netdev - Re: updated: kvm networking todo wiki

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Message-ID: <20130530134449.GA31649@redhat.com>
Date:	Thu, 30 May 2013 16:44:49 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Anthony Liguori <anthony@...emonkey.ws>
Cc:	Stefan Hajnoczi <stefanha@...il.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Jason Wang <jasowang@...hat.com>, herbert@...dor.hengli.com.au,
	kvm <kvm@...r.kernel.org>, qemu-devel <qemu-devel@...gnu.org>,
	netdev@...r.kernel.org,
	Linux Virtualization <virtualization@...ts.linux-foundation.org>,
	Dmitry Fleytman <dmitry@...nix.com>
Subject: Re: updated: kvm networking todo wiki

On Thu, May 30, 2013 at 08:40:47AM -0500, Anthony Liguori wrote:
> Stefan Hajnoczi <stefanha@...il.com> writes:
> 
> > On Thu, May 30, 2013 at 7:23 AM, Rusty Russell <rusty@...tcorp.com.au> wrote:
> >> Anthony Liguori <anthony@...emonkey.ws> writes:
> >>> Rusty Russell <rusty@...tcorp.com.au> writes:
> >>>> On Fri, May 24, 2013 at 08:47:58AM -0500, Anthony Liguori wrote:
> >>>>> FWIW, I think what's more interesting is using vhost-net as a networking
> >>>>> backend with virtio-net in QEMU being what's guest facing.
> >>>>>
> >>>>> In theory, this gives you the best of both worlds: QEMU acts as a first
> >>>>> line of defense against a malicious guest while still getting the
> >>>>> performance advantages of vhost-net (zero-copy).
> >>>>>
> >>>> It would be an interesting idea if we didn't already have the vhost
> >>>> model where we don't need the userspace bounce.
> >>>
> >>> The model is very interesting for QEMU because then we can use vhost as
> >>> a backend for other types of network adapters (like vmxnet3 or even
> >>> e1000).
> >>>
> >>> It also helps for things like fault tolerance where we need to be able
> >>> to control packet flow within QEMU.
> >>
> >> (CC's reduced, context added, Dmitry Fleytman added for vmxnet3 thoughts).
> >>
> >> Then I'm really confused as to what this would look like.  A zero copy
> >> sendmsg?  We should be able to implement that today.
> >>
> >> On the receive side, what can we do better than readv?  If we need to
> >> return to userspace to tell the guest that we've got a new packet, we
> >> don't win on latency.  We might reduce syscall overhead with a
> >> multi-dimensional readv to read multiple packets at once?
> >
> > Sounds like recvmmsg(2).
> 
> Could we map this to mergable rx buffers though?
> 
> Regards,
> 
> Anthony Liguori

Yes because we don't have to complete buffers in order.

> >
> > Stefan
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