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From:   John Garry <john.garry@huawei.com>
To:     <damien.lemoal@opensource.wdc.com>, <joro@8bytes.org>,
        <will@kernel.org>, <jejb@linux.ibm.com>,
        <martin.petersen@oracle.com>, <hch@lst.de>,
        <m.szyprowski@samsung.com>, <robin.murphy@arm.com>
CC:     <linux-doc@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <linux-ide@vger.kernel.org>, <iommu@lists.linux-foundation.org>,
        <iommu@lists.linux.dev>, <linux-scsi@vger.kernel.org>,
        <linuxarm@huawei.com>, John Garry <john.garry@huawei.com>
Subject: [PATCH v5 0/5] DMA mapping changes for SCSI core
Date:   Thu, 30 Jun 2022 20:08:07 +0800
Message-ID: <1656590892-42307-1-git-send-email-john.garry@huawei.com>
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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@huawei.com/

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