netdev - Re: IPv6: autoconfiguration and suspend/resume or link down/up

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Message-ID: <20110724202620.1456e742@nehalam.ftrdhcpuser.net>
Date:	Sun, 24 Jul 2011 20:26:20 -0700
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Nicolas de Pesloüan 
	<nicolas.2p.debian@...il.com>
Cc:	Herbert Xu <herbert@...dor.apana.org.au>,
	David Miller <davem@...emloft.net>, jbohac@...e.cz,
	netdev@...r.kernel.org
Subject: Re: IPv6: autoconfiguration and suspend/resume or link down/up

On Sun, 24 Jul 2011 10:35:58 +0200
Nicolas de Pesloüan <nicolas.2p.debian@...il.com> wrote:

> Le 24/07/2011 02:18, Herbert Xu a écrit :
> > On Sat, Jul 23, 2011 at 09:37:43AM -0700, Stephen Hemminger wrote:
> >>
> >> Would it be possible to do live migration without dropping carrier
> >> or setting interface down?
> >
> > I think LM uses the same mechanism as suspend and resume so whatever
> > happens in one case will happen in the other case as well.
> 
> So we need to distinguish between two kind of link events:
> 
> 1/ Really having the link goes down then up. This should trigger a renegotiation.
> 
> 2/ Having the system suspend then resume :
> 2a/ This should trigger link down/link up events to force a renegotiation, for normal suspend/resume 
> where the network might have changed between suspend and resume.
> 2/ This should *not* trigger link down/link up events to avoid a renegotiation (for live migration) 
> because it is assumed that the network didn't change while suspended.
> 
> Can't we allow the user to set a global "link-down-link-up-timeout" and only force a renegotiation 
> if the time between link down and link up events is longer than this timeout? Normal user would set 
> this timeout close to 0 (default value). Live migration user would set this timeout to about twice 
> the time it normally takes to do a live migration. That way, in a VM environment, if the 
> suspend/resume cycle happens to take far more than a normal live migration time, the kernel would 
> renegotiate, which sounds reasonable, from my point of view.

I hate building infrastructure where it is not needed.

Since virtual machines should be using virtio network devices, shouldn't
the suspend/resume in that device just work. It doesn't need to drop the link.



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