Ch. 9 PPT Flashcards
What is the aim of process scheduling?
Execute processes in a way such that system objectives are met
What is long term scheduling?
The decision to add to the pool of processes to be executed
What is medium term scheduling?
The decision to add the number of processes that are partially or fully in main memory.
What is short-term scheduling?
The decision as to which available process will be executed by the processor
What is IO scheduling?
The decision as to which process’s pending IP request shall be handled by an available IO device
What is the long-term scheduler?
It determines which programs are admitted to the system for processing, controlling the degree of multiprogramming
What is the medium-term scheduler?
Part of the process swapping function, makes swaps based upon memory requirements
What is the short term scheduler?
The dispatcher, decides what to execute next. Invoked when something might become blocked.
What is the main objective of the short term scheduler?
Optimize certain aspects of system behavior
What is user-oriented criteria for short term?
Relate to the user when determining what to do. like based on response time in an interactive system
What is system-oriented criteria for short term?
Focus in on efficient processor use. not as important on single user systems
What is decision mode?
It specifies the instances in time when the decision function is executed
What is nonpreemptive decision mode?
A process will continue running until it is blocked out
What is preemptive decision mode?
A currently running process can become blocked by the OS and moved to the ready state
What is first-come-first-served?
A scheduling policy in which a FIFO queue is implemented. Works better for large processes
What is round robin?
Scheduling policy in which processes are interrupted at regular intervals and swapped out. Also known as time slicing
What is shortest process next?
A scheduling policy in which the process with the shortest processing time is executed next. Might starve out larger processes
What is shortest remaining time?
A preemptive version of shortest process next. Same deal
What is highest response ratio next?
Choose the process with the greatest ratio of waiting time + expected service time to expected service time next.
How is unix scheduling handled?
Round robin within propriety queues
What are bands?
A way of optimizing access to blocked devices by quickly responding to system calls
What is fair share scheduling?
Scheduling decisions based on process sets, fairly distributing resources
