Re: [PATCH v7 1/1] s390x: KVM: guest support for topology function

[Pierre Morel]

On 2/18/22 16:10, Heiko Carstens wrote:
> > > > +       /* The real CPU backing up the vCPU moved to another socket
> > > > */
> > > > +       if (topology_physical_package_id(vcpu->cpu) !=
> > > > +           topology_physical_package_id(vcpu->arch.prev_cpu))
> > > > +               return true;
> > >
> > > Why is it OK to look just at the physical package ID here? What if the
> > > vcpu for example moves to a different book, which has a core with the
> > > same physical package ID?
> >
> > You are right, we should look at the drawer and book id too.
> > Something like that I think:
> >
> >          if ((topology_physical_package_id(vcpu->cpu) !=
> >               topology_physical_package_id(vcpu->arch.prev_cpu)) ||
> >              (topology_book_id(vcpu->cpu) !=
> >               topology_book_id(vcpu->arch.prev_cpu)) ||
> >              (topology_drawer_id(vcpu->cpu) !=
> >               topology_drawer_id(vcpu->arch.prev_cpu)))
> >                  return true;
>
> You only need to check if prev_cpu is present in topology_core_cpumask(cpu).

Yes, thanks.

Regards,
Pierre

--
Pierre Morel
IBM Lab Boeblingen