Comment 2 for bug 668799

Revision history for this message
Jan-Simon Möller (dl9pf) wrote :

Alternative testcase:
compile and "export OMP_NUM_THREADS=6" before running.

/******************************************************************************
* FILE: omp_mm.c
* DESCRIPTION:
* OpenMp Example - Matrix Multiply - C Version
* Demonstrates a matrix multiply using OpenMP. Threads share row iterations
* according to a predefined chunk size.
* AUTHOR: Blaise Barney
* LAST REVISED: 06/28/05
******************************************************************************/
#include <omp.h>
#include <stdio.h>
#include <stdlib.h>

#define NRA 620 /* number of rows in matrix A */
#define NCA 150 /* number of columns in matrix A */
#define NCB 70 /* number of columns in matrix B */

int main (int argc, char *argv[])
{
int tid, nthreads, i, j, k, chunk;
double a[NRA][NCA], /* matrix A to be multiplied */
        b[NCA][NCB], /* matrix B to be multiplied */
        c[NRA][NCB]; /* result matrix C */

chunk = 10; /* set loop iteration chunk size */

/*** Spawn a parallel region explicitly scoping all variables ***/
#pragma omp parallel shared(a,b,c,nthreads,chunk) private(tid,i,j,k)
  {
  tid = omp_get_thread_num();
  if (tid == 0)
    {
    nthreads = omp_get_num_threads();
    printf("Starting matrix multiple example with %d threads\n",nthreads);
    printf("Initializing matrices...\n");
    }
  /*** Initialize matrices ***/
  #pragma omp for schedule (static, chunk)
  for (i=0; i<NRA; i++)
    for (j=0; j<NCA; j++)
      a[i][j]= i+j;
  #pragma omp for schedule (static, chunk)
  for (i=0; i<NCA; i++)
    for (j=0; j<NCB; j++)
      b[i][j]= i*j;
  #pragma omp for schedule (static, chunk)
  for (i=0; i<NRA; i++)
    for (j=0; j<NCB; j++)
      c[i][j]= 0;

  /*** Do matrix multiply sharing iterations on outer loop ***/
  /*** Display who does which iterations for demonstration purposes ***/
  printf("Thread %d starting matrix multiply...\n",tid);
  #pragma omp for schedule (static, chunk)
  for (i=0; i<NRA; i++)
    {
    printf("Thread=%d did row=%d\n",tid,i);
    for(j=0; j<NCB; j++)
      for (k=0; k<NCA; k++)
        c[i][j] += a[i][k] * b[k][j];
    }
  } /*** End of parallel region ***/

/*** Print results ***/
printf("******************************************************\n");
printf("Result Matrix:\n");
for (i=0; i<NRA; i++)
  {
  for (j=0; j<NCB; j++)
    printf("%6.2f ", c[i][j]);
  printf("\n");
  }
printf("******************************************************\n");
printf ("Done.\n");

}