Re: [Qemu-devel] [PATCH] numa: Introduce MachineClass::auto_enable_numa for implicit NUMA node

[David Gibson]

On Thu, Aug 08, 2019 at 04:35:00PM +1000, David Gibson wrote:
> On Wed, Aug 07, 2019 at 02:52:56PM -0300, Eduardo Habkost wrote:
> > On Tue, Aug 06, 2019 at 02:50:55PM +0200, Igor Mammedov wrote:
> > > On Mon,  5 Aug 2019 15:13:02 +0800
> > > Tao Xu <address@hidden> wrote:
> > > 
> > > > Add MachineClass::auto_enable_numa field. When it is true, a NUMA node
> > > > is expected to be created implicitly.
> > > > 
> > > > Acked-by: David Gibson <address@hidden>
> > > > Suggested-by: Igor Mammedov <address@hidden>
> > > > Suggested-by: Eduardo Habkost <address@hidden>
> > > > Signed-off-by: Tao Xu <address@hidden>
> > [...]
> > > > +    mc->auto_enable_numa = true;
> > > 
> > > this will always create a numa node (that will affect not only RAM but
> > > also all other components that depends on numa state (like CPUs)),
> > > where as spapr_populate_memory() was only faking numa node in DT for RAM.
> > > It makes non-numa configuration impossible.
> > > Seeing David's ACK on the patch it might be fine, but I believe
> > > commit message should capture that and explain why the change in
> > > behavior is fine.
> > 
> > After a quick look, all spapr code seems to have the same
> > behavior when nb_numa_nodes==0 and nb_numa_nodes==1, but I'd like
> > to be sure.
> 
> That's certainly the intention.  If there are cases where it doesn't
> behave that way, it's a bug - although possible one we have to
> maintainer for machine compatibility.
> 
> > David and/or Tao Xu: do you confirm there's no ABI change at all
> > on spapr after implicitly creating a NUMA node?
> 
> I don't believe there is, no.

Oh, FWIW, the PAPR interface which is what defines the guest
environment has no notion of "non NUMA" except in the sense of a
system with exactly one NUMA node.

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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