Chapter 8 685
Command Definitions SP-Z
TUNE
OSCILLATE Sets the subqueue to oscillate behavior. If set, a process returns to the base
priority once its priority has decayed to the limit of the subqueue, even if it
has not completed a Dispatcher transaction.
tslice The number of milliseconds a process in a given subqueue can hold the
CPU. A process that has held the CPU continuously for this number of
milliseconds is interrupted. This value must be set to a multiple of 100
milliseconds and has a minimum value of 100 milliseconds.
OPERATION
The system manager uses the TUNE command to change the characteristics of the circular
scheduling subqueues to more efficiently manage the current processing load.
A process in the CS, DS, or ES scheduling subqueues typically begin execution at the base
priority. When the process stops (for disk I/O, terminal I/O, preemption, etc.), the amount
of CPU it has consumed is used to determine its new priority. If the process has completed
a Dispatcher transaction, typically by issuing a terminal read, its priority is reset to the
base, and the quantum value for that workgroup is recalculated. If the process has
exceeded the quantum (filter) value since its priority was last reduced, the priority is
decreased without exceeding the limit priority. If the boost property for the workgroup is
oscillate, process priorities are reset to the base value once they decay to the limit.
The parameters min and max refer to the absolute bounds of the quantum, or a filter
representing the average transaction time of processes in that subqueue. The quantum is
recomputed after every user Dispatcher transaction is complete, and then compared
against the CPU time of a process to determine whether the priority of the process should
be decreased.
NOTE With Release 5.0 of MPE/iX, all three circular scheduling subqueues, CS, DS,
and ES, have dynamically calculated quantums. By default, the DS and ES
subqueues have their bounds set to the same value.
If the values specified for max are too large, system response may become erratic. If they
are too small, excessive memory management may occur due to frequent process
swapping. Either case degrades system performance. The values for min and max may
range from 1 to 32,767. The recommended settings are listed in the table below.
The timeslice value determines how long a process in a given scheduling subqueue will be
allowed to hold the CPU. This value is different than the quantum, which determines how
rapidly process priorities decay. The timeslice does interrupt the process if the process is
interruptable. The timeslice is a multiple of 100 milliseconds and has a minimum value of
100 milliseconds.
The following default settings are established when the system is booted from the system
disk (a START RECOVERY or START NORECOVERY), unless the user has customized a TUNE
configuration.
START RECOVERY or START NORECOVERY
CQ base: 152 DQ base: 202 EQ base: 240
limit: 200 limit: 238 limit: 253
min: 1 min: 2000 min: 2000
