CPU Scheduling: All About its Role And Function

To complete the task on time, procedures and work are scheduled. Computer With the use of scheduling, one process can utilize the CPU to the greatest extent possible while another is put on hold or delayed owing to a lack of resources like I/O. Enhancing the system’s speed, fairness, and efficiency is the goal of CPU scheduling.

Arrival, burst, completion, turnaround, waiting, and reaction time are fundamental ideas in CPU scheduling that will be covered in this post which is curated by the expert at allassignmenthelp. These ideas can help us better grasp how operating systems control how processes run on computers by helping us understand how they are applied in various scheduling algorithms.

What Is CPU Scheduling?

CPU scheduling aims to optimize the utilization of the CPU. It is a process that allows the system to carry out multiple processes at once. In the case of scheduling, the CPU keeps a process on hold while the other one is being executed. This is done due to the unavailability of the resources. The scheduling ensures that all the processes in the CPU are being executed promptly and the system is utilizing its full capacity.

The CPU scheduling not only makes the system more efficient but it also increases the speed. When the scheduling is done, the operating system focuses on choosing and executing one of the processes available in the ready queue. A short-term scheduler or CPU scheduler is used to execute the selection process. It selects the processes which are ready to complete. The schedule also allocates the processes to the CPU. Now our assignment helpers from Australia will guide you through the waiting time in CPU.

Waiting Time in CPU

In computing, almost every program is executed based on some alternating cycle. When these programs are being executed, sometimes waiting for the input and the output becomes inevitable. It occurs due to the differences between the CPU and the memory speed. CPU can execute an instruction in a shorter time. On the contrary, fetching data from memory is a more time-consuming process.

CPU-Memory Speed Discrepancy:
- CPU executes instructions faster than memory fetches data, leading to idle CPU time during data retrieval.
Impact on Efficiency:
- Long waiting times and CPU idle cycles reduce system efficiency, making processes time-consuming.
Scheduling Solution:
- Scheduling systems manage process queues, enabling the CPU to execute tasks when others are waiting for input or output.
Preventing Loss of CPU Cycles:
- Scheduling ensures full utilization of CPU cycles, preventing wastage and improving overall system efficiency.
Challenges in Dynamic Conditions:
- Operating efficiently in varying dynamic conditions poses challenges, requiring fair and efficient scheduling strategies.
Task Prioritization:
- Prioritization of tasks is crucial for effective CPU process execution, ensuring critical tasks are handled promptly.

So, enhancing the efficiency of the system becomes quite challenging. The systems should operate fairly and efficiently. It becomes difficult in varying dynamic conditions. Additionally, prioritization of the tasks is another factor that needs to be considered while executing processes in the CPU. If it seems tough to you or you cannot understand it properly then you can reach out to programming assignment helper who will explain what is the concept of waiting in CPU scheduling in well manner.

Queues Involved in Scheduling

There are three types of queues which are involved with the CPU usage are—

Job queue: It includes all processes which are being or will be executed by the CPU. In other words, the processes which are once submitted to the CPU, reside in the job queue. The processes in the job queue are allocated by the long-term scheduler.
Ready queue: It includes the processes which are currently in memory only. These processes remain at the ready state. While being in the queue, the processes wait for execution. These processes are allocated by the CPU scheduler or the short-term CPU.
Device queue: It includes the processes which are waiting for a device. In a CPU, multiple processes can wait for the same device. In such situations, I/O completion sends the process back to the ready queue.

Components of CPU Scheduling

The scheduling process is done with the help of CPU Burst Cycle, Dispatcher and the scheduler.

CPU Burst Cycle: Every process includes a CPU burst cycle and I/O burst cycle. The duration of CPU burst cycle varies on the basis of the processes.
Scheduler: The scheduler operates when the processor becomes idle. It chooses another process which is ready to run from the queue. The storage structure of the ready queue plays a key role in determining which process needs to be executed. The algorithm is another factor that deals with the selection process. The scheduler works on the basis of these two factors and selects the most appropriate process accordingly.
Dispatcher: Dispatcher is another component that is involved in CPU scheduling. It is a module that plays a significant part in the scheduling process. It transfers the control of the CPU to the next process which needs to be executed as chosen by the short-term scheduler. The function is done in the following steps—

Switching of the processes
The user mode is switched
The processor reaches the appropriate location in the user program. The destination, in this case, is the same location where the program was left last time.

The dispatcher requires operating at a faster speed to manage every process switch. The time needed by the dispatcher in order to terminate one process and switch to another one is known as the Dispatch Latency.

There are some instances when there is a need for scheduling the CPU, these situations can be like Switching from Running State to Ready State, Switching from Running State to Ready State, Switching from Running State to Ready State and Switching from Waiting State to Ready State.

What Are the Different Terminologies to Take Care of In Any CPU Scheduling Algorithm?

Arrival Time: The time at which the process arrives in the ready queue.
Completion Time: The time at which the process completes its execution.
Burst Time: Time required by a process for CPU execution.
Turn Around Time: Time Difference between completion time and arrival time.

The primary goal of the process scheduling algorithm

Maximize CPU utilization. Make the CPU as busy as you can.
CPU allocation needs to be equitable.
Maximum throughput is required. i.e. The number of processes that finish running in a given amount of time ought to be maximized.
The shortest possible minimum turnaround time is the amount of time needed for a process to complete its execution.
The process shouldn’t starve in the ready queue, and there should be a minimal waiting duration.
The bare minimum of time needed to respond. It indicates that there should be as little time as feasible between a process’s initial reaction.

What Are The Different Types of CPU Scheduling Algorithms?

The scheduling in the CPU is done on the basis of different algorithms. The selection of the algorithm depends on a number of factors—

CPU Utilization

To ensure the best use of the CPU, preventing the wastage of the CPU cycle is necessary. It is achieved when the CPU works most of the time. Ideally, the CPU should utilize 100% of the time available to it. However, when a real system is considered, CPU utilization ranges from 40% in the case of the lightly loaded systems to 90%, in the case of the heavily loaded systems. It indicates that the workload of the system plays an important part in choosing the scheduling algorithm.

Throughput

The total number of processes finished per unit time by the CPU is described as the throughput. In other words, the total amount of work completed by the CPU in a unit of time is considered as the throughput. The throughput level varies with the process. In some cases, it might be 10/second while in others it can be reduced to 1/hour based on the requirement of specific processes.

Turnaround Time

It is the time which is required for executing the particular processes. It can also be described as the interval between the submission of one process to the time when the process is completed.

Waiting Time

It is the cumulative amount of period which the process spends by waiting in the queue at ready state. In other words, it can be described by the time after which the process gains control over the CPU.

Load Average

It indicates the average number of processes which are residing in the ready queue and waiting for their turn to take control over the CPU.

Response Time

When the CPU receives an instruction, it takes some time to respond. This duration is called the response time. While choosing the CPU scheduling, it is ensured that the Throughput and CPU utilization are maximized. It is also ensured that other factors are reduced to optimize utilization. It indicates that scheduling plays a key role in making the system faster and more efficient. The advantages obtained from the scheduling depend on the selection of the specific algorithms—

First Come First Serve

In the case of the “First come first serve” scheduling algorithm, the work is done in the same manner as the name suggests. It indicates that the process which is received by the CPU first is executed first. In other words, the process which sends a request to the CPU first gets the chance to be allocated first.

The First Come First Serve (FCFS) algorithm is simple to interpret and implement, making it advantageous for system programming. It operates on the principle of a queue data structure, where new processes are added to the tail and chosen for execution from the head. This mimics real-life scenarios like purchasing tickets from a counter.

However, FCFS has drawbacks. Firstly, it’s non-preemptive, meaning process priority is disregarded, potentially leading to lower-priority tasks being executed first. For instance, routine backup processes, despite being low priority, may monopolize CPU time, hindering system effectiveness. Additionally, FCFS fails to achieve optimal average waiting time and doesn’t utilize resources in parallel, resulting in poor resource utilization and the convoy effect.

Shortest Job First Scheduling

Reducing the waiting time is one of the key goals of the scheduling process. Shortest Job First Scheduling is one of the best approaches which minimising waiting time for particular processes. This type of scheduling is also applied in batch systems. This type of scheduling is categorized into two types. These are non-pre-emptive and Pre-emptive. For implementing the method successfully, knowledge of the duration time or the burst time is necessary for the processor. However, practically, knowing the duration time or the burst time is not possible for all the processes. It also indicates that the processor should be aware of the processes before execution. It is also not feasible in every case. The shortest job first scheduling provides the optimum result when every process or job is available at the same time. It indicates that the highest efficiency is achieved when all the processes have the same arrival time.

Priority Scheduling

In this scheduling system, every process is assigned a priority. The processes which are associated with the highest priority require being executed first. When the CPU encounters multiple processes with the same priority, the scheduling is done in FCFS manner. The priority of a task depends on different factors such as time requirements, memory requirements and other resource requirements.

Round Robin Scheduling

The round-robin is another schedule which is used to optimize the performance of the CPU. In this case, each process gets a fixed time to take control of the CPU for execution. The duration is called quantum. When a process gets the chance to be executed for a fixed time, it is preempted. After that time, other processes are executed. The Context switching saves the states of the pre-emptied processes.

Multilevel Scheduling

It is another type of algorithm. These algorithms are developed to deal with the situations in which the processes from the different classes are present. For instance, batch or interactive processes fall into different classes. The response time requirements for these processes are different. So, scheduling needs also vary. Additionally, the foreground processes are provided with higher priority than the background processes. When the multi-level queue scheduling algorithm is used, the ready queue is separated into different parts. Each process is allocated to one queue permanently. This allocation depends on the particular properties of the processes. For instance, the process priority, memory size and process type influence the allocation of sub-queues to the processes. The foreground and background processes are executed using separate queues.

Multilevel Feedback Queue Scheduling

In the case of a multilevel queue-scheduling algorithm, processes are assigned permanently to a queue after entering the system. Once assigned, the processes do not switch between queues. This algorithm is advantageous because of the low scheduling overhead. However, this is inflexible. It is a disadvantage of the process.

Wrap Up

Our lives are now influenced by computer technology. We can’t imagine a world without technology because everything depends on it. Operating systems such as Windows, and computer scheduling have made life easier for us through technology. Technology makes it possible to grow in one’s professional career and acquire critically important technical abilities. Will you be participating in this new field as well? Then you have to work hard as it is not an easy nut to crack. You can reach experts, they can make your academic journey easy. Also, you can pay someone to do your online class and reduce your stress if you require any additional help to raise your scores.

FAQs

Q. What is the difference between preemptive and non-preemptive scheduling?
Higher-priority tasks are interrupted by preemptive scheduling, whereas non-preemptive scheduling waits for processes to finish before switching.

Q. How do scheduling algorithms handle priority inversion?
Priority inversion is controlled by scheduling algorithms such as Ceiling Protocol and Priority Inheritance, which raise the priority of lower-priority activities that are holding resources for a short while.

Q. What are the factors considered when selecting a scheduling algorithm for a specific system?
Workload, process attributes, requirements for responsiveness, and resource use objectives for optimum system performance are among the factors taken into account.