Schedulability Requirements

Definition

A schedulability requirement is a performance requirement that specifies a minimum amount of the performance quality subfactor schedulability.

Objectives

The typical objectives of a schedulability requirement are to ensure that:

• Required events and behaviors can be accurately and precisely scheduled:
  • At specific times.
  • By specific times.
  • After specific time intervals.
• The scheduled events and behaviors happen as scheduled.

Measurements

Schedualability requirements are typically specified in terms of the following measurements:

• Clock time.
• Computer cycle time.
• Date.

Examples

The following are typical examples of schedulability requirements:

• “The temperature of the chemical mixing tank shall be read every 5 seconds.”
• “The monthly status report shall be produced between 11PM and 12PM the first business day of each month.”
• “The application shall periodically read the temperature sensors every three seconds.”
• “When in flight, if the avionics application cannot completely process the aileron position sensor readings within 30 miliseconds, then it shall abandon the incompletely processed readings and start over by taking and processing new readings.”

Guidelines

The following guidelines have been found to be useful when producing schedulability requirements:

• The scope of a schedulability requirement can be:
  • A business enterprise
  • An application
  • A component
  • A center
• Specify all required behaviors that must happen at or by specific times.
• Coordinate schedulability and associated jitter requirements.