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

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Message-ID: <OF025FB4DD.0A1D8CAD-ON65257798.00527BE1-65257798.005C0247@in.ibm.com>
Date:	Wed, 8 Sep 2010 22:17:18 +0530
From:	Krishna Kumar2 <krkumar2@...ibm.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	anthony@...emonkey.ws, Avi Kivity <avi@...hat.com>,
	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?

I have not tried this, though I added some minimal code in
virtio_net_load and virtio_net_save. I don't know what needs
to be done exactly at this time. I forgot to put this in the
"Next steps" list of things to do.

Thanks,

- KK

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