FIT2070 Lecture Notes - Lecture 9: Computer Multitasking, Transaction Processing System
13 Jun 2018
School
Department
Course
Professor
L9 - Processor Scheduling (in Uniprocessor)
● Aim to maximize the way the processor meets the system objectives like response
time, throughput and processor efficiency
● Broken down into these functions:
○ Long term scheduling
■ Decision to add to the pool of processes to be executed
○ Medium scheduling
■ Decision to add to the number of processes that are partially or fully in
main memory
○ Short Term scheduling
■ Decision as to which available process will be executed by the
processor
Long Term Scheduling
● Controls the degree of multiprogramming
● Determines which programs are admitting to the system for processing
Medium Term Scheduling
● Part of the swapping function
○ Based on the need to manage the degree of multiprogramming
Short Term Scheduling
● Dispatcher/CPU scheduler : decision of which process to execute next
● Run most frequently
● Invoked whenever an event occurs (clock interrupts/ IO interrupts…)
● Allocate processor time to optimise certain aspects of system behaviour
● Criteria
○ response time
○ Throughput - how many jobs and processes the processor can support in a
certain amount of time
Selection Function
● Determines which process, among ready processes, is selected next for execution
● Based on priority, resource requirements, or execution characteristics of the process
Decision Mode
● Non-preemptive
○ Once a process is in the running state it cannot be interrupted
● Preemptive
○ Currently running process may be interrupted and moved to Ready state by
the OS
○ May occur when new process arrives on an interrupt
Scheduling Policies
● First-Come-First-Served
Document Summary
Aim to maximize the way the processor meets the system objectives like response time, throughput and processor efficiency. Decision to add to the pool of processes to be executed. Decision to add to the number of processes that are partially or fully in main memory. Decision as to which available process will be executed by the processor. Determines which programs are admitting to the system for processing. Based on the need to manage the degree of multiprogramming. Dispatcher/cpu scheduler : decision of which process to execute next. Invoked whenever an event occurs (clock interrupts/ io interrupts ) Allocate processor time to optimise certain aspects of system behaviour. Throughput - how many jobs and processes the processor can support in a certain amount of time. Determines which process, among ready processes, is selected next for execution. Based on priority, resource requirements, or execution characteristics of the process. Once a process is in the running state it cannot be interrupted.
