State True/False

Question

a) CPU Utilization is highest in the case of SJF scheduling.

b) Total waiting time is highest in case of Round Robin scheduling.

Comments

B) true

A) I have doubt ..but if this question is asked in gate..I tick  "true"

because SJF have maximum throughput

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can we say, round robin waiting time is highest then it has least cpu utilisation ?

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@magma : dont u think there is a difference between cpu utilization and throughput.. as cpu utilization is the amount of time cpu will be busy exection given process.

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Hmmm

That means we  measure CPU utilization by  it's "efficiency" right ??

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yes right.

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then

a) is FALSE ??

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yes as each scheduling will have equal utilization of cpu.

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hmm thanks bro

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@ arvin what does CPU utilization mean here : https://gateoverflow.in/963/gate2003-77

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i just didnt added that it will be divided by total run time... because CPU utilization is given in term of percentage...

see they have considered a case where you have i/o time also defined for the system along with cpu time and when there will be much more ambiguity if we consider i/o burst time...

.

the question in the link is a uniprocessor and process are repeating alternately in that case... and here we dont have any data(specific).

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Almost all the processes undergo cycles of CPU and I/O bursts. In real systems CPU utilization ranges from 40% to 90%.

In case of FCFS, consider a situation that a long process appears and executes inside CPU while the shorter ones wait in the ready queue. Once longer one is done (done means maybe it terminates or requests for I/O) then the shorter ones in the queue will get their turn for CPU bursts while this longer goes for the I/O. Now shorter ones are done executing in CPU and comes for I/O and again they have to wait because this longer process is already there. At this point of time CPU remains idle. So this idleness will reduce the CPU utilization. 

In case of Round Robin about 10% of CPU time is wasted on context switching. Also if you go through the solution in https://gateoverflow.in/963/gate2003-77 we can see that CPU utilization is lesser than others.

In case of priority scheduling it depends on which basis the priority is given. If longer ones are given more priority then it may become same as the case that i mentioned in FCFS. If shorter ones are given more priority then it becomes same as SJF.

In case of SJF, since shorter ones are executed first so once the shorter processes have their CPU bursts they will move for I/O meanwhile the longer ones occupy CPU. When these are done with I/O bursts then they go for CPU again. Since these are shorter processes so they will need less time in I/O and will come back quickly for CPU..maybe even before the longer ones are done having their CPU bursts..So CPU hardly stays idle.

Among all these scheduling algorithms I think SJF has the highest CPU utilization.

SRTF can improve the waiting time but I doubt if it has any extra improvement on CPU utilization.

I have searched about it but couldn't find any specific answer. These are what I concluded. Correct me if I am wrong. I also took an example to check and SJF gave me the highest CPU utilization.

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can u give that example that u took.. @minipanda

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@arvin This one..