并行性

野性酷女 2022-08-03 00:53 87阅读 0赞

并行性：cpu处理指令是并行的，前一条指令处理时，紧接着前一条的指令也会开始处理，如果后一条指令和前一条指令无关，那么程序性能会得到提升，我们常常会把一个操作分解成几条指令并行来提升性能。

实例代码：

long long getSystemTime() {
            struct timeb t;
            ftime(&t);
            return 1000 * t.time + t.millitm;
    }
    
    
    int main()
    {
    	int                     * b_test_data = (int *)malloc(80000000*sizeof(int));
            int                             b_loop;
            long long               b_begin, b_end, b_ttl1 = 1, b_ttl2 = 1;
    
            for(b_loop = 0; b_loop < 80000000; b_loop++)
            {
                    b_test_data[b_loop] = 1;
            }
    
            b_begin = getSystemTime();
    
            for(b_loop = 0; b_loop < 80000000 - 1; b_loop += 2)
            {
                    b_ttl1 = b_ttl1*b_test_data[b_loop]*b_test_data[b_loop + 1];             
            }
            
            for(; b_loop < 80000000; b_loop++)
            {
                    b_ttl1 = b_ttl1*b_test_data[b_loop];
            }
    
            b_end = getSystemTime();
    
            printf("time = %lu, b_ttl = %lu\n", b_end - b_begin, b_ttl1);
            return 0;
    }

运行结果：

![Center][]

并行：

int main()
    {
    	int                     * b_test_data = (int *)malloc(80000000*sizeof(int));
            int                             b_loop;
            long long               b_begin, b_end, b_ttl1 = 1, b_ttl2 = 1;
    
            for(b_loop = 0; b_loop < 80000000; b_loop++)
            {
                    b_test_data[b_loop] = 1;
            }
    
            b_begin = getSystemTime();
    
            for(b_loop = 0; b_loop < 80000000 - 1; b_loop += 2)
            {
                    b_ttl1 = b_ttl1*b_test_data[b_loop];
                    b_ttl2 = b_ttl2*b_test_data[b_loop + 1];
            }
            b_ttl1 *= b_ttl2;
            for(; b_loop < 80000000; b_loop++)
            {
                    b_ttl1 = b_ttl1*b_test_data[b_loop];
            }
    
            b_end = getSystemTime();
    
            printf("time = %lu, b_ttl = %lu\n", b_end - b_begin, b_ttl1);
            return 0;
    }

运行结果：

![Center 1][]

[Center]: /images/20220731/32f0c776e426477982e553cfb3338303.png
[Center 1]: /images/20220731/99b3e47ca717483eb583cc76196c55f7.png