RE: [Xen-users] Live Migration with different hardware

["Petersson, Mats" <Mats.Petersson@xxxxxxx>]

> -----Original Message-----
> From: M.A. Williamson [mailto:maw48@xxxxxxxxxxxxxxxx] On 
> Behalf Of Mark Williamson
> Sent: 29 June 2007 16:15
> To: xen-users@xxxxxxxxxxxxxxxxxxx
> Cc: Petersson, Mats; Dominik Klein; Kyrios
> Subject: Re: [Xen-users] Live Migration with different hardware
> 
> > > Compare the output of this command on your machines:
> > > cat /proc/cpuinfo|grep flags
> >
> > That may well be the case. The "correct" test should really 
> be something
> > like:
> >
> > flags_new_cpu & ~flags_old_cpu != 0
> >
> > That means, no flags on the old cpu that doesn't exist on 
> the new CPU.
> >
> > I'm not sure how much, if any, flags are actually tested on the
> > migration path.
> 
> I don't think they are.
> 
> > The good thing is that if the migration fails due to 
> incompatible CPU's
> > (by testing flags) it should not "fail" the domain - that 
> is, the domain
> > should stay on the original machine and you should get an 
> error message
> > - at least that's how I understand it.
> 
> I don't think you can rely on this happening :-(

Yes, if there's no test, then it's not going to work.

[snip long explanation of why it doesn't work]

> > Yes, as long as you don't use "pci-passtrhough" to make a 
> PCI card (e.g.
> > network card) available directly to the domain, the guest 
> DOESN'T KNOW
> > what the REAL network card is [this makes the domain a 
> driver domain,
> > and driver domains aren't allowed to be migrated anyways - 
> that would be
> > TERRIBLY hard to implement, as there's no real good way to 
> transfer the
> > internal state of the hardware owned on one domain to the next one].
> 
> Domains with PCI access shouldn't be migrated or 
> saved/restored.  I think the 
> tools might allow this at the moment, but that's a bug and 
> should be fixed 
> (note to self: consider fixing this bug!)

That would be a good bug to fix... And I thought that I said that this
type of domain can't be migrated. 

I don't think it's very hard to discover if this domain has a PCI device
attached or not - but I haven't looked at it... 

--
Mats
> 
> Cheers,
> mark
> 



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