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

John Garry john.garry at huawei.com
Mon Sep 17 04:20:04 PDT 2018

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


> 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 <will.deacon at arm.com>
> Will
> .

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