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Embedded Systems Exercise 3 - HS 20204./6.11.2020Stefan Draskovic
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Stefan Draskovic 4./6.11.2020 1
Exercise structure
• Goal of today’s exercise:– Scheduling Aperiodic Tasks
• Agenda:– Wednesday 16:15 - 17:00 Introduction and solving a sample question (recorded)– Friday 16:15 - 17:00 Solutions (recorded)
• Available assistants:– Stefan Drašković– Luca Rufer
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Stefan Draskovic 4./6.11.2020 2
Exercise structure
• Interactions:– Exercise Zoom: Questions can be asked throughout the exercise in this room by
raising your hand. Please feel free to write in the chat in case we oversee yourquestion.
– Help Zoom: Student assistants are available after the session for questions and1-on-1 meetings.
– Matrix Chatroom: Questions that are relevant for everyone can be asked in theMatrix chatroom where the responsible assistants can answer as quickly as possible.
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Stefan Draskovic 4./6.11.2020 3
Content of today’s exercise
Scheduling Aperiodic Tasks: EDD, LDF, EDF, EDF*
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Stefan Draskovic 4./6.11.2020 4
Definitions Recap
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Stefan Draskovic 4./6.11.2020 5
Overview
• Last time: Cyclic Executive Scheduling– easy to implement– hard to derive Schedule– not so easy to analyze
• Today: EDD, EDF, LDF, EDF*– impractical or impossible to implement– easy to derive optimal schedule– easy to analyze
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Stefan Draskovic 4./6.11.2020 6
Scheduling aperiodic tasks with realtime constraints
Some known algorithms:
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Stefan Draskovic 4./6.11.2020 7
Earliest Due Deadline (EDD)
• Optimization goal:– minimize the maximum lateness
• Assumptions on the task set:– independent tasks– synchronous arrival times
• EDD is non preemptive
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Stefan Draskovic 4./6.11.2020 8
Earliest Due Deadline (EDD)
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Stefan Draskovic 4./6.11.2020 9
Task 1: Solution (and Clicker Question)
The task is schedulable
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Stefan Draskovic 4./6.11.2020 10
Latest Deadline First (LDF)
• Optimization goal:– minimize the maximum lateness
• Assumptions on the task set:– tasks with precedence constraints– synchronous arrival times
• LDF is non preemptive
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Stefan Draskovic 4./6.11.2020 11
Latest Deadline First (LDF)
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Stefan Draskovic 4./6.11.2020 12
Latest Deadline First (LDF)
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Stefan Draskovic 4./6.11.2020 13
Task 2: Solution
J1 J2
J3
J4
J5
J6
J7
J8
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Stefan Draskovic 4./6.11.2020 14
Task 2: Solution
J1 J2
J3
J4
J5
J6
J7
J8
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Stefan Draskovic 4./6.11.2020 15
Task 2: Solution
J1 J2
J3
J4
J5
J6
J7
J8
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Stefan Draskovic 4./6.11.2020 16
Task 2: Solution
J1 J2
J3
J4
J5
J6
J7
J8
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Stefan Draskovic 4./6.11.2020 17
Task 2: Solution
J1 J2
J3
J4
J5
J6
J7
J8
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Stefan Draskovic 4./6.11.2020 18
Task 2: Solution
J1 J2
J3
J4
J5
J6
J7
J8
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Stefan Draskovic 4./6.11.2020 19
Task 2: Solution
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Stefan Draskovic 4./6.11.2020 20
Earliest Deadline First (EDF)
• Optimization goal:– minimize the maximum lateness
• Assumptions on the task set:– independent tasks– arbitrary arrival times (dynamic arrivals)
• EDF is preemptive
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Stefan Draskovic 4./6.11.2020 21
Earliest Deadline First (EDF)
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Stefan Draskovic 4./6.11.2020 22
Earliest Deadline First (EDF)Guarantee:• Worst case finishing time of task i : fi = t +
∑ik=1 Ck (t)
• EDF guarantee condition: ∀t = 1, ..., n t +∑i
k=1 Ck (t) ≤ di• Algorithm:
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Stefan Draskovic 4./6.11.2020 23
Task 3: Solution
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Stefan Draskovic 4./6.11.2020 24
Task 3: Solution
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Stefan Draskovic 4./6.11.2020 25
Earliest Deadline First - Star (EDF*)
• Optimization goal:– minimize the maximum lateness
• Assumptions on the task set:– tasks with precedence relations– arbitrary arrival times (dynamic arrivals)
• EDF* is preemptive
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Stefan Draskovic 4./6.11.2020 26
Earliest Deadline First - Star (EDF*)
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Stefan Draskovic 4./6.11.2020 27
Earliest Deadline First - Star (EDF*)
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Stefan Draskovic 4./6.11.2020 28
Earliest Deadline First - Star (EDF*)
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Stefan Draskovic 4./6.11.2020 29
Task 4: Solution
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Stefan Draskovic 4./6.11.2020 30
Task 4: Solution
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Stefan Draskovic 4./6.11.2020 31
Task 5: Solution
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Stefan Draskovic 4./6.11.2020 32
Task 5: Solution
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Stefan Draskovic 4./6.11.2020 33
Task 5: Solution
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Stefan Draskovic 4./6.11.2020 34
Task 5: Solution
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Stefan Draskovic 4./6.11.2020 35
Questions?
Stefan DraskovicETZ G81+41 44 63 27033stefan.draskovic@tik.ee.ethz.ch
Institut für Technische Informatikund KommunikationsnetzeComputer Engineering andNetworks Laboratory Stefan Draskovic 4./6.11.2020 36
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