CPU Scheduling: Algorithms, Concepts, and Real-Time Systems

What is CPU scheduling?

It is about the OS choosing which process is the next one to use the CPU and for how long.

What does the choice of a specific CPU scheduling algorithm depend on?

It depends on the purpose of the OS and the type of ready queue used.

What is a CPU burst?

A period of time when a process wants to use the CPU only.

What is an I/O burst?

A period of time when a process wants to use an I/O device.

Why is it beneficial to schedule short CPU burst processes before long ones?

It keeps the ready queue short and minimizes waiting time.

What does it mean for a CPU scheduling algorithm to be preemptive?

It means a process can be sent back to the ready queue if the CPU is needed for something more important.

What does it mean for a CPU scheduling algorithm to be non-preemptive?

It means a process runs until it finishes its CPU burst without interruption.

What does it mean for a CPU scheduling algorithm to be starvation free?

No process in the ready queue will wait forever; every process will eventually use the CPU.

What is the First-Come-First-Served (FCFS) algorithm?

It treats the ready queue as a real line and is non-preemptive.

What are the advantages of the FCFS algorithm?

It is fast to choose the next process and is starvation-free.

What are the disadvantages of the FCFS algorithm?

It can lead to long waiting times.

What is the Round-Robin (RR) algorithm?

It treats the ready queue as a real line but is preemptive, using a time slice for CPU usage.

What are the advantages of the Round-Robin algorithm?

It is fast, starvation-free, and fair.

What are the disadvantages of the Round-Robin algorithm?

It can lead to long waiting times.

What is priority scheduling?

Every process has a priority that specifies its importance.

What are the advantages of priority scheduling?

It allows prioritization of important processes.

What are the disadvantages of priority scheduling?

It is not starvation-free.

What is aging in CPU scheduling?

A method to combat starvation by increasing the priority of a process over time.

What is priority inversion?

A situation where a higher priority process waits for a lower priority process without a good reason.

What is priority donation?

A method to counter priority inversions by elevating the priority of a lower process while it waits.

What is real-time scheduling?

An approach where the OS ensures that real-time processes meet their execution deadlines.

What are soft real-time systems?

Systems that try to meet CPU scheduling deadlines without guarantees.

What are hard real-time systems?

Systems that must meet CPU scheduling deadlines, and failing to do so is unacceptable.