This document describes the algorithms used to calculate the size of a virtual processor in a shared processor environment using the Power5 architecture. The IBM documentation does not fully explain this concept and this document attempts to clarify this issue.
When defining an LPAR through the HMC for the Power5 architecture,
the type of processors assigned to the LPAR must be defined. The
possible choices for this are: Dedicated and Shared. If
"Shared" is selected, the following input fields are
presented:
When entering "shared" mode processors, the "Processing units" input fields define the total amount of processing units that will be allocated to all virtual processors. This translates to the following algorithm:
Algorithm:
Vs = Pu / Vn
Rules:
1.00 Pu = 1 full power5 physical processor
Pu < Pt
Vn <= 64
Variable Definitions:
Vs = Virtual processor size
Pu = Physical processing units ( number of physical
processors )
Vn = Number of virtual processors assigned to LPAR
Pt = Total number of physical processors in frame
As an example of using this algorithm:
These values would allocate "0.5" physical processing units to the LPAR and "2" virtual processors. The size of each virtual processor would be "0.25" physical processing units.
Algorithm:
Vs = Pu / Vn
Vs = 0.5 / 2
Vs = 0.25
Variable Definitions:
Vs = Virtual processor size
Pu = Physical processing units ( number of physical
processors )
Vn = Number of virtual processors assigned to LPAR
Another example using this algorithm:
These values would allocate "2.5" physical processing units to the LPAR and "5" virtual processors. The size of each virtual processor would be "0.50" physical processing units.
Algorithm:
Vs = Pu / Vn
Vs = 2.5 / 5
Vs = 0.50
Variable Definitions:
Vs = Virtual processor size
Pu = Physical processing units ( number of physical
processors )
Vn = Number of virtual processors assigned to LPAR
A final example illustrating how the EGATE Proof of Concept LPAR's were configured:
In this example, if the desired number of physical processing units was allocated to the LPAR, "3.0" physical processing units would be allocated to the LPAR and "6" virtual processors. The size of each virtual processor would be "0.50" physical processing units.
Algorithm:
Vs = Pu / Vn
Vs = 3.0 / 6
Vs = 0.50
Variable Definitions:
Vs = Virtual processor size
Pu = Physical processing units ( number of physical
processors )
Vn = Number of virtual processors assigned to LPAR