Re: [Qemu-devel] snabbswitch integration with QEMU for userspace ethernet I/O

[Anthony Liguori]

Paolo Bonzini <address@hidden> writes:

> Il 27/05/2013 11:34, Stefan Hajnoczi ha scritto:
>> On Sun, May 26, 2013 at 11:32:49AM +0200, Luke Gorrie wrote:
>>> Stefan put us onto the highly promising track of vhost/virtio. We have
>>> implemented this between Snabb Switch and the Linux kernel, but not
>>> directly between Snabb Switch and QEMU guests. The "roadblock" we have hit
>>> is embarrasingly basic: QEMU is using user-to-kernel system calls to setup
>>> vhost (open /dev/net/tun and /dev/vhost-net, ioctl()s) and I haven't found
>>> a good way to map these towards Snabb Switch instead of the kernel.
>> 
>> vhost_net is about connecting the a virtio-net speaking process to a
>> tun-like device.  The problem you are trying to solve is connecting a
>> virtio-net speaking process to Snabb Switch.
>> 
>> Either you need to replace vhost or you need a tun-like device
>> interface.
>> 
>> How does your switch talk to hardware?
>
> And also, is your switch monolithic or does it consist of different
> processes?
>
> If you already have processes talking to each other, the first thing
> that came to my mind was a new network backend, similar to net/vde.c but
> more featureful (so that you support the virtio headers for offloading,
> for example).  Then you would use "-netdev snabb,id=net0 -device
> e1000,netdev=net0".

It would be very interesting to combine this with vmsplice/splice.

> It would be slower than vhost-net, for example no zero-copy
> transmission.

With splice, I think you could at least get single copy guest-to-guest
networking which is about as good as can be done.

Regards,

Anthony Liguori

>> 3. Use the kernel as a middle-man. Create a double-ended "veth"
>> interface and have Snabb Switch and QEMU each open a PF_PACKET
>> socket and accelerate it with VHOST_NET.
>
> As Michael, mentioned, this could be macvtap on the interface that you
> have already created in the switch and passed to vhost-net.  Then you do
> not have to do anything in QEMU.
>
> Paolo
>
>> If you are using the Linux network stack then it might be better to
>> integrate with vhost maybe as a tun-like device driver.
>> 
>> Stefan
>> 
>>