SJF scheduling

[bob]

You know SJF grabs the shortest burst task first and that keeps things moving fast in a processor queue. I see it cut average waits better than most others when bursts get predicted right. But you run into trouble if arrival times shift suddenly and a new short job pops in. Perhaps the system switches or holds depending on preemption mode. And that choice changes everything for response times in real runs. I notice non preemptive versions finish the current job no matter what arrives later. You get simpler code but longer jobs block everything behind them. Now think about how this optimality comes from always minimizing the next wait slice. It beats first come methods when loads mix short and long bursts together.
I recall you might test it with varying arrivals and see waits drop quick for small tasks. But starvation creeps in when longs sit idle forever waiting their turn. Perhaps the scheduler needs aging tricks to fix that yet that adds overhead you must track. And in practice knowing exact bursts upfront stays rare so estimates get used instead. You end up with approximations that still help but never hit perfect. Now the preemptive twist called shortest remaining time lets interrupts happen mid run. I found that boosts fairness a bit yet raises context switch costs in busy systems. It works great for interactive loads where quick responses matter most to users like you.
You see how it avoids convoy effects that plague other schedulers with mixed job sizes. But prediction errors throw off the whole order and create unexpected delays. I think measuring those errors in simulations shows big variance under heavy loads. Perhaps dynamic adjustments help yet they complicate the core logic you started with. And in architecture terms the ready queue must stay sorted by remaining time which eats cycles on each arrival. You benefit when workloads skew short but suffer if longs dominate the mix. Now consider multi processor extensions where affinity plays into selections too. It spreads short jobs across cores but migration costs add up fast. I notice cache effects matter here since short runs finish before thrashing happens much.
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