Re: [PATCH/RFC 0/1] Vhost User Cross Cable: Intro

[Stefan Hajnoczi <stefanha@gmail.com>]

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On Thu, Feb 13, 2020 at 03:48:59PM +0200, Nikos Dragazis wrote:
> On Tue, 14 Jan 2020 at 10:20 Stefan Hajnoczi
> <stefanha@gmail.com> wrote:
> > On Fri, Jan 10, 2020 at 10:34 AM Marc-André Lureau
> > <address@hidden> wrote:
> > > On Wed, Jan 8, 2020 at 5:57 AM V. <address@hidden> wrote:
> >
> > Hi V.,
> > I think I remember you from Etherboot/gPXE days :).
> >
> > > > 3.
> > > > Now if Cross Cable is actually a new and (after a code-rewrite of 10) a
> > > > viable way to connect 2 QEMU's together, could I actually
> > > > suggest a better way?
> > > > I am thinking of a '-netdev vhost-user-slave' option to connect (as client
> > > > or server) to a master QEMU running '-netdev vhost-user'.
> > > > This way there is no need for any external program at all, the master can
> > > > have it's memory unshared and everything would just work
> > > > and be fast.
> > > > Also the whole thing can fall back to normal virtio if memory is not shared
> > > > and it would even work in pure usermode without any
> > > > context switch.
> > > >
> > > > Building a patch for this idea I could maybe get around to, don't clearly
> > > > have an idea how much work this would be but I've done
> > > > crazier things.
> > > > But is this is something that someone might be able to whip up in an hour
> > > > or two? Someone who actually does have a clue about vhost
> > > > and virtio maybe? ;-)
> > >
> > > I believe https://wiki.qemu.org/Features/VirtioVhostUser is what you
> > > are after. It's still being discussed and non-trivial, but not very
> > > active lately afaik.
> >
> > virtio-vhost-user is being experimented with in the SPDK community but
> > there has been no activity on VIRTIO standardization or the QEMU
> > patches for some time.  More info here:
> > https://ndragazis.github.io/spdk.html
> >
> > I think the new ivshmem v2 feature may provide the functionality you
> > are looking for, but I haven't looked at them yet.  Here is the link:
> > https://www.mail-archive.com/address@hidden/msg668749.html
> >
> > And here is Jan's KVM Forum presentation on ivshmem v2:
> > https://www.youtube.com/watch?v=TiZrngLUFMA
> >
> > Stefan
> 
> 
> Hi Stefan,
> 
> First of all, sorry for the delayed response. The mail got lost
> somewhere in my inbox. Please keep Cc-ing me on all threads related to
> virtio-vhost-user.
> 
> As you correctly pointed out, I have been experimenting with
> virtio-vhost-user on SPDK and [1] is a working demo on this matter. I
> have been working on getting it merged with SPDK and, to this end, I
> have been interacting with the SPDK team [2][3] and mostly with Darek
> Stojaczyk (Cc-ing him).
> 
> The reason that you haven’t seen any activity for the last months is
> that I got a job and hence my schedule has become tighter. But I will
> definitely find some space and fit it into my schedule. Let me give you
> a heads up, so that we get synced:
> 
> Originally, I created and sent a patch (influenced from your DPDK patch
> [4]) to SPDK that was enhancing SPDK’s internal rte_vhost library with
> the virtio-vhost-user transport. However, a few weeks later, the SPDK
> team decided to switch from their internal rte_vhost library to using
> DPDK’s rte_vhost library directly [3]. Given that, I refactored and sent
> the patch for the virtio-vhost-user transport to the DPDK mailing list
> [5]. Regarding the virtio-vhost-user device, I have made some
> enhancements [6] on your original RFC device implementation and, as you
> may remember, I have sent some revised versions of the spec to the
> virtio mailing list [7].
> 
> At the moment, the blocker is the virtio spec. The last update on this
> was my discussion with Michael Tsirkin (Cc-ing him as well) about the
> need for the VIRTIO_PCI_CAP_DOORBELL_CFG and
> VIRTIO_PCI_CAP_NOTIFICATION_CFG configuration structures [8].
> 
> So, I think the next steps should be the following:
> 
> 1. merging the spec
> 2. adding the device on QEMU
> 3. adding the vvu transport on DPDK
> 4. extending SPDK to make use of the new vhost-user transport
> 
> To conclude, I still believe that this device is useful and should be
> part of virtio/qemu/dpdk/spdk and I will continue working on this
> direction.

Thanks for letting me know.  Feel free to resend the latest VIRTIO spec
changes to restart the discussion.  I am certainly interested.

Stefan

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