Below is the precedence graph for a set of tasks to be executed on a parallel processing system S.
What is the efficiency of this precedence graph on S if each of the tasks T1, T2, T3,….T8 takes the same time and the system S has five processors?
(A) 25%
(B) 40%
(C) 50%
(D) 90%
Answer: (B)
Explanation: It can be seen that along with the sequential execution of T1 and T2, (T3, T6), (T4, T7) and (T5, T8), all these three processes can be executed in parallel.
So total number of processes that can be executed in 4 units time using 5 available processors = 5*4 = 20
But here processes that are executing in 4 units time = 8
Throughput = 8/20 * 100 = 40%
So, option (B) is correct.
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