Commands Reference, Volume 5

When -r is used in combination without a new value, the nextboot value for tunable is displayed. When -p is used in combination without a new value, a value displays only if the current and next boot values for tunable are the same. Otherwise NONE displays as the value.

When used with -a or -o without specifying a new value, values are displayed only if the current and next boot values for a parameter are the same. Otherwise NONE displays as the value.

When used with -a or -o without specifying a new value, next boot values for tunables display instead of current values.

Name   Current  Default  Reboot   Minimum  Maximum  Unit  Type  Dependencies
       value    value    value    value    value
----------------------------------------------------------------------------

param1 5        2        4        1        10       MB/s     I  param2
                                                                param3

Parameters can be of the following types:
D for Dynamic if tunable can be changed at any time
S for Static if tunable can never be changed
R for Reboot if tunable can only be changed during reboot sequence.
B for Bosboot if tunable can only be changed by running bosboot and rebooting machine
M for Mount if tunable is only effective for filesystems or directory mountings
I for Incremental if tunable can only be incremented, except at boot time

Purpose:

Sets the number of intervening dispatches after which the SCHED_FIFO2 policy no longer favors a thread.

Values:

• Default: 7
• Range: 0 to 100
• Type: Dynamic

Diagnosis:

N/A

Tuning:

Once a thread is running with SCHED_FIFO2 policy, tuning of this variable may or may not have an effect on the performance of the thread and workload. Ideal values should be determined by trial and error.

Refer To:

Scheduling Policy for Threads

Purpose:

Used to determine when threads can be migrated to other processors.

Values:

• Default: 4
• Range: 0 to 100
• Type: Dynamic

Diagnosis:

N/A

Tuning:

This value is divided by 16 and then multiplied by the load average. The resulting value is used to determine if jobs should be migrated to other nodes (essentially does load balancing).

Purpose:

Keep fixed priority threads on global run queue.

Values:

• Default: 4
• Range: 0 to 1
• Type: Dynamic

Diagnosis:

N/A

Tuning:

If 1, then fixed priority threads are placed on the global run queue.

Refer To:

Scheduler Run Queue

Purpose:

Sets the number of times to spin on a kernel lock before going to sleep.

Values:

• Default: 1 on uniprocessor systems, -1 on MP systems, which means to spin up to 2³² times
• Range: -1 to 2³²
• Type: Dynamic

Diagnosis:

N/A

Tuning:

Increasing the value or setting it to -1 on MP systems may reduce idle time; however, it may also waste CPU time in some situations. Increasing it on uniprocessor systems is not recommended.

Refer To:

The schedtune -s Command

Purpose:

The number of clock ticks to wait before retrying a failed fork call that has failed for lack of paging space.

Values:

• Default: 10
• Range: a positive number of clock ticks bigger than 10
• Type: Dynamic

Diagnosis:

System is running out of paging space and process cannot be forked.

Tuning:

The system will retry a failed fork five times. For example, if a fork() subroutine call fails because there is not enough paging space available to create a new process, the system retries the call after waiting the specified number of clock ticks.

Refer To:

Tuning the fork() Retry Interval Parameter with schedtune

Purpose:

Sets the short term CPU usage delay rate.

Values:

• Default: 16
• Range: 0 to 32
• Type: Dynamic

Diagnosis:

N/A

Tuning:

The default is to decay short-term CPU usage by 1/2 (16/32) every second. Decreasing this value enables foreground processes to avoid competition with background processes for a longer time.

Refer To:

Tuning the Thread-Priority-Value Calculation

Purpose:

Sets the weighting factor for short-term CPU usage in priority calculations.

Values:

• Default: 16
• Range: 0 to 32
• Type: Dynamic

Diagnosis:

Run: ps al. If you find that the PRI column has priority values for foreground processes (those with NI values of 20) that are higher than the PRI values of some background processes (NI values > 20), you can reduce the r value.

Tuning:

The default is to include 1/2 (16/32) of the short term CPU usage in the priority calculation. Decreasing this value makes it easier for foreground processes to compete.

Refer To:

Tuning the Thread-Priority-Value Calculation

Purpose:

The number of clock ticks a thread can run before it is put back on the run queue.

Values:

• Default: 1
• Range: a positive integer value
• Type: Dynamic

Diagnosis:

N/A

Tuning:

Increasing this value can reduce overhead of dispatching threads. The value refers to the total number of clock ticks in a timeslice and only affects fixed-priority processes.

Refer To:

Modifying the Scheduler Time Slice with the schedtune Command

Purpose:

Used to adjust system clock with each clock tick in the correction range -1 to +1 seconds.

Values:

• Default: 100
• Range: 0 to 100
• Type: Dynamic

Diagnosis:

N/A

Tuning:

This is used to adjust clock drifts.

Purpose:

Sets the number of seconds that a recently resumed process that was previously suspended is exempt from suspension.

Values:

• Default: 2
• Range: 0 or a positive number
• Type: Dynamic

Diagnosis:

N/A

Tuning:

This parameter is only examined if thrashing is occurring.

Refer To:

VMM Memory Load Control Facility and Tuning VMM Memory Load Control with the schedtune Command

Purpose:

Sets the minimum number of processes that are exempt from suspension.

Values:

• Default: 2
• Range: 0 or a positive number
• Type: Dynamic

Diagnosis:

N/A

Tuning:

This number is in addition to kernel processes, processes with fixed priority less than 60, processes with pinned memory, or processes awaiting events. This parameter is only examined if there are threads on the suspended queue.

Refer To:

VMM Memory Load Control Facility and Tuning VMM Memory Load Control with the schedtune Command

Purpose:

Sets the system wide criteria used to determine when process suspension begins and ends (system is thrashing).

Values:

• Default: 6 unless system RAM is 128 MB or more (in this case it is 0)
• Range: 0 or a positive number
• Type: Dynamic

Diagnosis:

If v_repage_hi * page_outs/sec is > page_steals, then processes may get suspended.

Tuning:

If system is paging and causing scheduler to think it is thrashing but thrashing is not actually occurring, then it may be useful to desensitize the algorithm by decreasing the -h value or setting it to 0.

Refer To:

VMM Memory Load Control Facility and Tuning VMM Memory Load Control with the schedtune Command

Purpose:

Sets the per-process criterion used to determine which processes to suspend.

Values:

• Default: 4
• Range: 0 or a positive number
• Type: Dynamic

Diagnosis:

N/A

Tuning:

This requires a higher level of repaging by a given process before it is a candidate for suspension by memory load control. This parameter is examined only if thrashing is occurring.

Refer To:

VMM Memory Load Control Facility and Tuning VMM Memory Load Control with the schedtune Command

Purpose:

Sets the number of seconds to wait after thrashing ends before making suspended processes runnable.

Values:

• Default: 1
• Range: 0 or a positive number
• Type: Dynamic

Diagnosis:

N/A

Tuning:

This parameter is examined only if thrashing is occurring.

Refer To:

VMM Memory Load Control Facility and Tuning VMM Memory Load Control with the schedtune Command