Re: [PATCH v5 0/5] DMA mapping changes for SCSI core

[John Garry]

On 30/06/2022 13:08, John Garry wrote:

Hi Christoph,

Can you please consider picking up this series? A few things to note 
beforehand:

- I changed to only apply the mapping limit to SAS hosts in this 
version. I would need a fresh ack from Martin for those SCSI parts, but 
wanted to make sure you were ok with it.
- Damien had some doubt on updating the shost max_sectors as opposed to 
the per-request queue default, but I think he's ok with it - see patch 4/5

Thanks,
John


> 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