W3 CPU Scheduling

What is CPU scheduling?

It's the process that allows one process to use the CPU while another is waiting for resources, aiming to make the system efficient, fast, and fair. In essence, CPU scheduling manages how processes share the CPU time, optimizing overall system performance, turnaround time, and resource utilization.

Name the 4 types of scheduling decisions.

Long-term, Medium-term, Short-term, and I/O scheduling.

What state transitions does Long-term scheduling handle?

From "new" to "ready" or "ready suspended".

What is the role of the Medium-term scheduler?

Moves processes between suspended and main memory states, managing multiprogramming.

What triggers the Short-term scheduler?

Events like interrupts or system calls that may reassign the CPU.

What are the two parts of a scheduling policy?

Selection function and Decision mode.

What’s the difference between preemptive and non-preemptive scheduling?

Preemptive allows interruption; non-preemptive does not interrupt running processes.

What is FCFS scheduling?

First-Come, First-Served; non-preemptive scheduling that executes processes in order of arrival.

What’s a downside of FCFS?

Poor performance for time-sharing; can starve I/O bound processes.

How does Round Robin scheduling work?

Processes get a fixed time slice; preemptive based on a timer.

What issue can Round Robin have?

Poor for I/O bound processes and sensitive to time slice size.

What is Shortest Process Next (SPN)?

Non-preemptive scheduling based on the shortest job time.

What is starvation in scheduling?

When long processes are never scheduled due to frequent arrival of shorter ones.

What is Shortest Remaining Time (SRT)?

Preemptive version of SPN; always chooses the process with the shortest remaining time.

What is Highest Response Ratio Next (HRRN)?

Non-preemptive algorithm using the formula (Wait Time + Service Time) / Service Time.

How does Multilevel Feedback Queue work?

Processes move between priority queues based on behavior; preemptive and dynamic.

What is response time?

Time from when a process joins the ready queue to when it starts executing.

What is turnaround time?

Time from joining the ready queue to process completion.

What is throughput?

Number of processes completed in a given time.

What are UNIX system calls for process management?

fork(), execv(), and wait().