Installation guide

4.7 Administering CPU Resources Using the Class

Scheduler

The Class Scheduler provides you with a method of controlling the

execution of tasks or applications by restricting the length of time that they

can access the processor (CPU). For example, daemons such as the print

spooler can be given less access time. The CPU will then have more time

available to perform other tasks. To do this, you specify that the print

daemon, /usr/lbin/lpd is allowed to use no more than a certain

percentage of the available CPU time. You can group resource user

identiﬁers, such as a user’s UID (user identiﬁcation), into classes and

assign the required CPU access time to each class.

This feature can help you to allocate system resources so that the most

important work receives the required processing time. For example, you

may want to run two versions of a production database on your system.

One version is used as part of your business operations, while the other is

a test copy, with different tuning parameters. The test database can be

assigned to a different class so that your daily operations are not impacted

by the testing.

To set up and use the Class Scheduler, you must complete the following

steps:

• Plan the allocation of CPU resources

• Use class_admin to set up and maintain the class database

• Create classes and add members to the classes

• Verify class entries using the show command

• Save the entries to the database

• Enable Class Scheduling to start the daemon

You use the Class Scheduler commands to monitor and control scheduling

as follows:

• Execute class_admin commands such as stat from the command line

or a shell script without running an interactive session

• Use the runclass command to execute a task according to the

priorities set for a particular class

Note that it is not be necessary to perform tasks in the preceding speciﬁc

sequence. To resolve a resource sharing problem quickly, you can simply

execute a series of class_admin commands at the command line to

conﬁgure a default database, add classes and class members, and enable

the class scheduling daemon. The following sections suggest a systematic

approach to using class scheduling, although you can use it equally well to

create a quick ﬁx to a CPU resource sharing problem.

Customizing the System Environment 4–27