On Fri, Sep 11, 2015 at 6:21 PM, Ming Lin <mlin@xxxxxxxxxx> wrote: > On Fri, 2015-09-11 at 08:48 +0100, Stefan Hajnoczi wrote: >> On Thu, Sep 10, 2015 at 6:28 PM, Ming Lin <mlin@xxxxxxxxxx> wrote: >> > On Thu, 2015-09-10 at 15:38 +0100, Stefan Hajnoczi wrote: >> >> On Thu, Sep 10, 2015 at 6:48 AM, Ming Lin <mlin@xxxxxxxxxx> wrote: >> >> > These 2 patches added virtio-nvme to kernel and qemu, >> >> > basically modified from virtio-blk and nvme code. >> >> > >> >> > As title said, request for your comments. >> >> > >> >> > Play it in Qemu with: >> >> > -drive file=disk.img,format=raw,if=none,id=D22 \ >> >> > -device virtio-nvme-pci,drive=D22,serial=1234,num_queues=4 >> >> > >> >> > The goal is to have a full NVMe stack from VM guest(virtio-nvme) >> >> > to host(vhost_nvme) to LIO NVMe-over-fabrics target. >> >> >> >> Why is a virtio-nvme guest device needed? I guess there must either >> >> be NVMe-only features that you want to pass through, or you think the >> >> performance will be significantly better than virtio-blk/virtio-scsi? >> > >> > It simply passes through NVMe commands. >> >> I understand that. My question is why the guest needs to send NVMe commands? >> >> If the virtio_nvme.ko guest driver only sends read/write/flush then >> there's no advantage over virtio-blk. >> >> There must be something you are trying to achieve which is not >> possible with virtio-blk or virtio-scsi. What is that? > > I actually learned from your virtio-scsi work. > http://www.linux-kvm.org/images/f/f5/2011-forum-virtio-scsi.pdf > > Then I thought a full NVMe stack from guest to host to target seems > reasonable. > > Trying to achieve similar things as virtio-scsi, but all NVMe protocol. > > - Effective NVMe passthrough > - Multiple target choices: QEMU, LIO-NVMe(vhost_nvme) > - Almost unlimited scalability. Thousands of namespaces per PCI device > - True NVMe device > - End-to-end Protection Information > - .... The advantages you mentioned are already available in virtio-scsi, except for the NVMe command set. I don't understand what unique problem virtio-nvme solves yet. If someone asked me to explain why NVMe-over-virtio makes sense compared to the existing virtio-blk/virtio-scsi or NVMe SR-IOV options, I wouldn't know the answer. I'd like to learn that from you or anyone else on CC. Do you have a use case in mind? Stefan _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
