Re: [Xen-devel] SMP and VCPU migration.

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> I am working on SMP for xen-ia64.  The first step was to be able to use all
> the cpus but without considering VCPUs migration ie VCPU must be pinned to
> one CPU.
>
> Is it the same policy on x86 ?

They can be repinned (Stephan wrote a CPU rebalancer for this purpose) but 
this should only happen periodically: i.e. there's not a global work-stealing 
scheduler on a per-scheduler-period basis, a balancer has to come in 
periodically and move the vcpus about.  Presumably on IA64 you'd just need 
different time constants to avoid thrashing.

Can you manually repin VCPUs on IA64?  That's a handy feature to have, even 
without the automatic balancer.

Cheers,
Mark

> The migration cost is rather high on ia64 and may require a lot of
> inter-CPU traffic for coherency (TLB and cache management at least).  What
> about x86 ? How is the wbinvd instruction paravirualized/virtualized ?
>
> Thank you for your comments.
> Tristan.
>
>
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