CPU Related Topics :

CPU Related Concepts:

Shared (virtual) processor partitions (Micro-Partitions) can utilize additional resources from the shared processor pool when available. Dedicated processor partitions can only use the "desired" amount of CPU, and only above that amount if another CPU is (dynamically) added to the LPAR.

• An uncapped partition can only consume up to the number of virtual processors that it has. (Ie: A LPAR with 5 virtual CPUs, that is backed by a minimum of .5 physical CPUs can only consume up to 5 whole / physical CPUs.) A capped partition can only consume up to its entitled CPU value. Allocations are in increments of 1/100th of a CPU, the minimal allocation is 1/10th of a CPU for each virtual CPU.

• All Micro-Partitions are guaranteed to have at least the entitled CPU value. Uncapped partitions can consume beyond that value, capped cannot. Both capped and uncapped relinquish unused CPU to a shared pool. Dedicated CPU partitions are guaranteed their capacity, cannot consume beyond their capacity, and on Power 6 systems, can relinquish CPU capacity to a shared pool.

• All uncapped micro-partitions using the shared processor pool compete for the remaining resources in the pool. When there is no contention for unused resources, a micro-partition can consume up to the number of virtual processors it has or the amount of CPU resources available to the pool.

• The physical CPU entitlement is set with the "processing units" values during the LPAR setup in the HMC. The values are defined as:

› Minimum: The minimum physical CPU resource required for this partition to start.

› Desired: The desired physical CPU resource for this CPU. In most situations this will be the CPU entitlement. The CPU entitlement can be higher if resources were DLPARed in or less if the LPAR started closer to the minimum value.

› Maximum: This is the maximum amount of physical CPU resources that can be DLPARed into the partition. This value does not have a direct bearing on capped or uncapped CPU utilization.

• The virtual CPU entitlement is set in the LPAR configuration much like the physical CPU allocation. Virtual CPUs are allocated in whole integer values. The difference with virtual CPUs (from physical entitlements) is that they are not a potentially constrained resource and the desired number is always received upon startup. The minimum and maximum numbers are effectively limits on DLPAR operations.

Processor folding is an AIX CPU affinity method that insures that an AIX partition only uses as few CPUs as required. This is achieved by insuring that the LPAR uses a minimal set of physical CPUs and idles those it does not need. The benefit is that the system will see a reduced impact of configuring additional virtual CPUs. Processor folding was introduced in AIX 5.3 TL 3.

• When multiple uncapped micro-partitions compete for remaining CPU resources then the uncapped weight is used to calculate the CPU available to each partition. The uncapped weight is a value from 0 to 255. The uncapped weight of all partitions requesting additional resources is added together and then used to divide the available resources. The total amount of CPU received by a competing micro-partition is determined by the ratio of the partitions weight to the total of the requesting partitions. (The weight is not a nice value like in Unix.) The default priority for this value is 128. A partition with a priority of 0 is effectively a capped partition.

above figure shows that Virtualized and dedicated CPUs in a four CPU system with a single SPP.

    Dedicated CPU partitions do not have a setting for virtual processors. LPAR 3 in Figure 0 has a single dedicated CPU.

• LPAR 1 and LPAR2 in Figure 0 are Micro-Partitions with a total of five virtual CPUs backed by three physical CPUs. On a Power 6 system, LPAR 3 can be configured to relinquish unused CPU cycles to the shared pool where they will be available to LPAR 1 and 2 (provided they are uncapped).