Deployment Guidelines - IBM Power7 Optimization And Tuning Manual

Controlling prefetching in this way might not be appropriate if different applications are
running in a partition, because some applications might run best with prefetching enabled.
There are also mechanisms to control prefetching at the process level.
POWER7 allows not only prefetching to be enabled or disabled, but it also allows the
fine-tuning of the prefetch engine. Such fine-tuning is especially beneficial for
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scientific/engineering and memory-intensive applications. Hardware prefetch tuning is
autonomously used when DSO in AIX is enabled.
For more information about hardware prefetching, the DSO facility, and hardware and
operating system tuning and usage for optimum performance, see Chapter 2, "The POWER7
processor" on page 21, Chapter 4, "AIX" on page 67, and Chapter 5, "Linux" on page 97.
Scalability considerations
Aside from the scalability considerations already mentioned (such as AIX malloc tuning and
java/util/concurrent usage), there is one Linux operating system setting that enhances
scalability in some cases: setting sched_compat_yield to 1. This task is accomplished by
running the following command:
sysctl -w kernel.sched_compat_yield=1
This setting makes the Completely Fair Scheduler more compatible with earlier versions of
Linux. Use this setting for Java environments, such as for WebSphere Application Server. For
more information about multiprocessing with the Completely Fair Scheduler, go to:
http://www.ibm.com/developerworks/linux/library/l-cfs/?ca=dgr-lnxw06CFC4Linux

1.5.2 Deployment guidelines

This section discusses deployment guidelines as they relate to virtualized and non-virtualized
environments, and the effect of partition size and affinity on deployments.
Virtualized versus non-virtualized environments
Virtualization is a powerful technique that is applicable to situations where many applications
are consolidated onto a single physical server. This consolidation leads to better usage of
hardware and simplified system administration. Virtualization is efficient on the Power
Architecture, but it does come with some costs. For example, the Virtual I/O Server (VIOS)
partition that is allocated for a virtualized deployment consumes a portion of the hardware
resources to support the virtualization. For situations where few business-critical applications
must be supported on a server, it might be more appropriate to deploy with non-virtualized
resources. This situation is particularly true in cases where the applications have
considerable network requirements.
Virtualized environments offer many choices for deployment, such as dedicated or
non-dedicated processor cores and memory, IBM Micro-Partitioning® that uses fractions of a
physical processor core, and memory compression. These alternatives are explored in
Chapter 3, "The POWER Hypervisor" on page 55. When you set up a virtualized deployment,
it is important that system administrators have a complete understanding of the trade-offs
inherent in the different choices and the performance implications of those choices. Some
deployment choices, such as enabling memory compression features, can disable other
performance features, such as support for 64 KB memory pages.
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http://dl.acm.org/citation.cfm?id=2370837 (available for purchase or with access to the ACM Digital Library)
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Chapter 1. Optimization and tuning on IBM POWER7 and IBM POWER7+