4 CPU Scheduling Free Online FlashCards

What does CPU scheduling decide?

CPU scheduling chooses which ready thread runs on a processor next.

How is turnaround time defined?

Turnaround time is the time from a job’s arrival to its completion: $\text{completion time} - \text{arrival time}$.

Why run another ready thread when one blocks for I/O?

When a thread blocks for I/O, running another ready thread can keep the processor productive instead of idle.

What is the convoy effect in FCFS scheduling?

The convoy effect occurs when a long job at the front of the FCFS queue delays many shorter jobs.

When can SJF reduce average turnaround time?

When all jobs are available and their burst lengths are known, SJF can reduce average turnaround time by running the shortest job first.

How does SRTF choose which job to run?

SRTF is preemptive SJF: when a job becomes ready, the scheduler runs whichever has the shortest remaining expected CPU time.

How does Round Robin share the CPU?

Round Robin gives each ready thread a time quantum; if it has not finished, it moves to the back of the ready queue.

How does aging reduce starvation?

Aging gradually raises the priority of tasks that have waited a long time, reducing the risk that low-priority tasks starve.

How does an MLFQ adapt to task behavior?

An MLFQ moves tasks among queues based on observed behavior; for example, I/O-waiting tasks may be favored while long CPU-burst tasks move to lower priority.

Does high-priority scheduling guarantee every real-time deadline?

A high-priority policy alone does not guarantee that every deadline will be met; real-time scheduling must account for timing requirements.

What two concerns shape scheduling across multiple cores?

A multicore scheduler balances runnable work across cores to improve utilization and may keep a task on the same core to preserve useful processor state.

What makes a CPU scheduler preemptive?

A preemptive OS can interrupt a running thread and switch to another, supporting time-sharing and responsiveness.