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 this lot, but didn't have any way to justify at the time. The third patch can be ignored for the sake of API discussion, but is included for completeness. 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(-) -- 2.17.1.dirty _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
