Scheduling
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Round Robin
A pre-emptive scheduling algorithm designed for time sharing systems. The ready (to run) queue is treated as a circular queue. A small execution time interval is defined as the time slice.
Shortest Job First
A type of scheduling algorithm where the queue is sorted by expected execution time. New jobs are added accordingly to the queue.
First Come, First Served (FCFS)
The first job to enter the ready queue is the first to enter the running state.
Shortest Remaining Time
A type of scheduling algorithm where the queue is sorted by expected execution time. New and pre-empted jobs are added accordingly to the queue.
Multi-Level Feedback Queue (MLFQ)
A scheduling algorithm that deals with tasks based on a set of priorities and rules across different queues. Processes may get promoted, demoted or stay at the same level.
Preemptive scheduling algorithms
Round Robin, Shortest Remaining Time and MLFQ
Non preemptive scheduling algorithms
First Come First Served, Shortest Job First
Advantages of First Come First Served
*Simple to implement with a queue data structure. *Works well with processes which need shorter amounts of CPU time
Disadvantages of First Come First Served
*Longer processes may monopolise the CPU. *User may experience a lack of responsiveness. *Does not maximize throughput if there are longer processes.
Advantages of Round Robin
*Improves the throughput of processes and prevents longer processes from monopolising the CPU.
Disadvantages of Round Robin
*Swapping processes has an admin cost which can slow down if the time slice used is too small. *User may experience a lack of responsiveness if there are a large number of processes.
Advantages of Shortest Job First
*Prioritises processes using slower computer resources. *Prioritises GUI operations.
Disadvantages of Shortest Job First
*May suffer from starvation for longer processes. *Not as fair as other scheduling algorithms.
Advantages of Shortest Remaining Time
*Improves the throughput of processes. *Longer processes will increase in priority over time.
Disadvantages of Shortest Remaining Time
*May suffer from starvation for longer processes, but is mitigated. *Not as fair as other scheduling algorithms.
Advantages of MLFQ
*Prioritises processes using slower computer resources by promoting these processes. *Prioritises GUI operations as they will always enter at level 0.
Disadvantages of MLFQ
*Longer, poorly coded, processes may suffer from starvation.