System and user defaults system values: Processor multitasking

The Processor multitasking system value is also known as QPRCMLTTSK. You can use this system value to specify whether multitasking is on, off, or system controlled.

You can work with this system value from the character-based interface; it is not available in System i® Navigator.

Quick reference
Location	Character-based interface.
Special authority	All object (ALLOBJ) and security administrator (SECADM).
Default value	System controlled (2).
Changes take effect	The next time the system is restarted.
Lockable	No.

What can I do with this system value?

You can control processor multitasking. This system value controls whether the hardware processes only one or more than one task at a time on a processor.

This system value has the following values:

Off (0): Each processor supports the processing of only one task at any moment.
On (1): Processors can concurrently process multiple tasks.
System controlled (2): Processors can concurrently process multiple tasks. The system-controlled state also enables the operating system to occasionally limit a processor to processing one task at most.

The value that you specify should be based on performance and is workload dependent. By allowing multiple tasks per processor, the performance capacity of the system tends to increase. Therefore, the system processes more work. By limiting processors to run single tasks, the system tends to allow individual tasks to run faster.

Changes to the system value do not take effect until the next IPL. If you request a change to the state of on (1) or system controlled (2), the change takes effect only if the processor hardware supports the concept of simultaneous multithreading (SMT) or hardware multithreading (HMT). If unsupported, the system value change does not take effect.

On partitioned 8xx models, all partitions inherit the current value from the primary partition. Thus, only changes to the system value of the primary partition become effective. In order for changes to take effect, you need to perform an IPL operation for the primary partition. The default value is on (1) if supported by the system hardware. Otherwise the default value is off (0).

On 5xx models, the current value is partition independent. Thus, changes to the system value of a partition become effective only for that partition. In order for changes to take effect, you need to perform an IPL operation for that partition. The default value is system controlled (2).

The shipped value is system controlled (2); however, the value might change after the first IPL by the system automatically because the shipped value is not supported by the hardware on all systems. The shipped value might change after the first IPL. The following table describes various system environments and what the value changes to after the first IPL.

Primary or secondary partition attribute	Multitasking supported on the hardware	System model	Value after first IPL	Supported values
Primary or nonpartitioned	Yes	8`xx` models	1 (on)	On (1) or off (0)
Primary or nonpartitioned	No	8`xx` models	0 (off)	Off (0)
Secondary	Yes	8`xx` models	Inherits current value from primary partition	On (1) or off (0)
Secondary	No	8`xx` models	Inherits current value from primary partition	Off (0)
Not applicable¹	Yes	5`xx` models	2 (system controlled)	On (1), off (0) or system controlled (2)
Not applicable¹	No	5`xx` models	2 (system controlled)	Off (0) or system controlled (2)
¹ This type of model does not distinguish between primary or secondary partitions. Rather it is a partitioned system managed by the Hardware Management Console.

Note: To find out whether your system's hardware supports multitasking, you can change this system value to on (1) and then perform an IPL operation for the system. If the change takes effect, multitasking is supported. If the value does not change after the IPL, multitasking is not supported by the hardware.