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

[Pierre Morel <pmorel@linux.ibm.com>]

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