Process scheduling algorithms

Process scheduling algorithms

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  C.K.PITHAWALA COLLEGE OF ENGINEERING& TECHNOLOGY, SURAT Branch:- computer 2nd Year/4th SEM ALA Subject:- Operating System ALA Topic Name:- CPU Scheduling Algorithms Group No:-B4 Roll No. Enrolment No Name Submitted To Manan Shah Divyesh Mistry 403 405 401 420 459 160090107051 160090107049 160090107025 160090107044 160090107059 Shubham Sharma Pakshal Shah Hariom Maurya Pravin Rathod Naitik Vajani Chetan Sir Yogesh Sir
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  Process Scheduling Algorithms:FCFS – SJF – RR , Multiprocessor scheduling : Types , Performance evaluation of the scheduling
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  Contents: • Scheduling Algorithms:FIFO • Scheduling Algorithms: SJF • Scheduling Algorithms: RR • Multiprocessor Scheduling • Performance Evaluation of the Scheduling
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  FIFO • First comefirst serve scheduling method. • Non-preemptive CPU scheduling algorithm. • A queue is maintained containing the list of processes in the CPU. • The processes are dispatched according to their arrival time at a ready queue. CPU Ready queue
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  FIFO Advantages • Simple toimplement • Fine for most of the batch operating systems Disadvantages • It cannot guarantee short response time. • Turnaround time is unpredictable. • Average waiting time is often quite long.
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  FIFO PROCESS BURST TIME P14 P2 7 P3 3 P4 3 P5 5 P1 P2 P3 P4 P5 0 4 11 14 17 22
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  Shortest Job First: SJF • SJF algorithm handles the process based on the length of their CPU cycle time, the process with shortest runtime is completed first. • SJF scheduling algorithm may be preemptive or non-preemptive. • It is optimal only when all the processes are available at the same time and the CPU estimates are available.
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  Shortest Job First: SJF Advantages • Used frequently in long term scheduling. • It reduces average waiting time over FIFO algorithm. • It is appropriate for batch jobs for which run times are knows in advance. Disadvantages • It requires precise knowledge of how long a job or process will run which is not easily available.
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  Shortest Job First: SJF PROCESS BURST TIME P1 5 P2 2 P3 6 P4 4 P2 P4 P1 P3 0 2 6 11 17
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  Round Robin :RR • In RR algorithm, each process is given a limited amount of time slice and after the time expires the system allocates the CPU to next process in the ready queue. • RR is a preeemptive scheduling algorithm. • Here the ready queue is treated as a circular queue and follows FIFO scheme. • The CPU scheduler goes around the ready queue allocating the CPU to each process for given time interval.
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  Round Robin :RR Advantages • It is a simple scheduling algorithm and easy to implement in software. • Round robin scheduling is fair in the sense that every process gets an equal share of the CPU. • If we know the number of processes on the run queue, we can know the worst-case response time for a process. Disadvantages • If slicing time is too low, the processor output is reduced. More time is spent on context switching. • Higher Average Waiting Time • No priority: Round-robin scheduling, like other first-come, first-served methods, doesn't give special priority to more important tasks
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  Round Robin :RR PROCESS BURST TIME P1 5 P2 2 P3 6 P4 4 P3 P2 P3 P4 P1 P3 P4 P1 P3 0 2 4 6 8 10 12 14 15 17 Time Slice = 2 s
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  Multiprocessor Scheduling • Schedulingis two dimensional on a multiprocessor. • Scheduling on a multiprocessor involves three issues: a. The assignment of processes to processors. b. The use of multiprogramming on individual processors. c. The actual dispatching of a process. • A key design issue for a multiprocessor scheduling is the selection of process for execution. • A more sophisticated scheduling based on priority and past usage may lead to a better performance, compared with simpler FIFO algorithm.
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  Multiprocessor Scheduling • Multiprocessingenvironment can be achieved with the help of threads. • An application can be implemented as a set of threads, which cooperate and execute concurrently in the same address space. • Four general approaches of multiprocessor thread scheduling are: • Load sharing : Here threads are not assigned to a particular processor, when a processor is idle, it selects a thread from a global queue serving all processors. • Gang scheduling : A set of related threads is scheduled to run on a set of processors at the same time, on a one-to-one basis. • Dedicated processor scheduling : When application is scheduled, its threads are assigned to a processor. • Dynamic scheduling : No. of threads are altered dynamically by the application.
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  Performance Evaluation ofthe Scheduling • Performance evaluation of CPU Scheduling algorithm is done by the following 3 methods: • Deterministic Modelling : It uses analytic method. It takes a particular predetermined workload and defines the performance of each algorithm for that workload. • Queuing Models : In this method, a queueing model is constructed so that queue lengths and waiting time can be predicted for the given scheduling algorithm. • Simulations : Simulations creates a model of the system, then processes statistical on real data based on which necessary evaluation is done.
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  END OF PRESENTATION THANKYOU