Technical data

System Management Features
4.3 Class Scheduler for CPU Scheduling
To invoke the class scheduler, you use the SYSMAN interface. SYSMAN
allows you to create, delete, modify, suspend, resume, and display scheduling
classes. Table 4–1 shows the SYSMAN command, CLASS_SCHEDULE, and its
sub-commands.
Table 4–1 SYSMAN command: class_schedule
Sub-command Meaning
ADD Creates a new scheduling class
DELETE Deletes a scheduling class
MODIFY Modifies the characteristics of a scheduling class
SHOW Shows the characteristics of a scheduling class
SUSPEND Suspends temporarily a scheduling class
RESUME Resumes a scheduling class
By implementing the class scheduler using the SYSMAN interface, you create
a permanent database that allows OpenVMS to class schedule processes
automatically after a system has been booted and rebooted. This database resides
on the system disk in SYS$SYSTEM:VMS$CLASS_SCHEDULE.DATA. SYSMAN
creates this file as an RMS indexed file when the first scheduling class is created
by the SYSMAN command, CLASS_SCHEDULE ADD.
In a cluster environment, SYSMAN creates this database file in the
SYS$COMMON root of the [SYSEXE] directory. As a result, the database file is
shared among all cluster members. By using SYSMAN’s SET ENVIRONMENT
command, you can define scheduling classes either on a cluster-wide or per-node
basis.
If desired, a system manager (or application manager) uses the permanent class
scheduler to place a process into a scheduling class at process creation time.
When a new process is created, Loginout determines whether this process belongs
to a scheduling class. Given process information from the SYSUAF file, Loginout
then class schedules the process if Loginout determines that the process belongs
to a scheduling class.
By using the SYSMAN utility to perform class scheduling operations instead of
$SCHED system service, you gain the following benefits:
• You need not modify individual program images to control class scheduling.
You can add, delete, and modify scheduling classifications from the SYSMAN
utility.
• You can use SYSMAN to create a permanent class scheduling database file
which allows processes to be class scheduled at process creation time and
allows class definitions to be preserved in case of a system reboot.
For more detailed information, refer to the following manuals:
OpenVMS Programming Concepts Manual, Volume I
OpenVMS DCL Dictionary: N–Z
OpenVMS System Services Reference Manual: A–GETUAI
System Management Features 4–3