Lecture 13 - Real-time systems #

Scope of the lecture #

• Real-time (RT) systems
  • hard RT vs soft RT: characteristics and applications
  • RT systems vs desktop systems: display/user interaction, memory management, virtual memory, single/multi-purpose
  • “must have” of RT: preemptive, priority-based scheduling, preemptive kernels, minimized interrupt and dispatch latency
  • RT-specific CPU scheduling:
    • Rate-Monotonic Scheduling (RMS)- optimal assignment of static priorities for periodic tasks, pretty low worst-case CPU utilization (N(2^1/N-1))
    • Earliest Deadline First (EDF) scheduling - does not require that processes be periodic, nor must a process require a constant CPU time per burst; requires that a process announces its deadline to the scheduler when it becomes runnable.
    • Proportional share scheduling
  • POSIX scheduling policies
    • Real-time (RT): SCHED_FIFO, SCHED_RR, SCHED_SPORADIC
    • Non RT: SCHED_OTHER
  • Example RT systems - VxWorks, RTLinux

Reference #

1. Slides: RT_en.pdf
2. Textbook: chapter 19 - “Real-Time Systems”.
3. man: sched(7)