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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  • Schedulability test based on the WCRT
  • Computing Rwci
  • Example
  • Restrictions to the schedulability tests previously presented
  • Impact of non-preemption
  1. Fixed Priority Scheduling

Response-time analysis

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Last updated 2 years ago

For arbitrarily fixed priorities, including RM, DM and others, the Response Time Analysis is an exact test (i.e., a necessary and sufficient condition) in the following conditions:

  • full preemption, synchronous release, independent tasks and D ≤ T.

Worst-case response time (WCRT, Rwc, R,...) = maximum time interval between arrival and finish instants.

Schedulability test based on the WCRT

<=> task set is schedulable.

The WCRT of a given task occurs when the task is activated at the same time as all other high-priority tasks (critical instant).

Ii – interference caused by the execution of higher priority tasks.

Computing Rwci

The equation is solved iteratively. Stop conditions are:

  • A deadline is violated.

    • Rwci(m) > Di

  • Convergence (two successive iterations yield the same result).

    • Rwc i (m + 1) = Rwc i (m)

Algorithm

Example

Restrictions to the schedulability tests previously presented

The previous schedulability tests must be modified in the following cases:

  • Non-preemption.

  • Tasks not independent.

    • Share mutually exclusive resources.

    • Have precedence constrains.

  • It is also necessary to take into account the overhead of the kernel, because the scheduler, dispatcher and interrupts consume CPU time.

Impact of non-preemption

Repeat Step 3 until convergence or deadline violation