From mboxrd@z Thu Jan  1 00:00:00 1970
From: mlin@kernel.org (Ming Lin)
Date: Fri, 11 Sep 2015 10:21:41 -0700
Subject: [RFC PATCH 0/2] virtio nvme
In-Reply-To: <CAJSP0QXbjY5kbz0jTJSDyo=Zh9B+DRZorTY0m3bRC8yhJT=Nvw@mail.gmail.com>
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 <CAJSP0QXbjY5kbz0jTJSDyo=Zh9B+DRZorTY0m3bRC8yhJT=Nvw@mail.gmail.com>
Message-ID: <1441992101.802.11.camel@ssi>

On Fri, 2015-09-11@08:48 +0100, Stefan Hajnoczi wrote:
> On Thu, Sep 10, 2015@6:28 PM, Ming Lin <mlin@kernel.org> wrote:
> > On Thu, 2015-09-10@15:38 +0100, Stefan Hajnoczi wrote:
> >> On Thu, Sep 10, 2015@6:48 AM, Ming Lin <mlin@kernel.org> 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
- ....