[dm-devel] very slow dm-crypt write operation
Adrian B
adriab at gmail.com
Mon Jul 30 14:58:36 UTC 2007
Hi,
I am seeing very slow dm-crypt writes on a machine where CPU, disk
speed and even dm-crypt reads are normal.
It appears that kcryptd is scheduled insufficiently on the CPU(s)
when writing to dm-crypt devices. While reading, kcryptd is taking a
lot of CPU time, most of the time (top). But when writing, kcryptd is
taking a lot of pauses - I see intermittent activity where it uses the
CPU for a few seconds, then pauses for a long time, then it's up
again.
Any idea what's going on?
Writing a 1 GB file to dm-crypt takes 5 min (!):
time cp /tmp/1GB_File /mnt/dm-crypt/tmp/
real 5m21.123s
user 0m0.119s
sys 0m7.762s
Reading the same 1 GB file back from dm-crypt takes only 1.5 min:
time cp /mnt/dm-crypt/tmp/1GB_File /tmp
real 1m30.147s
user 0m0.125s
sys 0m7.522s
Copying the file without dm-crypt takes about 1 min:
time cp /tmp/1GB_File /tmp/Copy01
real 1m12.334s
user 0m0.090s
sys 0m5.856s
This is Fedora 7, kernel 2.6.22.1-33.fc7 #1 SMP Mon Jul 23 17:33:07
EDT 2007 i686 i686 i386 GNU/Linux.
Hardware is Intel 865G chipset, Pentium 4 CPU (HT), 2 GB RAM, ATA drive udma5.
Thank you.
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