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    Subjectdisk/crypto performance regression 2.6.31 -> 2.6.32 (mmap problem?)

    I have a system with 8 gigs of ram, c2d 2.4GHz and md
    raid6->crypto->lvm/lv->xfs that I've had for quite a while. It used to be
    raid5, but with 2.6.32 I was able to restripe it into a raid6.

    When under 2.6.32 (Linux ub 2.6.32-12-generic #16-Ubuntu SMP Thu Jan 28
    07:47:05 UTC 2010 x86_64 GNU/Linux) I'm seeing this in latency-top
    (sometimes worse, several seconds) when running rtorrent (which uses mmap)

    Cause Maximum Percentage
    Page fault 1580.4 msec 84.7 %
    Writing a page to disk 869.7 msec 2.2 %
    [xfs_ilock] 232.9 msec 2.3 %
    Truncating file 110.1 msec 0.3 %
    Waiting for TTY data 18.2 msec 0.0 %
    Reading EXT3 indirect blocks 10.0 msec 0.1 %
    Executing a program 9.8 msec 0.0 %
    Walking directory tree 8.7 msec 0.0 %
    Waiting for event (select) 5.0 msec 1.8 %

    swmike@ub:~$ free
    total used free shared buffers cached
    Mem: 8194328 6455004 1739324 0 2012 4343532
    -/+ buffers/cache: 2109460 6084868
    Swap: 0 0 0

    iostat -x 5 gives this:

    avg-cpu: %user %nice %system %iowait %steal %idle
    0.61 0.00 4.36 63.29 0.00 31.74

    Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm %util
    sda 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
    sdb 35.80 59.00 20.80 21.00 457.60 646.40 26.41 0.13 3.21 2.06 8.60
    sdc 33.20 74.40 21.60 26.40 491.20 814.40 27.20 0.23 4.88 3.29 15.80
    sdd 24.20 96.60 21.00 32.80 457.60 1040.00 27.84 0.31 5.84 4.16 22.40
    sde 25.60 94.80 18.80 33.60 420.80 1033.60 27.76 0.28 5.42 3.82 20.00
    md0 0.00 0.00 5.00 97.20 393.60 2390.40 27.24 0.00 0.00 0.00 0.00
    sdf 29.80 87.20 18.60 28.80 460.80 937.60 29.50 0.16 3.38 2.70 12.80
    sdg 35.80 61.80 20.60 19.60 476.80 657.60 28.22 0.26 5.92 3.38 13.60
    sdh 32.20 71.20 21.00 22.20 465.60 752.00 28.19 0.23 5.23 3.24 14.00
    dm-0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
    dm-1 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
    dm-2 0.00 0.00 5.00 132.40 393.60 2390.40 20.26 3.32 22.39 7.26 99.80
    dm-3 0.00 0.00 5.20 77.80 444.80 1841.60 27.55 3.32 37.08 12.05 100.00

    swmike@ub:/dev/mapper$ ls -l
    total 0
    crw-rw---- 1 root root 10, 59 2010-02-05 17:57 control
    brw-rw---- 1 root disk 252, 2 2010-02-15 13:55 md0_crypt
    brw-rw---- 1 root disk 252, 0 2010-02-15 13:55 sdb1_crypt
    brw-rw---- 1 root disk 252, 1 2010-02-15 13:55 ub-root
    brw-rw---- 1 root disk 252, 3 2010-02-15 13:55 vg01-home

    So from what I can gather, even though it's moving very little traffic
    thru the crypt layer, this is still the bottleneck (when just copying a
    single file I can easily get 50+ megabyte/s thru the crypto layer). Top
    indicates low cpu usage but still high load of course, since rtorrent is
    "blocking" most of the time (unresponsive to interactive input).

    top - 17:34:54 up 14 days, 37 min, 6 users, load average: 3.60, 3.90, 3.89
    Tasks: 237 total, 2 running, 235 sleeping, 0 stopped, 0 zombie
    Cpu0 : 1.7%us, 8.6%sy, 0.0%ni, 55.1%id, 30.9%wa, 2.3%hi, 1.3%si, 0.0%st
    Cpu1 : 1.4%us, 11.1%sy, 0.0%ni, 2.8%id, 81.9%wa, 0.0%hi, 2.8%si, 0.0%st
    Mem: 8194328k total, 8143856k used, 50472k free, 2136k buffers
    Swap: 0k total, 0k used, 0k free, 5625364k cached

    PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
    9950 root 20 0 0 0 0 S 5 0.0 1012:29 md0_raid5
    25684 root 20 0 0 0 0 R 9 0.0 342:58.88 kcryptd
    22007 swmike 20 0 325m 170m 140m D 5 2.1 87:09.82 rtorrent
    15543 swmike 20 0 124m 24m 3296 S 1 0.3 78:25.01 rtorrent
    31346 swmike 9 -11 327m 5940 4200 S 0 0.1 43:12.09 pulseaudio

    When I was running 2.6.31 (ubuntu 9.10) kernel I didn't see this problem
    at all, though things have changed in that I'm now running raid6 instead
    of raid5, but from the iostat it looks like the disk+md layer is not
    causing this behaviour (before in 2.6.31 that was the bottleneck but not
    anymore).

    Here is an example of when I dd a large file instead, note the dm-2
    behaviour:

    avg-cpu: %user %nice %system %iowait %steal %idle
    29.10 0.00 70.90 0.00 0.00 0.00

    Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm %util
    sda 0.00 0.00 3.00 0.00 54.40 0.00 18.13 0.01 4.00 1.33 0.40
    sdb 42.80 1990.20 3.40 75.40 369.60 16537.60 214.56 0.20 2.51 0.79 6.20
    sdc 38.60 1993.40 3.20 75.20 334.40 16563.20 215.53 0.10 1.22 0.56 4.40
    sdd 31.80 1990.40 2.20 75.00 272.00 16537.60 217.74 0.12 1.53 0.65 5.00
    sde 31.80 1986.80 2.20 75.40 272.00 16512.00 216.29 0.25 3.20 1.11 8.60
    md0 0.00 0.00 0.00 777.20 0.00 99225.60 127.67 0.00 0.00 0.00 0.00
    sdf 28.80 1993.40 2.00 75.40 246.40 16563.20 217.18 0.06 0.80 0.52 4.00
    sdg 36.80 1999.20 3.00 75.80 318.40 16612.80 214.86 0.56 7.13 1.73 13.60
    sdh 17.60 1993.20 1.80 75.60 155.20 16563.20 216.00 0.02 0.26 0.21 1.60
    dm-0 0.00 0.00 3.00 0.00 54.40 0.00 18.13 0.01 4.00 1.33 0.40
    dm-1 0.00 0.00 3.00 0.00 54.40 0.00 18.13 0.01 4.00 1.33 0.40
    dm-2 0.00 0.00 0.00 0.00 0.00 0.00 0.00 14696.19 0.00 0.00 100.00
    dm-3 0.00 0.00 0.00 9051.80 0.00 963836.80 106.48 14696.19 468.84 0.11 100.00
    sdj 24.80 1999.00 2.20 76.00 216.00 16612.80 215.20 0.10 1.25 0.72 5.60

    avg-cpu: %user %nice %system %iowait %steal %idle
    24.82 0.00 73.27 1.91 0.00 0.00

    Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm %util
    sda 0.00 0.00 1.20 0.00 24.00 0.00 20.00 0.00 3.33 3.33 0.40
    sdb 3.00 3288.00 0.20 83.40 25.60 26972.80 322.95 0.16 1.91 1.89 15.80
    sdc 6.00 3287.80 0.80 83.60 54.40 26972.80 320.23 0.19 2.25 2.13 18.00
    sdd 7.20 3283.40 1.00 83.00 65.60 26932.80 321.41 0.29 3.40 2.45 20.60
    sde 7.20 3283.80 1.00 82.60 65.60 26932.80 322.95 0.25 3.01 2.39 20.00
    md0 0.00 0.00 0.00 3665.20 0.00 161574.40 44.08 0.00 0.00 0.00 0.00
    sdf 1.20 3283.80 0.60 82.60 14.40 26932.80 323.88 0.21 2.50 2.33 19.40
    sdg 3.00 3285.00 0.20 83.20 25.60 26947.20 323.41 0.29 3.43 2.45 20.40
    sdh 1.20 3283.80 0.60 82.60 14.40 26932.80 323.88 0.20 2.43 2.28 19.00
    dm-0 0.00 0.00 1.20 0.00 24.00 0.00 20.00 0.00 3.33 3.33 0.40
    dm-1 0.00 0.00 1.20 0.00 24.00 0.00 20.00 0.00 3.33 3.33 0.40
    dm-2 0.00 0.00 0.00 3872.40 0.00 334886.40 86.48 9989.29 6114.24 0.26 100.00
    dm-3 0.00 0.00 0.00 2731.80 0.00 178907.60 65.49 9989.30 8667.10 0.37 100.00
    sdj 4.20 3283.80 0.80 82.60 40.00 26932.80 323.41 0.18 2.16 2.13 17.80

    avg-cpu: %user %nice %system %iowait %steal %idle
    30.89 0.00 65.09 4.02 0.00 0.00

    Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm %util
    sda 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
    sdb 12.00 3141.00 0.80 78.20 102.40 25680.00 326.36 0.15 1.85 1.77 14.00
    sdc 9.00 3141.20 0.60 78.20 76.80 25756.80 327.84 0.14 1.83 1.75 13.80
    sdd 9.00 3140.80 0.60 78.60 76.80 25755.20 326.16 0.32 4.04 2.30 18.20
    sde 9.00 3140.60 0.60 78.80 76.80 25755.20 325.34 0.27 3.38 2.14 17.00
    md0 0.00 0.00 0.00 1685.80 0.00 154444.80 91.62 0.00 0.00 0.00 0.00
    sdf 6.00 3141.00 0.40 78.40 51.20 25755.20 327.49 0.16 2.03 1.93 15.20
    sdg 9.00 3142.60 0.60 78.40 76.80 25769.60 327.17 0.48 6.08 3.32 26.20
    sdh 6.00 3141.20 0.40 77.80 51.20 25678.40 329.02 0.14 1.74 1.71 13.40
    dm-0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
    dm-1 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
    dm-2 0.00 0.00 0.00 0.00 0.00 0.00 0.00 9797.52 0.00 0.00 100.00
    dm-3 0.00 0.00 0.20 2035.60 1.60 135518.80 66.57 9797.52 3423.06 0.49 100.00
    sdj 9.00 3142.40 0.60 78.60 76.80 25769.60 326.34 0.18 2.25 1.97 15.60

    Any ideas? What more information can I collect to help look into this
    issue? Currently I'm running with:

    swmike@ub:~$ cat /etc/sysctl.conf | grep vm
    vm.dirty_background_ratio = 1
    vm.dirty_ratio = 60

    Setting this to 10/30 or something alike doesn't really change the
    behaviour with rtorrent. I've also mucked around with io scheduler,
    running deadline right now, doesn't see much difference between them under
    2.6.32 and this problem.

    --
    Mikael Abrahamsson email: swmike@swm.pp.se


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