[Beowulf] Scaling issues on Xeon E5-2680

[Jon Tegner]

Found out what was wrong...

Turned out the hardware was delivered with 15 of the 16 memory slots 
populated!!!!

No wonder we had performance issues!

Anyway, thanks a a lot, all who answered!

/jon

On 02/29/2016 06:48 PM, Josef Weidendorfer wrote:
> Am 28.02.2016 um 16:27 schrieb Jon Tegner:
>> For one of our applications (CFD/OpenFOAM) we have noticed that the
>> calculation runs faster using 12 cores on 4 nodes compared to when using
>> 24 cores on 4 nodes.
> If this is OpenMP within each node...
> This may be an effect of first touch going wrong with lots of remote
> memory accesses, especially with huge pages.
> Checking with numatop may be useful (how much local vs. remote accesses),
> see https://github.com/01org/numatop
>
> Josef
>
>> In our environment we also have older AMD hardware (nodes with 4 CPUs
>> with 12 cores each), and here we don't see these strange scaling issues.
>>
>> System is CentOS-7, and communication is over FDR Infiniband. BIOS is
>> recently updated, and hyperthreading is disabled.
>>
>> Feel a bit lost here, and any hints on how to proceed with this are
>> greatly appreciated!
>>
>> Thanks,
>>
>> /jon
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