On Fri, 2015-09-18 at 14:09 -0700, Nicholas A. Bellinger wrote: > 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. Learned vhost architecture: http://blog.vmsplice.net/2011/09/qemu-internals-vhost-architecture.html The nice thing is it is not tied to KVM in any way. For SCSI, there are "virtio-scsi" in guest kernel and "vhost-scsi" in host kernel. For NVMe, there is no "virtio-nvme" in guest kernel(just unmodified NVMe driver), but I'll do similar thing in Qemu with vhost infrastructure. And there is "vhost_nvme" in host kernel. For the "virtqueue" implementation in qemu-nvme, I'll possibly just use/copy drivers/virtio/virtio_ring.c, same as what linux/tools/virtio/virtio_test.c does. A bit more detail graph as below. What do you think? .-----------------------------------------. .------------------------. | Guest(Linux, Windows, FreeBSD, Solaris) | NVMe | qemu | | unmodified NVMe driver | command | NVMe device emulation | | | -------> | vhost + virtqueue | '-----------------------------------------' '------------------------' | | ^ passthrough | kick/notify NVMe command | via eventfd userspace via virtqueue | | | v v | ---------------------------------------------------------------------------------- .-----------------------------------------------------------------------. kernel | LIO frontend driver | | - vhost_nvme | '-----------------------------------------------------------------------' | translate ^ | (NVMe command) | | to | v (LBA, length) | .----------------------------------------------------------------------. | LIO backend driver | | - fileio (/mnt/xxx.file) | | - iblock (/dev/sda1, /dev/nvme0n1, ...) | '----------------------------------------------------------------------' | ^ | submit_bio() | v | .----------------------------------------------------------------------. | block layer | | | '----------------------------------------------------------------------' | ^ | | v | .----------------------------------------------------------------------. | block device driver | | | '----------------------------------------------------------------------' | | | | | | | | v v v v .------------. .-----------. .------------. .---------------. | SATA | | SCSI | | NVMe | | .... | '------------' '-----------' '------------' '---------------' _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
