Systems that require results within deadlines. Focuses on deadlines, latency, and periodic tasks. Scheduler must support preemptive, priority-based scheduling.
Safety-Critical System
Section titled “Safety-Critical System”A real-time system with catastrophic results in case of failure.
Periodic Real-Time Task
Section titled “Periodic Real-Time Task”Each task has:
- Processing time
- Deadline
- Period
- Must satisfy:
- Rate =
Hard Real-Time
Section titled “Hard Real-Time”Where deadlines must never be missed. Single missed deadline implies system failure. Scheduler must have the ability to meet deadlines.
Soft Real-Time
Section titled “Soft Real-Time”Where deadlines are important but not critical. Occasional misses are acceptable.
Algorithms
Section titled “Algorithms”Rate Monotonic Scheduling
Section titled “Rate Monotonic Scheduling”Aka. RMS. Priority = inverse of period.
Works only if CPU load is below schedulable limit. Can still miss deadlines.
Earliest Deadline First
Section titled “Earliest Deadline First”Aka. EDF. Earlier deadline means higher priority.
Proportional-Share Scheduling
Section titled “Proportional-Share Scheduling”System has total shares. Each task gets shares. Each task is ensured to get fraction of CPU time.