Specifies whether processor multi-tasking is on, off, or determined by the system. (QPRCMLTTSK)
Processor multi-tasking, also known as QPRCMLTTSK, is a member of the system and user defaults category of i5/OS™ system values. You can work with this system value from the character-based interface; it is not in iSeries™ Navigator. You can use this system value to specify whether multi-tasking is on, off, or system controlled. To learn more, keep reading.
| Quick reference | |
|---|---|
| Location | Character-based interface |
| Special authority | All object (*ALLOBJ) and security administrator (*SECADM) |
| Default value | System controlled (2) |
| Changes take effect | At the next restart of the server |
| Lockable | No |
Use this system value to control processor multi-tasking. To learn more about how a processor does this, see multi-threading.
This system value has three possible values, off (0), on (1), and system controlled (2), and controls whether the hardware executes only one or more than one task at a time on a processor. The off (0) state means that each processor supports the execution of only one task at any moment in time. The states on (1) and system controlled (2) allow processors to concurrently execute multiple tasks, with the difference being that the system controlled state gives permission to the operating system to occasionally limit a processor to executing at most one task. The state system controlled is the default value. 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 executes more work. On the other hand, by limiting processors to execute single tasks, the system tends to allow individual tasks to execute 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 multi-threading (SMT) or hardware multi-threading (HMT). If unsupported, the system value change does not take effect.
On partitioned AS/400® 7xx and iSeries 8xx servers, all partitions inherit the current value from the primary partition. Thus, only changes to the system value of the primary partition may become effective. In order for changes to take effect, an IPL of the primary partition is required. The default value is on (1) if supported by the system hardware. Otherwise the default value is off (0).
On eServer™ i5 servers, the current value is partition independent. Thus, changes to the system value of a partition may become effective for only that partition. In order for changes to take effect, an IPL of only that partition is required. The default value is system controlled (2).
The shipped value is system controlled (2); however, the value may 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 may change after the first IPL. The following table describes various system environments and what the value will change to after the first IPL:
| Primary/secondary partition attribute | Multi-tasking supported on the hardware | Server model | Value after first IPL | Supported values |
|---|---|---|---|---|
| Primary or non-partitioned | Yes | AS/400 7xx or iSeries 8xx | 1 (on) | On (1) or off (0) |
| Primary or non-partitioned | No | AS/400 7xx or iSeries 8xx | 0 (off) | Off (0) |
| Secondary | Yes | AS/400 7xx or iSeries 8xx | Inherits current value from primary partition | On (1) or off (0) |
| Secondary | No | AS/400 7xx or iSeries 8xx | Inherits current value from primary partition | Off (0) |
| Not applicable * | Yes | eServer i5 | 2 (system controlled) | On (1), off (0) or system controlled (2) |
| Not applicable * | No | eServer i5 | 2 (system controlled) | Off (0) or system controlled (2) |
* This type of server does not distinguish between primary or secondary partitions. Rather it is a partitioned server managed by the Hardware Management Console for eServer.
To learn more, go to the system and user defaults system values overview topic. If you are looking for a specific system value or category of system values, try using the i5/OS system value finder.
In addition, see multi-threading to learn more about processor multi-tasking.