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Date: Thu, 07 Jun 2007 19:18:44 +0200
From: Axel Gembe <ago@...tart.eu.org>
To: linux-kernel@...r.kernel.org
Subject: Speed problem with device mapper or dm-crypt
My system is the latest Gentoo with kernel 2.6.22-rc3 on an Athlon XP box.
The kernel version didn't make a difference, I've only recently tried
many 2.6 kernels.
I'm using the command
cryptsetup -c aes -s 128 -h sha256 create crypt-theke /dev/hdg5
to create a encrypted mapper device on which an ext3 filesystem lives
with these mount options:
/dev/mapper/crypt-theke /mnt/hd/wd200 ext3 noatime,noauto 0 0
The speed from the device is fine when I read from /dev/mapper/crypt-theke:
cat /dev/mapper/crypt-theke > /dev/null
this is very fast and produces this vmstat 1:
procs -----------memory---------- ---swap-- -----io---- -system--
----cpu----
r b swpd free buff cache si so bi bo in cs us
sy id wa
1 1 160 8260 216060 367104 0 0 34560 0 533 1285 0
81 0 19
2 1 160 8608 248296 334100 0 0 34304 0 525 1273 1
80 0 19
1 1 160 8336 281056 301084 0 0 34560 0 535 1277 0
82 0 18
but it is very sluggish when I read from /mnt/hd/wd200:
cat /mnt/hd/wd200/bigfile > /dev/null
this is lagging the whole system and produces this vmstat 1:
procs -----------memory---------- ---swap-- -----io---- -system--
----cpu----
r b swpd free buff cache si so bi bo in cs us
sy id wa
1 1 160 8004 494120 65388 0 0 4248 0 550 1582 3
14 0 83
1 1 160 7764 490284 69484 0 0 4100 0 537 1364 0
12 0 88
1 1 160 7884 486448 73196 0 0 3716 0 503 1280 0
12 0 88
This confuses me. Why would using a filesystem in between produce such
high wait times ?
Is the IO cat makes any different ?
Here are some more values:
Reading from the underlying device:
filesrv1 ~ # dd if=/dev/hdg5 of=/dev/null bs=1024 count=256000
256000+0 records in
256000+0 records out
262144000 bytes (262 MB) copied, 4.35061 s, 60.3 MB/s
Produced this vmstat 1:
procs -----------memory---------- ---swap-- -----io---- -system--
----cpu----
r b swpd free buff cache si so bi bo in cs us
sy id wa
1 1 160 8428 388644 180548 0 0 26112 0 477 1128 1
16 52 31
2 0 160 7936 386904 180512 0 0 59008 88 753 1926 0
41 0 59
1 1 160 8164 404388 160256 0 0 59776 0 751 1911 2
40 0 58
2 0 160 7876 461776 99924 0 0 59520 0 754 1903 1
41 0 58
1 0 160 7804 507704 51560 0 0 51584 0 686 1722 0
38 13 49
Reading from the mapper device:
filesrv1 ~ # dd if=/dev/mapper/crypt-theke of=/dev/null bs=1024
count=256000
256000+0 records in
256000+0 records out
262144000 bytes (262 MB) copied, 7.8481 s, 33.4 MB/s
Produced this vmstat 1:
procs -----------memory---------- ---swap-- -----io---- -system--
----cpu----
r b swpd free buff cache si so bi bo in cs us
sy id wa
1 1 160 7664 527800 31244 0 0 28476 60 524 1135 1
71 10 18
1 1 160 7508 529224 30788 0 0 33024 0 532 1237 1
77 0 22
2 1 160 8412 534228 26708 0 0 32644 96 549 1240 1
83 0 16
2 0 160 8332 535992 26004 0 0 32768 0 539 1217 2
80 0 18
2 1 160 8412 537180 26020 0 0 32940 0 548 1257 2
84 0 14
3 1 160 8152 538752 26012 0 0 33280 8 525 1244 1
77 0 22
2 1 160 7660 540568 26016 0 0 32788 0 537 1302 1
82 0 17
1 0 160 8240 541296 25984 0 0 30336 0 516 1184 0
74 8 18
Reading from a big file on the mounted filesystem:
filesrv1 ~ # dd if=/mnt/hd/wd200/bigfile of=/dev/null bs=1024
count=256000
256000+0 records in
256000+0 records out
262144000 bytes (262 MB) copied, 67.2541 s, 3.9 MB/s
Produced this vmstat 1:
procs -----------memory---------- ---swap-- -----io---- -system--
----cpu----
r b swpd free buff cache si so bi bo in cs us
sy id wa
3 1 160 7556 264780 292864 0 0 4484 112 538 1576 4
16 0 80
1 1 160 7916 260816 296448 0 0 3588 0 492 1205 0
12 0 88
1 1 160 8036 256852 300288 0 0 3844 8 541 1307
1 8 0 91
1 1 160 7632 253272 304640 0 0 4356 0 527 1359 7
14 0 79
1 1 160 8348 248540 308608 0 0 3972 0 516 1261
0 9 0 91
1 1 160 8168 244964 312448 0 0 3844 0 501 1254 0
12 0 88
1 1 160 8352 240312 316848 0 0 4484 0 505 1241 0
10 0 90
1 1 160 7896 237764 320304 0 0 3588 48 490 1232 6
12 0 82
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