Re: [PATCH 1/3] cpu/SMT: create and export cpu_smt_possible()

[Paolo Bonzini]

On 16/09/19 19:16, Jim Mattson wrote:
>> KVM needs to know if SMT is theoretically possible, this means it is
>> supported and not forcefully disabled ('nosmt=force'). Create and
>> export cpu_smt_possible() answering this question.
> It seems to me that KVM really just wants to know if the scheduler can
> be trusted to avoid violating the invariant expressed by the Hyper-V
> enlightenment, NoNonArchitecturalCoreSharing. It is possible to do
> that even when SMT is enabled, if the scheduler is core-aware.
> Wouldn't it be better to implement a scheduler API that told you
> exactly what you wanted to know, rather than trying to infer the
> answer from various breadcrumbs?

Yes, however that scheduler API could also rely on something like
cpu_smt_possible(), at least in the case where core scheduling is not
active, so this is still a step in the right direction.

Paolo