IBM Power System POWER7 Series, Optimization And Tuning Manual

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Chapter 1. Optimization and tuning on IBM POWER7 and IBM
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Instead, the focus has shifted to delivering multiple cores per processor chip, and to delivering
more hardware threads in each core (known as simultaneous multi-threading (SMT), in IBM
Power Architecture terminology). This situation means that some of the best opportunities for
improving the performance of an application are in delivering scalable code by having an
application make effective use of multiple concurrent threads of execution.
Coupled with the trend toward aggressive multi-core and multi-threaded designs, there are
changes in the amount of cache and memory bandwidth available to each hardware thread.
Cache sizes and chip-level bandwidth are increasing at a slower rate than the growth of
hardware threads, meaning that the amount of cache per thread is not growing as rapidly. In
some cases, it decreases from one generation to the next. Again, this situation shows where
deeper analysis and performance optimization efforts can provide some benefits.
1.5 Optimizing performance on POWER7
This section provides guidance for optimizing code performance on POWER7 when you use
the AIX or Linux operating systems. The processor is a superset of the POWER7
processor, so all optimizations described for POWER7 apply equally for . We cover
the more prominent performance opportunities that are noted in past optimization efforts. The
guidance is organized in to three broad categories:
1. Lightweight tuning and optimization guidelines
Lightweight tuning covers simple prescriptive steps for tuning application performance on
POWER7. These simple steps can be carried out without detailed knowledge of the
internals of the application that is being optimized and usually without modifying the
application source code. Simple system utilization and performance tools are used for
understanding and improving your application performance. The steps and tools are
general guidelines that apply to all types of applications. Although they are simple and
straightforward, they often lead to significant performance improvements. It is possible to
accomplish these steps in as little as two days or so for a small application, or, at most, two
weeks for a large and complex application.
2. Deployment guidelines
Deployment guidelines cover tuning considerations that are related to the:
– Configuration of a POWER7 system to deliver the best performance
– Associated runtime configuration of the application itself
There are many choices in a deployment, some of which are unrelated to the performance
of a particular application, and so, at best, this section can present some guidelines and
preferred practices. Understanding logical partitions (LPARs), energy management, I/O
configurations, and using multi-threaded cores are examples of typical system
considerations that can impact application performance.
Performance improvement: Consider lightweight tuning to be the starting point for any
performance improvement effort.
Performance improvement: Consider deployment guidelines to be the second
required activity for any reasonably extensive performance effort.