作者piimaila (haha)
看板LinuxDev
标题[问题] 关於Linux写档问题?
时间Fri Dec 26 12:09:28 2008
简单的程式 如附录二
但是在读写档案时, 出现了一些不可思议的结果一
但是我看dd的原始码
(
http://www.koders.com/c/fid8FA83D210BAE79DA3A7C4088AC9C54909DC88C8D.aspx)
小弟的东西根本和dd一模一样, 但是dd到了 bs=4 後, 速度都很平均, 这才正常
而小弟的程式出现不正确的结果, 请问问题到底出在哪呢?
================附录一=================================
Block Size: 2 Speed: 1.375332 MB/S
Block Size: 4 Speed: 2.805992 MB/S
Block Size: 8 Speed: 6.129276 MB/S
Block Size: 16 Speed: 11.170536 MB/S
Block Size: 32 Speed: 26.849388 MB/S
Block Size: 64 Speed: 48.011832 MB/S
Block Size: 128 Speed: 97.772515 MB/S
Block Size: 256 Speed: 158.443034 MB/S
Block Size: 512 Speed: 282.057241 MB/S
Block Size:1024 Speed: 470.192368 MB/S
======================================================
=================附录二================================
#include <stdio.h>
#include <string.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <stdlib.h>
#define MAX_Block 1024 //byte
#define FileSize 5 //MB
int main(int argc, char **argv){
char *buf;
int outfd;
double t1,t2;
struct timeval timep;
int BUF_SIZE, i;
int TempFileSize = 1024*1024 * FileSize; //5MB
BUF_SIZE = 2;
while( BUF_SIZE <= MAX_Block) {
buf = (char *)malloc(BUF_SIZE);
memset(buf, 'a' , BUF_SIZE);
outfd = open("tempfile", O_WRONLY | O_CREAT | O_TRUNC, 0666);
gettimeofday(&timep, NULL);
t1 = timep.tv_sec+(timep.tv_usec/1000000.0);
for(i=0; i< TempFileSize/BUF_SIZE; i++){
write(outfd, buf, BUF_SIZE);
}//for
gettimeofday(&timep, NULL);
t2=timep.tv_sec+(timep.tv_usec/1000000.0);
close(outfd);
printf("Block Size:%4d\tSpeed: %.6lf MB/S\n",BUF_SIZE, FileSize/(t2-t1) );
free(buf);
BUF_SIZE = BUF_SIZE * 2;
}//while
}//main
--
※ 发信站: 批踢踢实业坊(ptt.cc)
◆ From: 59.120.70.34
1F：推 Neo1978:应该是 buffer cache 的关系... 12/26 12:47
2F：→ Neo1978:试试看使用 O_DIRECT，但是不一定 work... 12/26 12:54