netdev - Re: [RFC PATCH 0/4] Implement multiqueue virtio-net

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Date:	Wed, 8 Sep 2010 16:12:41 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Krishna Kumar2 <krkumar2@...ibm.com>
Cc:	Avi Kivity <avi@...hat.com>, anthony@...emonkey.ws,
	davem@...emloft.net, kvm@...r.kernel.org, mst@...hat.com,
	netdev@...r.kernel.org, rusty@...tcorp.com.au
Subject: Re: [RFC PATCH 0/4] Implement multiqueue virtio-net

On Wednesday 08 September 2010, Krishna Kumar2 wrote:
> > The new guest and qemu code work with old vhost-net, just with reduced
> > performance, yes?
> 
> Yes, I have tested new guest/qemu with old vhost but using
> #numtxqs=1 (or not passing any arguments at all to qemu to
> enable MQ). Giving numtxqs > 1 fails with ENOBUFS in vhost,
> since vhost_net_set_backend in the unmodified vhost checks
> for boundary overflow.
> 
> I have also tested running an unmodified guest with new
> vhost/qemu, but qemu should not specify numtxqs>1.

Can you live migrate a new guest from new-qemu/new-kernel
to old-qemu/old-kernel, new-qemu/old-kernel and old-qemu/new-kernel?
If not, do we need to support all those cases?

	Arnd
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