Logical processors

A logical core may be taken offline as the result of an z/OS® operator entering an z/OS CONFIG command to take one (or more) CPs offline. When this is done, z/OS performs the work necessary to no longer dispatch work on the CP(s), and then executes a service call instruction to request that PR/SM take the logical cores(s) offline. See z/OS MVS System Commands for further detail on the CONFIG command. Lastly, a logical core may be taken off line at the next activation of the partition by reducing the number of CPs defined for a logical partition in the image profile for the logical partition.

The maximum number of logical processors for each logical partition is defined at logical partition activation, and remains fixed for the duration of the activation. Each of these logical cores is represented by a data structure that is associated only with its specific logical partition. There are no circumstances where a logical core can be "transferred" to another logical partition, nor is there a capability within the system to accomplish this.

When a logical core is taken offline, the data structure that represents it is marked as "offline", and continues to be maintained in PR/SM-accessible storage, remaining absolutely bound to its logical partition for the duration of that partition's activation. An offline logical core presents a checkstopped status when interrogated by the other logical cores in the partition. An offline logical core can be restored to the online status by issuing an z/OS CONFIG command. z/OS uses the service call instruction to request PR/SM bring an offline logical core back on line. If successful, z/OS prepares its control structures to add the CP to its pool of available resources.