sysv_hash_locks(5)                                       sysv_hash_locks(5)
                          Tunable Kernel Parameters



 NAME    [Toc]    [Back]
      sysv_hash_locks - System V IPC hashed spinlock pool size

 VALUES    [Toc]    [Back]
    Failsafe
      128

    Default    [Toc]    [Back]
      128

    Allowed values    [Toc]    [Back]
      Minimum: 64

      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
      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,



 Hewlett-Packard Company            - 1 -      HP-UX 11i Version 2: Sep 2004






 sysv_hash_locks(5)                                       sysv_hash_locks(5)
                          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
      http://docs.hp.com.

 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),
      semume(5), semvmx(5).


 Hewlett-Packard Company            - 2 -      HP-UX 11i Version 2: Sep 2004