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xen-devel
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
ryanh@xxxxxxxxxx
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