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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  • LSF Scheduling
  • Example
  • FCFS Scheduling
  • Example
  1. Dynamic Priority Scheduling

Other deadline assignment criteria

PreviousAnalysis: CPU Load AnalysisNextThe priority inversion problem

Last updated 2 years ago

LSF Scheduling

Least Slack First : Executes first the task with smaller slack (Li (t)=di −ci (t))

LSF vs EDF short comparison.

  • LS is optimal (as EDF)

  • As the slack ↑ the priority ↓

  • Priority of ready tasks increases as time goes by.

    • Rescheduling only on instants where there are activations or terminations.

  • Priority of the task in the running state does not change.

    • In EDF the priorities of all tasks (ready and executing) increase equally as time goes by.

  • Causes an higher number of preemptions than EDF (and thus higher overhead).

  • No significant advantages with respect to EDF!

Example

FCFS Scheduling

Execute tasks as they arrive. Priority depends on the arrival order. A brief comparison between FCFS and EDF/LLF.

  • Non optimal.

    • May lead to deadline misses even with very low CPU utilization rates.

  • Job age ↑ Priority ↑

  • Priority of the ready and running tasks increases as time goes by (an in EDF).

  • New jobs always get the lower priority.

  • There are no preeemptions (smaller overhead and facilitates the implementation).

  • Very poor temporal behavior!

Example

When the “age” is the same the tie break criteria is decisive!