Re: [PATCH v2 4/7] util: Add write-only "node-affinity" property for ThreadContext

[David Hildenbrand <david@redhat.com>]

On 11.10.22 08:03, Markus Armbruster wrote:
> David Hildenbrand <david@redhat.com> writes:
> 
>> Let's make it easier to pin threads created via a ThreadContext to
>> all CPUs currently belonging to a given set of NUMA nodes -- which is the
>> common case.
>>
>> "node-affinity" is simply a shortcut for setting "cpu-affinity" manually
>> to the list of CPUs belonging to the set of nodes. This property can only
>> be written.
>>
>> A simple QEMU example to set the CPU affinity to Node 1 on a system with
>> two NUMA nodes, 24 CPUs each:
>>      qemu-system-x86_64 -S \
>>        -object thread-context,id=tc1,node-affinity=1
>>
>> And we can query the cpu-affinity via HMP/QMP:
>>      (qemu) qom-get tc1 cpu-affinity
>>      [
>>          1,
>>          3,
>>          5,
>>          7,
>>          9,
>>          11,
>>          13,
>>          15,
>>          17,
>>          19,
>>          21,
>>          23,
>>          25,
>>          27,
>>          29,
>>          31,
>>          33,
>>          35,
>>          37,
>>          39,
>>          41,
>>          43,
>>          45,
>>          47
>>      ]
> 
> Double-checking my understanding: on this system, the even CPUs belong
> to NUMA node 0, and the odd ones to node 1.  Setting node-affinity=1 is
> therefore sugar for setting cpu-affinity to the set of even CPUs.
> Correct?

Yes!

# lscpu
...
NUMA:
   NUMA node(s):          2
   NUMA node0 CPU(s):     0,2,4,6,8,10,12,14,16,18,20,22,24,26,28,30,32,34,36,38,40,42,44,46
   NUMA node1 CPU(s):     1,3,5,7,9,11,13,15,17,19,21,23,25,27,29,31,33,35,37,39,41,43,45,47


> 
>> We cannot query the node-affinity:
>>      (qemu) qom-get tc1 node-affinity
>>      Error: Insufficient permission to perform this operation
> 
> The error message is somewhat misleading.  "Insufficient permission"
> suggests this could work if I had more "permission".  Not the case.  The
> message comes from object_property_get(), i.e. it's not this patch's
> fault.  I'll post a patch to improve it.
> 

I agree, thanks!

-- 
Thanks,

David / dhildenb