timeslice man page on HP-UX

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timeslice(5)							  timeslice(5)

NAME
       timeslice - scheduling interval in clock ticks per second

VALUES
   Failsafe
       Where defines the number of clock ticks per second for which the system
       is configured.

   Default
       Where is equal to

   Allowed values
       Any value in the range of is allowed.

       A value of indicates no	timeslice  based  scheduling  preemption,  and
       threads	will  continue	to  run	 until	they voluntarily switch out or
       higher priority threads preempt them.

   Recommended values
       Use the default value in normal cases.  In special cases where  quicker
       round robin scheduling is required, a value of may be used.  However, a
       change in value may have a direct impact on system  performance.	  Cus‐
       tomers  must  evaluate performance impact in their workload environment
       before changing the value on production systems.

DESCRIPTION
       The tunable defines the scheduling time interval that a thread may exe‐
       cute on a processor before the kernel scheduler will context switch out
       the thread for other same priority  threads  to	run.   When  a	thread
       starts  executing  on  a processor, the thread is set up to run for the
       number of ticks in the tunable.	On every clock interrupt that a thread
       is  found  executing, the time quantum balance for the thread is decre‐
       mented, and when the  balance  reaches  zero,  the  thread  is  context
       switched out.

       The  value  controls  one  method of user preemption that the operating
       system implements.  A larger value will reduce  preemption  of  running
       threads;	 however,  there  are  other  reasons  for  user preemption of
       threads, and the tunable has no control there.

       A change in the value may have direct impact on system  throughput  and
       response	 times.	  A  very  small  value may result in too many context
       switches, and a very large  value  may  result  in  the	starvation  of
       runnable threads.

   Who Is Expected to Change This Tunable?
       Anyone.

   Restrictions on Changing
       Changes to this tunable take effect at the next reboot.

   When Should the Value of This Tunable Be Raised?
       Since  the tunable is globally applicable to all threads (except in the
       system, irrespective of their scheduling policies and priorities.   Any
       increase in value of this tunable will give equal time quantum boost to
       all threads.

       If the system has too many context switches due to preemptions,	caused
       by  higher  priority  threads,  you can raise the value to provide more
       time for lower priority threads to execute  when	 they  get  scheduled,
       because higher priority threads will preempt the lower priority threads
       when they become runnable.

   What Are the Side Effects of Raising the Value?
       Raising the value of the tunable may cause starvation of some  threads,
       as  they have to wait longer for their turn to execute.	This may cause
       performance throughput issues.

   When Should the Value of This Tunable Be Lowered?
       The tunable value should be lowered if better  turnaround  in  response
       time  is required at the cost of additional context switches.  When the
       system does not have too many compute intensive	applications,  threads
       will  block  and	 preempt  much more frequently without utilizing their
       complete time quantum.

   What Are the Side Effects of Lowering the Value?
       The lowering of the tunable will result in many more  context  switches
       which  will increase the time spent in SYSTEM space and less time spent
       in USER space.  Also, the applications that are compute intensive  will
       suffer performance degradation.

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

WARNINGS
       All HP-UX kernel tunable parameters are release specific.  This parame‐
       ter 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 val‐
       ues.  For information about the effects of installation on tunable val‐
       ues, 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 HP.

			   Tunable Kernel Parameters		  timeslice(5)
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