>----- Original Message -----
>From: "Jan Heichler" <jan.heich...@gmx.net>
>To: "richard walsh" <richard.wa...@comcast.net>
>Cc: beowulf@beowulf.org
>Sent: Saturday, April 11, 2009 3:56:10 AM GMT -05:00 US/Canada Eastern
>Subject: Re[2]: [Beowulf] Nehalem memory configs
>
>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.
64 GB/sec is the right dual-socket theoretical number for this situation, and
Intel
presents the value of 33 GB/sec for the stream triad for the dual socket
boards,
so 35 GB/sec could be a copy perhaps, but nothing was mentioned about any
benchmark in the memory piece. In any case, I think we have the right
theoretical
and probable real-world numbers expressed here, if people were wondering.
rbw
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