[Beowulf] NUMA zone weirdness
jcownie at cantab.net
Mon Dec 19 11:42:16 PST 2016
Can hwloc detect this and give a suitably large complaint?
James Cownie <jcownie at cantab.net> (and intel, as I’m sure most of you know…)
> On 18 Dec 2016, at 21:28, Brice Goglin <brice.goglin at gmail.com> wrote:
> Do you know if all your CPU memory channels are populated? CoD requires
> that each half of the CPU has some memory DIMMs (so that each NUMA node
> actually contains some memory). If both channels of one half are empty,
> the NUMA node might somehow disappear.
> Le 16/12/2016 23:26, Elken, Tom a écrit :
>> Hi John and Greg,
>> You showed Nodes 0 & 2 (no node 1) and a strange CPU assignment to nodes!
>> Even though you had Cluster On Die (CoD) Endabled in your BIOS, I have never seen that arrangement of Numa nodes and CPUs. You may have a bug in your BIOS or OS ?
>> With CoD enabled, I would have expected 4 NUMA nodes, 0-3, and 6 cores assigned to each one.
>> The Omni-Path Performance Tuning User Guide
>> does recommend Disabling CoD in Xeon BIOSes (Table 2 on P. 12), but it's not considered a hard prohibition.
>> Disabling improves some fabric performance benchmarks, but Enabling helps some single-node applications performance, which could outweigh the fabric performance aspects.
>>> -----Original Message-----
>>> From: Beowulf [mailto:beowulf-bounces at beowulf.org] On Behalf Of Greg
>>> Sent: Friday, December 16, 2016 2:00 PM
>>> To: John Hearns
>>> Cc: Beowulf Mailing List
>>> Subject: Re: [Beowulf] NUMA zone weirdness
>>> Wow, that's pretty obscure!
>>> I'd recommend reporting it to Intel so that they can add it to the
>>> descendants of ipath_checkout / ipath_debug. It's exactly the kind of
>>> hidden gotcha that leads to unhappy systems!
>>> -- greg
>>> On Fri, Dec 16, 2016 at 03:52:34PM +0000, John Hearns wrote:
>>>> Problem solved.
>>>> I have changed the QPI Snoop Mode on these servers from
>>>> ClusterOnDIe Enabled to Disabled and they display what I take to be correct
>>>> behaviour - ie
>>>> [root at comp006 ~]# numactl --hardware
>>>> available: 2 nodes (0-1)
>>>> node 0 cpus: 0 1 2 3 4 5 6 7 8 9 10 11
>>>> node 0 size: 32673 MB
>>>> node 0 free: 31541 MB
>>>> node 1 cpus: 12 13 14 15 16 17 18 19 20 21 22 23
>>>> node 1 size: 32768 MB
>>>> node 1 free: 31860 MB
>>>> node distances:
>>>> node 0 1
>>>> 0: 10 21
>>>> 1: 21 10
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