ECE344-Lecture20-Scheduling

ECE344-Lecture20-Scheduling - Lecture 20: Scheduling David...

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1 Lecture 20: Scheduling David Lie ECE344 University of Toronto
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2 ECE344: Operating Systems Overview Purpose of scheduling Scheduling Algorithms Multiprocessor Issues Modern Systems
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3 ECE344: Operating Systems Purpose of Scheduling OS scheduler decides when a thread should be run – i.e., when a thread should be allocated a processor Programs generally have two broad behaviors: – Bursts of computation on the CPU – Bursts of I/O with devices – A CPU-bound program is limited by CPU resources • Has more CPU bursts – An I/O-bound program is limited by I/O resources • Has few CPU bursts When a program performs I/O, CPU is not needed: – Scheduler runs another program to keep CPU busy – Improves CPU utilization
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4 ECE344: Operating Systems Scheduling Goals Scheduling goals depend on system environment: 1. Batch systems • Mainly shared, computational systems, • Examples: Servers, supercomputers, clusters CPU Utilization : % of time that CPU is busy (not idle) Throughput: nr. of programs that complete per unit time 2. Interactive (or general-purpose) systems • Short running programs, interactive users, weak time constraints • Examples: Desktops, cell phones Response time: time between receiving request and starting to produce output
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5 ECE344: Operating Systems Scheduling Mechanism: A Review When does the scheduler run? – Scheduler runs when thread state changes or on preemption
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This document was uploaded on 02/20/2012.

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ECE344-Lecture20-Scheduling - Lecture 20: Scheduling David...

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