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DescriptionMikuláš Patočka
2011-07-25 21:49:42 UTC
Sysfs contains algorithms that perform quadratically with respect to the number of entries in a directory. As a result, sysfs slows down operation when working with many (thousands ~ ten thousands) block devices.
Comment 2RHEL Program Management
2011-07-25 22:20:15 UTC
This request was evaluated by Red Hat Product Management for inclusion
in a Red Hat Enterprise Linux maintenance release. Product Management has
requested further review of this request by Red Hat Engineering, for potential
inclusion in a Red Hat Enterprise Linux Update release for currently deployed
products. This request is not yet committed for inclusion in an Update release.
We need good performance when working with many (thousands) block devices.
These tests were done:
1. create 10000 block devices
time for i in `seq 0 9999`; do echo $i; dmsetup create test$i --notable; done
2. list the devices
time ls -la /sys/block
3. flush cache and list the devices
echo 3 >/proc/sys/vm/drop_caches; time ls -la /sys/block
4. remove the devices
time dmsetup remove_all
Time before the patches (on current RHEL-6 kernel):
141s, 2.1s, 2.4s, 63s
Time after the patches
25s, 0.5s, 0.8s, 8.8s
The effect of individual patches on upstream kernel 3.0-rc7 can be seen here:
http://www.redhat.com/archives/dm-devel/2011-July/msg00073.html
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory, and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.
http://rhn.redhat.com/errata/RHSA-2011-1530.html