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Re: [Qemu-devel] [RFC 0/6] enable numa configuration before machine_init
From: |
Eduardo Habkost |
Subject: |
Re: [Qemu-devel] [RFC 0/6] enable numa configuration before machine_init() from HMP/QMP |
Date: |
Fri, 20 Oct 2017 17:53:09 -0200 |
User-agent: |
Mutt/1.9.0 (2017-09-02) |
On Fri, Oct 20, 2017 at 12:21:30PM +1100, David Gibson wrote:
> 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.
On PC, ACPI NUMA information only refer to CPU APIC IDs, which
identify individual CPU threads; it doesn't care about CPU
socket/core/thread topology. If I'm not mistaken, the
socket/core/thread topology is not represented in ACPI at all.
Some guest OSes, however, may get very confused if they see an
unexpected NUMA/CPU topology. IIRC, it was possible to make old
Linux kernel versions panic by generating a weird topology.
--
Eduardo
- Re: [Qemu-devel] [RFC 0/6] enable numa configuration before machine_init() from HMP/QMP, (continued)
- Re: [Qemu-devel] [RFC 0/6] enable numa configuration before machine_init() from HMP/QMP, Igor Mammedov, 2017/10/18
- Re: [Qemu-devel] [RFC 0/6] enable numa configuration before machine_init() from HMP/QMP, Daniel P. Berrange, 2017/10/18
- Re: [Qemu-devel] [RFC 0/6] enable numa configuration before machine_init() from HMP/QMP, Igor Mammedov, 2017/10/18
- Re: [Qemu-devel] [RFC 0/6] enable numa configuration before machine_init() from HMP/QMP, Daniel P. Berrange, 2017/10/18
- Re: [Qemu-devel] [RFC 0/6] enable numa configuration before machine_init() from HMP/QMP, Eduardo Habkost, 2017/10/18
- Re: [Qemu-devel] [RFC 0/6] enable numa configuration before machine_init() from HMP/QMP, Daniel P. Berrange, 2017/10/18
- Re: [Qemu-devel] [RFC 0/6] enable numa configuration before machine_init() from HMP/QMP, Eduardo Habkost, 2017/10/18
- Re: [Qemu-devel] [RFC 0/6] enable numa configuration before machine_init() from HMP/QMP, David Gibson, 2017/10/19
- Re: [Qemu-devel] [RFC 0/6] enable numa configuration before machine_init() from HMP/QMP, Paolo Bonzini, 2017/10/19
- Re: [Qemu-devel] [RFC 0/6] enable numa configuration before machine_init() from HMP/QMP, David Gibson, 2017/10/19
- Re: [Qemu-devel] [RFC 0/6] enable numa configuration before machine_init() from HMP/QMP,
Eduardo Habkost <=
- Re: [Qemu-devel] [RFC 0/6] enable numa configuration before machine_init() from HMP/QMP, Igor Mammedov, 2017/10/23
- Re: [Qemu-devel] [RFC 0/6] enable numa configuration before machine_init() from HMP/QMP, Igor Mammedov, 2017/10/23
- Re: [Qemu-devel] [RFC 0/6] enable numa configuration before machine_init() from HMP/QMP, Eduardo Habkost, 2017/10/25
- Re: [Qemu-devel] [RFC 0/6] enable numa configuration before machine_init() from HMP/QMP, Daniel P. Berrange, 2017/10/25
- Re: [Qemu-devel] [RFC 0/6] enable numa configuration before machine_init() from HMP/QMP, Eduardo Habkost, 2017/10/25
- Re: [Qemu-devel] [RFC 0/6] enable numa configuration before machine_init() from HMP/QMP, Igor Mammedov, 2017/10/19
- Re: [Qemu-devel] [RFC 0/6] enable numa configuration before machine_init() from HMP/QMP, Daniel P. Berrange, 2017/10/19
- Re: [Qemu-devel] [RFC 0/6] enable numa configuration before machine_init() from HMP/QMP, Eduardo Habkost, 2017/10/19
- Re: [Qemu-devel] [RFC 0/6] enable numa configuration before machine_init() from HMP/QMP, Daniel P. Berrange, 2017/10/20
- Re: [Qemu-devel] [RFC 0/6] enable numa configuration before machine_init() from HMP/QMP, Eduardo Habkost, 2017/10/20