double a[N][N],b[N][N],c[N][N] ;

void normal(){
   int i,j,k;
   for (i=0;i<N;i++){
      for (j=0;j<N;j++){
         c[i][j] = 0.0;
         for (k=0;k<N;k++){
            c[i][j] += a[i][k]*b[k][j];
         }
      }
   }
}

Download : http://gd.tuwien.ac.at/perf/benchmark/aburto/mm/mm.c

Compile : gcc mm.c -O -DUNIX -DN=1400 -o mm

Launch 10 times : mm -n and give mean time.