命名管道的通信效率的测试

C/C++ code

write.c#include <unistd.h>#include <stdlib.h>#include <stdio.h>#include <string.h>#include <fcntl.h>#include <limits.h>#include <sys/types.h>#include <sys/stat.h>#include <pthread.h>#include <time.h>#define FIFO_NAME "/tmp/my_fifo"#define BUFFER_SIZE PIPE_BUF   //4096#define TEN_MEG (1024 * 1024 * 1) //决定每次循环传输数据的大小void* thread_tick(void* arg)  //用来测试管道会不会阻塞进程{    printf("hello, world!\n");    sleep(1);}void* thread_write(void* arg){    int pipe_fd;    int res;    int bytes_sent = 0;    char buffer[BUFFER_SIZE ];    int count=0;    //决定总共循环多少次    if (access(FIFO_NAME, F_OK) == -1) {        res = mkfifo(FIFO_NAME, 0777);        if (res != 0) {            fprintf(stderr, "Could not create fifo %s\n", FIFO_NAME);            exit(EXIT_FAILURE);        }    }     while(count<1){    printf("write: Process %d opening FIFO O_WRONLY\n", getpid());    pipe_fd = open(FIFO_NAME, O_WRONLY);    printf("write: Process %d result %d \n", getpid(), pipe_fd);    if (pipe_fd != -1) {        while(bytes_sent < TEN_MEG) {            res = write(pipe_fd, buffer, BUFFER_SIZE);            if (res == -1) {                fprintf(stderr, "Write error on pipe\n");                exit(EXIT_FAILURE);            }            bytes_sent += res;        }        (void)close(pipe_fd);    }    else {        exit(EXIT_FAILURE);    }    printf("write: Process %d finished , count =%d\n", getpid(),count);    count++;  }}int main(){    pthread_t write;    pthread_t tick;    int resw, rest ;        rest = pthread_create(&tick, NULL, thread_tick, 0);    if(rest != 0)    {        perror("tick thread creation failed\n");        exit(EXIT_FAILURE);    }    resw = pthread_create(&write, NULL, thread_write, 0);    if(resw != 0)    {        perror("write thread creation failed\n");        exit(EXIT_FAILURE);    }    resw = pthread_join(write, 0);    rest = pthread_join(tick, 0);    return 0;}

C/C++ code

read.c#include <unistd.h>#include <stdlib.h>#include <stdio.h>#include <string.h>#include <fcntl.h>#include <limits.h>#include <sys/types.h>#include <sys/stat.h>#define FIFO_NAME "/tmp/my_fifo"#define BUFFER_SIZE PIPE_BUF  //4096int main(){    int pipe_fd;    int res;    char buffer[BUFFER_SIZE ];    int bytes_read = 0;    int count =0;    memset(buffer, '\0', sizeof(buffer));    while(count < 1){    printf("read: Process %d opening FIFO O_RDONLY\n", getpid());    pipe_fd = open(FIFO_NAME, O_RDONLY);    printf("read: Process %d result %d\n", getpid(), pipe_fd);    if (pipe_fd != -1) {        do {            res = read(pipe_fd, buffer, BUFFER_SIZE);            bytes_read += res;        } while (res > 0);        (void)close(pipe_fd);    }    else {        exit(EXIT_FAILURE);    }    printf("read: Process %d finished, %d bytes read , count =%d\n", getpid(), bytes_read,count);    count++;  }}

目的：测试命名管道的通信效率
1）在后台运行write程序（向管道内写数据）
2）前台运行read程序（从管道内读数据），并利用Linux系统函数time 记录read的运行时间
3）通过改变两个程序中的while循环次数来改变每次测试的通信数据的大小

我的测试结果是基于每次循环传输1M。
但是如果总共传输的数据不变，但是每次循环传输的数据变大（即循环次数变小了），那么程序的运行时间也会变大。
例如，总共传输50M，我循环50次，每次1M和循环1次，每次50M花费的时间是不一样的。
问题：
1）为什么会出现上面这中情况？
2）命名管道的传输速度跟哪些因素有关系？会受到CPU的运行速度和内存大小的影响么？


[解决办法]
你循环50次，至少有50次的系统调用
而循环1次，只有一次系统调用