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Date:   Wed, 6 Jul 2022 14:40:44 +0100
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Subject: Re: [PATCH v5 0/5] DMA mapping changes for SCSI core
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>
References: <1656590892-42307-1-git-send-email-john.garry@huawei.com>
From:   John Garry <john.garry@huawei.com>
In-Reply-To: <1656590892-42307-1-git-send-email-john.garry@huawei.com>
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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@huawei.com/
> 
> Changes since v4:
> - tweak libata and other patch titles
> - Add Robin's tag (thanks!)
> - Clarify description of new DMA mapping API