CPU Scheduling Algorithms in OS | Types of CPU Scheduling

CPU scheduling is the process of deciding which process gets to use the CPU at a given time, based on various scheduling algorithms. Now, in this tutorial we are going to explain what is CPU Scheduling Algorithms in OS? And different types of CPU Scheduling algorithm in Operating System with ease. At the end of this post, you will be completely educated with CPU Scheduling Algorithms without any hindrance.

What is CPU Scheduling in Operating System?

CPU scheduling is the procedure of an operating system that determines which process should be allocated to the CPU (Central Processing Unit) at any given time. The goal of CPU scheduling is to improve the efficiency of the system by maximizing the use of CPU resources, minimizing the response time for user requests, and ensuring fair allocation of resources among all active processes.

CPU-Schedulings-and-it-types

In a multitasking environment, where multiple processes are running concurrently, the CPU scheduler determines which process will execute next. The scheduler selects the next process from the ready queue, which is a list of processes that are waiting to be executed. The scheduling algorithm used by the CPU scheduler determines the order in which processes are selected from the ready queue.

CPU Scheduling Tutorial Headlines:

In this section, we will show you all headlines about this entire article; you can check them as your choice; below shown all:

  1. What is CPU Scheduling in Operating System?
  2. Why to Need for CPU Scheduling Algorithm
  3. CPU Scheduler in OS
  4. CPU Scheduling Dispatcher
  5. CPU Scheduling Criteria
  6. CPU Scheduling Algorithm Terminologies
  7. Different Types of CPU Scheduling Algorithms

A) Pre-emptive Scheduling

  • Priority Scheduling
  • Longest Remaining Job First Scheduling
  • Shortest Remaining Job First Scheduling
  • Round Robing Scheduling

B) Non-Preemptive Scheduling

  • Shortest Job First Scheduling
  • First Come First Server Scheduling
  • Longest Job First Scheduling
  • Highest Response Ratio Next Scheduling

Let’s Get Started!!

Why to Need for CPU Scheduling Algorithm

CPU scheduling algorithms are necessary because modern computer systems often have multiple processes and threads competing for CPU time. The CPU can only execute one process at a time, so the operating system must determine which process to run next and for how long. This is where the CPU scheduling algorithm comes into play.

Also Read: Process Life Cycle in Operating System | Process State in OS

The main objectives of a CPU scheduling algorithm are:

Maximize CPU Utilization: The algorithm should try to keep the CPU as busy as possible so that no time is wasted.

Fairness: Each process should get a fair share of the CPU time so that no process is starved of CPU time.

Response Time: The algorithm should try to minimize the time it takes for a process to get a response.

Throughput: The algorithm should try to maximize the number of processes that are completed per unit time.

Turnaround Time: The algorithm should try to minimize the time it takes for a process to complete.

Without a good CPU scheduling algorithm, the operating system may not be able to make optimal use of the CPU, resulting in slow performance, low throughput, or even system crashes. Therefore, CPU scheduling algorithms are essential for efficient utilization of system resources and providing a good user experience.

CPU Scheduler in OS

A CPU scheduler is a component of an operating system that is responsible for allocating the CPU (Central Processing Unit) time to various processes and threads that are running on the system. The CPU scheduler is designed to ensure that the CPU is utilized effectively and that all processes and threads have a fair share of CPU time.

Also Read: Longest Remaining Time First (LRTF) Scheduling with Examples & Programs!!

The CPU scheduler works by maintaining a queue of processes and threads that are waiting for CPU time. When the CPU becomes available, the scheduler selects the next process or thread to run based on a set of scheduling policies. These policies can be based on various factors, such as the priority of the process, the amount of CPU time the process has already used, the deadline for completing the task, and so on.

The choice of scheduling algorithm can have a significant impact on system performance and resource utilization. A well-designed CPU scheduler can help to ensure that the system is responsive and efficient, while a poorly designed scheduler can lead to problems such as process starvation, poor resource utilization, and degraded system performance.

CPU Scheduling Dispatcher

The CPU scheduling dispatcher is an essential component of the operating system responsible for selecting which process should be executed next on the CPU. Its primary function is to manage the scheduling queue of processes waiting for the CPU and select the next process to be run based on the scheduling algorithm implemented by the operating system.

Also Read: What is Process in OS? Types of Process in Operating System!!

When a process requests CPU time, it is added to the scheduling queue. The dispatcher is responsible for selecting the next process to be executed from the queue and allocating CPU time to it. The dispatcher performs context switching, which involves saving the state of the currently running process, loading the state of the next process to be run, and transferring control to the new process.

The dispatcher needs to be efficient in selecting processes and allocating resources to ensure that the operating system runs smoothly. The scheduling algorithm used by the dispatcher plays a critical role in the system’s overall performance. Different algorithms prioritize different criteria such as the length of the process, its priority, or the time it has been waiting in the queue.

CPU Scheduling Criteria

The criteria are as follows:

CPU Utilization: The operating system tries to keep the CPU busy all the time. Therefore, it chooses the process that will utilize the CPU to the maximum.

Throughput: The number of processes that complete their execution per unit of time is called throughput. The operating system aims to maximize the throughput by selecting the processes that can be completed quickly.

Turnaround Time: Turnaround time is the time taken by a process to complete from submission to termination. The operating system tries to minimize the turnaround time by selecting the process that will finish the soonest.

Waiting Time: Waiting time is the time that a process spends in the ready queue waiting for CPU time. The operating system tries to minimize the waiting time by selecting the process that has been waiting the longest.

Response Time: Response time is the time taken by the system to respond to a user’s request. The operating system tries to minimize the response time by selecting the process that will give a quick response to the user.

Priority: Priority scheduling is used to assign priority to the processes. The operating system gives higher priority to the processes that are more important.

These criteria are used by the operating system to schedule the processes in the CPU, and the choice of criteria depends on the requirements of the system.

CPU Scheduling Algorithm Terminologies

There are several terms that are commonly used in CPU scheduling algorithms:

Process: A program in execution is known as a process.

Arrival Time: The time at which a process arrives in the system.

Burst Time: The amount of time a process requires to complete its execution.

Completion Time: The time at which a process completes its execution.

Turnaround Time: The total amount of time a process takes from arrival to completion. (Turn Around Time = Completion Time – Arrival Time)

Waiting Time: The amount of time a process spends waiting in the ready queue. That means (Waiting Time = Turn Around Time – Burst Time)

Response Time: Response time is the amount of time it takes for a process to start running after a request has been made. In CPU scheduling, response time is an important metric because it determines how quickly a user or system can interact with a process.

Context Switching: The process of switching the CPU from one process to another.

Pre-emptive Scheduling: A scheduling algorithm in which the CPU can be taken away from a process before it completes its execution.

Non-preemptive Scheduling: A scheduling algorithm in which the CPU cannot be taken away from a process before it completes its execution.

Different Types of CPU Scheduling Algorithms

CPU scheduling algorithm is divided into two different categories and here will discuss all CPU scheduling algorithms with comparison like as:

types-of-CPU-Scheduling-algorithms

1) Pre-emptive Scheduling

Pre-emptive scheduling is a method that helps to manage the execution of multiple processes or threads. In pre-emptive scheduling, the operating system can interrupt a currently executing process or thread and allocate the CPU to another process or thread that has a higher priority.

This means that the operating system can forcibly stop the execution of a lower-priority process or thread in order to give the CPU to a higher-priority process or thread that needs to run. Pre-emptive scheduling ensures that the CPU is always allocated to the process or thread that has the highest priority at any given time, which helps to maximize system throughput and minimize response times.

Pre-emptive scheduling is often used in real-time systems and in systems that require a high level of responsiveness or concurrency. It is also used in multi-tasking operating systems that need to manage the execution of multiple processes or threads simultaneously.

There are different types of pre-emptive scheduling algorithm such as:

A) Priority Scheduling: Priority scheduling is a method of scheduling processes or threads in an operating system where each process or thread is assigned a priority value. The priority value is typically an integer that indicates the relative importance of the process or thread compared to other processes or threads in the system.

In priority scheduling, the operating system assigns CPU time to the process or thread with the highest priority value. If multiple processes or threads have the same priority, they are scheduled using a different scheduling algorithm, such as round-robin scheduling.

Priority Scheduling Pros

Here are some advantages of priority scheduling:

High-Priority Tasks are Given Preference: In priority scheduling, the process with the highest priority is executed first. This ensures that important tasks are completed first, which can be crucial in certain applications, such as real-time systems.

Efficient Use of Resources: Priority scheduling can ensure that resources are efficiently utilized, as high-priority processes are executed first, reducing waiting times and improving system performance.

Prioritization of Critical Processes: Priority scheduling can be used to give priority to critical processes such as emergency services or critical system processes. This ensures that these processes are always given priority, even when the system is under heavy load.

Flexibility: Priority scheduling is a flexible algorithm that can be used in various applications. It allows for the dynamic adjustment of priorities based on the changing needs of the system, ensuring that the most important processes are always given priority.

Fairness: Priority scheduling can also be used to ensure fairness in resource allocation. By assigning priorities based on the needs of the system, processes that require more resources can be given higher priorities, ensuring that all processes receive their fair share of system resources.

Priority Scheduling Drawbacks

There are also some limitations that need to be considered:

Starvation: If high-priority processes are constantly being introduced to the system, lower-priority processes may not get a chance to execute. This can lead to starvation, where a process is never executed, causing a system deadlock or loss of data.

Inefficient Use of Resources: While priority scheduling can be an efficient way to utilize resources, it can also lead to inefficient use of resources if the highest priority processes are not always the most important. Lower-priority processes may be waiting for resources that are being used by higher-priority processes, even if those processes don’t require the resources as urgently.

Complexity: Priority scheduling can be a complex algorithm to implement, requiring additional overhead to assign and adjust priorities. This can increase the overall system overhead and reduce system performance.

Priority Inversion: If a low-priority process holds a resource that a high-priority process needs, the high-priority process may be blocked, leading to priority inversion. This can cause delays and reduced system performance.

Difficulty in Setting Priorities: Setting priorities can be difficult, as it may be hard to determine the importance of each process. If priorities are set incorrectly, it can lead to inefficient use of resources and reduced system performance.

B) Longest Remaining Job First Scheduling: Longest Remaining Job First (LRJF) scheduling algorithm selects the process with the largest estimated remaining processing time to execute next. This means that the process with the most work remaining is given priority over the others.

The LRJF algorithm is similar to the Shortest Remaining Time First (SRTF) algorithm, but instead of choosing the process with the smallest remaining time, it chooses the process with the largest remaining time. This makes LRJF a non-preemptive algorithm, as once a process is selected for execution, it is allowed to run until completion without interruption.

LRJF Scheduling Algorithm Pros

LRJF scheduling algorithm has several advantages, including:

Reduced Average Waiting Time: LRJF scheduling can reduce the average waiting time for processes with long execution times because they are given priority over shorter processes. This can result in a more efficient use of CPU resources.

Better Throughput: By prioritizing longer processes, LRJF can improve the overall throughput of the system by completing more work in a given amount of time.

Less Frequent Context Switches: LRJF is a non-preemptive algorithm, which means that once a process is selected for execution, it is allowed to run until completion without interruption. This can result in fewer context switches, which can improve overall system performance.

Efficient for Batch Systems: LRJF is particularly well-suited for batch processing systems where there are many long-running processes that need to be completed in a specific order.

LRJF Scheduling Algorithm Drawbacks

The Longest Remaining Job First (LRJF) scheduling algorithm also has some disadvantages, including:

Starvation: The prioritization of longer processes can lead to shorter processes being starved of CPU time, as they may never get a chance to run if there are always longer processes in the queue.

High Average Waiting Time: LRJF can result in a higher average waiting time for shorter processes, as they are constantly being pushed back in the queue in favor of longer processes.

Poor Responsiveness: LRJF is a non-preemptive algorithm, which means that once a process is selected for execution, it is allowed to run until completion without interruption. This can result in poor responsiveness for interactive systems, where shorter processes may need to be executed quickly in response to user input.

Difficulty in Estimating Remaining Time: Estimating the remaining processing time for a process accurately can be difficult, and incorrect estimations can lead to inefficient use of CPU resources.

C) Shortest Remaining Job First Scheduling: Shortest Remaining Time First (SRTF) scheduling algorithm is going to use in operating systems for executing processes efficiently. It is also known as Shortest Remaining Job First (SRJF) or Preemptive SJF scheduling.

In SRTF, the process with the shortest estimated run time is given priority, and the CPU is allocated to that process. If a new process arrives with a shorter expected run time than the currently running process, the running process is preempted, and the new process is executed. The process with the shortest remaining time is always given the CPU until it completes or is preempted by another process with a shorter remaining time.

SRJF Scheduling Algorithm Pros

Shortest Remaining Job First (SRJF) scheduling has several advantages over other scheduling algorithms:

  • It results in a shorter average turnaround time and waiting time because the process with the shortest remaining time is given priority. This leads to a higher throughput and better overall system performance.
  • It is a preemptive scheduling algorithm, which means that if a new process arrives with a shorter remaining time than the currently running process, the running process is preempted. This ensures that the CPU is always allocated to the process with the shortest remaining time, resulting in faster completion times for short processes.
  • SRTF is a dynamic scheduling algorithm, which means that it can adapt to changes in the workload. If short processes arrive frequently, they will be executed quickly, and if long processes arrive, they will be given more CPU time.
  • It does not suffer from convoy effect, which is a problem in other scheduling algorithms like First Come First Serve (FCFS) where a long-running process can hold up other short processes behind it. In SRTF, short processes are given priority, regardless of their arrival time.
  • SRTF can handle both interactive and batch processing well because it prioritizes short processes, which are typically associated with interactive tasks, while still allowing longer processes to run when they are the only ones available.

SRJF Scheduling Algorithm Drawbacks

Shortest Remaining Job First (SRJF) scheduling has some disadvantages, which include:

  • SRTF is a preemptive scheduling algorithm, which means that there is a high context-switch overhead. This is because the algorithm needs to frequently interrupt running processes to allocate the CPU to the process with the shortest remaining time. The overhead of context-switching can significantly impact system performance.
  • The algorithm can potentially lead to starvation of long-running processes if short processes keep arriving. This is because the short processes will always be given priority over long processes, which can result in long processes waiting for an extended period. This can negatively impact the overall system performance.
  • SRTF is a dynamic scheduling algorithm, which means that it requires accurate estimations of the remaining time of processes. Estimating the remaining time of processes can be challenging, and inaccurate estimates can result in inefficient use of system resources.
  • SRTF requires a sophisticated scheduling mechanism that continuously monitors the state of the system, identifies the process with the shortest remaining time, and preemptively allocates the CPU to that process. This can be challenging to implement, especially in complex systems.
  • SRTF is not a fair scheduling algorithm because short processes are always given priority over long processes, which can negatively impact the overall system performance.

D) Round Robing Scheduling: In round-robin scheduling, processes are executed in a cyclic way, where each process gets a fixed amount of time called a time quantum or time slice to run on the CPU. Once a process has used up its time quantum, it is preempted and the next process in the queue is given a chance to run.

The basic idea behind round-robin scheduling is to provide fair CPU time to all processes in the system, preventing any process from monopolizing the CPU. The length of the time quantum can be adjusted depending on the needs of the system and the nature of the processes being run.

Round Robing Scheduling Algorithm Pros

Round-robin scheduling has several advantages, as follow them:

Fairness: Round-robin scheduling provides fair allocation of CPU time to all processes. Each process gets an equal amount of time to execute, which ensures that no process monopolizes the CPU.

Low Latency: Round-robin scheduling has low latency since each process gets a time quantum before being preempted, which means that no process has to wait for a long time to start executing.

Good Response Time: Round-robin scheduling provides good response time to interactive processes since they get a chance to execute frequently.

Easy to Implement: Round-robin scheduling is easy to implement since it only requires a simple queue data structure to maintain the list of processes.

Good for Time-Sharing Systems: Round-robin scheduling is well suited for time-sharing systems where multiple users are sharing the same system since it provides fair allocation of CPU time to all users.

Dynamic Priority: Round-robin scheduling can be modified to incorporate dynamic priority by adjusting the length of the time quantum based on the priority of the process. This allows high-priority processes to get more CPU time than low-priority processes.

Round Robing Scheduling Algorithm Drawbacks

While round-robin scheduling has several advantages, it also has some disadvantages, including:

High Overhead: Round-robin scheduling can result in high overhead due to frequent context switching between processes, which can reduce the overall system performance.

Inefficient for Long Processes: If there are long-running processes in the system, round-robin scheduling may not be the best choice since these processes will have to wait for their turn to execute, even if they do not need to use the CPU for their entire time quantum.

Time Quantum Setting: Setting the appropriate length for the time quantum is crucial for the performance of round-robin scheduling. If the time quantum is too short, the overhead of context switching will be high, and if it is too long, the response time for interactive processes will be slow.

Not Suitable for Real-Time Systems: Round-robin scheduling may not be suitable for real-time systems; because it does not provide any guarantees on the maximum waiting time for a process to execute.

Starvation: Round-robin scheduling can result in the starvation of low-priority processes since they will always be preempted by high-priority processes.

2) Non-Preemptive Scheduling

Non-preemptive scheduling is a scheduling technique where a process or task is allowed to run until it completes or enters a waiting state voluntarily. In non-preemptive scheduling, the CPU is allocated to a process and remains with that process until it either completes or enters a waiting state.

This scheduling technique is also known as cooperative scheduling because the process cooperates with the scheduler by relinquishing the CPU when it is done with its task. Non-preemptive scheduling is useful for processes that need to complete a task without interruption, such as printing a large document or copying a file.

There are different types of Non preemptive scheduling algorithm, including:

A) Shortest Job First Scheduling: In SJF scheduling, the process with the smallest execution time is selected for execution first. This algorithm can be implemented in both preemptive and non-preemptive modes.

In non-preemptive SJF, once a process has been allocated the CPU, it keeps the CPU until it finishes its execution. On the other hand, in preemptive SJF, if a new process arrives with a smaller burst time than the currently executing process, the currently executing process is interrupted, and the new process is executed first.

SJF Scheduling Algorithm Pros

The advantages of Shortest Job First (SJF) scheduling are as follows:

Reduces Waiting Time: SJF scheduling aims to reduce the average waiting time of processes by giving priority to the processes with the shortest execution time. This results in faster completion of processes and reduces the waiting time of other processes in the queue.

Increases Throughput: The SJF scheduling algorithm can improve system throughput by executing processes more efficiently, allowing more processes to be completed within a given time period.

Fairness: SJF scheduling ensures fairness by allocating the CPU time to processes based on their burst time. Shorter processes are given higher priority, which can prevent longer processes from monopolizing the CPU.

Efficient Use of Resources: SJF scheduling ensures that the CPU is utilized efficiently by running shorter processes first, which frees up the CPU for other processes.

No Starvation: SJF scheduling guarantees that every process eventually gets CPU time, as there is no concept of aging. Even if a process has a long burst time, it will eventually get its turn.

SJF Scheduling Algorithm Drawbacks

The disadvantages of Shortest Job First (SJF) scheduling are as follows:

Execution Time Prediction: The main disadvantage of SJF scheduling is that it requires accurate information about the execution time of each process, which may not always be available. If the predicted burst time of a process is inaccurate, it can lead to inefficient CPU utilization and increased waiting time.

Prioritization of Short Processes: SJF scheduling gives priority to shorter processes, which can lead to longer processes being starved of CPU time if a large number of short processes are in the queue.

Preemption Overhead: In the case of preemptive SJF scheduling, the overhead of context switching between processes can be high, leading to reduced system performance.

Inherent Delay: In non-preemptive SJF scheduling, longer processes can be delayed, leading to increased waiting time and potentially longer completion times.

Not Suitable for Real-Time Systems: SJF scheduling is not suitable for real-time systems where the response time of a process is critical, as SJF scheduling does not guarantee a fixed response time for any process.

B) First Come First Server Scheduling: First Come First Serve (FCFS) scheduling algorithm operates on the principle of serving tasks in the order they arrive. The first task that arrives is the first one to be served, and so on.

In FCFS scheduling, the CPU is allocated to the first process in the ready queue. The process then runs until it either completes its execution or it goes into a waiting state. Once the first process has finished, the CPU is allocated to the next process in the queue, and so on.

This scheduling algorithm is simple to implement, but it may not be optimal in all situations. For example, if a long-running process arrives first, it will hold the CPU for an extended period, causing shorter processes to wait in the queue, which can lead to longer response times for those tasks

FCFS Scheduling Algorithm Pros

The First Come First Serve (FCFS) scheduling algorithm has some advantages:

Simple to Implement: FCFS is a simple and easy-to-understand scheduling algorithm that does not require complex calculations or heuristics to determine which process to run next.

Fairness: FCFS provides fairness to the processes in the system. Since the processes are served in the order they arrive, no process is given priority over another.

No Starvation: In FCFS, every process eventually gets a chance to run, even if it has to wait for a long time. This ensures that no process is left behind or starved of CPU time.

No Overhead: FCFS has no overhead associated with scheduling decisions, which means that it is less likely to cause CPU overhead or consume additional resources.

Predictable Behavior: FCFS provides predictable behavior, as the execution order of the processes is determined solely by their arrival time. This makes it easier to estimate and forecast the performance of the system.

FCFS Scheduling Algorithm Drawback

Although First Come First Serve (FCFS) scheduling algorithm has some advantages, it also has some disadvantages, including:

Poor Turnaround Time: FCFS scheduling can lead to poor turnaround time, especially if a long-running process arrives first. This is because shorter processes have to wait in the queue, resulting in a longer waiting time and hence a longer turnaround time.

Inefficient Utilization of CPU: In FCFS, the CPU is allocated to the first process in the queue, regardless of its length. This can lead to inefficient utilization of the CPU, as a long-running process may hold the CPU for an extended period, while shorter processes have to wait.

No Priority: FCFS does not take into account the priority of the process. This can be a problem in real-time systems, where certain tasks require higher priority than others.

Convoy Effect: FCFS can lead to the convoy effect, where a long-running process can hold up the queue of shorter processes behind it, resulting in a longer waiting time and overall inefficiency.

Not Suitable for Interactive Systems: FCFS is not suitable for interactive systems, where quick response time is essential, and the user’s interaction is critical.

C) Longest Job First Scheduling: Longest Job First (LJF) scheduling is a CPU scheduling algorithm that selects the process with the largest CPU burst time to execute first. In other words, the process with the longest expected processing time is given the highest priority.

The basic idea behind LJF scheduling is that longer jobs, which typically have higher processing requirements, will take longer to complete, and hence may cause longer wait times for other processes in the queue. By executing the longest job first, the average waiting time of all the processes in the queue can be minimized.

LJF Scheduling Algorithm Pros

The Longest Job First (LJF) scheduling algorithm has several advantages, including:

Minimizes Average Waiting Time: By executing the longest job first, LJF scheduling minimizes the average waiting time for all the processes in the queue. This is because the longer jobs tend to cause longer wait times for other processes, and executing them first can help reduce this effect.

Simple and Easy to Implement: LJF scheduling is a simple and easy-to-implement algorithm that does not require a lot of overhead. This makes it suitable for systems with limited resources or where efficiency is a top priority.

Works Well for Batch Processing: Since LJF scheduling is non-preemptive, it is well suited for batch processing systems where jobs are executed without user interaction. This can help improve the overall system efficiency and throughput.

Provides Fairness: LJF scheduling can provide a fair allocation of resources among processes, as each process is given an equal opportunity to execute based on its CPU burst time.

LJF Scheduling Algorithm Drawbacks

The Longest Job First (LJF) scheduling algorithm also has some disadvantages, including:

Poor Response Time: LJF scheduling may result in poor response time for shorter processes as they have to wait for the longer processes to finish. This can be problematic in interactive systems where user responsiveness is a priority.

Inefficient for Short Processes: LJF scheduling can be inefficient for short processes as they may end up waiting for a long time before they get executed. This can lead to poor system throughput and can reduce the overall efficiency of the system.

Can Cause Starvation: LJF scheduling can cause starvation for shorter processes, especially if there are a large number of long processes in the queue. This means that shorter processes may never get a chance to execute, leading to reduced system efficiency and fairness.

Non-Preemptive Nature: LJF scheduling is a non-preemptive algorithm, which means that once a process starts executing, it cannot be interrupted until it completes its CPU burst. This can lead to longer waiting times for other processes in the queue.

D) Highest Response Ratio Next Scheduling: Highest Response Ratio Next (HRRN) scheduling algorithm selects the process with the highest response ratio as the next process to run. The response ratio is defined as the ratio of the sum of the waiting time and the execution time to the execution time. The idea behind this algorithm is to give priority to processes that have been waiting for a long time and have a short execution time, as they will have a high response ratio.

To implement the HRRN algorithm, the scheduler maintains a list of ready processes and calculates the response ratio for each process in the list. The process with the highest response ratio is selected for execution. If multiple processes have the same highest response ratio, the scheduler selects the one that arrived first.

HRRN Scheduling Algorithm Pros

The HRRN (Highest Response Ratio Next) scheduling algorithm has several advantages, including:

Fairness: HRRN scheduling is a non-preemptive scheduling algorithm that gives priority to processes that have been waiting for a long time and have a short execution time. This ensures that all processes get a chance to run and complete, leading to a fair distribution of CPU time.

High Throughput: HRRN scheduling can achieve a high throughput, as it prioritizes short processes with long waiting times. This ensures that more processes are completed in a shorter amount of time, which can lead to a higher system throughput.

Low Turnaround Time: HRRN scheduling can help reduce the turnaround time for processes. By prioritizing processes with a high response ratio, the algorithm ensures that processes with shorter execution times are completed quickly, which can reduce the overall turnaround time for processes.

Low Waiting Time: HRRN scheduling can also help reduce the waiting time for processes. By prioritizing processes that have been waiting for a long time, the algorithm ensures that processes are executed as soon as possible, which can reduce the overall waiting time for processes.

HRRN Scheduling Algorithm Drawbacks

While HRRN (Highest Response Ratio Next) scheduling has some advantages, it also has some disadvantages, including:

Overhead: The HRRN scheduling algorithm requires a lot of calculations to determine the response ratio for each process in the ready queue. This overhead can be significant, particularly in systems with a large number of processes.

Starvation: HRRN scheduling can lead to starvation of long-running processes. This is because the algorithm always prioritizes processes with the highest response ratio, which may result in long-running processes being repeatedly passed over in favor of shorter processes with higher response ratios.

Unpredictability: The HRRN scheduling algorithm is not very predictable, as the response ratio changes over time as processes wait in the ready queue. This can make it difficult to estimate the completion time for processes, which can be problematic for certain types of applications.

Inefficiency: In some cases, HRRN scheduling can be less efficient than other scheduling algorithms, particularly when there are many long-running processes in the system. This is because the algorithm prioritizes short processes with high response ratios, which may not be the best use of CPU time in all situations.

Final Verdicts

Making ensure, in this post, you have been completely aware about what is CPU Scheduling Algorithms in OS? And different types of CPU Scheduling algorithm in Operating System with ease. If this content is helpful for you, then share it along with your friends, family members or relatives over social media platforms like as Facebook, Instagram, Linked In, Twitter, and more.

Also Read: Multiprogramming Operating System: Example, Types, and Advantage!!

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