[RFC PATCH 0/2] virtio nvme

Ming Lin
Thu, 17 Sep 2015 23:31:27 -0000

On Wed, 2015-09-16 at 23:10 -0700, Nicholas A. Bellinger
wrote:
> Hi Ming & Co,
>
> On Thu, 2015-09-10 at 10:28 -0700, Ming Lin 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 at
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.
>
> <SNIP>
>
> > >
> > > At first glance it seems like the virtio_nvme guest driver is
just
> > > another block driver like virtio_blk, so I'm not clear why a
> > > virtio-nvme device makes sense.
> >
> > 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                         |

'-------------------------------------'