CPU Virtualization - Power 5 Based

On a Power 5 system it is possible to create a logical parition with dedicated processor or shared processor. The concept of shared processore refers to virtualization of CPU's processing unit.

Power5 introduced the concept of "Global Shared Processor Pool". It contains group of processor that will be shared among the logical partition that are created using the shared resources (CPU).

Processing unit of a CPU is always measured in 1/10 th of the CPU Power.  So, with the single CPU 1/10=0.1 Processing unit can be assigned to a logical partition. So a single CPU can support 10 LPAR's (logically).

The granulartiy of increasing the processing unit is 0.01 ( As per IBM Standards).

The above diagram shows a P5 machine with 6 Physical Processors.
The machine has 4 partitions namely A,B,C and D.

Partitions A and B are created with the dedicated processors. 3 Processor per partition. So, A and B are allocated with 6 Physical Processor.

Remaining processors available : 16-(3+3)=10 Processors.

Processing unit of a single processor is expressed as 1/10, therefore 10 Processors hold : 10*10 : 100 Processing units.

The 10 Processors are combined in a "Global Shared Processor Pool" with the processing capacity of 100 units.

Logical Partitions use these processing units as a Virtual Processor. i.e., Virtual processors provide required amount of processing units to the logical partitions.

Now, Partition C has 52 Processing units with 7 virtual processor and Partition D has 23 Processing units with 5 Virtual Processor.

So, Total processing units occupied by C and D : 52+23=75 Processing units.

Now, available processing unit in the Global Shared Processor Pool = 100-75 = 25 Processing units.

These 25 Processing units are not allocated.

No.of Processing unit allocated to a partition is called : Entitlement.

Capped Partition: Partition cannot get more processing unit than that of allocated to it.

Uncapped Partition: Partition can acquire more processing unit than that of allocated to it.

Similarily, an "uncapped partition" can also consume less processing units than that of allocated to it. This should give a clear understanding between "Physical consumption" and "Entitlement consumption".

Physical Consumption: Refer to percentage of processor power/unit consumed by a partition.

Entitlement Consumption: Refer to percentage of processor power/unit currently consumed compared to the no.of processing units allocated to that partition.

So, its evident that an "uncapped partition" can have an "Entitlement Consumption" of more than 100%.