IBM Power System POWER7 Series, Optimization And Tuning Manual

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POWER7 and Optimization and Tuning Guide
For example:
ppc64_cpu --smt=1 Sets the SMT mode to ST.
ppc64_cpu --smt Shows the current SMT mode.
When you run in these modes, the logical processor numbering does not change. However, in
SMT2 mode, only every second logical processor is available (0, 2, 4, and so on), or in ST
mode, only every fourth logical processor is available (0, 4, 8, and so on).
High SMT modes are best for maximizing total system throughput, while lower SMT modes
might be appropriate for high performance threads and low latency applications. For code
with low levels of instruction-level parallelism (often seen in Java code, for example), high
SMT modes are generally preferred.
The setaffinity API allows processes and threads to have affinity to specific
logical processors.
For more information about this topic, see 5.2, “Related publications” on page 106.
Using setaffinity to bind to specific logical processors
The setaffinity API allows processes and threads to have affinity to specific logical
processors. The number and numbering of logical processors is a product of the number of
processor cores (in the partition) and the SMT capability of the machine (four-way SMT
for POWER7).
Linux completely fair scheduler
Java applications scale better on Linux in some cases if the sched_compat_yield scheduler
tunable is set to 1 by running the following command:
sysctl -w kernel.sched_compat_yield=1
5.2 Related publications
The publications that are listed in this section are considered suitable for a more detailed
discussion of the topics that are covered in this chapter:
򐂰 Red Hat Enterprise Linux 6 Performance Tuning Guide, Optimizing subsystem throughput
in Red Hat Enterprise Linux 6, Edition 3.0, found at:
http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/6/html-single/Perfor
mance_Tuning_Guide/index.html
򐂰 SUSE Linux Enterprise Server System Analysis and Tuning Guide (Version 11 SP2),
found at:
http://www.suse.com/documentation/sles11/pdfdoc/book_sle_tuning/book_sle_tuning
.pdf