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. Robin. [1] https://lists.linuxfoundation.org/pipermail/iommu/2018-August/029303.html Robin Murphy (3): iommu: Add fast hook for getting DMA domains iommu/dma: Use fast DMA domain lookup arm64/dma-mapping: Mildly optimise non-coherent IOMMU ops arch/arm64/mm/dma-mapping.c | 10 +++++----- drivers/iommu/dma-iommu.c | 23 ++++++++++++----------- drivers/iommu/iommu.c | 9 +++++++++ include/linux/iommu.h | 1 + 4 files changed, 27 insertions(+), 16 deletions(-) -- 2.19.0.dirty _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
