openmp with single processor
 

Hi everyone,

I found that my openmp parallelized fortran code runs slower when run on one processor as compared to the same but unparallelized code. (I have used ifort compiler)

Can someone tell me why is this so?

Is it because the compiler itself tries to parallelise a serial code and when the code is parallel it doesn't?

How high is the slowdown you observe for the parallel code?
A few percent could be explained by the overhead introduced by the parallelization.

how do you set the OS parameters NCPUS and OMP_NUM_THREADS?