How to configure the AIX V5.3 Workload Manager to reserve CPU time for the root userid
The AIX Workload Manager (WLM) can be configured so that if/when many application processes are consuming all available CPU, it will still be possible to log in to the server as root and take action quickly. Please note that this best practice has a down side - root can consume all available CPU time if enough work is lauched. While WLM remains enabled, any root process which uses lots of CPU time will have a much greater impact on server performance than before. Configuring AIX system hang detection
is another option to permit quick intervention when all available CPU is consumed.
Here are instructions cribbed from the Setting up AIX Workload Manager in 30 minutes article on the IBM developerWorks web site:
# wlmcntrl -q # Confirm that WLM is not yet running
1495-054 WLM is stopped
# lsclass -f # Confirm that default WLM class config has not been changed
System:
memorymin = 1
Default:
Shared:
#
# wlmcntrl -p # Start WLM in passive mode
#
# # Make sure root users are in System class and all other users are in Default class
# ps -e -o class,pid,tag,user,group,comm,args | sort | more
CLASS PID TAG USER GROUP COMMAND COMMAND
Default 12680 - daemon sys rpc.statd /usr/sbin/rpc.statd -d 0 -t 50
Default 16980 - guest usr sleep sleep 30
Default 17972 - guest usr bsh -bsh
Default 18408 - guest usr sshd sshd: guest@pts/1
System 1 - root system init /etc/init
System 3658 - root system dtlogin dtlogin <:0> -daemon
System 4922 - root system dtlogin /usr/dt/bin/dtlogin -daemon
System 5300 - root system syncd /usr/sbin/syncd 60
...
System 19488 - root system sshd sshd: root@pts/0
System 20836 - root system inetd /usr/sbin/inetd
#
# # Move Default class down to tier one, so it is below the System class, which gives
# # root users first crack at CPU resources
# chclass -a tier=1 Default
#
# wlmcntrl -u # Tell WLM to pick up the configuration change
# lsclass -f # Confirm that Default tier change happened
System:
memorymin = 1
Default:
tier = 1
Shared:
#
# topas -w 2 # Start topas and display top two busiest WLM classes
...
#
# wlmcntrl -a # Start WLM in active mode
Use
to configure WLM so it gets started at AIX boot time.
If issues with WLM are suspected, use
to put WLM back in passive mode or use
to disable WLM completely.
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