Tunable Kernel Parameters
NAME [Toc] [Back]
sysv_hash_locks - System V IPC hashed spinlock pool size
VALUES [Toc] [Back]
Default [Toc] [Back]
Allowed values [Toc] [Back]
Maximum: 32768 or semmni whichever is smaller.
Required to be a power of two.
DESCRIPTION [Toc] [Back]
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 [Toc] [Back]
Changes to this tunable take effect at the next reboot.
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
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 variables. The tunables must be evaluated as a
system to ensure they reflect the application requirements. The
semaphore tunables include semaem, semmni, semmns, semmnu, semmsl,
Hewlett-Packard Company - 1 - HP-UX 11i Version 2: Sep 2004
Tunable Kernel Parameters
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.
WARNINGS [Toc] [Back]
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 parameter 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
AUTHOR [Toc] [Back]
sysv_hash_locks was developed by AT&T.
SEE ALSO [Toc] [Back]
sema(5), semaem(5), semmni(5), semmns(5), semmnu(5), semmsl(5),
Hewlett-Packard Company - 2 - HP-UX 11i Version 2: Sep 2004 [ Back ]