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

On 17/09/2018 12:20, John Garry wrote:

On 14/09/2018 13:48, Will Deacon wrote:

quoted

Hi Robin,

Hi Robin,

I just spoke with Dongdong and we will test this version also so that we
may provide a "Tested-by" tag.

I tested this, so for series:
Tested-by: John Garry <redacted>

Thanks,
John

Thanks,
John

quoted

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

quoted

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

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