[Omp] Could you help me about this problem?

[宋刚]

Hi,
   We used the OpenMP to parallel a subroutine(only a loop) of a program
recently. When I set different thread number, the time they took is just
like the below:
   1 thread:  20s
   2 threads: 11s
   3 threads: 10s
   4 threads:  7s
   5 threads: 11s
   6 threads: 19s
   8 threads: 23s
  The machine we used is a smp node(dual core) of a cluster. What I
can't understand is that why the time between 2 threads and 3 threads is
so small?
  Can you give some sound reason to explain it to me?
  Thank you very much!!!
 
from David
 
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