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Re: [Xen-devel] How to query the number of vcpus?

* Ian Pratt <m+Ian.Pratt@xxxxxxxxxxxx> [2005-05-02 09:07]:
> > > I think so -- might as well get the interface right. I was thinking 
> > > something like the fd mask that get's passed to select, where you 
> > > sepcify the highest set bit.
> > 
> > In some cases Xen returns a cpumap to the guest (in 
> > getdomaininfo). In that case the fd mask trick won't really 
> > work as the guest needs to know in advance the biggetst map 
> > that Xen may return. Anyway, a map of
> > 256 bits is going to give us a fair amount of headroom I think.
> Why do we need to ever return a cpumap to the guest? Being able to read
> CPU pining information out isn't very useful, and both CPUs and VCPUs
> can be enumerated in the normal manner. Is there something I've
> forgotten?

If I were writing a load-balancing app I'd like to know where a domains'
vcpus are pinnable.  You had previously requested the cpumap to support
setting a list of physical cpus on which a vcpu can run.  It seems odd
(to me) to allow the setting of a variable, but to not be able to see what
the current value is.  Such an interface requires me to always send a
pin operation to ensure the cpumap is set how I want since I cannot
confirm the current value.

Ryan Harper
Software Engineer; Linux Technology Center
IBM Corp., Austin, Tx
(512) 838-9253   T/L: 678-9253

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