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

[Christian Limpach <Christian.Limpach@xxxxxxxxxxxx>]

On Wed, Jan 05, 2005 at 09:06:10AM -0600, Andrew Theurer wrote:
> >I don't think there's significant overhead if there's only a single
> >virtual cpu pinned to one physical cpu so I wouldn't expect a noticeable
> >performance advantage if we handled this case differently.
> >
> Hopefully soon I can get some performance tests going and we can see if 
> there's any issues here.  My other concern would be on larger (multi 
> numa-node) systems, even with one to one mapping, that the hardware 
> topology (numa) information does not make it to the SMP guest -it would 
> be nice to take advantage of the numa work developed in the linux kernel 
> over that last 2 years.  I am not sure exactly what impact this could be.

Yes, this is probably even needed on 2-cpu with 2 hyperthreads systems.
Right now, all virtual cpus are presented as independent physical cpus
to the domains and the domains can't easily tell if two virtual cpus
run on different physical cpus, on different hyperthreads on the same
cpu or on the same hyperthread.  If we export this information to the
guest, we'll then probably also have to have a way to inform the guest
if a virtual cpu is moved to a different hyperthread or physical cpu.

    christian



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