CPU Configuration Guidelines for vPars

6 Summary

A workload must be characterized in order to configure a system for consistent performance. Choose

a metric to optimize for (response time, throughput, or utilization) and specify a configuration with

enough memory and I/O to sustain the peak workload. Use the method presented in this paper to

establish the minimum and maximum CPU configuration parameters.

For vPars version prior to A.04.01, the bound to unbound CPU ratio can be determined by using the

method detailed in section 3. Bound CPU’s will have I/O interrupts assigned to them and can not be

migrated. There should be enough bound CPU’s in the partition to meet the desired performance

objective. A good rule of thumb is to allocate at least as many bound CPU’s as unbound CPU’s.

The dynamic CPU migration capabilities of A.04.01 allow for more flexible movement of CPU’s which

in turn can translate to higher CPU utilization. If the desired effect is to match the semantics of bound

and unbound CPU’s then configure the minimum CPU’s with path based semantics. The

unbound/floaters are then added and deleted with count based semantics.

To fully utilize the CPU’s during idle or low usage conditions, set the minimum CPU requirement of the

vPar to one and migrate CPU’s to where they can be utilized. When the CPU’s are migrated back to

the vPar, the I/O interrupts may need to be redistributed. If the CPU’s present before and after the

migration are the same then restoring the interrupt assignments can be performed by using the intctl –r

command (must save the interrupt assignments before the migrations). If the CPU’s are not the same

then use the intctl command to manually distribute the I/O interrupts.