Subject: Re: [RFC PATCH 34/35] Add the Xen virtual network device driver.

From: Christian Limpach <[email-masked]>
Date: Tue, 9 May 2006 15:00:27 +0100

On Tue, May 09, 2006 at 11:26:03PM +1000, Herbert Xu wrote:
> Christian Limpach <[email-masked]> wrote:
> > 
> > Possibly having to page in the process and switching to it would add
> > to the live migration time.  More importantly, having to install an
> > additional program in the guest is certainly not very convenient.
> 
> Sorry I'm still not convinced.  What's there to stop me from suspending
> my laptop to disk, moving it from port A to port B and resuming it?
> 
> Wouldn't I be in exactly the same situation? By the same reasoning we'd
> be adding a gratuitous ARP routine to every single laptop network driver.

It is the same situation except that in the laptop case you don't care
that reconfiguring your network will take a second or a few.  For live
migration we're looking at network downtime from as low as 60ms to
something like 210ms on a busy virtual machine.  I'm not saying that
a userspace solution wouldn't work but it would probably add a measurable
delay to the network downtime during live migration.

You might also find the following paper an interesting read:
http://www.cl.cam.ac.uk/Research/SRG/netos/papers/2005-migration-nsdi-pre.pdf

    christian