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If a system uses preemptive SJF scheduling but the burst times of processes are not known in advance and must be estimated, which challenge is most likely to affect scheduling accuracy?

hard🎤 Interviewer Follow-up Q15 of Q15
Operating Systems - Shortest Job First (SJF) - Preemptive vs Non-Preemptive
If a system uses preemptive SJF scheduling but the burst times of processes are not known in advance and must be estimated, which challenge is most likely to affect scheduling accuracy?
AIncorrect burst time estimates can cause frequent unnecessary preemptions
BThe scheduler will always pick the wrong process due to estimation errors
CNon-preemptive scheduling must be used instead to avoid errors
DStarvation is eliminated because estimates prevent preemption
Step-by-Step Solution

  1. Step 1: Understand burst time estimation impact

    Estimations can be inaccurate, causing the scheduler to preempt based on wrong assumptions.

  2. Step 2: Analyze consequences

    Frequent unnecessary preemptions increase overhead and reduce efficiency.

  3. Step 3: Why other options are incorrect

    B: Scheduler won't always pick wrong process; estimates can be close.
    C: Non-preemptive scheduling is a design choice, not forced by estimation.
    D: Starvation is not eliminated by estimates; it depends on scheduling policy.

  4. Final Answer:

    Option A -> Option A

  5. Quick Check:

    Estimation errors cause scheduling inefficiency via unnecessary preemptions.
Quick Trick: Bad burst time estimates cause too many preemptions in preemptive SJF [OK]
Common Mistakes:
MISTAKES
  • Assuming estimates always cause wrong scheduling
  • Believing estimation removes starvation
Trap Explanation:
PITFALL
  • Option A is too absolute; option D incorrectly links estimation to starvation elimination.
Interviewer Note:
CONTEXT
  • Tests deep understanding of practical challenges in implementing preemptive SJF with unknown burst times.
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