[PATCH v2 0/3] iommu: Avoid DMA ops domain refcount contention

Hi Robin,

On Wed, Sep 12, 2018 at 04:24:11PM +0100, Robin Murphy wrote:

John raised the issue[1] that we have some unnecessary refcount contention
in the DMA ops path which shows scalability problems now that we have more
real high-performance hardware using iommu-dma. The x86 IOMMU drivers are
sidestepping this by stashing domain references in archdata, but since
that's not very nice for architecture-agnostic code, I think it's time to
look at a generic API-level solution.

These are a couple of quick patches based on the idea I had back when
first implementing iommu-dma, but didn't have any way to justify at the
time. However, the reports of 10-25% better networking performance on v1
suggest that it's very worthwhile (and far more significant than I ever
would have guessed).

As far as merging goes, I don't mind at all whether this goes via IOMMU,
or via dma-mapping provided Joerg's happy to ack it.

I think it makes most sense for Joerg to take this series via his tree.

Anyway, I've been running them on my TX2 box and things are happy enough,
so:

Tested-by: Will Deacon <redacted>

Will