Question

For Multiple-Level Queues Scheduling,

• What is the arrival time, completion time, burst time, turnaround time, and the waiting time?
• discuss these terms further as they pertain to the efficiency of the algorithm as well as properties such as starvation.
• Pros and Cons of Multiple-Level Queues Scheduling

Answer 1

Arrival time (AT) - Whenever a process gets into the ready queue, then that is called arrival time. That is the time at which it is ready to get executed.

Completion time (CT) - The time at which the process finishes the execution of a process.

Burst time (BT) - The amount of time that is required by the CPU to finish the process.

Turn around time (TAT) - The total time passed by from the time the process is submitted to the time the process is completed in the system, i.e. TAT=CT(Completion time)-AT(Arrival time).

Waiting time (WT) - The amount of the total time spent by a process waiting in the ready queue to get into the CPU, i.e. WT= TAT(Turn around time) - BT(Burst time).

For example-

These are the basic terms which are used in different types of algorithm, such as FCFS, SJF, SRTF, Round Robin and many more. According to the algorithm, the efficiency differs. If we compare all the types of algorithm then we will see that Round Robin algorithm has the maximum efficiency and suffers from least starvation as every processes gets equal amount of time to get executed.

Multiple-level queue scheduling or multiprocessor feedback queue scheduling is that the processes can move between the queues now. In this type of scheduling, the ready queue is divided into a number of multiple queues of different priorities. The jobs are assigned to the queues by the system based on their CPU-burst characteristics, which means, if a process consumes more CPU time it will brought to a lower priority queue. I/O bound jobs stay in the higher priority queues and CPU bound jobs move to lower priority queues. However, these lower priority processes will be promoted to higher priority queues after a certain time interval. This technique is also known as aging.

The pros is that it has low scheduling overhead and cons is that it is not flexible.