I am attaching a sample piece of code to show the behavior.
This simply tries to grow a file as fast as it can using different methods.
Use with caution as it does not stop, and will fill the disk if you let it run.
Run as "nfstest -m <filename>" where <filename> is on an nfs mount.
-Kenny
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/* test the write throughput of a sliding mmap window vs simple FILE* */
#define _GNU_SOURCE
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <string.h>
#include <unistd.h>
#include <time.h>
#include <errno.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/time.h>
int total_bytes = 0;
int last_bytes = 0;
struct timeval last_time;
void timeout(int i)
{
struct timeval now;
gettimeofday(&now, 0);
(void) i;
{
double time_diff = (now.tv_sec - last_time.tv_sec) + ((now.tv_usec - last_time.tv_usec) / 1000000.);
int new_bytes = total_bytes;
int diff = new_bytes - last_bytes;
printf("wrote %dk %dM bytes in %f seconds -> %fM/sec\n", diff / 1024, diff / (1024 * 1024), time_diff, (diff / (time_diff * 1000000.)));
last_bytes = new_bytes;
last_time = now;
}
}
void do_mapwrite(int fd)
{
/* lets write as fast as we can.... */
int const window_size = 2 * 1024 * 1024; /* 16k */
int const window_pages = window_size / 4096;
int file_page_offset = 0;
long long file_size = window_size;
ftruncate64(fd, file_size);
{
char* mapping_start = (char*)mmap64(0, window_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
/* scribble into buffer and walk the window */
for (;;) {
memset(mapping_start, 0, window_size);
/* grow file */
file_size += window_size;
ftruncate64(fd, file_size);
file_page_offset += window_pages;
/*msync(mapping_start, window_size, MS_SYNC);*/
/*munmap(mapping_start, window_size);*/
/*mapping_start = (char*)mmap64(mapping_start, window_size, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_FIXED, fd, file_size - window_size);*/
remap_file_pages(mapping_start, window_size, 0, file_page_offset, MAP_SHARED);
total_bytes += window_size;
}
}
}
void do_filewrite(int fd)
{
FILE* ptr = fdopen(fd, "w+");
int line_len = 80;
char* buf = (char*)malloc(line_len);
memset(buf, 0, line_len);
for (;;) {
fwrite(buf, line_len, 1, ptr);
total_bytes += line_len;
}
}
void do_syswrite(int fd)
{
int line_len = 64 * 1024;
char* buf = (char*)malloc(line_len);
memset(buf, 0, line_len);
for (;;) {
write(fd, buf, line_len);
total_bytes += line_len;
}
}
int main(int argc, char* argv[])
{
if (argc != 3) {
printf("usage: %s -[mfw] <filename>\n", argv[0]);
return 0;
}
if ((argv[1][0] != '-') ||
((argv[1][1] != 'm') &&
(argv[1][1] != 'w') &&
(argv[1][1] != 'f'))) {
printf("usage: %s -[mfw] <filename>\n", argv[0]);
return 0;
}
int fd = open(argv[2], O_RDWR | O_CREAT | O_LARGEFILE | O_DIRECT, 0644);
if (fd < 0) {
perror("open");
return 0;
}
/* start the clock... */
signal(SIGALRM, timeout);
{
struct itimerval itv;
itv.it_interval.tv_sec = 1;
itv.it_interval.tv_usec = 0;
itv.it_value = itv.it_interval;
setitimer(ITIMER_REAL, &itv, 0);
}
switch (argv[1][1]) {
case 'm': do_mapwrite(fd); break;
case 'f': do_filewrite(fd); break;
case 'w': do_syswrite(fd); break;
}
return 0;
}
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