Lecture21nFull - COT 4600 Operating Systems Spring 2011...

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Click to edit Master subtitle style 8/1/11 Lecture 21 COT 4600 Operating Systems Spring 2011 Dan C. Marinescu Office: HEC 304 Office hours: Tu-Th 5:00-6:00 PM
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Lecture 21 8/1/11 Lecture 21 - Thursday April 7, 2011 n Last time: ¨ Scheduling n Today: ¨ The scheduler ¨ Multi-level memories n Next Time: ¨ Memory characterization ¨ Multilevel memories management using virtual memory ¨ Adding multi-level memory management to virtual memory ¨ Page replacement algorithms 22
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Lecture 21 8/1/11 The scheduler n The system component which manages the allocation of the processor/core. n It runs inside the processor thread and implements the scheduling policies. n Other functions ¨ Determines the burst ¨ Manages multiple queues of threads Lecture 20 33
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Lecture 21 8/1/11 CPU burst n 44 Lecture 20
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Lecture 21 8/1/11 Estimating the length of next CPU burst n Done using the length of previous CPU bursts, using exponential averaging 1 0 , 3. burst CPU next for the value predicted 2. burst CPU of length actual 1. 1 = = + α τ n th n n t ( 29 . 1 1 n n n t - + = = 55 Lecture 20
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Lecture 21 8/1/11 Exponential averaging n l =0 ¨ ¨ Recent history does not count n l =1 ¨ &n+1 = & t n ¨ Only the actual last CPU burst counts n If we expand the formula, we get: l n +1 = 5 t n +(1 - t )t tn -1 + … +( 1 - “ )j tn - j + … +( 1 - “ )n +1 “ 0 n Since both ± and (1 - & ) are less than or equal to 1, each successive term has less weight than its predecessor 66 Lecture 20
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Lecture 21 8/1/11 Predicting the length of the next CPU burst 77 Lecture 20
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Lecture 21 8/1/11 Multilevel queue n Ready queue is partitioned into separate queues each with its own scheduling algorithm : ¨ foreground (interactive) % RR ¨ n Scheduling between the queues
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This note was uploaded on 07/30/2011 for the course COP 4600 taught by Professor Montagne during the Spring '08 term at University of Central Florida.

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Lecture21nFull - COT 4600 Operating Systems Spring 2011...

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