12 01 2023 E TS

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Advanced Operating Systems - Part A, January 12th, 2023 Exercises and solutions Exam finalization Question 1.1 This is part A of the AOS’s exam and today you are finalising your entire grade. You must express now how you have finalised part B. The answer is mandatory for the entire exam. Exercise 2 — Open and closed questions (Points 15) Question 2.1 (Points 5) Describe the following scheduling classes in the Linux operating system. Please use capital letters and respect the space allocated to each class. Solution • SCHED_RR: used for the set of real-time processes, with normal priority π ∈ [0, 99]. Threads of equal priority π are scheduled in a round-robin fashion with a certain timeslice. • SCHED_FIFO: used of the set of real-time processes, with normal priority π ∈ [0, 99]. When a task of this type is picked up by the scheduler, it will not be preempted. • SCHED_OTHER: Class used for the conventional time-shared processes. In modern linux it is based on the completely fair scheduling algorithm and that uses soft priority mechanism based on the ’nice’ value ν (ν ∈ [−20, +19], π ∈ [100 − 139]). For each process p, its time-slice is computed as: τp = f (ν0, . . . , νp, . . . , νn−1, ¯τ , µ) ∼ max( λp ¯τ∑ λi , µ) where ¯τ is called schedule latency , µ is called minimum granularity while λi(νi) is the weight associated with a process, a sort of priority. It has exponential formula, i.e., λi = k × b−νi (current values k = 1024, b=1.25) • SCHED_BATCH: Like SCHED_OTHER but with a longer timeslice (1.5s) thereby allowing tasks to run longer and make better use of caches but at the cost of interactivity. This is well suited for batch jobs. • SCHED_DEADLINE: Higher priority with respect to FIFO/RR; it is an implementation of the Earliest Deadline First (EDF) scheduling…