Transcription of Scheduling: Introduction - University of Wisconsin–Madison
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Scheduling: Introduction - University of Wisconsin–Madison
7 scheduling : IntroductionBy now low-levelmechanismsof running processes ( , context switch-ing) should be clear; if they are not, go back a chapter or two, and read thedescription of how that stuff works again. However, we have yet to un-derstand the high-levelpoliciesthat an OS scheduler employs. We willnow do just that, presenting a series ofscheduling policies(sometimescalleddisciplines) that various smart and hard-working people have de-veloped over the origins of scheduling , in fact, predate computer systems; earlyapproaches were taken from the field of operations management and ap-plied to computers. This reality should be no surprise: assembly linesand many other human endeavors also require scheduling , and many ofthe same concerns exist therein, including a laser-like desire for thus, our problem:THECRUX: HOWTODEVELOPSCHEDULINGPOLICYHow should we develop a basic framework for thinking aboutscheduling policies? What are the key assumptions?
FIFO has a number of positive properties: it is clearly simple and thus easy to implement. And, given our assumptions, it works pretty well. Let’s do a quick example together. Imagine three jobs arrive in the system, A, B, and C, at roughly the same time (T arrival = 0). Because FIFO has to put some job first, let’s assume that while they ...
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