sema(5) [hpux man page]

sema(5) 							File Formats Manual							   sema(5)

NAME

       sema - enable or disable System V IPC semaphores at boot time

DESCRIPTION

       The tunable is obsolete.  The System V IPC semaphore subsystem is always enabled.

   Overview
       System V IPC is comprised of mechanisms for arbitrary processes to send and receive data messages, share virtual address space and use sem-
       aphores to synchronize execution.

       A System V semaphore is a synchronization method for user processes to synchronize or serialize access to common data and resources.   Each
       semaphore "set" has an ID, but each set can contain one or more independent semaphores.

       Semaphore  sets are created or initially accessed through using an application-specified "key", which can be generated by Operations on the
       set are performed through and Semaphore sets are removed through or the command.

WARNINGS

       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 tun-
       able values, 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

       ipcs(1),   ipcrm(1),  semget(2),  semop(2),  semctl(2),	semaem(5),  semmni(5),	semmns(5),  semmnu(5),	semmsl(5),  semume(5),	semvmx(5),
       sysv_hash_locks(5).

							     Tunable Kernel Parameters							   sema(5)

sysv_hash_locks(5)						File Formats Manual						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 sep-
       arate 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
       memory user needed for spinlocks but to also avoid the contention of having 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 contention on these locks.  This could happen as a result of a very large
       increase to the tunable, coupled with very heavy use of semaphore operations.

   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 semaphore tunables include and Specifically, significant changes in the
       number of semaphore IDs via the tunable may require changes in the tunable.

       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 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  tun-
       able  values,  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)