Re: [PATCH v3 3/4] scsi: core: Cap shost max_sectors according to DMA optimum mapping limits

John Garry
2022-06-09T17:54:11Z

On 09/06/2022 18:18, Bart Van Assche wrote:
>>>
>>> SCSI host bus adapters that support 64-bit DMA may support much
>>> larger transfer sizes than 128 KiB.
>>
>> Indeed, and that is my problem today, as my storage controller is
>> generating DMA mapping lengths which exceeds 128K and they slow
>> everything down.
>>
>> If you say that SRP enjoys best peformance with larger transfers then
>> can you please test this with an IOMMU enabled (iommu group type DMA
>> or DMA-FQ)?
>
> Hmm ... what exactly do you want me to test? Do you perhaps want me to
> measure how much performance drops with an IOMMU enabled?

Yes, I would like to know of any performance change with an IOMMU
enabled and then with an IOMMU enabled and including my series.

> I don't have
> access anymore to the SRP setup I referred to in my previous email. But
> I do have access to devices that boot from UFS storage. For these
> devices we need to transfer 2 MiB per request to achieve full bandwidth.

ok, but do you have a system where the UFS host controller is behind an
IOMMU? I had the impression that UFS controllers would be mostly found
in embedded systems and IOMMUs are not as common on there.

Thanks,
John