Re: Re: [virtio-comment] About adding a new device type virtio-nvme

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Jan 18, 2023 at 10:49:23AM +0800, äèä wrote:
> On Tue, 17 Jan 2023 11:01:37 -0500, Stefan wrote:
> 
> >On Tue, Jan 17, 2023 at 10:04:07AM +0800, äèä wrote:
> 
> >> On Wed, 11 Jan 2023 10:16:55 -0500, Stefan wrote:
> >>
> >>
> >> >>On Wed, Jan 11, 2023 at 11:21:35AM +0800, äèä wrote:
> >> >> As we know, nvme has more features than virtio-blk. For example, with the development of virtualization IO offloading to hardware, virtio-blk and NVME-OF offloading to hardware >are developing rapidly. So if virtio and nvme are combined into Virtio-NvMe, Is it necessary to add a device type Virtio-NvMe ?
> >>
> >>
> >>
> >> Â
> >>
> >>
> >>
> >> >Hi,
> >> >In theory, yes, virtio-nvme can be done. The question is why do it?
> >>
> >>
> >>
> >> >NVMe already provides a PCI hardware spec for software and hardware
> >> >implementations to follow. An NVMe PCI device can be exposed to the
> >> >guest and modern operating systems recognize it without requiring new
> >> >drivers.
> >>
> >>
> >> >The value of VIRTIO here is probably in the deep integration into the
> >> >virtualization stack with vDPA, vhost, etc. A virtio-nvme device can use
> >> >all these things whereas a PCI device needs to do everything from
> >> >scratch.
> >>
> >> The NVME technology and ecosystem are complete. However, in virtualization scenarios, NVME devices can only use PCIe pass-through . When NVME and virtio combine to connect to the vDPA ecosystem, live migration is supported.
> >>
> >>
> >> >Let's not forget that virtio-blk is widely used and new commands are
> >> >being added as needed. Which NVMe features are you missing in
> >> >virtio-blk?
> >>
> >> With the introduction of the concept of DPU, a large number of vendors are offloading virtual devices to hardware. The back-end of Virtio-blk does not support remote storage. Therefore, Virtio-Nvme-of can well combine the advantages of remote storage and virtio live migration
> >
> >virtio-blk is just a storage interface, whether that storage is local or
> >remote is up to the device implementation. The block device could be
> >located on Ceph, NFS, etc.
> >Â
> >Each virtio-blk device is a single block device. There is no
> >standardized management protocol in virtio-blk for connecting to remote
> >block devices. I'm aware of hardware virtio-blk devices that connect to
> >remote storage. Configuration is performed through an out-of-band
> >management interface.
> >Â
> >Maybe when you say virtio-blk doesn't support remote storage this is
> >what you mean?
> 
> 
> 
> Yes, virtio-blk devices offlaod to hardware, For example, DPU and SmartNIC.
> So, compare virtio-nvme with virtio-blk and NVME.
> 
> 
> 
> 
> 
> Stefan
> 


Let's circle back a bit. You asked:
	So if virtio and nvme are combined into Virtio-NvMe, Is it
	necessary to add a device type Virtio-NvMe ?
And the answer seems to be:
	not without much more in the way of motivation.

-- 
MST