power software i perfmgmt processor lpar.pdf

STG Cross Platform Systems Performance

Introduction
Welcome to “Under the Hood: Logical Partitions on POWER7”. In this paper we will show you what is
really going on under the abstractions being provided for logical partitions. Reading this, we are
assuming that you are familiar with the view of logical partitions provided by the HMC. You already
know that you can specify:
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Each partition’s entitled capacity – its “Entitlement” - in terms of whole or fractional processor units
(1.0 processor units is approximately one core’s worth of processing capacity),
The amount of memory that each partition will be allocated,
Whether the partition is designated as a dedicated-processor or shared-processor partition, and
The number of Virtual Processors, along with many more configuration settings.

These abstractions are handy in understanding the basics of logical partitioning, but there are also some
interesting subtleties that you might also want to influence. This paper will allow you to peek under the
hood, to better understand what is really going on, and from there to more intelligently control your multipartitioned system. This is not a “Virtualization for Dummies” paper. After you read this you will be
much more familiar with processor virtualization.
In getting there, we’ll be looking at performance considerations relating to
• Virtual Processors
• Partition Entitlement
• Capped and Uncapped Shared-Processor Partitions
• CPU Utilization and the Measurement of Consumed Compute Capacity
• Simultaneous Multi-Threading as it relates to Processor Virtualization
• Virtualization Effects of Non-Uniform Memory-based Topologies
This document is not intended to be a comprehensive “best practices” document for LPAR performance.
Reference the POWER7 Virtualization Best Practices Guide for more details:

POWER7 Virtualization Best Practices Guide
Although much of this performance discussion is applicable to any operating system (OS), be aware that
as we discuss the related performance implications of operating system design, the operating system of
interest here is primarily IBM i.

POWER7 Logical Partitions

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