REAL-TIME SCHEDULING

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: yused in most commercial RTs of today ytasks are aperiodic, no static scheduling is possible ysome short-term scheduling such as shortest deadline first is used. yUntil the task completes we do not know whether it has met the deadline.