My understanding is that the Intel chips do not have an IOMMU at this time.
however this just means that the kernel and drivers have to fall back to the non-zero-copy mechanism if the hardware doesn't support scatter-gather nativly
it's a matter of useing it if it's there, and doing the best you can if it's not (and remember that if you compile the kernel for Opteron-only as opposed to K8 architecture you get more performance becouse you get to leave out the tests for the IOMMU and the code to handle it, so it doesn't always cost you :-)
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