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Re: [Xen-devel] SMP guest support in unstable tree.

On Thu, Dec 16, 2004 at 10:50:21AM +1100, James Harper wrote:
> Cool. Can you elaborate on 'highly experimental'? I'm now running the
> 'stable' distribution but would consider using unstable for this feature
> if it were vaguely reliable.

On one hand it seems quite stable (doing kernel compiles for example)
but on the other hand it occasionally happens that dom0 doesn't boot --
once a domain has completed boot, it seems fine though, so far I've
only seen one lockup of a 32-vcpu domain running on a 4-cpu machine, which
is not a very practical setup anyway.  Also a malicious SMP guest might
be able to crash Xen.

> How does migration work between SMP & non SMP servers? I'd assume that
> running a domain with more cpu's than physically exist would take a
> performance hit, but do you know how much? If I migrate a domain from a
> dual cpu server to a single cpu server, is there an easy way of telling
> the domain to only use 1 cpu now please?

Migration doesn't work for SMP guests (at least it's not tested and
somewhat unlikely to work).  We haven't really decided how to do migration
for SMP guests yet, one option would be to shutdown all cpus but one and
then do a regular migration.  We will definitely look into adding cpu
hotplug support so that one can add/remove cpus from a running domain.


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