timeslice(5)timeslice(5)NAMEtimeslice - 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)
