Explain Deadline monotonic real time scheduling algorithmswith example.

Deadline Monotonic Scheduling (DMS) is a priority assignment algorithm used in real-time systems. It is an optimal static priority scheduling algorithm used for scheduling a set of periodic tasks on a single processor system.

Here's a step-by-step explanation of how it works:

1. Task Characteristics: In DMS, each task is characterized by its execution time, period, and deadline. The execution time is the time taken by the task to execute, the period is the time interval after which the task repeats, and the deadline is the time by which the task must be completed.

2. Priority Assignment: DMS assigns priorities to tasks based on their deadlines. The task with the shortest deadline is given the highest priority, and the task with the longest deadline is given the lowest priority.

3. Scheduling: Once the priorities are assigned, the tasks are scheduled according to their priorities. The task with the highest priority is scheduled first, followed by the task with the next highest priority, and so on. If two tasks have the same deadline, the task that arrived first is given higher priority.

4. Preemption: DMS is a preemptive scheduling algorithm. This means that if a higher priority task arrives while a lower priority task is executing, the lower priority task is preempted (i.e., temporarily stopped) and the higher priority task is scheduled to execute.

Let's consider an example:

Suppose we have three tasks T1, T2, and T3 with deadlines 5, 10, and 15 respectively. According to DMS, T1 will be given the highest priority because it has the shortest deadline, followed by T2 and then T3. So, the scheduling order will be T1, T2, T3.

If T1 is executing and T2 arrives, T1 will continue to execute because it has a higher priority. But if T1 is executing and a new instance of T1 arrives, the currently executing T1 will be preempted and the new instance of T1 will be scheduled to execute because it has a higher priority.