Chapter 4 - Processor Management. Introduction - Processor Management. Process Manager Job Scheduling Process Scheduling Interrupt Management. Introduction - Processor Management. Single-user systems the processor is busy only when the user is executing a job at other times it is idle.
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A single processor can be shared by several jobs or processes if the OS has:
to determine when to stop one job & proceed with another
in charge of job scheduling
in charge of process scheduling
Takes over after a job has been placed on the READY queue by the Job Scheduler
manages jobs swapped out & in to allow jobs to be completed faster
See Fig. 4.1 p.79
As a job moves through the system, it’s always in one of five states (or at least three)
See Fig. 4.2 p.79
Each process in a system is represented by data structures (PCB) that contain basic job information
See Fig. 4.3 p.80
See Fig. 4.4 p.82
Before the OS can schedule jobs in a multiprogramming environment, it needs to resolve three system limitations:
What is a “good” process scheduling policy?
“Good” process scheduling policy contradictions
Problem: Job claims the CPU for a very long time before issuing an I/O request
Solution: Process Scheduler uses a timing mechanism and periodically interrupts running processes when a predetermined slice of time has expired.
Six common process scheduling algorithms
See Fig. 4.5 & 4.6 p.85
See Fig. 4.7 p.86
See Fig. 4.8 & 4.9 p.88-89
time slice is called a time quantum & its size is crucial to system performance
These rules are used in some systems are flexible
See Fig. 4.10&11 p.90-91
Four primary methods of movement
See Tab 4.1 p.95