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Commands Reference, Volume 5

schedtune Command


Compatibility script to set parameters of the CPU scheduler and Virtual Memory Manager.


schedtune [ -D ]

schedtune [ -d Number ] [ -e Number ] [ -f Number ] [ -h Number ] [ -m Number ] [ -p Number ] [ -r Number ] [ -t Number ] [ -w Number ]


The schedtune sample program is being phased out and will not be supported in future releases. It is being replaced by the schedo command which can be used to set the same parameters as schedtune did in previous release. In AIX 5.2, a compatibility script calling schedo is provided to help the transition.

The schedtune command can only be executed by root. Changes made by the schedtune command last until the next reboot of the system. In AIX 5.2, schedo can be used to make changes permanent.

Attention: Misuse of this scipt can cause performance degradation or operating-system failure. Be sure that you have studied the appropriate tuning sections of the AIX 5L Version 5.2 Performance Management Guide before using schedtune to change system parameters.


If no flags are specified, schedo -a is called to display the current values.

-D Calls schedo -D to restore the default values.
-a Number Calls schedo -o affinity_lim=Number to set the number of context switches after which the SCHED_FIF02 policy no longer favors a thread.
-b Number Calls schedo -o idle_migration_barrier=Number to set the idle migration barrier.
-c Number Calls schedo -o %usDelta=Number to control the adjustment of the clock drift.
-d Number Calls schedo -o sched_D=Number to set the factor used to decay CPU usage.
-e Number Calls schedo -o v_exempt_seconds=Number to set the time before a recently suspended and resumed process is eligible for resuspension.
-f Number Calls schedo -o pacefork=Number to set the number of clock ticks to delay before retrying a failed fork call.
-F Number Calls schedo -o fixed_pri_global=Number to keep fixed priority threads in the global run queue.
-h Number Calls schedo -o v_repage_hi=Number to change the system wide criterion used to determine when process suspension begins and ends.
-m Number Calls schedo -o v_min_process=Number to set the minimum multiprogramming level.
-p Number Calls schedo -o v_repage_proc=Number to change the per process criterion used to determine which processes to suspend.
-r Number Calls schedo -o sched_R=Number to set the rate at which to accumulate CPU usage.
-s Number Calls schedo -o maxspin=Number to set the number of times to spin on a lock before sleeping.
-t Number Calls schedo -o timesplice=Number to set the number of 10ms time slices.
-w Number Calls schedo -o v_sec_wait=Number to set the number of seconds to wait after thrashing ends before adding processes back into the mix.
-? Displays a brief description of the command and its parameters.

See the schedo command's Tunable Parameters section.

Related Information

The schedo command

Real-Memory management.

Modifications to vmtune and schedtune in AIX 5L Version 5.2 Performance Management Guide.

Tuning VMM Memory Load Control with the schedtune Command.

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