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Re: [Qemu-devel] [RFC 0/6] enable numa configuration before machine_init


From: Paolo Bonzini
Subject: Re: [Qemu-devel] [RFC 0/6] enable numa configuration before machine_init() from HMP/QMP
Date: Thu, 19 Oct 2017 14:23:04 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0

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.

Paolo

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