Real-Time Scheduling

>Static table-driven approach
>For periodic tasks.
>Input for analysis consists of : periodic arrival time, execution time, ending time, priorities.
>Inflexible to dynamic changes.
>General policy: earliest deadline first.
>Static priority-driven preemptive scheduling
>For use with non-RT systems: Priority based preemptive scheduling.
>Priority assignment based on real-time constraints.
>Example: Rate monotonic algorithm
>Dynamic planning-based scheduling
>After the task arrives before execution begins, a schedule is prepared that includes the new as >well as the existing tasks.
>If the new one can go without affecting the existing schedules than nothing is revised.
>Else schedules are revised to accommodate the new task.
>Remember that sometimes new tasks may be rejected if deadlines cannot be met.
>Dynamic best-effort scheduling:
>used in most commercial RTs of today
>tasks are periodic, no static scheduling is possible
some short-term scheduling such as shortest deadline first is used.
>Until the task completes we do not know whether it has met the deadline.