System information

374 Logical Partitions on System i5
12.2.1 QTHDRSCAFN (thread affinity)
This specifies whether secondary threads will have affinity to the same group of processors
and memory as the initial thread or not. It also specifies the degree to which the system tries
to maintain the affinity between threads and the subset of system resources they are
assigned.
A change made to this system value takes effect immediately for all jobs that become active
after the change, but only if they retrieve their affinity values from the system value. Jobs and
threads that are currently active will continue to run with the affinity values in which they were
started. New jobs and threads that get their affinity values from jobs that are currently active,
(for example, batch immediate jobs or secondary threads that inherit attributes from the initial
thread) will continue to use the values stored in the initiating job or thread, rather than the
current system value.
In addition, you can use the
automatically adjust thread resources (QTHDRSCADJ) system
value to distribute the use of system resources.
Thread affinity
This specifies whether or not secondary threads are grouped with the initial thread. Select
one of the following choices:
򐂰 Secondary threads use same processors and memory as initiating thread
(*GROUP)
This indicates that secondary threads have a preference for the same group of processors
and memory as the initial thread. Multi-threaded workloads that share data between the
threads within a job may perform better when using this option.
򐂰 Secondary threads do not use same processors and memory as initiating thread
(*NOGROUP)
This indicates that secondary threads do not have a preference for the same group of
processors and memory as the initial thread. Workloads that use the full processing power
of a system may perform better when using this option.
򐂰 Level of affinity
This specifies the degree to which the threads try to use the subset of system resources in
which they have a preference. Select one of the following choices:
– Threads will only use resources they have affinity to (*HIGH).
– Threads will only use the subset of system resources they have affinity to, and will wait
until they become available.
򐂰 Threads use any resource (*NORMAL)
Threads will use any processor or memory in the system if the resources they have affinity
to are not readily available.
12.2.2 QTHDRSCADJ (automatically adjust thread resources)
This specifies whether the system should dynamically make adjustments to the affinity of
threads currently running on the system (1) or not (0). If some resources are being used more
than others, the system may reassign some of the threads running on the more heavily used
resources to have affinity to the less used resources.
If you have specified to group secondary threads using the thread affinity (QTHDRSCAFN)
system value, the threads within one process will all be moved as a group. If jobs have been
logically grouped with the routing entry or prestart job entry, the entire group will be moved
together. If this option is selected, the system will attempt to distribute work evenly across all
the system's resources.