Messages in this thread | | | From | John Garry <> | Subject | [PATCH RFC v2 0/4] iommu/arm-smmu-v3: Improve cmdq lock efficiency | Date | Tue, 16 Jun 2020 21:59:49 +0800 |
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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 increase: Before: 1310 IOPs After: 1630 IOPs
I also have a test harness to check the rate of DMA map+unmaps we can achieve:
CPU count 32 64 128 Before: 63187 19418 10169 After: 93287 44789 15862
(unit is map+unmaps per CPU per second)
There's no specific problem that I know of with this series, as previous issues should now be fixed - but I'm a bit nervous about how we deal with the queue being full and wrapping.
And I want to test more.
Thanks
[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 | 210 ++++++++++++++++++++++-------------- 1 file changed, 131 insertions(+), 79 deletions(-)
-- 2.26.2
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