What is CPU Scheduling?
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 any resource like I/O etc, thereby making full use of CPU. The aim of CPU scheduling is to make the system efficient, fast and fair.
Why do we need Scheduling?
A typical process involves both I/O time and CPU time. In a uni programming system like MS-DOS, time spent waiting for I/O is wasted and CPU is free during this time. In multi programming systems, one process can use CPU while another is waiting for I/O. This is possible only with process scheduling.
Multiple-Processor Scheduling in Operating System
In multiple-processor scheduling multiple CPU’s are available and hence Load Sharing becomes possible. However multiple processor scheduling is more complex as compared to single processor scheduling. In multiple processor scheduling there are cases when the processors are identical i.e. HOMOGENEOUS, in terms of their functionality, we can use any processor available to run any process in the queue.
Two State Process Model
Two-state process models are:
Running and Not Running
Running :In the Operating system, whenever a new process is built, it is entered into the system, which should be running.
Not Running :The process that are not running are kept in a queue, which is waiting for their turn to execute. Each entry in the queue is a point to a specific process.
First-come, First-served
Layaknya mengantri pada restoran, pada Scheduling, terdapat algoritma yang bernama First-come, First-serve dimana algoritma ini merupakan algoritma paling sederhana, tetapi algoritma ini dapat menyebabkan short processes menunggu proses yang sangat lama.
What is meant by CPU Burst and I/O Burst?
Think of a “burst” as a brief stretch of “run as fast as you can go until you can’t.”
A CPU bursts when it is executing instructions; an I/O system bursts when it services requests to fetch information. The idea is that each component operates until it can’t.
A CPU can run instructions from cache until it needs to fetch more instructions or data from memory. That ends the CPU burst and starts the I/O burst. The I/O burst read or writes data until the requested data is read/written or the space to store it cache runs out. That ends an I/O burst.
IMPLEMENTING REAL-TIME SCHEDULING IN A TIME-SHARING OPERATING SYSTEM
Real-time scheduling berkaitan dengan cara memenuhi batasan waktu tugas yang berjalan dalam lingkungan waktu nyata. Untuk menghindari perilaku tak terduga, distribusi sumber daya sistem juga harus dijadwalkan.
Comparison of Scheduling Algorithms
Sekarang, Anda pasti sudah memahami bagaimana CPU dapat menerapkan algoritme penjadwalan yang berbeda untuk menjadwalkan proses. Sekarang, mari kita periksa keuntungan dan kerugian dari setiap algoritma penjadwalan yang telah kita pelajari sejauh ini.
Priority CPU Scheduling
In this tutorial we will understand the priority scheduling algorithm, how it works and its advantages and disadvantages. In the Shortest Job First scheduling algorithm, the priority of a process is generally the inverse of the CPU burst time, i.e. the larger the burst time the lower is the priority of that process.
In case of priority scheduling the priority is not always set as the inverse of the CPU burst time, rather it can be internally or externally set, but yes the scheduling is done on the basis of priority of the process where the process which is most urgent is processed first, followed by the ones with lesser priority in order.
Scheduling in Real-Time Systems
Sebuah real-time scheduling system terdiri dari scheduler, jam, dan elemen perangkat keras pemrosesan. Dalam sistem real-time, proses atau tasks memiliki schedulability; tasks diterima oleh real-time system dan diselesaikan sebagaimana ditentukan oleh task deadline tergantung pada karakteristik scheduling algorithm.