[Beowulf] bizarre scaling behavior on a Nehalem

Mikhail Kuzminsky kus at free.net
Fri Aug 14 19:10:42 EDT 2009


In message from Tom Elken <tom.elken at qlogic.com> (Fri, 14 Aug 2009 
13:57:53 -0700):
>> On Behalf Of Bill Broadley
>
>> I put DDR3-1333 in the machine, but the bios seems to want to run 
>>them
>> at
>> 1066, 
>
>How many dimms per memory channel do you have?
>
>My understanding (which may be a few months old) is that if you have 
>more than one dimm per memory channel, DDR3-1333 dimms will run at 
>1066 speed;
>i.e. on your 1-CPU system, if you have 6 dimms, you have 2 per memory 
>channel.
>
>> I'm not sure exactly what speed they are running at.
>
>Your results look excellent, so I wouldn't be surprised if they are 
>running at 1333.

I have 12-18 GB/s on 4 threads of stream/ifort w/DDR3-1066 on dual 
 E5520 server. But it works under "numa-bad" kernel w/o control of 
numa-efficient allocation.

Mikhail 

>
>-Tom
>
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