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If burst times are unknown and must be estimated dynamically, which modification to preemptive SJF scheduling is most effective to maintain efficiency and fairness?

hard🎤 Interviewer Follow-up Q10 of Q15
Operating Systems - Shortest Job First (SJF) - Preemptive vs Non-Preemptive
If burst times are unknown and must be estimated dynamically, which modification to preemptive SJF scheduling is most effective to maintain efficiency and fairness?
AUse exponential averaging to predict burst times and adjust scheduling accordingly
BSwitch to non-preemptive SJF to avoid estimation errors
CIgnore burst time estimates and use FCFS scheduling
DAssign fixed priorities regardless of burst time estimates
Step-by-Step Solution
Solution:

  1. Step 1: Understand burst time estimation techniques

    Exponential averaging provides adaptive, smooth estimates of burst times.

  2. Step 2: Evaluate scheduling impact of estimates

    Using estimates allows preemptive SJF to approximate optimal scheduling despite unknowns.

  3. Step 3: Analyze alternatives

    Non-preemptive or FCFS ignore dynamic info; fixed priorities lose responsiveness.

  4. Final Answer:

    Option A -> Option A

  5. Quick Check:

    Exponential averaging enables adaptive preemptive SJF scheduling [OK]
Quick Trick: Exponential averaging adapts burst time estimates [OK]
Common Mistakes:
MISTAKES
  • Switching to non-preemptive due to estimation difficulty
  • Ignoring burst times and using FCFS
  • Assigning fixed priorities without adaptation
Trap Explanation:
PITFALL
  • Candidates often fail to apply dynamic estimation techniques to preemptive scheduling.
Interviewer Note:
CONTEXT
  • Tests knowledge of practical scheduling adaptations when burst times are unknown.
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