[Omp] openMP threads not starting simultaneously

[Chandan Basu]

Hi all,
Please help me with a question related to openMP parallelization. I am running the following code on a 8 core intel clovertown machine. The code is compiled by intel c compiler, icc, with -openmp option. The code compiles and runs without trouble. It also creates 8 openmp threads as set in the program. But If I look at the processor utilization (by using top command) it shows that only one core is being used. Timing wise also the 8 thread case is taking more time than one thread case. It seems threads are running sequentially. Can any one explain if there is a bug in the code :
 
----------------------------------
/*
The following code runs a random number generator funtion fun1 on all the threads. The purpose of this code is to see if all the processor cores are fully utilized.
*/
#include<stdio.h>
#include<omp.h>

int fun1();

int main(int argc, char *argv[])
{

  int		provided;
  int		rank;
  int		size;
  int		id;
  int		i, cnt[10];
  int		flag;
  int		n;

  for(i = 0; i< 10; i++)
	cnt[i] = 0;

  omp_set_num_threads(8);

  #pragma omp parallel private(id)
  {
    id = omp_get_thread_num();

    cnt[id] = fun1(); 
    #pragma omp barrier
  }
  omp_set_num_threads(1);
}


/*This function runs a random generator for some time*/

int fun1()
{
  int i, col, cnt;
  cnt = 0;
  for(i=0; i< MAX; i++)
  	for(col = 0; col < 200; col++)
            cnt += rand();
  return cnt;
}
--------------------------
Thanks
Chandan
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