Re: [bug report] iommu_dma_unmap_sg() is very slow then running IO from remote numa node

[Ming Lei <ming.lei@redhat.com>]

On Fri, Jul 09, 2021 at 11:26:53AM +0100, Robin Murphy wrote:
> On 2021-07-09 09:38, Ming Lei wrote:
> > Hello,
> > 
> > I observed that NVMe performance is very bad when running fio on one
> > CPU(aarch64) in remote numa node compared with the nvme pci numa node.
> > 
> > Please see the test result[1] 327K vs. 34.9K.
> > 
> > Latency trace shows that one big difference is in iommu_dma_unmap_sg(),
> > 1111 nsecs vs 25437 nsecs.
> 
> Are you able to dig down further into that? iommu_dma_unmap_sg() itself
> doesn't do anything particularly special, so whatever makes a difference is
> probably happening at a lower level, and I suspect there's probably an SMMU
> involved. If for instance it turns out to go all the way down to
> __arm_smmu_cmdq_poll_until_consumed() because polling MMIO from the wrong
> node is slow, there's unlikely to be much you can do about that other than
> the global "go faster" knobs (iommu.strict and iommu.passthrough) with their
> associated compromises.

Follows the log of 'perf report'

1) good(run fio from cpus in the nvme's numa node)

-   34.86%     1.73%  fio       [nvme]              [k] nvme_process_cq                                                      ▒
   - 33.13% nvme_process_cq                                                                                                  ▒
      - 32.93% nvme_pci_complete_rq                                                                                          ▒
         - 24.92% nvme_unmap_data                                                                                            ▒
            - 20.08% dma_unmap_sg_attrs                                                                                      ▒
               - 19.79% iommu_dma_unmap_sg                                                                                   ▒
                  - 19.55% __iommu_dma_unmap                                                                                 ▒
                     - 16.86% arm_smmu_iotlb_sync                                                                            ▒
                        - 16.81% arm_smmu_tlb_inv_range_domain                                                               ▒
                           - 14.73% __arm_smmu_tlb_inv_range                                                                 ▒
                                14.44% arm_smmu_cmdq_issue_cmdlist                                                           ▒
                             0.89% __pi_memset                                                                               ▒
                             0.75% arm_smmu_atc_inv_domain                                                                   ▒
                     + 1.58% iommu_unmap_fast                                                                                ▒
                     + 0.71% iommu_dma_free_iova                                                                             ▒
            - 3.25% dma_unmap_page_attrs                                                                                     ▒
               - 3.21% iommu_dma_unmap_page                                                                                  ▒
                  - 3.14% __iommu_dma_unmap_swiotlb                                                                          ▒
                     - 2.86% __iommu_dma_unmap                                                                               ▒
                        - 2.48% arm_smmu_iotlb_sync                                                                          ▒
                           - 2.47% arm_smmu_tlb_inv_range_domain                                                             ▒
                              - 2.19% __arm_smmu_tlb_inv_range                                                               ▒
                                   2.16% arm_smmu_cmdq_issue_cmdlist                                                         ▒
            + 1.34% mempool_free                                                                                             ▒
         + 7.68% nvme_complete_rq                                                                                            ▒
   + 1.73% _start


2) bad(run fio from cpus not in the nvme's numa node)
-   49.25%     3.03%  fio       [nvme]              [k] nvme_process_cq                                                      ▒
   - 46.22% nvme_process_cq                                                                                                  ▒
      - 46.07% nvme_pci_complete_rq                                                                                          ▒
         - 41.02% nvme_unmap_data                                                                                            ▒
            - 34.92% dma_unmap_sg_attrs                                                                                      ▒
               - 34.75% iommu_dma_unmap_sg                                                                                   ▒
                  - 34.58% __iommu_dma_unmap                                                                                 ▒
                     - 33.04% arm_smmu_iotlb_sync                                                                            ▒
                        - 33.00% arm_smmu_tlb_inv_range_domain                                                               ▒
                           - 31.86% __arm_smmu_tlb_inv_range                                                                 ▒
                                31.71% arm_smmu_cmdq_issue_cmdlist                                                           ▒
                     + 0.90% iommu_unmap_fast                                                                                ▒
            - 5.17% dma_unmap_page_attrs                                                                                     ▒
               - 5.15% iommu_dma_unmap_page                                                                                  ▒
                  - 5.12% __iommu_dma_unmap_swiotlb                                                                          ▒
                     - 5.05% __iommu_dma_unmap                                                                               ▒
                        - 4.86% arm_smmu_iotlb_sync                                                                          ▒
                           - 4.85% arm_smmu_tlb_inv_range_domain                                                             ▒
                              - 4.70% __arm_smmu_tlb_inv_range                                                               ▒
                                   4.67% arm_smmu_cmdq_issue_cmdlist                                                         ▒
            + 0.74% mempool_free                                                                                             ▒
         + 4.83% nvme_complete_rq                                                                                            ▒
   + 3.03% _start


Thanks, 
Ming