[Beowulf] Nehalem memory configs

Peter Kjellstrom cap at nsc.liu.se
Thu Apr 9 03:35:52 EDT 2009


On Wednesday 08 April 2009, Jan Heichler wrote:
...
> JL> Peter Kjellstrom wrote:
...
> >> Can anyone confirm that mixing different sizes of dimms, even when
> >> keeping to a by-three-symmetric configuration, actually does degrade
> >> performance?
> >>
> >> That is, first hand information that config 1 will be slower than config
> >> 2:
> >>
> >> 1: two sockets, 3x 1G and 3x 2G per socket RDIMM (total 18G @1066)
> >> 2: two sockets, 6x 1G(or 2G) per socket RDIMM (total 12G (or 24G) @1066)
> >>
> >> /Peter
>
> JL> I can confirm it because I've got it on a test box I've been running :)
>
> Can you give us the result of a stream-benchmark? with 12 x RDIMM in
> asymmetric config and 6 x RDIMM ? both running at 1066?

Note that both my configs 1 and 2 above are 12xRDIMM and "symmetric". The only 
thing that differs is wether it's purely one DIMM size or two.

12x vs 6x @1066 is a completely different config and I wouldn't be surprised 
to see a performance difference.

/Peter
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