[Beowulf] Nehalem memory configs

Jan Heichler jan.heichler at gmx.net
Sat Apr 11 00:56:10 PDT 2009


Hallo richard,

Freitag, 10. April 2009, meintest Du:



> Kilian CAVALOTTI wrote:
>> On Wednesday 08 April 2009 19:48:30 Joe Landman wrote:
>>> As an FYI, Beowulf veteran Jeff Layton wrote up a nice article on
>>> memory
>>> configuration issues for Nehalem (I had seen some discussion on this
>>> previously).
>>>
>>> Link is here:
>>> http://www.delltechcenter.com/page/04-08-2009+-+Nehalem+and+Memory+Configur
>>> ations
>>
>> That's a great write-up, gathering all the useful information in one
>> place. A must read. Thanks Jeff!
It is a good write up, very good ... but there looks to be an error under "Memory Bandwidth
Performance" ... first, for socket-local-memory, I am not sure of the relevance of
the QPI GT rate.  I would calculate the maximum rate to socket-local-memory
with 1 DIMM per channel at:
 
1.333 GHz  x 3 Channels x 8 bytes =  31.992 GBytes/sec 
 
not 35 GByters/sec.  Maybe I am doing something wrong.  ´



I understood the 35 GB/s to be the transfer rate that you reach when accessing Memory with 8 Cores. So it involves 6 Channels (2 CPUs, 3 channels each). ~64 GB/s (theory) - 35 GB/s (real life). Makes sense to me. 

Jan                            
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