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Date: Wed, 23 Sep 2015 08:25:44 -0400
From: Boris Ostrovsky <boris.ostrovsky@oracle.com>
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To: Juergen Gross <jgross@suse.com>,
        Dario Faggioli <dario.faggioli@citrix.com>
CC: "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
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Subject: Re: [Xen-devel] [PATCH RFC] xen: if on Xen, "flatten" the scheduling
 domain hierarchy
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On 09/23/2015 03:35 AM, Juergen Gross wrote:
>
> Depends on the hardware. On some AMD processors one socket covers
> multiple NUMA nodes. This is the critical case. set_sched_topology()
> will be called on those machines possibly multiple times when bringing
> up additional cpus.
>
>> I'm asking because trying this out, right now, is not straightforward,
>> as PV vNUMA, even with Wei's Linux patches and with either yours or
>> mine one, still incurs in the CPUID issue... I'll try that ASAP, but
>> there are a couple of things I've got to finish for the next few days.
>>
>>> One of NUMA and Xen will win and
>>> overwrite the other's settings.
>>>
>> Not sure what this means, but as I said, I'll try.
>
> Make sure to use the correct hardware (I'm pretty sure this should be
> the AMD "Magny-Cours" [1]).
>
>
> Juergen
>
> [1]: 
> http://developer.amd.com/resources/documentation-articles/articles-whitepapers/introduction-to-magny-cours/
>


There are few family 0x10 and 0x15 processors that are like that. You 
can see whether you have such a system by comparing number of NUMA nodes 
with number of physical IDs, e.g.:

[root@ovs106 ~]# numactl --hardware |grep available
available: 4 nodes (0-3)
[root@ovs106 ~]# grep "physical id" /proc/cpuinfo | uniq
physical id    : 0
physical id    : 1
[root@ovs106 ~]#


-boris