Advanced POWER Virtualization on IBM System p5 - Previous ...

The following rules of thumb should be considered when configuring the number
of virtual processors in shared-processor partitions:
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The number of virtual processors in a shared-processor partition should not
exceed the number of physical processors in the shared-processor pool.
The number of virtual processors in a capped shared-processor partition
should not exceed the entitlement rounded up to the nearest whole number.
For versions of AIX 5L prior to V5.3 Maintenance Level 3 or with later versions
of AIX 5L with the virtual processor folding feature disabled, the sum of all the
virtual CPUs in all active shared-processor partitions should not be greater
than four times the number of physical processors in the shared-processor
pool.
For versions of AIX 5L after Version 5.3 ML3 with virtual processor folding, an
excessive virtual CPU count has a very low performance impact.
Capped or uncapped partitions?
Capped partitions will never exceed their entitlements, even if they are
overloaded and there are unused resources in the system. Generally, the use of
capped partitions is to be discouraged; use uncapped partitions and prioritize the
allocation of spare capacity using partition weights.
5.6.2 <strong>Virtualization</strong> and applications
Some applications and middleware products are not able to adapt to dynamic
reconfiguration changes, for example, the product starts a number of processes
based on the number of configured processors. If the application requires more
computing power, adding additional processors will not have any effect without
shutting down the application and restarting it. Using shared processors, it is
possible to change the entitlement of virtual processors to change the processing
resources available to the application. Because the processor count does not
change, then applications that are not DR aware do not have to be restarted.
If an application or workload environment is cache sensitive or cannot tolerate
the variability introduced with resource sharing, it should be deployed in a
dedicated processor partition with SMT disabled. In dedicated partitions, the
entire physical processor is assigned solely to the partition.
5.6.3 Resource management
PLM and WLM provide resource and workload management. Some applications
and middleware also provide their own resource management and in particular
databases. Care should be taken when using the resource management tools in
AIX 5L and the <strong>POWER</strong> Hypervisor with such applications and middleware.
Chapter 5. System management 357