputing.com>
Date: Thu, 20 Dec 2007 15:22:13 -0600
From: Steve Wise <swise@opengridcomputing.com>
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To: benh@au1.ibm.com
CC: Roland Dreier <rdreier@cisco.com>,
       Benjamin Herrenschmidt <bherren@au1.ibm.com>,
       linux-kernel@vger.kernel.org,
       OpenFabrics General <general@lists.openfabrics.org>,
       Wen Xiong <wenxiong@us.ibm.com>, Olof Johansson <olof@lixom.net>,
       Paul Mackerras <pmac@au1.ibm.com>
Subject: Re: [ofa-general] iommu dma mapping alignment requirements
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Benjamin Herrenschmidt wrote:
> On Thu, 2007-12-20 at 13:29 -0600, Steve Wise wrote:
> 
>> Or based on the alignment of vaddr actually...
> 
> The later wouldn't be realistic. What I think might be necessay, though
> it would definitely cause us problems with running out of iommu space
> (which is the reason we did the switch down to 4K), is to provide
> alignment to the real page size, and alignement to the allocation order
> for dma_map_consistent.
> 
> It might be possible to -tweak- and only provide alignment to the page
> size for allocations that are larger than IOMMU_PAGE_SIZE. That would
> solve the problem with small network packets eating up too much iommu
> space though.
> 
> What do you think ?

That might work.

If you gimme a patch, i'll try it out!

Steve.
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