Hi, The code below may be useful for doing simple testing of the O_SYNC and f[data]sync code in the kernel. It times various combinations of updates-in-place and appends under various synchronisation mechanisms, making it possible to see clearly whether fdatasync is skipping inode updates for updates-in-place, for example. --Stephen synctest.c: #include <assert.h> #include <unistd.h> #include <stdlib.h> #include <stdio.h> #include <string.h> #include <errno.h> #include <signal.h> #include <sys/fcntl.h> #include <sys/stat.h> #include <sys/vfs.h> #include <sys/resource.h> int iterations = 1000; struct timeval last_stopwatch_time; void stopwatch() { struct timeval now; int delta; gettimeofday(&now, 0); delta = (now.tv_sec - last_stopwatch_time.tv_sec) * 1000000 + (now.tv_usec - last_stopwatch_time.tv_usec); printf ("Stopwatch: elapsed time %d.%03d seconds\n", delta / 1000000, (delta / 1000) % 1000); last_stopwatch_time = now; } int main() { int fd, syncfd; int i; int err; char c; fd = open("syncfile", O_CREAT|O_TRUNC|O_RDWR, 0666); if (fd < 0) { perror("open"); exit(1); } syncfd = open("syncfile", O_RDWR|O_SYNC, 0666); if (syncfd < 0) { perror("open"); exit(1); } c = -1; err = pwrite(fd, &c, 1, 0); if (err != 1) { perror("pwrite"); exit(1); } gettimeofday(&last_stopwatch_time, 0); /* First pass: do nothing but fsync */ printf ("Performing %d fsyncs:\n", iterations); for (i=0; i<iterations; i++) fsync(fd); printf ("done. \n"); stopwatch(); /* Next pass: do nothing but fdatasync */ printf ("Performing %d fdatasyncs:\n", iterations); for (i=0; i<iterations; i++) fdatasync(fd); printf ("done. \n"); stopwatch(); /* Next pass: do fsync with a file read in each pass to force an * atime timestamp update */ printf ("Performing %d atime fsyncs:\n", iterations); for (i=0; i<iterations; i++) { pread(fd, &c, 1, 0); fsync(fd); } printf ("done. \n"); stopwatch(); /* Next pass: do fdatasync with a file read in each pass to * force an atime timestamp update */ printf ("Performing %d atime fdatasyncs:\n", iterations); for (i=0; i<iterations; i++) { pread(fd, &c, 1, 0); fdatasync(fd); } printf ("done. \n"); stopwatch(); /* Next pass: do fdatasync with a file write in each pass: this * should do a real sync of the data, but not of the inode. */ printf ("Performing %d write fdatasyncs:\n", iterations); for (i=0; i<iterations; i++) { pwrite(fd, &c, 1, 0); fdatasync(fd); } printf ("done. \n"); stopwatch(); /* Next pass: do fdatasync with a file append in each pass: this * should do a real sync of the data, and should also sync the * inode for the new i_size. */ printf ("Performing %d append fdatasyncs:\n", iterations); for (i=0; i<iterations; i++) { pwrite(fd, &c, 1, i); fdatasync(fd); } printf ("done. \n"); stopwatch(); /* Next pass: do fsync with a file write in each pass: this * should do a real sync of the data and inode in each round, * resulting in much head banging. */ printf ("Performing %d write fsyncs:\n", iterations); for (i=0; i<iterations; i++) { pwrite(fd, &c, 1, 0); fsync(fd); } printf ("done. \n"); stopwatch(); /* Next pass: do O_SYNC writes. */ printf ("Performing %d O_SYNC writes:\n", iterations); for (i=0; i<iterations; i++) { pwrite(syncfd, &c, 1, 0); } printf ("done. \n"); stopwatch(); /* Next pass: do O_SYNC appends. */ ftruncate(syncfd, 0); fsync(syncfd); printf ("Performing %d O_SYNC appends:\n", iterations); for (i=0; i<iterations; i++) { pwrite(syncfd, &c, 1, i); } printf ("done. \n"); stopwatch(); return 0; } - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] Please read the FAQ at http://www.tux.org/lkml/