Scheduling%20Basic%20Concepts%20Ref:%20Hard%20Real-Time%20Computing%20Systems%20Giorgio%20Buttazzo%20%20Processes%20-%20Tasks%20%20-%20Threads

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SchedulingBasic ConceptsRef Hard Real-Time
Computing SystemsGiorgio ButtazzoProcesses -
Tasks - Threads
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Nostalgia
Apollo Guidance Computer First
Microprocessor Microcontroller
Automobile Computers 2006 1-2 million lines
of code
2010 10 million lines of code
99 of todays computers are in embedded
systems
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The Osborne I (1981)
First Portable Computer

• Hardware
• Dual 5¼-inch floppy disk drives
• 4 MHz Z80 CPU
• 65 kilobytes main memory
• Fold-down keyboard doubling as the computer
  case's lid
• 5-inch, 52 character 24 line monochrome CRT
  display
• Parallel printer port
• Serial port for use with external modems or
  serial printers

Software CPM Word Star
SuperCalc Dbase II CBasic
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(No Transcript)
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Orientation

• Schedule
• An assignment of tasks to the processor, so that
  each task is executed until completion
• Scheduling Policy
• Tasks assigned according to a predefined
  criterion
• Scheduling Algorithm
• The set of rules that determines the ordering of
  tasks
• Active Task ? Ready Task ? Running Task
• (Ready Queue)
  (Dispatching)

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Ready Queue
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Definition of Schedule

• What does it say?

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Preemptive Schedules
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Categories of Schedules
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Deadlines

• Deadline
• Absolute with respect to real-time (time
  zero)
• Relative with respect to arrival time

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Real-Time Task Parameters
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Real-Time Task Parameters
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Periodic vs Aperiodic Tasks
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Precedence Constraints
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Precedence Example
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Critical Sections
Binary Semaphore
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Critical Section Example
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Critical Section Model
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Definition of Scheduling Problems
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Classification of Scheduling Algorithms
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Guarantee-Based Algorithms
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Domino Effect Degradation