Jump to content United States-English
HP.com Home Products and Services Support and Drivers Solutions How to Buy
» Contact HP
More options
HP.com home
HP-UX Reference > S


Tunable Kernel Parameters
HP-UX 11i Version 3: February 2007

Technical documentation

» Feedback
Content starts here

 » Table of Contents

 » Index


sysv_hash_locks — System V IPC hashed spinlock pool size






Allowed values

Minimum: 64

Maximum: 32768 or semmni whichever is smaller.

Required to be a power of two.


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.

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 semaphore 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 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, 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.


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 http://docs.hp.com.


sysv_hash_locks was developed by AT&T.

Printable version
Privacy statement Using this site means you accept its terms Feedback to webmaster
© 1983-2007 Hewlett-Packard Development Company, L.P.