11. WORKLOAD CHARACTERIZATION › 11.6 Case Studies › 11.6.1 Batch Job Class › 11.6.1.1 Problem Description

11.6.1.1 Problem Description

This problem asks you to determine a new set of resource-
limited job classes for an installation.  Job class
structures are generally established to meet two objectives
(FER78, ART79a):

o  Provide operational controls
o  Facilitate scheduling and implement service policies

You usually establish job classes that you define to meet the
first objective for reasons other than resource requirements.
For example, online systems like IMS and CICS are often run
in unique job classes to avoid interference with other
workloads.  Also, many computer centers use one or two job
classes to segregate production jobs from the remainder of
their workload.

Job classes that you establish to meet the second objective
provide your users with alternative classes to which they can
assign their jobs based on resource requirements.  Typically,
the service objective of a job class decreases (that is, jobs
have longer turnaround times) as its resource requirements
increase.  Using a job class structure that focuses on
scheduling and service has a number of potential benefits:

o  Many jobs can be completed in a short time (assuming
   demand) since the job classes representing smaller jobs
   may be expedited.

o  The availability of better turnaround time for the smaller
   classes may encourage users to conserve resources.

o  Job scheduling is simplified since each job class
   represents a homogeneous set of jobs.

Clustering is an ideal approach to this problem since we want
to exploit the natural characteristics of the workload.  If
we arbitrarily select job classes, we might select classes
that split normal resource consumption patterns or choose
some that are too large or small to be useful.

For this sample installation, we investigated job classes
based on CPU time, print lines, and tape drives.  We selected
these resources to quantify the system, output, and operator
requirements presented by the jobs.  Although a number of
other features could have been selected, only three were
chosen to keep the resulting job class structure as simple as
possible.