Week 5A: CPU Scheduling

Multiprogramming

maximum CPU utilization can be obtained

CPU-I/O Burst Cycle

process execution consists of a cycle of CPU execution and I/O wait; CPU burst followed by I/O burst

CPU scheduler

selects from among the processes in ready queue, and allocates a CPU core to one of them

Preemptive

a process is forced out of the CPU even if it doesn't need to; can result in race conditions when data are shared among several processes; virtually all modern operating systems including Windows, MacOS, Linux, and UNIX use this scheduling algorithm

Nonpreemptive

once a process is selected to run, it won't be forced to leave even if a shorter process arrives in the ready queue

Dispatcher module

gives control of the CPU to the process selected by the CPU scheduler; this involves switching context, switching to user more, jumping to the proper location in the user program to restart that program

Dispatch latency

time it takes for the dispatcher to stop one process and start another running

CPU utilization

[ Scheduling Criteria ] keep the CPU as busy as possible (maximize)

Throughput

[ Scheduling Criteria ] number of processes that complete their execution per time unit (maximize)

Turnaround time

[ Scheduling Criteria ] amount of time to execute a particular process (minimize)

Waiting time

[ Scheduling Criteria ] amount of time a process has been waiting in the ready queue (minimize)

Response

[ Scheduling Criteria ] amount of time it takes from when a request was submitted until the first response is produced (minimize)