On Fri, Sep 11, 2015 at 6:21 PM, Ming Lin [off-list ref] wrote:

On Fri, 2015-09-11 at 08:48 +0100, Stefan Hajnoczi wrote:

quoted

On Thu, Sep 10, 2015 at 6:28 PM, Ming Lin [off-list ref] wrote:

quoted

On Thu, 2015-09-10 at 15:38 +0100, Stefan Hajnoczi wrote:

quoted

On Thu, Sep 10, 2015 at 6:48 AM, Ming Lin [off-list ref] wrote:

quoted

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