Scheduing

* Mode
- Process Contention Scope
- System Contention Scope

* Types
- Time Sharing with Equal or Dynamic Priority (Fair)
- Realtime with Different and Static Priority (Non-fair in order to have predicable response): Preemptive for different priority and Round-Robin (time slicing) for the same priority

* Priority Assignment
Pre-condition:
All tasks have worst-case execution times that are less than or equal to their deadlines.
- Rate Monotonic Scheduling
For periodic tasks and task deadlines are in the end of period, tasks with shorter period have higher priority.
- Minimum Interarrival Time Scheduling
For aperiodic tasks and task deadlines are equal to their minimum interarrival time, tasks with shorter arrival time have higher priority.
- Deadline Monotonic Scheduling
For periodic or aperiodic tasks and task deadlines are shorter than their periods or minimum interarrival time, tasks with shorter deadline have higher priority.

* Issues
- Priority inversion
It involves at least three threads of different priorities. The solutions are priority inheritance and priority ceiling. Mutex supports to solve this problem generally. When use the preemptive lock, the priority inversion might happen since the task with higher priority could not be executed in time.