Notes - MIECT
Sistemas Operativos E De Tempo-real
Notes - MIECT
Sistemas Operativos E De Tempo-real
  • Sistemas Operativos e de Tempo-real
  • Basic Concepts About Real-Time Systems
    • Preliminaries
    • Definitions
    • Objective of the Study of RTS
    • Requirements of Real-Time Systems
  • Real Time Model
    • Real Time Model
    • Temporal Control
    • Task states and execution
    • Kernel/RTOS Architecture
      • Time Management Functions
    • Examples of RTOS
  • Practical Class 01
    • Real-Time Services in Linux
    • Using the Linux real-time services
  • Scheduling Basics
    • Basic concepts
    • Scheduling Algorithms
      • Basic algorithms
    • Static Cyclic Scheduling
    • Exercise
  • Fixed Priority Scheduling
    • Online scheduling with fixed priorities
    • Schedulability tests based on utilization
      • Deadline Monotonic Scheduling DM
    • Response-time analysis
  • Practical Class 2
    • Xenomai brief introduction
    • API
    • Developing an application
  • Dynamic Priority Scheduling
    • On-line scheduling with dynamic priorities
    • Analysis: CPU utilization bound
    • Analysis: CPU Load Analysis
    • Other deadline assignment criteria
  • Exclusive Access to Shared Resources
    • The priority inversion problem
    • Techniques for allowing exclusive access
    • Priority Inheritance Protocol
    • Priority Ceiling Protocol
    • Stack Resource Policy
    • Notes
  • Aperiodic Servers
    • Joint scheduling of periodic and aperiodic tasks
    • Aperiodic Servers
    • Fixed Priority Servers
    • Dynamic Priority Servers
  • Limited preemption, release jitter and overheads
    • Non-preemptive scheduling
    • Impact of Release Jitter
    • Accounting for overheads
    • Considerations about the WCET
  • Profiling and Code Optimization
    • Code optimization techniques
      • CPU independent optimization techniques
      • Cache impact
      • Optimization techniques dependent on memory architecture
      • Architecture-dependent optimization techniques
    • Profiling
  • Multiprocessor Scheduling, V1.2
    • Introduction
    • Definitions, Assumptions and Scheduling Model
    • Scheduling for Multicore Platforms
    • Task allocation
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  • Scheduling Definition
  • Scheduling problem
  • Exercise
  1. Scheduling Basics

Basic concepts

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Last updated 2 years ago

Scheduling Definition

Task scheduling (also applies to messages, with due adaptations).

  • Sequence of task executions (jobs) in one or more processors.

  • Application of (time) in (task set), assigning to each time instant “t” a task/job “i” that executes in that time instant.

  • σ(t) is a step function, which can be expressed e.g. as a Gantt graph.

A schedule is called feasible if it fulfills all the task requirements.

  • temporal, non-preemption, shared resources, precedences, ...

A task set is called schedulable if there is at least one feasible schedule for that task set.

Scheduling problem

Given:

  • A task set.

  • Requirements of the tasks (or cost function).

Find a time attribution of processor(s) to tasks so that:

  • Tasks are completely executed, and

  • Meet they requirements (or minimize the cost function).

E.g. J = Ji (Ci = 1, ai = 1, Di = 5), i = {1..5}

Exercise

Build a Gantt diagram for the execution of the following periodic tasks, admitting Di = Ti and no preemption.

  • τ = {(1, 5)(6, 10)}

Is the execution order important? Why?

Solution

After 10, the process repeat