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Re: [Xen-devel] What is the target CPU "topology" of an SMP HVM machine?

On mer, 2013-08-14 at 21:06 +0100, Andrew Cooper wrote:
> On 14/08/13 20:23, Eric Shelton wrote:
> > So, seeing as this information is being closely interrogated, what is
> > the target virtual CPU topology?  How should this be reported via
> > CPUID and MSR?  Darwin appears to be trying to determine or take into
> > account things such as a number of packages, dies per package, cores
> > per pie & package, and threads/logical CPUs per core & package; the
> > degrees of sharing of caches by CPUs at various cache levels, and the
> > presence of hyperthreading.
> Xen by default advertises all VCPUs as separate sockets, to try and
> dissuade "clever" schedulers from doing dumb things based on false
> information.
Are we absolutely sure about this? I'm asking because Elena run into a
similar issue, i.e., seeing some vCPUs being advertised as
threads/siblings (although that was a pv-guest)... Am I right Elena?

I think she also has a patch that she may be able to share soon, which
does right the masking of some of the CPUID stuff, as it looks like some
false information was reaching out to the Linux Scheduler! :-O

I'm not sure this is the exact same issue, though.... Elena, could you
tell something more about this?


<<This happens because I choose it to happen!>> (Raistlin Majere)
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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