Wednesday, July 8, 2009

Aix - Logical Partitioning - Virtual Processor Assignment

Aix - Logical Partitioning - Virtual Processor Assignment

If you create a partition profile that is set to use shared processors, the HMC calculates a minimum, maximum, and desired number of virtual processors for
the partition profile. The calculation is based upon the minimum, maximum, and desired 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 desired number of virtual processors is the desired number of processing units (rounded up to the next whole number). For example, if the desired number of processing units is 2.8, the default desired 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 (4 times 2).

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

For example, you create a partition profile on the HMC with the following processor unit settings.
• Minimum processing units 1.25
• Desired 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
• Desired virtual processors 4
• Maximum virtual processors 10


When you activate the logical partition using this partition profile on the HMC, the operating system sees four processors, because the logical partition is activated with the desired value of four virtual processors. Each of these virtual processors has 0.95 processing units supporting the work assigned to the processor. After the logical partition is activated, you can use dynamic logical partitioning to change the number of virtual processors on the logical partition to any number between 2 and 10, so long as 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, bear in mind that you will have less processing power supporting the work assigned to each processor.

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