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sysv_hash_locks.5 (2010 09)

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sysv_hash_locks(5) sysv_hash_locks(5)
(Tunable Kernel Parameters)
NAME
sysv_hash_locks - System V IPC hashed spinlock pool size
VALUES
Failsafe
128
Default
128
Allowed values
Minimum: 64
Maximum: 32768 or semmni whichever is smaller.
Required to be a power of two.
DESCRIPTION
Note: If the DynSysVSem optional product bundle is installed then this tunable is ignored and has no
effect. Each semaphore ID has a separate lock.
The
sysv_hash_locks tunable specifies the size of the hashed spinlock (kernel data structures used
for synchronization) pool (number of available spinlocks). The System V IPC semaphore functions
acquire hashed spinlocks based on the semaphore ID. The spinlocks are hashed to avoid the memory
user needed for semmni spinlocks but to also avoid the contention of having just one spinlock.
For more information about System V semaphores, refer to the Overview section of the sema (5) manpage.
Who Is Expected to Change This Tunable?
Those who have identified, through kernel performance analysis, local system performance issues with
these locks. HP experience is that very few customers need to adjust this tunable.
Restrictions on Changing
Changes to this tunable take effect at the next reboot.
Note: If the DynSysVSem optional product bundle is installed then changes to this tunable are ignored
and have no effect.
When Should the Value of This Tunable Be Raised?
This tunable should be raised if performance analysis shows high contention on these locks. This could
happen as a result of a very large increase to the
semmni tunable, coupled with very heavy use of sema-
phore operations.
When Should the Value of This Tunable Be Lowered?
If
semmni is no longer as large, and/or spinlock contention is no longer an issue.
What Other Tunable Values Should Be Changed at the Same Time?
All the System V semaphore tunables are interrelated and should not be treated as independent vari-
ables. The tunables must be evaluated as a system to ensure they reflect the application requirements.
The semaphore tunables include
semaem, semmni, semmns, semmnu, semmsl, semume, semvmx, and
sysv_hash_locks. Specifically, significant changes in the number of semaphore IDs via the semmni
tunable may require changes in the sysv_hash_locks tunable.
Note: If the DynSysVSem optional product bundle is installed then the
semmnu, semume, and
sysv_hash_locks tunables are ignored and have no effect.
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.
Installation of optional kernel software, from HP or other vendors, may cause changes to tunable parame-
ter values. After installation, some tunable parameters may no longer be at the default or recommended
values. For information about the effects of installation on tunable values, consult the documentation for
the kernel software being installed. For information about optional kernel software that was factory
installed on your system, see HP-UX Release Notes at http://www.hp.com/go/hpux-core-docs.
HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1

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