CPU scheduling is a process which allows one process to use the CPU while the execution of another process is on hold(in waiting state) due to unavailability of. CPU Scheduling Algorithms are used to assign the processes to the CPU. There are various CPU Scheduling Algorithms. Practice Problems based on. Avg. Wait = 0+8+14+15+24 = 61/5 = ms Avg. TAT = 8+14+15+24+27 = ms. Shortest Job First. P5. P2. P1. P4. CPU Scheduling Exercises. Problem 1.
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What is CPU Scheduling?
Schfduling is CPU Scheduling? The scheduler selects from among the processes in memory that are ready to execute, and allocates the CPU to one of them.
The Process Scheduler then alternately selects jobs from each queue and assigns them to the CPU based on the algorithm assigned to the queue.
It is the only method that can be used on certain hardware platforms, because It does not require the special hardware for example: Schsduling process is assigned a priority.
Operating System Scheduling algorithms
To decide which process to execute first and which process to execute last to achieve maximum CPU utilisation, computer scientists have defined some algorithms, they are:. The dispatcher is the module that gives control of the CPU to the process selected by the short-term scheduler.
When a process switches from the numegicals state to the ready state for example, when an interrupt occurs. It is the average number of processes residing in the ready queue waiting for their turn to get into the CPU.
At times it is necessary to run a certain task that has a higher priority before another task although it is running. In general CPU utilization and Throughput are maximized and other factors are reduced for proper optimization. We will be discussing all the scheduling algorithms, one by one, in detail ccpu the next tutorials.
Priority scheduling is a non-preemptive algorithm and one of the most common scheduling algorithms in batch systems. The time taken by the dispatcher to stop numericalss process and start another process is known as the Dispatch Latency. The dispatcher should be as fast as possible, given that it is invoked during every process switch.
Process with highest priority is to be executed first and so on. When a process terminates. Non-preemptive algorithms are designed so that once a process enters the running state, it cannot be preempted until it completes its allotted time, whereas the preemptive scheduling is based on priority where a scheduler may preempt a low priority running process anytime when a high priority process enters into a ready state.
The processor is allocated to the job closest to completion but it can be preempted by a newer ready job with shorter time to completion. Whenever the CPU becomes idle, the operating numeriicals must select one of cpk processes in the ready numericalls to be executed. In this type of Scheduling, the tasks are usually assigned with priorities.
It is the total number of processes completed per unit time or rather say total amount of work done in a unit of time. Once a process is executed for a given numericale period, it is preempted and other process executes for a given time period.
There are many different criterias to check when considering the “best” scheduling algorithm, they are:. Another component involved in the CPU scheduling function is the Dispatcher.
The interval from time of submission of the process to the time of completion of the process Wall clock time. There is a choice, however in circumstances 2 and 3. The sum of the periods spent waiting in the ready queue amount of time a process has been waiting in the ready queue to acquire get control on the CPU. The selection process is carried out by the short-term scheduler or CPU scheduler.
This scheduling method is used by the Microsoft Windows 3. Dispatch Latency can be explained using the below figure: In circumstances 1 and 4, there is no choice in terms of scheduling.
A Process Scheduler schedules different processes to be assigned to the CPU based on particular scheduling algorithms.
A new process if one exists in the ready queue must be selected for execution. Switching context Switching to user mode Jumping to the scgeduling location in the user program to restart that program from where it left last time. Amount of time it takes from when a request was submitted until the first response is produced. Remember, it is the time till the first response and not the completion of process execution final response.
The aim of CPU scheduling is to make the system efficient, fast and fair.