sysv_hash_locks man page on HP-UX

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sysv_hash_locks(5)					    sysv_hash_locks(5)

NAME
       sysv_hash_locks - System V IPC hashed spinlock pool size

VALUES
   Failsafe
   Default
   Allowed values
       or 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  tunable  specifies	the  size  of the hashed spinlock (kernel data
       structures used for synchronization) pool (number  of  available	 spin‐
       locks).	 The System V IPC semaphore functions acquire hashed spinlocks
       based on the semaphore ID.  The spinlocks are hashed to avoid the  mem‐
       ory  user needed for spinlocks but to also avoid the contention of hav‐
       ing just one spinlock.

       For more information about System V semaphores, refer to the 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  con‐
       tention	on these locks.	 This could happen as a result of a very large
       increase to the tunable, coupled with very heavy use of semaphore oper‐
       ations.

   When Should the Value of This Tunable Be Lowered?
       If  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	 sema‐
       phore  tunables	include	 and  Specifically, significant changes in the
       number of semaphore IDs via the tunable may require changes in the tun‐
       able.

       Note:   If the DynSysVSem optional product bundle is installed then the
       and tunables are ignored and have no effect.

WARNINGS
       All HP-UX kernel tunable parameters are release specific.  This parame‐
       ter  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  val‐
       ues.  For information about the effects of installation on tunable val‐
       ues, consult the documentation for the kernel software being installed.
       For  information	 about	optional  kernel  software  that  was  factory
       installed on your system, see at

AUTHOR
       was developed by AT&T.

SEE ALSO
       sema(5),	 semaem(5),  semmni(5),	  semmns(5),   semmnu(5),   semmsl(5),
       semume(5), semvmx(5).

			   Tunable Kernel Parameters	    sysv_hash_locks(5)
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