nkthread(5)                                                     nkthread(5)
                          Tunable Kernel Parameters



 NAME    [Toc]    [Back]
      nkthread - limits the number of threads allowed to run simultaneously

 VALUES    [Toc]    [Back]
    Failsafe
      8416

    Default    [Toc]    [Back]
      ((nproc*2)+16) or 8416

    Allowed values    [Toc]    [Back]
      200 - 250,000

      nkthread must be greater than nproc + 100.

      nkthread must be greater than max_thread_proc.

      This may be set higher, but more will not be used.

    Recommended values    [Toc]    [Back]
      Unless there are heavily threaded applications on the system, the
      default formula is adequate if nproc is tuned correctly.

 DESCRIPTION    [Toc]    [Back]
      The nkthread tunable controls the absolute number of threads allowed
      on a system at any given time.  Increasing it will allow more threads,
      and lowering it will restrict the number of threads.

      It can be determined that nkthread is too low when the kthread: table
      is full message is seen in the message buffer.  The message can be
      read via dmesg or syslog.  This message indicates that an application
      was unable to create a thread.  Setting nkthread too low can cause
      application failures due to an inability to create new threads or fork
      new processes.

      It can be determined how many threads have been used simultaneously
      prior to the above message by calling pstat_dynamic and examining the
      psd_numkthreadsallocd.  This field indicates the "high water" mark of
      the number of threads that have been simultaneously used.

    Who Is Expected to Change This Tunable?
      Anyone expecting to run large numbers of threads.

    Restrictions on Changing    [Toc]    [Back]
      None.  This tunable is dynamic.

    When Should the Value of This Tunable Be Raised?
      This value should be increased, either directly or as a result of
      tuning nproc, on most systems that are running many threads or
      processes.




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






 nkthread(5)                                                     nkthread(5)
                          Tunable Kernel Parameters



    What are the Side Effects of Raising the Value?
      None.

    When Should the Value of This Tunable Be Lowered?
      The value should be lowered only to limit the number of threads on the
      system, or when there is memory pressure and the value of nkthread is
      far above the expected usage.

    What are the Side Effects of Lowering the Value?
      Increased risk of application failure do to the inability to create
      new threads or fork new processes.

    What Other Tunable Values Should Be Changed at the Same Time?
      None.

 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]
      nkthread was developed by HP.

 SEE ALSO    [Toc]    [Back]
      max_thread_proc(5), nproc(5).


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