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Professur Betriebssysteme
Exercise task pool - Topic block 3
Real-Time Systems Marcel Richter, Theresa Werner Task 1 There are two broad categories of scheduling algorithms mentioned in the lecture. Name them and their di erences. Which one is better? Task 2 As jobs and tasks are only di erent points of view, jobs have timing parameters, too. Which of the timing parameters for jobs can be derived directly from the task parame- ters and which cannot. In addition name two factors that may influence these timing paramters! Task 3 List the first 3 jobs for each task of the given task sets by providing all parameters which can be directly derived from the task descriptions! i) T = ) Ti ( Pi, ei )
= ) T 1 (8 , 2) , T 2 (3 , 1) , T 3 (6 , 2)
ii) T = ) Ti ( i, Pi, ei, Di )
= ) T 1 (2 , 5 , 2 , 4) , T 2 (1 , 4 , 1 , 3)
Task 4 Name the standard assumptions and explain in short why each of them makes the scheduling problem easier to handle! Task 5 There are two major approaches to priority-based policies: policies with fixed and variable i
onlineandofflineonlineisbetterasthepriority
is decidedduringruntimegivingitmoreflexibility
priorities. Decide for the following policies if jobs of the tasks have fixed or variable priorities! Explain in short why that is the case for periodic tasks. Try to find special cases where the the di erentiation might not be clear while only looking at the priorites of the jobs.
- Job priority is equal to the inverse of their task’s execution time.
- Job priority is equal to their arrival time, i.e. jobs which arrive earlier are executed first.
- Job priority is equal to the completion time of the job which preceded it, i.e. the job with the highest value will go first. The first job gets the priority equal to the index of their task.
- Job priority is equal to the completion time minus the starting time of the previous job. The first job will use the execution time of its task as its priority where a higher value is a lower priority.
- Every 5 time units all jobs are assigned priorities according to their remaining execution time. Task 6 Decide for each of the following task sets if they are schedulable under EDF. If a task set is schedulable create a schedule until time point 16 and execute all jobs according to the EDF policy! a) T = { Ti ( Pi, ei )} = { T 1 (16 , 4) , T 2 (8 , 3) , T 3 (4 , 1)} b) T = { Ti ( Pi, ei )} = { T 1 (7 , 3) , T 2 (4 , 1) , T 3 (12 , 5)} c) T = { Ti ( Pi, ei, Di )} = { T 1 (4 , 1 , 3) , T 2 (16 , 6 , 11) , T 3 (8 , 2 , 4)} ii
