Chapter 6: Modifying System Parameters for Performance Benefits

Chapter 6: Modifying System Parameters for Performance Benefits

Overview

Up to this point, we have been reviewing software and hardware that applies to both systems and clusters. In this chapter, we will review some of the SYSGEN parameters that we have covered. If you do not feel that this review is necessary for you, feel free to skip this chapter. Table 6.1 covers scheduling parameters, and Table 6.2 covers memory resource parameters.

Table 6.1: Scheduling Parameters

Parameter

Description

Quantum

Determines the time slice that a process will be able to use within the round-robin scheduling algorithm.

Also is used to ensure the minimum amount of time a computable process will receive before it is swapped out, although this time is not guaranteed.

The following special SYSGEN parameters are associated with process scheduling and Quantum:

IOTA ? deducted from Quantum every time the process enters a WAIT state; this deduction will force a Quantum end of even very I/O bound processes (default value of "2" means two 10-millisecond ticks).

PIXSCAN ? indicates how many processes will receive a priority boost every second; solves the problem of a low-priority job (below DEFPRI) that has a lock on a critical resource blocking the system because the job cannot get sufficient CPU resources to release the lock.

PRIORITY_OFFSET

Used to affect processes with priorities 0 to 15; indicates the difference in priority required to interrupt the current process by a computable process; the default is zero.

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