[PATCH 0/4] iommu/arm-smmu-v3: Improve cmdq lock efficiency

John Garry john.garry at huawei.com
Mon Jun 22 13:28:36 EDT 2020

As mentioned in [0], the CPU may consume many cycles processing
arm_smmu_cmdq_issue_cmdlist(). One issue we find is the cmpxchg() loop to
get space on the queue takes approx 25% of the cycles for this function.

This series removes that cmpxchg().

For my NVMe test with 3x NVMe SSDs, I'm getting a ~24% throughput
Before: 1310 IOPs
After: 1630 IOPs

I also have a test harness to check the rate of DMA map+unmaps we can

CPU count	32	64	128
Before:		63187	19418	10169
After:		93287	44789	15862

(unit is map+unmaps per CPU per second)

[0] https://lore.kernel.org/linux-iommu/B926444035E5E2439431908E3842AFD24B86DB@DGGEMI525-MBS.china.huawei.com/T/#ma02e301c38c3e94b7725e685757c27e39c7cbde3

John Garry (4):
  iommu/arm-smmu-v3: Fix trivial typo
  iommu/arm-smmu-v3: Calculate bits for prod and owner
  iommu/arm-smmu-v3: Always issue a CMD_SYNC per batch
  iommu/arm-smmu-v3: Remove cmpxchg() in arm_smmu_cmdq_issue_cmdlist()

 drivers/iommu/arm-smmu-v3.c | 233 +++++++++++++++++++++++-------------
 1 file changed, 151 insertions(+), 82 deletions(-)


More information about the linux-arm-kernel mailing list