linux-kernel - Re: [PATCH 1/2] IOMMU Identity Mapping Support: iommu_identity

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Date:	Thu, 18 Jun 2009 11:13:35 -0700
From:	Chris Wright <chrisw@...s-sol.org>
To:	Fenghua Yu <fenghua.yu@...el.com>
Cc:	David Woodhouse <dwmw2@...radead.org>,
	"'Linus Torvalds'" <torvalds@...ux-foundation.org>,
	"'Stephen Rothwell'" <sfr@...b.auug.org.au>,
	"'Andrew Morton'" <akpm@...ux-foundation.org>,
	"'Ingo Molnar'" <mingo@...e.hu>,
	"'Christopher Wright'" <chrisw@...hat.com>,
	"'Allen Kay'" <allen.m.kay@...el.com>,
	"'iommu'" <iommu@...ts.linux-foundation.org>,
	"'lkml'" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] IOMMU Identity Mapping Support:
	iommu_identity_mapping definition

* Fenghua Yu (fenghua.yu@...el.com) wrote:
> IOMMU Identity Mapping Support: iommu_identity_mapping definition
> 
> Identity mapping for IOMMU defines a single domain to 1:1 map all pci devices
> to all usable memory.
> 
> This will reduces map/unmap overhead in DMA API's and improve IOMMU performance.
> On 10Gb network cards, Netperf shows no performance degradation compared to
> non-IOMMU performance.
> 
> This method may lose some of DMA remapping benefits like isolation.
> 
> The first patch defines iommu_identity_mapping varialbe which controls the
> identity mapping code and is 0 by default.

The only real difference between "pt" and "identity" is hardware support.
We should have a single value we don't have to tell users to do different
things depending on their hardware (they won't even know what they have)
to achieve the same result.

thanks,
-chris
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