计算PI的值

xuyuanchao

在fedora.unix-center.net上的实验结果，加速比基本上约等于2。
-bash-3.2$gcc –xopenmp –o 2 2.c
-bash-3.2$ ./2
the whole processing time of the program is 0.951687 seconds
pi=3.141593
-bash-3.2$gcc –o 1 1.c
-bash-3.2$ ./1
the whole processing time of the program is 1.791129 seconds
pi=3.141593

同样的程序运行在t10000.unix-center.net上，效果完全不一样，具体原因还在寻找中。

-bash-3.00$ CC -o 11 1.c
-bash-3.00$ ./11
the whole processing time of the program is 33.903705 seconds
pi=3.141593
-bash-3.00$ CC –xopenmp –O3 –o22  2.c

-bash-3.00$ ./22
the whole processing time of the program is 7.478114 seconds
pi=3.141593

串行代码1.c

#include
#include  
#include  
#include  
static long num_steps = 100000000;
double step;
int   main(void)
{

struct timeval starttime,endtime;
double timepast;
int i;  
double x, pi, sum = 0.0;
step = 1.0/(double) num_steps;
gettimeofday(&starttime,NULL);
     for (i=0;i
                                  x = (i+0.5)*step;  
                                sum = sum + 4.0/(1.0+x*x);   
              }
gettimeofday(&endtime,NULL);
        timepast=((double)(endtime.tv_sec-starttime.tv_sec)*1000000+(double)(endtime.tv_usec-starttime.tv_usec))/1000000;
          printf("the whole processing time of the program is %lf seconds\n",timepast);

                 pi = step * sum;
    printf("pi=%lf\n",pi);
     return 0;
}



并行代码2.c


#include
#include
#include  
#include  
#include  
static long num_steps = 100000000;
double step;
int   main(void)
{

struct timeval starttime,endtime;
double timepast;
int i;  
double x, pi, sum = 0.0;
step = 1.0/(double) num_steps;
omp_set_num_threads(4);
gettimeofday(&starttime,NULL);
#pragma omp parallel for private(x)  reduction(+:sum)
           for (i=0;i
                                  x = (i+0.5)*step;  
                                sum = sum + 4.0/(1.0+x*x);   
              }
gettimeofday(&endtime,NULL);
        timepast=((double)(endtime.tv_sec-starttime.tv_sec)*1000000+(double)(endtime.tv_usec-starttime.tv_usec))/1000000;
          printf("the whole processing time of the program is %lf seconds\n",timepast);

                 pi = step * sum;
         printf("pi=%lf\n",pi);
        return 0;
}





本文来自ChinaUnix博客，如果查看原文请点：http://blog.chinaunix.net/u2/86537/showart_1964048.html