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 IBM® Navigator for i.

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.

The shipped value is system controlled (2); however, the value might change after the first IPL by the system automatically if the shipped value is not supported by the hardware.

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.