Re: [Xen-devel] [PATCH RFC] xen: if on Xen, "flatten" the scheduling domain hierarchy

From: Boris Ostrovsky
Date: Wed Sep 23 2015 - 08:27:26 EST


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
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