On 31/01/2018 20:38, Jason Gunthorpe wrote: > On Wed, Jan 31, 2018 at 02:27:01PM +0200, Marcel Apfelbaum wrote: > >> It is good to know, but still, passing so much information to kernel >> when we can rather "compress" it, maybe it worth a second thought. > > Not sure. Have to see the whole thing.. > >>> Well, actually, only a 3rd :| The new MR would likely be 0 based, but >>> the VM guest doesn't know about this. So you'd need an API that can do >>> arbitrary based to really solve your probably. I guess all HW should >>> be able to do this so maybe it is OK? >> >> The way we solve "the other" half is by intercepting the post-send >> requests in hypervisor. At hypervisor level we don't have contiguous virtual >> addresses anymore, but we don't need them for 0 based MRs: >> The guest still register regular MRs, while the hypervisor will >> register a 0 based MR save the guest virtual address of the MR. >> At post-send we simply substract the saved MR base address from the work request >> buffers and we are back to 0 based MR. > Hi Jason, > That only works for lkeys, the rkey expoeses the base address to the > remote - the HV can't fix it.. > Thanks for the clarification. What we really need is to allow to map a list of pages to a IOVA different from the process address space, e.g guest supplied IOVA. Something like req_mr (list_of_process_va_pages, base_other_iova, len_other_iova) Do think the new API can support that? Thanks, Marcel >> Do you have a model in mind? We would really want to try it out. >> >> By the way, I tried to search in the kernel for vendors implementing >> it and I saw maybe one vendor... so maybe 0 based MR is a nice idea >> but nothing more. > > Try the mlx drivers, I think at least one of them can do it today. > > Jason > -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
