Linux Virtualization - May 2013 - updated: kvm networking todo wiki

On Fri, May 24, 2013 at 08:47:58AM -0500, Anthony Liguori
wrote:
> "Michael S. Tsirkin" <mst at redhat.com> writes:
> 
> > On Fri, May 24, 2013 at 05:41:11PM +0800, Jason Wang wrote:
> >> On 05/23/2013 04:50 PM, Michael S. Tsirkin wrote:
> >> > Hey guys,
> >> > I've updated the kvm networking todo wiki with current
projects.
> >> > Will try to keep it up to date more often.
> >> > Original announcement below.
> >> 
> >> Thanks a lot. I've added the tasks I'm currently working
on to the wiki.
> >> 
> >> btw. I notice the virtio-net data plane were missed in the wiki.
Is the
> >> project still being considered?
> >
> > It might have been interesting several years ago, but now that linux
has
> > vhost-net in kernel, the only point seems to be to
> > speed up networking on non-linux hosts.
> 
> Data plane just means having a dedicated thread for virtqueue processing
> that doesn't hold qemu_mutex.
> 
> Of course we're going to do this in QEMU.  It's a no brainer.  But
not
> as a separate device, just as an improvement to the existing userspace
> virtio-net.
> 
> > Since non-linux does not have kvm, I doubt virtio is a bottleneck.
> 
> 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).
Great idea, that sounds very intresting.

I'll add it to the wiki.

In fact a bit of complexity in vhost was put there in the vague hope to
support something like this: virtio rings are not translated through
regular memory tables, instead, vhost gets a pointer to ring address.

This allows qemu acting as a man in the middle,
verifying the descriptors but not touching the

Anyone interested in working on such a project?
> > IMO yet another networking backend is a distraction,
> > and confusing to users.
> > In any case, I'd like to see virtio-blk dataplane replace
> > non dataplane first. We don't want two copies of
> > virtio-net in qemu.
> 
> 100% agreed.
> 
> Regards,
> 
> Anthony Liguori
> 
> >
> >> > ----
> >> >
> >> > I've put up a wiki page with a kvm networking todo list,
> >> > mainly to avoid effort duplication, but also in the hope
> >> > to draw attention to what I think we should try addressing
> >> > in KVM:
> >> >
> >> > http://www.linux-kvm.org/page/NetworkingTodo
> >> >
> >> > This page could cover all networking related activity in KVM,
> >> > currently most info is related to virtio-net.
> >> >
> >> > Note: if there's no developer listed for an item,
> >> > this just means I don't know of anyone actively working
> >> > on an issue at the moment, not that no one intends to.
> >> >
> >> > I would appreciate it if others working on one of the items
on this list
> >> > would add their names so we can communicate better.  If
others like this
> >> > wiki page, please go ahead and add stuff you are working on
if any.
> >> >
> >> > It would be especially nice to add autotest projects:
> >> > there is just a short test matrix and a catch-all
> >> > 'Cover test matrix with autotest', currently.
> >> >
> >> > Currently there are some links to Red Hat bugzilla entries,
> >> > feel free to add links to other bugzillas.
> >> >
> >> > Thanks!
> >> >

"Michael S. Tsirkin" <mst at redhat.com>
writes:
> On Fri, May 24, 2013 at 08:47:58AM -0500, Anthony Liguori wrote:
>> "Michael S. Tsirkin" <mst at redhat.com> writes:
>> 
>> > On Fri, May 24, 2013 at 05:41:11PM +0800, Jason Wang wrote:
>> >> On 05/23/2013 04:50 PM, Michael S. Tsirkin wrote:
>> >> > Hey guys,
>> >> > I've updated the kvm networking todo wiki with
current projects.
>> >> > Will try to keep it up to date more often.
>> >> > Original announcement below.
>> >> 
>> >> Thanks a lot. I've added the tasks I'm currently
working on to the wiki.
>> >> 
>> >> btw. I notice the virtio-net data plane were missed in the
wiki. Is the
>> >> project still being considered?
>> >
>> > It might have been interesting several years ago, but now that
linux has
>> > vhost-net in kernel, the only point seems to be to
>> > speed up networking on non-linux hosts.
>> 
>> Data plane just means having a dedicated thread for virtqueue
processing
>> that doesn't hold qemu_mutex.
>> 
>> Of course we're going to do this in QEMU.  It's a no brainer. 
But not
>> as a separate device, just as an improvement to the existing userspace
>> virtio-net.
>> 
>> > Since non-linux does not have kvm, I doubt virtio is a bottleneck.
>> 
>> 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).
>
> Great idea, that sounds very intresting.
>
> I'll add it to the wiki.
>
> In fact a bit of complexity in vhost was put there in the vague hope to
> support something like this: virtio rings are not translated through
> regular memory tables, instead, vhost gets a pointer to ring address.
>
> This allows qemu acting as a man in the middle,
> verifying the descriptors but not touching the
>
> Anyone interested in working on such a project?
It would be an interesting idea if we didn't already have the vhost
model where we don't need the userspace bounce.  We already have two
sets of host side ring code in the kernel (vhost and vringh, though
they're being unified).

All an accelerator can offer on the tx side is zero copy and direct
update of the used ring.  On rx userspace could register the buffers and
the accelerator could fill them and update the used ring.  It still
needs to deal with merged buffers, for example.

You avoid the address translation in the kernel, but I'm not convinced
that's a key problem.

Cheers,
Rusty.