From mboxrd@z Thu Jan  1 00:00:00 1970
From: mlin@kernel.org (Ming Lin)
Date: Thu, 17 Sep 2015 16:31:27 -0700
Subject: [RFC PATCH 0/2] virtio nvme
In-Reply-To: <1442470241.23132.77.camel@haakon3.risingtidesystems.com>
References: <1441864112-12765-1-git-send-email-mlin@kernel.org>
 <CAJSP0QUmtgoh23G3u64xRnBbJkAoO19AEi=vkyPPyg9n9jqC2Q@mail.gmail.com>
 <1441906098.18716.21.camel@ssi>
 <1442470241.23132.77.camel@haakon3.risingtidesystems.com>
Message-ID: <1442532687.4750.6.camel@ssi>

On Wed, 2015-09-16@23:10 -0700, Nicholas A. Bellinger wrote:
> Hi Ming & Co,
> 
> On Thu, 2015-09-10@10:28 -0700, Ming Lin 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.
> 
> <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                         |
                                       '-------------------------------------'