[Beowulf] bizarre scaling behavior on a Nehalem

Bill Broadley bill at cse.ucdavis.edu
Fri Aug 14 15:47:31 EDT 2009


Mikhail Kuzminsky wrote:
> In message from Bill Broadley <bill at cse.ucdavis.edu> (Thu, 13 Aug 2009
> 17:09:24 -0700):
> 
> Do I unerstand correctly that this results are for 4 cores& 4 openmp
> threads ? And what is DDR3 RAM: DDR3/1066 ?

4 cores and 8 openmp threads.

4 threads is slightly faster:
Function      Rate (MB/s)   Avg time     Min time     Max time
Copy:       23670.3046       0.0135       0.0135       0.0136
Scale:      23304.9257       0.0138       0.0137       0.0139
Add:        21951.8053       0.0219       0.0219       0.0219
Triad:      21538.2451       0.0223       0.0223       0.0224

I put DDR3-1333 in the machine, but the bios seems to want to run them at
1066, I'm not sure exactly what speed they are running at.
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