IBM Power7 Optimization And Tuning Manual page 32

– execrset -c 32-47 -m 0 -e
Server instance>
– execrset -c 48-63 -m 0 -e
Server instance>
Some important items to understand in this example are:
For a particular number of instances and available cores, the most important consideration
is that each instance of an application runs only on the cores of one POWER7 processor
chip.
Memory and logical processor binding is not done independently because doing so can
negatively affect performance.
The workload must be evenly distributed over WebSphere Application Server processes
for the binding to be effective.
There is an assumed mapping of logical processors to cores and chips, which is always
established at boot time. This mapping can be altered if the SMT mode of the system is
changed by running smtctl -w now. It is always best to reboot to change the SMT mode of
a partition to ensure that the assumed mapping is in place.
Along with the operating system facilities for manually establishing cache and memory affinity,
the AIX Active System Optimizer (ASO) can be enabled to autonomously establish
enhanced affinity.
For more information about ASO, the MEMORY_AFFINITY environment variable, the execrset
command, and related environment variables and commands, see Chapter 4, "AIX" on
page 67.
The same forced affinity can be established on Linux by running taskset or numactl.
For example:
numactl -C 0-15 -l
instance>
numactl -C 16-31 -l
instance>
numactl -C 32-47 -l
instance>
numactl -C 48-63 -l
instance>
The -l option on these numactl commands is the equivalent of the AIX MEMORY_AFFINITY=MCM
environment variable setting.
Even for partitions of eight cores or less, better cache affinity can be established with multiple
application instances by using logical processor binding commands. With eight cores or less,
the performance effects typically range up to about 10% improvement with binding. For
partitions of more than eight cores that span more than one POWER7 processor chip, using
manual affinity results in significantly higher performance.
Shared resource environments
Virtualized deployments that share cores among a set of partitions also can use logical
processor binding to ensure good affinity within the guest operating system (AIX). However,
the real dispatching of physical cores is handled by the underlying host operating system
(POWER Hypervisor).
16
POWER7 and POWER7+ Optimization and Tuning Guide
<command to start third WebSphere Application
<command to start fourth WebSphere Application
<command to start first WebSphere Application Server
<command to start second WebSphere Application Server
<command to start third WebSphere Application Server
<command to start fourth WebSphere Application Server