On 11.09.2010, dave b wrote: > A simple test is just to dd if=/dev/zero of=DELETEME for a short time > and the system will stall rather a lot - it is not a complete lock up > - just the entire system is unresponsive for large periods at a time > (from around 30seconds - to 2 minutes). This is most likely due to the massive disk i/o which is generated by the dd command. > This may be related to > http://thread.gmane.org/gmane.linux.kernel.mm/51444 . I think this is completely unrelated, it's more a kind of a disk scheduler issue. I can't compare directly, because I'm running XFS on all of my machines, but you could try to fine-tune your disk scheduler. In any case, writing a big file and work on the same disk at the same time will always give you, hmmm.. "some delay", even without using encryption. Ok, let's give it a short run on one of my machines, a 10 GB file zeroed out using the dd command you mentioned, on /home, encrypted with dmcrypt/LUKS, and running Theodore Tso's fsync-tester on the same partition: htd@liesel:~/fs> ./fsync-tester fsync time: 0.5354 fsync time: 0.1496 fsync time: 0.2655 fsync time: 5.1740 fsync time: 6.0126 fsync time: 3.7945 fsync time: 19.0478 fsync time: 11.2006 fsync time: 4.5590 fsync time: 0.1663 fsync time: 0.3466 fsync time: 2.2969 fsync time: 0.7246 fsync time: 0.3036 fsync time: 6.2057 fsync time: 0.1042 fsync time: 0.7644 fsync time: 0.9193 fsync time: 0.1738 fsync time: 0.7413 fsync time: 18.2807 fsync time: 1.1971 fsync time: 0.2808 fsync time: 0.2364 fsync time: 0.3220 fsync time: 0.2108 fsync time: 0.2831 fsync time: 2.6023 fsync time: 14.0767 fsync time: 23.4450 fsync time: 3.2213 fsync time: 4.3488 fsync time: 12.5578 fsync time: 0.2359 ^C htd@liesel:~/fs> You can see stalls up to 23 secs here, too. I'm using the latest kernel 2.6.36-rc3 from Linus' git repository, with the "global workqueue per cpu" patch from Andi Kleen on top of it (which should not give any performance boost here in this case). Scheduler is cfq, tuned this way: echo cfq > /sys/block/sda/queue/scheduler echo "1" > /sys/block/sda/queue/iosched/low_latency echo "8" > /sys/block/sda/queue/iosched/slice_idle echo "8" > /sys/block/sda/queue/iosched/quantum liesel:/home/htd/fs # xfs_repair -V xfs_repair version 2.10.1 mount: /dev/mapper/home on /home type xfs (rw,noatime,logbsize=256k,logbufs=2,nobarrier,inode64) /* * 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; char buf[SIZE]; fd = open("fsync-tester.tst-file", O_WRONLY|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); } } _______________________________________________ dm-crypt mailing list dm-crypt@xxxxxxxx http://www.saout.de/mailman/listinfo/dm-crypt
