Re: SMMU Cmdq Related Patch Unable to Reproduce Performance Improvement

On 2021/6/26 22:33, 李泽斌 wrote:

Hi all

I am recently curious about a patch mentioned in OpenEuler Kernel Meeting about SMMU. The patch name is "iommu/arm-smmu-v3: Reduce contention during command-queue insertion", and it has been merged, the commit link is here(https://github.com/torvalds/linux/commit/587e6c10a7ce89a5924fdbeff2ec524fbd6a124b).

But I find it difficult to reproduce the huge performance improvement, and I notice that there is an evaluation result figure in the meeting. So I turn to you guys for help. I wonder if you can provide more evaluation details to reproduce the improvement. TIA

First，it only works in strict mode on ARM64, so please make sure: "iommu.passthrough=1" or "iommu.strict=0" is not set. Second, only some high-end peripherals have this performance bottleneck. For example: 1) 100Gb/s or higher NIC interconnection (direct connection), use command 'iperf' to test it 2) Attach more than 12 SSDs or NVMEs to the PCI expander, use command 'fio' to test it

For most low-speed devices, their performance in strict mode is close to iommu.passthrough=1. There is no room for further optimization.

Best Regards

Zebin Li

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