On Fri, 2015-09-18 at 11:12 -0700, Ming Lin wrote: > On Thu, 2015-09-17 at 17:55 -0700, Nicholas A. Bellinger wrote: > > On Thu, 2015-09-17 at 16:31 -0700, Ming Lin wrote: > > > On Wed, 2015-09-16 at 23:10 -0700, Nicholas A. Bellinger wrote: > > > > Hi Ming & Co, <SNIP> > > > > > I think the future "LIO NVMe target" only speaks NVMe protocol. > > > > > > > > > > Nick(CCed), could you correct me if I'm wrong? > > > > > > > > > > For SCSI stack, we have: > > > > > virtio-scsi(guest) > > > > > tcm_vhost(or vhost_scsi, host) > > > > > LIO-scsi-target > > > > > > > > > > For NVMe stack, we'll have similar components: > > > > > virtio-nvme(guest) > > > > > vhost_nvme(host) > > > > > LIO-NVMe-target > > > > > > > > > > > > > I think it's more interesting to consider a 'vhost style' driver that > > > > can be used with unmodified nvme host OS drivers. > > > > > > > > Dr. Hannes (CC'ed) had done something like this for megasas a few years > > > > back using specialized QEMU emulation + eventfd based LIO fabric driver, > > > > and got it working with Linux + MSFT guests. > > > > > > > > Doing something similar for nvme would (potentially) be on par with > > > > current virtio-scsi+vhost-scsi small-block performance for scsi-mq > > > > guests, without the extra burden of a new command set specific virtio > > > > driver. > > > > > > Trying to understand it. > > > Is it like below? > > > > > > .------------------------. MMIO .---------------------------------------. > > > | Guest |--------> | Qemu | > > > | Unmodified NVMe driver |<-------- | NVMe device simulation(eventfd based) | > > > '------------------------' '---------------------------------------' > > > | ^ > > > write NVMe | | notify command > > > command | | completion > > > to eventfd | | to eventfd > > > v | > > > .--------------------------------------. > > > | Host: | > > > | eventfd based LIO NVMe fabric driver | > > > '--------------------------------------' > > > | > > > | nvme_queue_rq() > > > v > > > .--------------------------------------. > > > | NVMe driver | > > > '--------------------------------------' > > > | > > > | > > > v > > > .-------------------------------------. > > > | NVMe device | > > > '-------------------------------------' > > > > > > > Correct. The LIO driver on KVM host would be handling some amount of > > NVMe host interface emulation in kernel code, and would be able to > > decode nvme Read/Write/Flush operations and translate -> submit to > > existing backend drivers. > > Let me call the "eventfd based LIO NVMe fabric driver" as > "tcm_eventfd_nvme" > > Currently, LIO frontend driver(iscsi, fc, vhost-scsi etc) talk to LIO > backend driver(fileio, iblock etc) with SCSI commands. > > Did you mean the "tcm_eventfd_nvme" driver need to translate NVMe > commands to SCSI commands and then submit to backend driver? > IBLOCK + FILEIO + RD_MCP don't speak SCSI, they simply process I/Os with LBA + length based on SGL memory or pass along a FLUSH with LBA + length. So once the 'tcm_eventfd_nvme' driver on KVM host receives a nvme host hardware frame via eventfd, it would decode the frame and send along the Read/Write/Flush when exposing existing (non nvme native) backend drivers. This doesn't apply to PSCSI backend driver of course, because it expects to process actual SCSI CDBs. > But I thought the future "LIO NVMe target" can support frontend driver > talk to backend driver directly with NVMe commands without translation. > The native target_core_nvme backend driver is not processing nvme commands per-say, but simply exposing nvme hardware queue resources to a frontend fabric driver. For the nvme-over-fabrics case, backend nvme submission/complete queues are mapped to RDMA hardware queues. So essentially the nvme physical region page (PRP) is mapped to ib_sgl->addr. For a 'tcm_eventfd_nvme' style host-paravirt fabric case, it's less clear how exposing native nvme backend hardware resources would work, or if there is a significant performance benefit over just using submit_bio() for Read/Write/Flush. --nab _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
