[LU-3944] something wrong with "lctl conf_param" to set MDS/OSS thread count

• Type: Bug
• Resolution: Won't Fix
• Priority: Minor
• Affects Version/s: Lustre 2.4.1, Lustre 2.5.0
• Severity: 3
• Assignee: Emoly Liu
• Reporter: Emoly Liu

Description

We found this problem during reviewing lustre manual chapter 31.9. Usually, we can set threads_min like

lctl set_param mds.MDS.mdt_readpage.threads_min=16

But if we use conf_param to set it permanently, it will fail. It can be reproduced by the following steps:
1)lctl conf_param lustre.mdt.mdt_readpage.threads_min=16
no error is reported, but dmesg shows

Lustre: Setting parameter lustre-MDT0000.mdt.mdt_readpage.threads_min in log lustre-MDT0000
LustreError: 1273:0:(obd_config.c:1591:class_config_llog_handler()) MGC10.211.55.18@tcp: cfg command failed: rc = -38
Lustre:    cmd=cf00f 0:lustre-MDT0000  1:mdt.mdt_readpage.threads_min=16  

2)since the previous lctl cmd doesn't report error, when you umount and remount mds next time, you will see "Function not implemented".

BTW, "lctl set_param -P" introduced by LU-3155, a new method to set parameter permanently for lustre 2.5 and later, has no such problem.