Re: [Qemu-devel] [RFC 0/6] enable numa configuration before machine_init() from HMP/QMP

[David Gibson]

On Thu, Oct 19, 2017 at 02:23:04PM +0200, Paolo Bonzini wrote:
> On 19/10/2017 13:49, David Gibson wrote:
> > Note that describing socket/core/thread tuples as arch independent (or
> > even machine independent) is.. debatable.  I mean it's flexible enough
> > that most platforms can be fit to that scheme without too much
> > straining.  But, there's no arch independent way of defining what each
> > level means in terms of its properties.
> > 
> > So, for example, on spapr - being paravirt - there's no real
> > distinction between cores and sockets, how you divide them up is
> > completely arbitrary.
> 
> Same on x86, actually.
> 
> It's _common_ that cores on the same socket share L3 cache and that a
> socket spans an integer number of NUMA nodes, but it doesn't have to be
> that way.
> 
> QEMU currently enforces the former (if it tells the guest at all that
> there is an L3 cache), but not the latter.

Ok.  Correct me if I'm wrong, but doesn't ACPI describe the NUMA
architecture in terms of this thread/core/socket heirarchy?  That's
not true for PAPR, where the NUMA topology is described in an
independent set of (potentially arbitrarily nested) nodes.

-- 
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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