[Openmp-dev] OpenMP slower than serial ( sometmes )

[Victor Rodriguez]

HI

I am new in Open MP and willing to learn . I am reading the Open MP
documentation and this tutorial

https://computing.llnl.gov/tutorials/openMP/exercise.html

I am really new to parallel programming , I have been searching over
diferent examples and at the end I am trying to create a simple loop faster
in omp than without, here is my code:

 #include
<omp.h>
 #include
<stdio.h>
 #define N
100000


  main
()

{



      int
i;
      float a[N], b[N],
c[N];


      /* Some initializations
*/
      for (i=0; i < N;
i++)
            a[i] = b[i] = i *
1.0;


      double start =
omp_get_wtime();



omp_set_dynamic(0);

omp_set_num_threads(4);


      #pragma omp parallel shared(a,b,c)
private(i)

{


              #pragma omp for
schedule(static)
              for (i=0; i < N;
i++)
                      c[i] = a[i] +
b[i];


                }  /* end of parallel section
*/


      double end =
omp_get_wtime();



printf("%f\n",start);

printf("%f\n",end);
      printf("%f\n",end -
start);


  }

Same code but with out the #pragma sections , the problem is that is not
always faster than serial code, some times serial code is even faster .

Any clue is more than welcome, if this is not he mailing list to post this
please tell me. I am really interested to lear Open MP

Thanks a lot and regards
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