1. Construct an EDF schedule with HVDF scheduling policy for the following tasks

Question

1. Construct an EDF schedule with HVDF scheduling policy for the following tasks. What is the total value obtained? Ti =(ci ,pi): T1 = (6, 24); T2 = (4, 8); T3 = (4, 8); T4 = (4, 12). The values of these tasks are 2, 3, 1, and 2 respectively. Note: Schedule tasks based on deadline as the primary criteria for priority assignment (EDF); if there is a tie in priority, then choose the task with HVDF (High Value Density First) basis. 2. Assume that the system has only aperiodic tasks and each task requires exclusive access to a resource “R” for their entire duration of execution. Aperiodic tasks: Ti =(ri,ci ,di ,vi ): T1 = (0, 4, 12, 4); T2 = (1, 2, 5, 2); T3 = (3, 3, 6, 3),T4 = (6, 2, 10, 2), where ri,ci ,di , and vi are the ready time, computation time, deadline, and value of the task, respectively. Show the schedules produced by the EDF and Clairvoyant scheduling algorithms. What is the “value ratio” for this example?

Explanation / Answer

The tasks can be scheduled provided the total utilization is 1. Hence, u1 + u2 + u3 1 => u1 + u2 + E3/p3 1 => 0.33 + 0.4 + E3/8 1 => E3 should be reduced from 3 to 2.16 Hence the modified Tasks are T1=(3, 1), T2=(5, 2) and T3=(8, 2.16) For ease of scheduling consider T3(8,2), where slack time may arise. EKT 424 REAL-TIME SYSTEM UniMAP Question 3: Reschedule the new tasks from Question (2) in the interval (0, 21) and show that the tasks are schedulable by EDF algorithm. Answer: Hence the following tasks need to schedule T1=(3, 1), T2=(5, 2) and T3=(8, 2) Time Ready to Run Schedule 0 T2.1 T3.1 T1.1 1 T3.1 T2.1 2 T3.1 T2.1 3 (D= T1.1) T3.1 T1.2 4 T3.1 5 (D= T2.1) T2.2 T3.1 6 (D= T1.2) T2.2 T1.3 7 T2.2 T2.2 8 (D= T3.1) T3.2 T2.2 9 (D= T1.3) T3.2 T1.4 10 (D= T2.2) T3.2 T2.3 11 T3.2 T2.3 12 (D= T1.4) T3.2 T1.5 13 T3.2 14 T3.2 15 (D= T1.5) & (D= T2.3) T2.4 T1.6 16 (D= T3.2) T3.3 T2.4 17 T3.3 T2.4 18 (D= T1.6) T3.3 T1.7 19 T3.3 20 (D= T2.4) T2.5 T3.3 21 (D= T1.7 ) T2.5 T1.8 Hence the tasks are schedulable according to EDF scheduler.

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