4. In work-conserving scheduling a processor is never kept idle if there are one

Question

4. In work-conserving scheduling a processor is never kept idle if there are one or more ready processes on the system.

Can a non-work-conserving schedule be the optimal schedule that produces the highest speedup for some concurrent application running on a non-preemptive environment on some given number of processors?

If your answer is NO then prove that a non-work-conserving schedule can never be the optimal non-preemptive schedule for any concurrent application.

If your answer is YES, show with the help of an example that such a non-work-conserving schedule can actually be the optimal non-preemptive schedule for a given application and system. [Assume that the system you are concerned with contains at least four processors and the applications that run on the system contain 10 or more processes].

Explanation / Answer

My Answer is Yes.

Non-work conserving is better for non-preemptive schedulers.
In non work conserving each packet will assigned with some time (eligible time). So even though server is idle, or if none of the packets are eligible then none of the packets are transmitted.

We can prove this by contradiction. As we know already FCFS (First come First Server scheduling) algorithm is woek conserving scheduling.
So we have four processors (P1,P2,P3,P4)
And 10 processes p00,p11,p22 ... p99

Consider an bank transaction case. This is non-preemptive process scheduling.
In banking sector, consider four processes [p00,p11,p22,p33] are given to processors since the no one processor will be in idle state in work conserving scheduling. So if all processes start to withhdraw money, where bank balance is not enough to debt all four process money then we will be conflict. So here in case of non-preemptive process scheduling this work conserving scheduling failed. But in non-work scehduling it will work since when both processors and process are eligible then packets will be sent. Hence proved.

In simple words explainatoin example:
Consider bank balance is having $1000
All four process started to debit $700 each. If they four do the debit operation at a time, then it leads to conflict since all process may not be able to withdraw
since in the mean time other process may withdraw $700. so remaiing balance would be (1000-700) = $300
So other three process will fail.

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