Messages in this thread | | | Date | Thu, 9 Jun 2022 10:18:40 -0700 | Subject | Re: [PATCH v3 3/4] scsi: core: Cap shost max_sectors according to DMA optimum mapping limits | From | Bart Van Assche <> |
| |
On 6/9/22 01:00, John Garry wrote: > On 08/06/2022 22:07, Bart Van Assche wrote: >> On 6/8/22 10:50, John Garry wrote: >>> Please note that this limit only applies if we have an IOMMU enabled >>> for the scsi host dma device. Otherwise we are limited by dma direct >>> or swiotlb max mapping size, as before. >> >> 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? 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.
Thanks,
Bart.
| |