sched_thread_affinity.5 (2010 09)

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sched_thread_affinity(5) sched_thread_affinity(5)
(Tunable Kernel Parameters)
NAME
sched_thread_affinity - adjust scheduler thread affinity
VALUES
Failsafe
6
Default
6
Allowed values
Any value in the range of 1 to
10 is allowed.
A value of
1 indicates weak thread affinity, and the threads may run on different processors. A value of
10 indicates strong thread affinity, and the threads will likely remain on the same processor.
Recommended values
Use the default value in normal cases.
In special cases where it is imperative that threads run as quickly as possible, a value closer to
1 may be
used. However, this may lead to an increase in cache misses.
Customers must evaluate the performance impact in their workload environment before changing the
value of this tunable on production systems.
DESCRIPTION
The
sched_thread_affinity
tunable defines on which processor a thread may likely run. A thread
with lower affinity may move from one processor to another during its lifetime, whereas a thread with
higher affinity will likely experience minimal movement across processors.
A change in the
sched_thread_affinity
value may have direct impact on system throughput and
response times. A very small value may result in threads being run much quicker at the possible expense
of higher cache misses, and a very large value may result in threads being run less frequently if they
have run (or are running) on a loaded processor, with a possible benefit of improved cache affinity.
I/O intensive applications are likely to benefit from a lower value for this tunable.
Who Is Expected to Change This Tunable?
Anyone.
Restrictions on Changing
Changes to this tunable take effect immediately.
When Should the Value of This Tunable Be Raised?
Any increase in the value of this tunable will cause most threads to remain on the processor where they
have run during their lifetimes.
What Are the Side Effects of Raising the Value?
Raising the value of the
sched_thread_affinity tunable may cause some threads to wait to run,
even though there may be less loaded or idle processors in the system.
When Should the Value of This Tunable Be Lowered?
The
sched_thread_affinity tunable value should be lowered if the workload expects to run as
quickly as possible, regardless of whether it is moved from processor to processor at the cost of possible
increases in cache misses.
What Are the Side Effects of Lowering the Value?
Lowering
sched_thread_affinity may result in an increase in cache misses as threads begin to run
on different processors during their lifetimes.
What Other Tunable Values Should Be Changed at the Same Time?
None.
WARNINGS
All HP-UX kernel tunable parameters are release specific. This parameter may be removed or have its
meaning changed in future releases of HP-UX.
HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1