Re: [PATCH 1/2] IOMMU Identity Mapping Support:iommu_identity_mapping definition

From: Chris Wright
Date: Thu Jun 18 2009 - 14:17:14 EST

* Fenghua Yu (fenghua.yu@xxxxxxxxx) 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.

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