Preemptive and Non-Preemptive Kernel

The fundamental building block of an operating system, the kernel controls actions involving the CPU, memory, and input/output devices. These resources are distributed to various tasks or processes according to the kernel's scheduling mechanism.

The kernel is the most crucial element of an operating system and is in charge of managing system resources and offering services to user programs. The use of a preemptive or non-preemptive kernel is one of the important choices an operating system designer must make.

A preemptive kernel is one that can switch to another process in the middle of a running one without the running process's consent. As a result, the kernel has the ability to terminate any process that is now active and switch its resources to one that is awaiting execution. The scheduler in a preemptive kernel is in charge of selecting which process gets the CPU next. Real-time operating systems, where it is essential to make sure that processes fulfill their deadlines, frequently employ preemptive kernels.

Comparison Between Preemptive and Non-Preemptive Kernel

Kernels utilize two different kinds of scheduling algorithms: preemptive and non-preemptive. The operating system can pause a process that is currently running in a preemptive kernel in order to give the CPU a higher-priority task. Better responsiveness and resource management are made possible by this method, but it may also lead to higher overhead and a possible decline in total system performance.

• A non-preemptive kernel, in contrast, enables a running job to retain the CPU until it freely releases the processor. This strategy can save overhead and boost system throughput, but it can also result in sluggish response and the possible starving of low-priority processes.

• The central element of an operating system, or kernel, controls system resources and offers a platform on which programs may execute. The scheduler, which is in charge of assigning CPU time to processes, is part of the kernel.

• Process scheduling is the primary distinction between preemptive and non-preemptive kernels.

The scheduler can halt a running process in a preemptive kernel to make room for another one. As a result, if the scheduler decides that another process has a higher priority, it may decide to pre-empt a current process. Either a timer interrupt or the readiness of a higher priority task might cause this. A non-preemptive kernel, in contrast, prevents the scheduler from interrupting an active process. Instead, for another process to execute, a process must actively give up control of the CPU.

Preemptive vs Non-Preemptive Scheduling Algorithms

Both preemptive and non-preemptive kernels can be utilized with a wide variety of scheduling methods. The system's unique requirements and the workload it is expected to manage to determine the scheduling algorithm to use. The properties of some of the most popular scheduling algorithms are listed below −

First Come, First Served (FCFS)

A non-preemptive scheduling mechanism called FCFS allots CPU time to processes in the chronological order in which they arrive. This implies that the first process to arrive will receive CPU time first. FCFS's key benefit is that it is straightforward and simple to deploy. Nevertheless, if the initial process takes a long time to finish, it may result in lengthy wait times for processes that come later.

Shortest Job First (SJF)

A non-preemptive scheduling mechanism called FCFS allots CPU time to processes in the chronological order in which they arrive. This implies that the first process to arrive will receive CPU time first. FCFS's key benefit is that it is straightforward and simple to deploy. Nevertheless, if the initial process takes a long time to finish, it may result in lengthy wait times for processes that come later.

Round Robin (RR)

With the help of the preemptive scheduling algorithm RR, CPU time is allotted to processes in set time slices. The scheduler gives each process a certain amount of time to complete its work before moving on to the next process in the queue. The primary benefit of RR is that it guarantees equitable CPU time distribution to all programs and can reduce waiting times for low-priority tasks. The frequent context shift, meanwhile, might also result in excessive overhead.

Priority Scheduling

A scheduling method known as priority scheduling gives processes different priority levels based on their significance or urgency. For real-time applications or mission-critical systems, higher-priority processes are granted CPU time before lower-priority activities. It is possible to implement priority scheduling with either a preemptive or non-preemptive kernel.

Advantages and Disadvantages

There are certain benefits to preemptive scheduling algorithms and kernels over non-preemptive ones. Preemptive scheduling's key benefit is that it may make sure high-priority programs get CPU time when they require it. This is crucial for real-time systems since a processing lag might have negative effects. Also, by requiring programs to give up control of the CPU after a predetermined length of time, preemptive scheduling can assist prevent processes from monopolizing the CPU. This can enhance system performance generally and lessen the chance of crashes brought on by resource exhaustion.

Preemptive scheduling, but, might potentially have significant drawbacks. Due to the frequent context switches, one significant disadvantage is that it might result in high overhead. Context switching is the time- and resource-consuming operation of saving the state of one process while it is still operating and loading the state of the next process. If the system contains many processes that preempt often, this might become an issue.

Scheduling algorithms and non-preemptive kernels both have benefits and drawbacks. Due to the scheduler's lack of necessity to pause active processes, non-preemptive scheduling can decrease the overhead of context switching. Non-preemptive scheduling may also be more straightforward and straightforward to use than preemptive scheduling.

Non-preemptive scheduling, however, can also result in higher wait times for low-priority activities, which can negatively affect the performance of the entire system. Moreover, it does not ensure that high-priority programs would receive CPU time when required.

Real - World Examples

Depending on their particular needs, several real-world operating systems utilize both preemptive and non-preemptive scheduling methods. For instance, Windows utilizes a priority-based scheduling algorithm with a preemptive kernel to prioritize processes according to their significance. Moreover, Linux employs a preemptive kernel with a number of scheduling algorithms, such as a priority-based scheduler and a round-robin scheduler.

Early iterations of macOS, in contrast, had a cooperative multitasking technique with a non-preemptive kernel that required programs to voluntarily cede CPU control. Preemptive kernels are the hybrid scheduling method used in current versions of macOS, which combines priority-based and time-sliced scheduling.

Conclusion

In conclusion, the system's unique requirements and the workload it is anticipated to handle determine whether a preemptive or non-preemptive kernel and scheduling algorithm should be used. High overhead from frequent context switches might result from preemptive scheduling, which can guarantee that high-priority activities receive CPU time when they are required. Non-preemptive scheduling can save overhead, but it also increases the amount of time low-priority processes must wait before moving on. Both scheduling algorithm types are prevalent in real-world operating systems, therefore when developing an operating system, developers must carefully weigh the benefits and drawbacks of each.