*nix Documentation Project
·  Home
 +   man pages
·  Linux HOWTOs
·  FreeBSD Tips
·  *niX Forums

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


 pfdat_hash_locks(5)                                     pfdat_hash_locks(5)
                          Tunable Kernel Parameters

 NAME    [Toc]    [Back]
      pfdat_hash_locks - determines the size of the pfdat 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 used for synchronization) which
      allow only the spinlock 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 pfdat data structure

    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 pfdat
      structures.  Typically, such a system would be a large memory system
      with a large amount 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 pfdat structures are present and requiring

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

 pfdat_hash_locks(5)                                     pfdat_hash_locks(5)
                          Tunable Kernel Parameters

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

    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]
      pfdat_hash_locks was developed by HP.

 Hewlett-Packard Company            - 2 -      HP-UX 11i Version 2: Sep 2004
[ Back ]
 Similar pages
Name OS Title
hdlpreg_hash_locks HP-UX determines the size of the pregion spinlock pool
region_hash_locks HP-UX determines the size of the region spinlock pool
sysv_hash_locks HP-UX System V IPC hashed spinlock pool size
eqmemsize HP-UX determines the minimum size (in pages) of the equivalently mapped reserve pool
tcphashsz HP-UX determines the size of the networking hash tables
acl_size Tru64 Determines the size of the contiguous, persistent representation of the given ACL
vx_ninode HP-UX Determines the internal node table size
st_large_recs HP-UX determines maximum logical record size allowed through the stape driver
XmStringExtent Tru64 A compound string function that determines the size of the smallest rectangle that will enclose the ...
st_fail_overruns HP-UX determines whether variable block mode read requests smaller than the physical record size will fail
Copyright © 2004-2005 DeniX Solutions SRL
newsletter delivery service