RT Computing
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What is RT computing?Types of tasks Classifications of RT systems what is predictability ? Scheduling Scheduling algorithms
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RT Computing
- 1. REAL TIME COMPUTING: A NEW DISCIPLINE OF COMPUTER SCIENCE AND ENGINEERING By Rezhin Nwree Bayar Shahab
- 2. OUTLINE ֍ What is RT computing? ֍ Types of tasks ֍ Classifications of RT systems ֍ what is predictability ? ֍ Scheduling ֍Scheduling algorithms 2 1/14/2017
- 3. WHAT IS RT COMPUTING? ▪ Components of RT Computing Very precise timing High degree of reliability The environment of operation 3 1/14/2017
- 4. TYPES OF TASKS ▪ Periodic tasks ▪ Time-critical tasks ▪ Regular intervals ▪ Aperiodic tasks ▪ Event based tasks 1/14/2017 4
- 5. CLASSIFICATIONS OF RT SYSTEMS Based on their deadlines tasks care classified as: Hard RT Meet required deadlines within the bounded time otherwise it may lead to catastrophic error (periodic tasks) Firm RT Missing a deadline may not cause a catastrophic or fatal error, but may cause undesired effects or may degrade the performance of the system(aperiodic tasks) Soft RT Missing a deadline may not be catastrophic and cause fatal errors, but they are undesired and unwanted(Best effort). 1/14/2017 5
- 6. WHAT IS PREDICTABILITY ▪ Demonstrate at design time that constraints of all tasks can be met with 100% certainty (periodic hard deadline tasks ) ▪ Constraints could be: ▪ Time ▪ Resource ▪ Precedence ▪ Performance ▪ Environment ▪ Task characteristics i.e. # of tasks, their execution time 1/14/2017 6
- 7. PREDICTABILITY CONT. ▪ Probabilistic guarantee ▪ A given task has a certain probability of meeting its constraints ▪ Run-time deterministic guarantee ▪ At run-time the system determine if the task’s constraints can be met or not. (Dynamically arriving aperiodic tasks) ▪ Specification violation 1/14/2017 7
- 8. SCHEDULING 1/14/2017 8 ▪ Process of Determining when and where each task will be executed ▪ Schedulability study(feasibility) Infeasible schedule feasible schedule
- 9. SCHEDULING ALGORITHMS ▪ RT applications can have different scheduling algorithms depending on several cases: ▪ Periodic or Aperiodic tasks ▪ Peermptible and Non-peermptible tasks ▪ Uniprocessor and Multiprocessor 1/14/2017 9
- 10. SCHEDULING ALGORITHMS ▪ Uniprocessor systems ▪ Static priority algorithm(RM)- Optimal among static ▪ Dynamic priority algorithm(EDF) – Optimal among both ▪ Multiple processor systems ▪ Static algorithm (List scheduling) ▪ Dynamic algorithm ▪ Centralized – central processor distributed to other processor ▪ Distributed – Tasks are scheduled by each processor autonomously 1/14/2017 10
Editor's Notes
- Precise timing - The correctness of a computation depends not only on the logical correctness but also on the time at which the results are produced
- Periodic tasks are Time-critical tasks - Deadlines of critical tasks must be met regardless of any other tasks. Periodic tasks could also be time-critical
- Hard RT- Nuclear reactor control Firm RT- Loosing some bits from codec of music, OR transaction in Database systems Soft RT- Delay in loading a website degrades the system Deadlines come from the applications, Type of Application and Environment set the type of RT as Hard Firm or soft
- Predictable – RT systems have to be predictable to have reliable results and they have to be tested at design time(Test-Bench)
- Specification violation proposed to use an on-line monitor to record violations. This record can later be used to modify the assumed worst case values.
- When Determine the next task? Where Which processor ? Objective of scheduling in RT and Non-RT applications: RT applications meet timing constraint of the individual tasks Non RT-Applications minimizing the total time required to execute all the tasks
- RM and EDF and List scheduling are scheduling Periodic tasks with hard deadlines For Static Multiple processor there is NP-Hard problem Transfer policy local processor and location policy transfer to another processor