Real-Time Scheduling
Scheduling, in general, can be thought of as the process through which the operating system allocates system resources to a set of tasks or processes. Real-time scheduling is a kind of scheduling that can be applied to systems whereby tasks have to be executed within strict time constraints and, therefore, need to be completed within a certain deadline. In other words, real-time systems require predictable and reliable timing behavior.
The primary goal of real-time scheduling is to run the tasks within their allocated time frames, also commonly called deadlines. To ensure this, each task is assigned a priority, normally dependent on its deadline, though it may take into consideration other aspects like relative importance and resource needs of the task. Subsequently, the scheduler chooses a task with the highest priority to execute.
Important features of real-time scheduling are:
Predictability: A scheduler should be able to predict when a task will be finished to ensure that the deadlines will be met.
Reliability: When failures occur, a system should be able to recover from them and further meet the deadlines.
Responsiveness: When events or changes of the state happen, the system has to promptly react on them.
The real-time scheduling algorithms can be divided into two classes:
Rate Monotonic Scheduling (RMS): This algorithm grants each task a fixed priority based on its period, which is a time measure between consecutive executions.
Earliest Deadline First: This algorithm assigns to each task a priority, depending on its deadline. The earlier the deadline, the higher the priority of the task.
Real-time scheduling can find applications in:
Embedded systems: Examples include automotive control systems, medical devices, and industrial control systems. Robotics: Real-time scheduling operates robotic movements and functions.
Telemetry: Application in aircraft and spacecraft control systems.
Briefly, real-time scheduling is concerned with the part of operating systems that must rely on predictable and dependable timing behavior. The algorithms for real-time scheduling ensure timely execution within the tasks' time constraints to meet the performance and safety requirements of the system by granting tasks priorities based on their deadlines among other factors.
