Question

10. (10 pts) A process runs on an average for T msec before blocking for
some I/O activity. A context switch takes on an average S msec. For
round-robin scheduling with a quantum of Q msec (S not included in
Q), give a formula for CPU eciency for each of the following (de ne
CPU eciency as the fraction of time spent running the process):
(a) Q = 1.
(b) S < Q < T.
(c) Q is nearly 0.

Answer 1

Griven Avesage time that a pocess uns before blocking yo r 、T msec -) Context SultchTime,' s' msec if 0 msec, then to un the pnces o requires (T/) cont Soltches CPo efficienefuu cRu time t(it s) l tS

b) Given Date Avevage time that a PDs funs, before blocking for yo → Context Supitch time = ts' m sec -) Time Quantum ะ 、6" msec ,'T, -msec it s <a<T, to run the proces for T mse c , 1 vequires (T/a) context suoitches Hence, (sine,Crime xt sultche) over head [T/a) x S = TS CPU Effiiencuseful cPo tne (usefud o te+ tfu ovehead) T. AT+TS ズ

c sneasly o o, then almost there りeeds to te a context-satch. 'sl msec these ω、ll be a cm text[With Hence 0 Hence no cPo efftciend The eitreny es to o as 4gos te ceny oes to 0 as