This chapter begins with an examination of the three types of processor scheduling, showing how they are related. We see that long-term scheduling and mediumterm scheduling are driven primarily by performance concerns related to the degree of multiprogramming. | Chapter 9 Uniprocessor Scheduling Types of Processor Scheduling Scheduling Algorithms Scheduling An OS must allocate resources amongst competing processes. The resource is allocated by means of scheduling - determines which processes will wait and which will progress. The resource provided by a processor is execution time. Overall Aim of Scheduling The aim of processor scheduling is to assign processes to be executed by the processor over time, in a way that meets system objectives, such as response time, throughput, and processor efficiency. Scheduling Objectives The scheduling function should Share time fairly among processes Prevent starvation of a process Use the processor efficiently Have low overhead Prioritise processes when necessary (. real time deadlines) Types of Scheduling Scheduling and Process State Transitions Long-term scheduling is performed when a new process is created. Medium-term scheduling is a part of the swapping function. Short-term . | Chapter 9 Uniprocessor Scheduling Types of Processor Scheduling Scheduling Algorithms Scheduling An OS must allocate resources amongst competing processes. The resource is allocated by means of scheduling - determines which processes will wait and which will progress. The resource provided by a processor is execution time. Overall Aim of Scheduling The aim of processor scheduling is to assign processes to be executed by the processor over time, in a way that meets system objectives, such as response time, throughput, and processor efficiency. Scheduling Objectives The scheduling function should Share time fairly among processes Prevent starvation of a process Use the processor efficiently Have low overhead Prioritise processes when necessary (. real time deadlines) Types of Scheduling Scheduling and Process State Transitions Long-term scheduling is performed when a new process is created. Medium-term scheduling is a part of the swapping function. Short-term scheduling is the actual decision of which ready process to execute next. Focus of this chapter Nesting of Scheduling Functions Queuing Diagram Scheduling is a matter of managing queues to minimize queuing delay and to optimize performance. Long-Term Scheduling Determines which programs are admitted to the system for processing May be first-come-first-served According to criteria such as priority, I/O requirements or expected execution time Controls the degree of multiprogramming More processes, smaller percentage of time each process is executed Medium-Term Scheduling Part of the swapping function Swapping-in decisions are based on the need to manage the degree of multiprogramming the memory requirements of the swapped-out processes Short-Term Scheduling Short-term scheduler is known as the dispatcher. Executes most frequently to decide which process to execute next Invoked when an event occurs Clock interrupts I/O interrupts Operating system calls Roadmap Types of
