On 7/9/22 01:17, John Garry wrote: > On 07/07/2022 21:35, Martin K. Petersen wrote: >> Christoph, >> >>> Yes, I've mostly been waiting for an ACK from Martin. >> Sorry, I'm on vacation this week. The series looks OK to me although I >> do agree that it would be great if the max was reflected in the queue's >> hard limit and opt in the soft limit. > > Ah, I think that I misunderstood Damien's question. I thought he was > asking why not keep shost max_sectors at dma_max_mapping_size() and then > init each sdev request queue max hw sectors at dma_opt_mapping_size(). I was suggesting the reverse :) Keep the device hard limit (max_hw_sectors) to the max dma mapping and set the soft limit (max_sectors) to the optimal dma mapping size. > > But he seems that you want to know why not have the request queue max > sectors at dma_opt_mapping_size(). The answer is related to meaning of > dma_opt_mapping_size(). If we get any mappings which exceed this size > then it can have a big dma mapping performance hit. So I set max hw > sectors at this ‘opt’ mapping size to ensure that we get no mappings > which exceed this size. Indeed, I think max sectors is 128Kb today for > my host, which would be same as dma_opt_mapping_size() value with an > IOMMU enabled. And I find that only a small % of request size may exceed > this 128kb size, but it still has a big performance impact. > >> >> Acked-by: Martin K. Petersen<martin.petersen@xxxxxxxxxx> > > Thanks, > John -- Damien Le Moal Western Digital Research
