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  man pages->HP-UX 11i man pages -> region_hash_locks (5)              


 region_hash_locks(5)                                   region_hash_locks(5)
                          Tunable Kernel Parameters

 NAME    [Toc]    [Back]
      region_hash_locks - determines the size of the region spinlock pool

 VALUES    [Toc]    [Back]

    Allowed values    [Toc]    [Back]
      64 to 262144

 DESCRIPTION    [Toc]    [Back]
      Global kernel structures containing information on a running process
      or memory usage are frequently accessed or modified by several threads
      concurrently.  To prevent race conditions, these structures are
      protected by spinlocks (kernel data structures used for
      synchronization) which allow only the spinlock 'holder' to proceed,
      while all others attempting to access the structure must wait.

      Hashed spinlocks are used when each instance of such a data structure
      is to be protected, and there are several instances.  Using a single
      spinlock for all instances would cause too much contention, but using
      one spinlock per structure wastes memory while the majority of the
      locks are unused at any given time.

      By allocating a pool of hashed locks, a hash function picks one lock
      per group of structures, reducing contention while conserving memory.
      This tunable sets the size of such a pool for the region data
      structure spinlocks.

    Who Is Expected to Change This Tunable?
      Only HP Field engineers should change the value of 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 on systems with both low memory
      contention and high lock contention due to a large number of region
      structures.  Typically, such a system would be a large memory system
      with a large number of processes or threads.

    What Are the Side Effects of Raising the Value?
      More memory is used by the kernel.

    When Should the Value of This Tunable Be Lowered?
      This tunable should only be lowered on systems with high contention
      for physical memory and few processes and threads.  The memory saved
      by making the table smaller will be freed for general use, and could
      cause contention if many regions are present and requiring locks.

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

 region_hash_locks(5)                                   region_hash_locks(5)
                          Tunable Kernel Parameters

    What Are the Side Effects of Lowering the Value?
      Hash contention for region locks is more likely, which increases the
      possibility of threads needing to wait on the lock shared between two
      or more regions.

    What Other Tunables Should Be Changed at the Same Time?

 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]
      region_hash_locks was developed by HP.

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