lecture4

lecture4 - Process Scheduling and Implementation Scheduling...

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Process Scheduling and Implementation Scheduling Last lecture we discussed half of process scheduling, when a process givesupthe CPU. Today we start with the other half, which process is scheduled to takeits place. This is our first introduction to scheduling algorithms which will be a repeating topic in the course. Operating systems schedule pages of memory ,disk blocks, and several other things. The algorithms discussed today and variations on them tuned for specific other applications are important tools for your bag of OS degisn tricks. Whynot just pick a process at random? Congratulations, that’ sascheduling discipline - random scheduling. It has the advantages that it’ seasy to implement, but givessomewhat unpredicatable results. N. B. if you have a homogeneous set of jobs, it may be an effective scheduling mechanism! All scheduling mechanisms involvedesign tradeoffs. The relevant parameters to trade offinprocess scheduling include: Response Time Time for processes to complete. the OS may want to favorcertain types of processes or to minimize a statis- tical property likeaverage time Implementation Time This includes the complexity of the algorithm and the maintenance Overhead Time to decide which process to schedule and to collect the data needed to makethat selection Fairness To what extent are different users’ processes treated differently Some Scheduling Disciplines First-In-First-Out (FIFO) and Round Robin The ready queue is a single FIFO queue where the next process to be run is the one at the front of the queue. Processes are added to the back of the ready queue. This is a simple discipline to implement, and with equal sized quanta on a preemptive scheduling system results in each process getting roughly an equal time on the processor.
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lecture4 - Process Scheduling and Implementation Scheduling...

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