4.1.4 Explain how the queuing routine and the scheduler work together to load application programs.
Long-term Scheduling
• The long-term, or admission, scheduler decides which jobs or processes are to be admitted to the ready queue.
• When an attempt is made to execute a program, its admission to the set of currently executing processes is either authorized or delayed by the long-term scheduler.
• Thus, this scheduler dictates what processes are to run on a system, and the degree of concurrency to be supported at any one time Medium-term Scheduling
• The mid-term scheduler may decide to swap out a process which :
- has not been active for some time, or a process which has a low priority,
- or a process which is page faulting frequently,
- or a process which is taking up a large amount of memory in order to free up main memory for other processes, swapping the process back in later when more memory is available,
- or when the process has been unblocked and is no longer waiting for a resource. Short-term Scheduling
• Also known as the dispatcher.
• Decides which of the ready, in-memory processes are to be executed (allocated a CPU) next following a clock interrupt, an IO interrupt, an operating system call or another form of signal.
• Makes scheduling decisions much more frequently than the long-term or mid-term schedulers Scheduling Algorithms
• In computer science, a scheduling algorithm is the method by which threads, processes or data flows are given access to system resources.
• Example: processor time, communications bandwidth.
• This is usually done to load balance a system effectively or achieve a target quality of service.
• Scheduling algorithms:
- first in first out (FIFO)
- round robin scheduling
- shortest remaining time
- shortest remaining time
-priority
-multilevel queue
Long-term Scheduling
• The long-term, or admission, scheduler decides which jobs or processes are to be admitted to the ready queue.
• When an attempt is made to execute a program, its admission to the set of currently executing processes is either authorized or delayed by the long-term scheduler.
• Thus, this scheduler dictates what processes are to run on a system, and the degree of concurrency to be supported at any one time Medium-term Scheduling
• The mid-term scheduler may decide to swap out a process which :
- has not been active for some time, or a process which has a low priority,
- or a process which is page faulting frequently,
- or a process which is taking up a large amount of memory in order to free up main memory for other processes, swapping the process back in later when more memory is available,
- or when the process has been unblocked and is no longer waiting for a resource. Short-term Scheduling
• Also known as the dispatcher.
• Decides which of the ready, in-memory processes are to be executed (allocated a CPU) next following a clock interrupt, an IO interrupt, an operating system call or another form of signal.
• Makes scheduling decisions much more frequently than the long-term or mid-term schedulers Scheduling Algorithms
• In computer science, a scheduling algorithm is the method by which threads, processes or data flows are given access to system resources.
• Example: processor time, communications bandwidth.
• This is usually done to load balance a system effectively or achieve a target quality of service.
• Scheduling algorithms:
- first in first out (FIFO)
- round robin scheduling
- shortest remaining time
- shortest remaining time
-priority
-multilevel queue
Comments
Post a Comment