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Question

Consider n processes sharing the CPU in round robin fashion. Assuming that each process switch takes s seconds. What must be the quantum size q such that the overhead resulting from process switching is minimized but, at the same time each process is guaranteed to get its turn at the CPU at least every t seconds ? 

a.

q ≤ (t – ns)/ (n – 1)

b.

q≥(t−ns)/(n−1)

c.

q ≤ (t - ns)/ (n + 1)

d.

q ≥ (t - ns)/(n + 1)

Answer: (b).q≥(t−ns)/(n−1)

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Q. Consider n processes sharing the CPU in round robin fashion. Assuming that each process switch takes s seconds. What must be the quantum size q such that the overhead resulting...
beena : June 26, 2023

Explanation: Each process will get CPU for q seconds and each process wants CPU again after t seconds.
Thus, there will be (n-1) processes once after current process gets CPU again. Each process takes s seconds for context switch.

(Qp1)(s)(Qp2)(s)(Qp3)(s)(Qp1)
It can be seen that since P1 left and arrived again, there have been n context switches and (n-1) processes. Thus, equation will be:
q*(n-1) + n*s <= t
q*(n-1) <= t - n*s
q <= (t-n.s) / (n-1)
So, option (A) is correct.

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