L4-ProcessScheduling

L4-ProcessScheduling - Process Scheduling CSIS0230A Lecture...

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Process Scheduling CSIS0230A Lecture Four Basic terms & definitions Scheduling algorithms Case studies
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Recommended Reading Chapter 8 of Operating Systems, 3rd edition by Deitel et. al except sections 8.9 & 8.10 CSIS0230A Principles of Operating Systems 2
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References Chapter 8, 20 & 21 of Operating Systems, 3rd edition by Deitel et. al Chapter 9 & 10 of Operating Systems: Internals and Design Principles, 6th edition by William Stallings Chapter 5 of Operating System Principles, 7th edition by Silberschatz et. al Chapter 4 of Operating Systems - A Concept-Based Approach, 2nd edition by D.M. Dhamdhere A. Kumar, “Multiprocessing with the Completely Fair Scheduler”, IBM CSIS0230A Principles of Operating Systems 3
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Processor Scheduling Is the activity of selecting the next process/thread to be serviced by the processor(s) Scheduling policy used by the OS influences Quality of service provided to users Effective use of resources System performance CSIS0230A Principles of Operating Systems 4
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Scheduling Levels High-level / Job / Long-term scheduling Deals with creating a new process Controls number of processes in system at one time degree of multiprogramming Intermediate-level / Medium-term scheduling Deals with swapping processes in/out Responds to fluctuations in system load Low-level / Short-term scheduling What process should we run next? Assigns processors to processes CSIS0230A Principles of Operating Systems 5
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Scheduling Terms & Concepts CPU-bound (compute-bound) process When running, tends to use all the processor time that allocated to it I/O-bound process When running, tends to use the processor only briefly before generating I/O request and relinquishes the processor Service time - total of CPU time and I/O time required by a task to complete its operation Depends on the application behavior CSIS0230A Principles of Operating Systems 6
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Scheduling Terms & Concepts (2) Waiting time - amount of time a process has been waiting in the ready queue Depends on the scheduling policy Response time - amount of time it takes from when a request was submitted until the response is produced An important factor of interactive tasks Turnaround time - amount of time to execute a particular process (from submission to complete servicing) An important factor of non-interactive tasks CSIS0230A Principles of Operating Systems 7
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Scheduling Terms & Concepts (3) Throughput - average # of processes that complete their execution per time unit Fairness - all similar processes are treated the same, and no process can suffer indefinite postponement due to scheduling Predictability - a given process should run in about the same amount of time under similar system loads A wide variation in response or turnaround time is distracting to users CSIS0230A Principles of Operating Systems 8
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Preemptive vs. Nonpreemptive Scheduling Preemptive Running process may be switched to Ready state
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