[Beowulf] Single threaded memory bandwidth compared between Nehalem-EP and Westmere-EX

Reuti reuti at staff.uni-marburg.de
Fri Oct 18 03:32:00 PDT 2013


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Hi,

Am 18.10.2013 um 05:34 schrieb Christopher Samuel:

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> We've got a group who bought themselves a 16 core 1.5TB Westmere-EX
> system and are getting what they consider to be poor memory bandwidth
> compared to an older 8 core Nehalem-EP system.

Can you specify the CPUs in question?


> Same CPU clock speed (2.6GHz), same memory speed (1067MHz), but about
> half the memory bandwidth (single threaded). I've run my own tests
> with the Stream benchmark and can confirm the same.

Is the speed limited by the memory chips or the mainboard, or the population on the mainboard (i.e. often the speed drops when all DIMM banks are used).

- -- Reuti


> For instance, the Nehalem-EP system typically gets around 12GB/s for
> triad and the Westmere-EX system gets around 4.5 GB/s.
> 
> Now I know that I can use 16 threads (one per core) on Westmere-EX and
> get far better performance, but that doesn't interest them.
> 
> I realise that the memory controller architecture is very different
> between EP and EX models, but is there any inherent reason why that
> should result in such poorer single threaded performance?
> 
> All the best,
> Chris
> - -- 
> Christopher Samuel        Senior Systems Administrator
> VLSCI - Victorian Life Sciences Computation Initiative
> Email: samuel at unimelb.edu.au Phone: +61 (0)3 903 55545
> http://www.vlsci.org.au/      http://twitter.com/vlsci
> 
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