My OpenMP (C) parallel code is slower than the serial bitonic sort code and although I have done all the possible combinations I could think of, I can't find the problem.
Here is part of the code:
void recBitonicSortOpenMP( int lo, int cnt, int dir ) {
if ( cnt > 1 ) {
int k = cnt / 2;
#pragma omp parallel sections
{
#pragma omp section
recBitonicSortOpenMP( lo, k, ASCENDING );
#pragma omp section
recBitonicSortOpenMP( lo + k, k, DESCENDING );
}
bitonicMergeOpenMP( lo, cnt, dir );
}
}
It is an implementation of Bitonic Sort.
For recursive problems like this use OpenMP tasks, not nested parallelism and sections. http://cs.umw.edu/~finlayson/class/fall16/cpsc425/notes/24-sorting.html gives you a good example to follow...