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Date:   Fri, 18 Feb 2022 18:08:32 +0100
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Subject: Re: [PATCH v7 1/1] s390x: KVM: guest support for topology function
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To:     Heiko Carstens <hca@linux.ibm.com>
Cc:     Nico Boehr <nrb@linux.ibm.com>, kvm@vger.kernel.org,
        linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
        borntraeger@de.ibm.com, frankja@linux.ibm.com, cohuck@redhat.com,
        david@redhat.com, thuth@redhat.com, imbrenda@linux.ibm.com,
        gor@linux.ibm.com, wintera@linux.ibm.com, seiden@linux.ibm.com
References: <20220217095923.114489-1-pmorel@linux.ibm.com>
 <20220217095923.114489-2-pmorel@linux.ibm.com>
 <f0bf737abf480d6d16af6e5335bb195061f3d076.camel@linux.ibm.com>
 <97af6268-ff7a-cfb6-5ea4-217b5162cfe7@linux.ibm.com>
 <Yg+23xh7DDSRHFxK@osiris>
From:   Pierre Morel <pmorel@linux.ibm.com>
In-Reply-To: <Yg+23xh7DDSRHFxK@osiris>
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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