Hi all, Waiting for the command queue to drain for CMD_SYNC completion is likely a contention hotspot on high-core-count systems. If the SMMU is coherent and supports MSIs, though, we can use this cool feature (as suggested by the architecture, no less) to make syncs effectively non-blocking for anyone other than the caller.
I don't have any hardware that supports MSIs, but this has at least passed muster on the Fast Model with cache modelling enabled - I'm hoping the Qualcomm machines have the appropriate configuration to actually test how well it works in reality. If it is worthwhile, I do have most of a plan for how we can do something similar in the non-MSI polling case (it's mostly a problem of handling the queue-wrapping edge cases correctly). Robin. Robin Murphy (3): iommu/arm-smmu-v3: Specialise CMD_SYNC handling iommu/arm-smmu-v3: Forget about cmdq-sync interrupt iommu/arm-smmu-v3: Utilise CMD_SYNC MSI feature drivers/iommu/arm-smmu-v3.c | 117 +++++++++++++++++++++++++++++--------------- 1 file changed, 77 insertions(+), 40 deletions(-) -- 2.13.4.dirty _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
