Re: [BUG] bad performance and system stalls when using dm-crypt

[dave b <db.pub.mail@xxxxxxxxx>]

Here is what I would consider a better test, imho :)
/*
 * fsync-tester.c
 *
 * Written by Theodore Ts'o, 3/21/09.
 *
 * This file may be redistributed under the terms of the GNU Public
 * License, version 2.
 */

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <time.h>
#include <fcntl.h>
#include <string.h>

#define SIZE (32768*32)

static float timeval_subtract(struct timeval *tv1, struct timeval *tv2)
{
	return ((tv1->tv_sec - tv2->tv_sec) +
		((float) (tv1->tv_usec - tv2->tv_usec)) / 1000000);
}

int main(int argc, char **argv)
{
	int fd;
	struct timeval tv, tv2, tv3, tv4;
	char buf[SIZE];

	fd = open("fsync-tester.tst-file", O_RDWR|O_CREAT);
	if (fd < 0) {
		perror("open");
		exit(1);
	}
	memset(buf, 'a', SIZE);
	while (1) {
		pwrite(fd, buf, SIZE, 0);
		gettimeofday(&tv, NULL);
		fsync(fd);
		gettimeofday(&tv2, NULL);
		printf("fsync time: %5.4f\n", timeval_subtract(&tv2, &tv));
		sleep(1);

		gettimeofday(&tv3, NULL);
		pread(fd, buf, SIZE, 0);
		gettimeofday(&tv4, NULL);
		printf("pread time: %5.4f\n", timeval_subtract(&tv4, &tv3));
		sleep(1);
	}
}

--- fsync-tester.c	2010-09-11 17:25:53.000000000 +1000
+++ mine.c	2010-09-11 18:57:36.000000000 +1000
@@ -27,10 +27,10 @@
 int main(int argc, char **argv)
 {
        int fd;
-       struct timeval tv, tv2;
+       struct timeval tv, tv2, tv3, tv4;
        char buf[SIZE];

-       fd = open("fsync-tester.tst-file", O_WRONLY|O_CREAT);
+       fd = open("fsync-tester.tst-file", O_RDWR|O_CREAT);
        if (fd < 0) {
                perror("open");
                exit(1);
@@ -43,6 +43,12 @@
                gettimeofday(&tv2, NULL);
                printf("fsync time: %5.4f\n", timeval_subtract(&tv2, &tv));
                sleep(1);
+
+               gettimeofday(&tv3, NULL);
+               pread(fd, buf, SIZE, 0);
+               gettimeofday(&tv4, NULL);
+	         printf("pread time: %5.4f\n", timeval_subtract(&tv4, &tv3));
+               sleep(1);
        }
 }

This still isn't as good a test as I would like :)

./mine.out
fsync time: 0.0264
pread time: 0.0009
fsync time: 0.0415
pread time: 0.0008
fsync time: 2.4119
pread time: 1.0698
fsync time: 19.5375
pread time: 0.0009
fsync time: 15.9053
pread time: 0.0009
fsync time: 6.3872
pread time: 3.6912
fsync time: 6.8910
pread time: 0.0099
fsync time: 4.0445
pread time: 0.3053
fsync time: 8.3816
pread time: 0.3386
fsync time: 6.0976
pread time: 0.0009
fsync time: 0.0236
pread time: 0.0008
fsync time: 0.0255

So when I try to do other things I see the pread time go way up :)
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