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

[David Hildenbrand]

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