Lec18-Scheduling I

Lec18-Scheduling I - National University of Computer &...

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Operating System Operating System Spring 09 Spring 09 National University National University Lec18-Scheduling Lec18-Scheduling Prepared by Prepared by Uzma Maroof Uzma Maroof [email protected] [email protected]
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2 Reference Material Reference Material Chapter 2 CPU Scheduling Operating system concepts Sixth edition Silberschatz
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3 Scheduling Scheduling Short term scheduler (CPU Schedular) Whenever the CPU becomes idle, a process must be selected for execution The Process is selected from the Ready queue Ready queue is not necessarily a FIFO queue It can be Priority based A Tree Unordered linked list etc
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4 When to select a new process to When to select a new process to Run Run Four circumstances New Exit Admit Release Running Ready Dispatch Time-out Blocked Event occurs Event wait 1. Wait for I/O/ waitpid()/ P()/ Acquire() etc 2. Interrupt occurs, move from Running to Ready 3. Event I/O Completion/ exit(0) / V() / Release() 4. A Process terminates
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5 Only the case 1 and 4 Must select a new process, if any, from the Ready Queue Non Preemptive Scheduling Non Preemptive Scheduling New Exit Admit Release Running Ready Dispatch Time-out Blocked Event occurs Event wait 1. Wait for I/O/ waitpid()/ P()/ Acquire() etc 4. A Process terminates
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6 Non Preemptive Scheduling Non Preemptive Scheduling Once the CPU has been allocated to a process The process keeps it until It Terminates Or has to wait for: I/O Mutex Child process Semaphore Conditional Variables etc There is no way, to get the CPU back, FORCEFULLY
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This note was uploaded on 01/23/2011 for the course COE 10001 taught by Professor Abad during the Spring '09 term at Alfaisal University.

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Lec18-Scheduling I - National University of Computer &...

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