Processor resource assignment in partition profiles

When you create a partition profile for a logical partition, you can set up the allocated, minimum, and maximum amounts of processor resources that you want for the logical partition.

The allocated value is the resource amount that the logical partition gets if you do not over commit the resource on the managed system. If the allocated amount of resources is available when you activate the partition profile, then the logical partition starts with the allocated amount of resources. However, if the allocated amount of resources is not available when you activate the partition profile, then the resources on your managed system are over committed. If the amount of resources that are available on the managed system is equal to or greater than the minimum amount of resources in the partition profile, then the logical partition starts with the available amount of resources. If the minimum amount of resources is not met, then the logical partition does not start.

If the managed system allows the configuration of multiple shared processor pools, then you can limit the number of processors that are used by a specific group of logical partitions by configuring a shared processor pool for those logical partitions and reassigning those logical partitions to that shared processor pool. For example, if you use per-processor licensing for IBM® i, and you have a limited number of IBM i licenses for your managed system, you can create a shared processor pool for the IBM i logical partitions on the managed system and set the maximum number of processing units for that shared processor pool to be equal to the number of IBM i licenses on the managed system. If you configure a shared processor pool and assign logical partitions to that shared processor pool, the number of processing units that are used by those logical partitions plus the number of processing units that are reserved for the use of uncapped logical partitions within the shared processor pool cannot exceed the maximum number of processing units that you set for that shared processor pool.

If you create a partition profile that is set to use shared processors, the HMC calculates a minimum, maximum, and allocated number of virtual processors for the partition profile. The calculation of virtual processors is based on the minimum, maximum, and allocated number of processing units that you specify for the partition profile. By default, the virtual processor settings are calculated as follows:
  • The default minimum number of virtual processors is the minimum number of processing units (rounded up to the next whole number). For example, if the minimum number of processing units is 0.8, the default minimum number of virtual processors is 1.
  • The default allocated number of virtual processors is the allocated number of processing units (rounded up to the next whole number). For example, if the allocated number of processing units is 2.8, the default allocated number of virtual processors is 3.
  • The default maximum number of virtual processors is the maximum number of processing units rounded up to the next whole number and multiplied by two. For example, if the maximum number of processing units is 3.2, the default maximum number of virtual processors is 8 (four times 2).

When you activate the logical partition that uses the partition profile on the HMC, the allocated number of virtual processors is assigned to the logical partition. You can then use dynamic partitioning to change the number of virtual processors to any number between the minimum and maximum values, providede the number of virtual processors is greater than the number of processing units that are assigned to the logical partition. Before you change the default settings, performance modeling must be performed.

For example, you create a partition profile on the HMC with the following processor unit settings.
  • Minimum processing units 1.25
  • Allocated processing units 3.80
  • Maximum processing units 5.00
The default virtual processor settings for this partition profile on the HMC are as follows.
  • Minimum virtual processors 2
  • Allocated virtual processors 4
  • Maximum virtual processors 10

When you activate the logical partition by using this partition profile on the HMC, four processors are available to the operating system because the logical partition is activated with the allocated value of four virtual processors. Each of these virtual processors has 0.95 processing units to support the work that is assigned to the processor. After the logical partition is activated, you can use dynamic partitioning to change the number of virtual processors on the logical partition to any between number 2 - 10, provided the number of virtual processors is greater than the number of processing units that are assigned to the logical partition. If you increase the number of virtual processors, less processing power is available to support the work that is assigned to each processor.