[LU-715] Value read from qos_threshold_rr file does not match value written

• Type: Bug
• Resolution: Fixed
• Priority: Minor
• Fix Version/s: Lustre 2.2.0, Lustre 1.8.8
• Affects Version/s: Lustre 1.8.6
• Environment: CentOS 5.6
• Assignee: Andreas Dilger
• Reporter: Rick Mohr

Description

After I change the value of qos_threshold_rr by writing to /proc/fs/lustre/lov/<fsname>-mdtlov/qos_threshold_rr, the value I read back is usually one less than the value I wrote:

[root]# echo 17 > qos_threshold_rr
[root]# cat qos_threshold_rr
16%

This is not the case for values 0 or 100:

[root]# echo 100 > qos_threshold_rr
[root]# cat qos_threshold_rr
100%
[root]# echo 0 > qos_threshold_rr
[root]# cat qos_threshold_rr
0%

I realize this is an artifact of the way the value is stored. (Value range 0-100 is converted to 0-256 when written, and then converted back when read.) However, it is confusing to write one value and then read back a different value. This could be especially problematic when the value is 1:

[root]# echo 1 > qos_threshold_rr
[root]# cat qos_threshold_rr
0%

Anyone reading a value of 0 would not know whether the value had been set to 0 or 1.

If the behavior of Lustre cannot be modified, then the documentation should probably be updated to explain it.

Issue Links

• Trackbacks: Lustre 1.8.x known issues tracker While testing against Lustre b18 branch, we would hit known bugs which were already reported in Lustre Bugzilla https://bugzilla.lustre.org/. In order to move away from relying on Bugzilla, we would create a JIRA
• Trackbacks: Changelog 1.8 Changes from version 1.8.7wc1 to version 1.8.8wc1 Server support for kernels: 2.6.18308.4.1.el5 (RHEL5) Client support for unpatched kernels: 2.6.18308.4.1.el5 (RHEL5) 2.6.32220.13.1.el6 (RHEL6) Recommended e2fsprogs version: 1.41.90....
• Trackbacks: Changelog 2.2 version 2.2.0 Support for networks: o2iblnd OFED 1.5.4 Server support for kernels: 2.6.32220.4.2.el6 (RHEL6) Client support for unpatched kernels: 2.6.18274.18.1.el5 (RHEL5) 2.6.32220.4.2.el6 (RHEL6) 2.6.32.360....