SchedulingFeb10

SchedulingFeb10 - ProcessScheduling B.Ramamurthy Page1...

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10/16/10 Page 1 Process Scheduling B.Ramamurthy
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10/16/10 Page 2 Introduction An important aspect of multiprogramming is  scheduling. The resources that  are  scheduled are IO and processors.  The goal is to achieve High processor utilization High throughput number of processes completed per unit time Low response time time elapse from the submission of a request to the  beginning of the response
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10/16/10 Page 3 Topics for discussion Motivation Types of scheduling Short-term scheduling Various scheduling criteria Various algorithms Priority queues First-come, first-served Round-robin Shortest process first Shortest remaining time and others
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10/16/10 Page 4 The CPU-I/O Cycle We observe that processes require alternate  use of processor and I/O in a repetitive  fashion Each cycle consist of a CPU burst (typically of  5 ms) followed by a (usually longer) I/O burst  A process terminates on a CPU burst CPU-bound processes have longer CPU  bursts than I/O-bound processes 
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10/16/10 Page 5 CPU/IO Bursts Bursts of CPU usage alternate with periods of I/O  wait a CPU-bound process an I/O bound process
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10/16/10 Page 6 Motivation Consider these programs with processing- component and IO-component indicated by  upper-case and lower-case letters respectively.   A1   a1    A2   a2     A3 0    30    50   80   120 130   ===> JOB A   B1   b1   B2 0    20   40   60  ====> JOB B   C1  c1   C2   c2  C3  c3   C4   c4    C5   0  10   20    60  80  100 110  130  140  150 =>JOB  C
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10/16/10 Page 7 Motivation The starting and ending time of each  component are indicated beneath the  symbolic references (A1, b1 etc.) Now lets consider three different ways for  scheduling: no overlap, round-robin, simple  overlap. Compare utilization U =                   time CPU busy / total run time
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10/16/10 Page 8 Scheduling Criteria CPU utilization – keep the CPU as busy as  possible Throughput – # of processes that complete 
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SchedulingFeb10 - ProcessScheduling B.Ramamurthy Page1...

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