As reported in [0], DMA mappings whose size exceeds the IOMMU IOVA caching limit may see a big performance hit. This series introduces a new DMA mapping API, dma_opt_mapping_size(), so that drivers may know this limit when performance is a factor in the mapping. The SCSI SAS transport code is modified only to use this limit. For now I did not want to touch other hosts as I have a concern that this change could cause a performance regression. I also added a patch for libata-scsi as it does not currently honour the shost max_sectors limit. [0] https://lore.kernel.org/linux-iommu/20210129092120.1482-1-thunder.leizhen@xxxxxxxxxx/ Changes since v4: - tweak libata and other patch titles - Add Robin's tag (thanks!) - Clarify description of new DMA mapping API Changes since v3: - Apply max DMA optimial limit to SAS hosts only Note: Even though "scsi: core: Cap shost max_sectors only once when adding" is a subset of a previous patch I did not transfer the RB tags - Rebase on v5.19-rc4 John Garry (5): dma-mapping: Add dma_opt_mapping_size() dma-iommu: Add iommu_dma_opt_mapping_size() scsi: core: Cap shost max_sectors according to DMA limits only once scsi: scsi_transport_sas: Cap shost max_sectors according to DMA optimal limit ata: libata-scsi: Cap ata_device->max_sectors according to shost->max_sectors Documentation/core-api/dma-api.rst | 14 ++++++++++++++ drivers/ata/libata-scsi.c | 1 + drivers/iommu/dma-iommu.c | 6 ++++++ drivers/iommu/iova.c | 5 +++++ drivers/scsi/hosts.c | 5 +++++ drivers/scsi/scsi_lib.c | 4 ---- drivers/scsi/scsi_transport_sas.c | 6 ++++++ include/linux/dma-map-ops.h | 1 + include/linux/dma-mapping.h | 5 +++++ include/linux/iova.h | 2 ++ kernel/dma/mapping.c | 12 ++++++++++++ 11 files changed, 57 insertions(+), 4 deletions(-) -- 2.35.3
