scholarly journals Partially clairvoyant scheduling for aggregate constraints

2005 ◽  
Vol 2005 (4) ◽  
pp. 225-240
Author(s):  
K. Subramani
Keyword(s):  
Real Time ◽  
Performance Metrics ◽  
Model Performance ◽  
Timing Constraints ◽  
Start Time ◽  
Real Time Scheduling ◽  
Time Scheduling ◽  
Execution Times ◽  
Relative Timing Constraints ◽  
Time Systems

The problem of partially clairvoyant scheduling is concerned with checking whether an ordered set of jobs, having nonconstant execution times and subject to a collection of imposed constraints, has a partially clairvoyant schedule. Variability of execution times of jobs and nontrivial relationships constraining their executions, are typical features of real-time systems. A partially clairvoyant scheduler parameterizes the schedule, in that the start time of a job in a sequence can depend upon the execution times of jobs that precede it, in the sequence. In real-time scheduling, parameterization of the schedule plays an important role in extending the flexibility of the scheduler, particularly in the presence of variable execution times. It has been shown that the existence of partially clairvoyant schedules can be determined in polynomial time, when the constraints are restricted to be “standard,” that is, relative timing constraints. In this paper, we extend the class of constraints for which partially clairvoyant schedules can be determined efficiently, to include aggregate constraints. Aggregate constraints form a strict superset of standard constraints and can be used to model performance metrics.

scholarly journals Task-Level Re-Execution Framework for Improving Fault Tolerance on Symmetry Multiprocessors

Symmetry ◽  
2019 ◽  
Vol 11 (5) ◽  
pp. 651 ◽  
Author(s):  
Hyeongboo Baek ◽  
Jaewoo Lee
Keyword(s):  
Real Time ◽  
Fault Tolerant ◽  
Target System ◽  
Real Time Systems ◽  
Software Faults ◽  
Real Time Scheduling ◽  
Time Scheduling ◽  
Hard Real Time ◽  
Deployed Systems ◽  
Time Systems

Hard real-time systems are employed in military, aeronautics, and astronautics fields where deployed systems are susceptible to software faults that can result in functional errors. Thus, there is a need to use fault-tolerant (FT) real-time scheduling. Among the various fault-tolerant real-time scheduling techniques, re-execution has been applied widely to existing real-time systems owing to its simplicity and applicability. However, re-execution requires multiple executions of every task, and some tasks miss their deadlines owing to the prolonged execution time; therefore, it has been found to be suitable for only soft real-time systems. In this paper, we propose an FT policy that can be incorporated into most (if not all) existing real-time scheduling algorithms on multiprocessor systems, which improves the reliability of the target system without a tradeoff against schedulability. As a case study, we apply the FT policy to existing fixed-priority scheduling and earliest deadline zero-laxity scheduling, and we demonstrate that it enhances reliability without schedulability loss.

New Hybrid Genetic Based Approach for Real-Time Scheduling of Reconfigurable Embedded Systems

2018 ◽  
Vol 10 (1) ◽  
pp. 23-36
Author(s):  
Ibrahim Gharbi ◽  
Hamza Gharsellaoui ◽  
Sadok Bouamama
Keyword(s):  
Embedded System ◽  
Real Time ◽  
Scheduling Algorithm ◽  
Journal Article ◽  
Real Time Systems ◽  
Software Faults ◽  
Real Time Scheduling ◽  
Time Scheduling ◽  
Algorithmic Approaches ◽  
Time Systems

This journal article deals with the problem of real-time scheduling of operating systems (OS) tasks by a hybrid genetic-based scheduling algorithm. Indeed, most of real-time systems are framed with aid of priority-based scheduling algorithms. Nevertheless, when such a scenario is applied to save the system at the occurrence of hardware-software faults, or to improve its performance, some real-time properties can be violated at run-time. In contrast, most of the applications of real-time systems are based on timing constraints, i.e. OS tasks should be scheduled properly to finish their execution within the time specified by the real-time systems. For this reason, the authors propose in their article, a hybrid genetic-based scheduling approach that automatically checks the systems feasibility after any reconfiguration scenario was applied to an embedded system. A benchmark example is given, and the experimental results demonstrate the effectiveness of the originally proposed genetic-based scheduling approach over other such classical genetic algorithmic approaches.

scholarly journals Rigorous implementation of real-time systems – from theory to application

2013 ◽  
Vol 23 (4) ◽  
pp. 882-914 ◽  
Author(s):  
TESNIM ABDELLATIF ◽  
JACQUES COMBAZ ◽  
JOSEPH SIFAKIS
Keyword(s):  
Real Time ◽  
Physical Model ◽  
Timing Constraints ◽  
Abstract Model ◽  
Real Time Systems ◽  
Execution Engine ◽  
Execution Platform ◽  
Implementation Method ◽  
Execution Times ◽  
Time Systems

The correct and efficient implementation of general real-time applications remains very much an open problem. A key issue is meeting timing constraints whose satisfaction depends on features of the execution platform, in particular its speed. Existing rigorous implementation techniques are applicable to specific classes of systems, for example, with periodic tasks or time-deterministic systems.We present a general model-based implementation method for real-time systems based on the use of two models: •An abstract model representing the behaviour of real-time software as a timed automaton, which describes user-defined platform-independent timing constraints. Its transitions are timeless and correspond to the execution of statements of the real-time software.•A physical model representing the behaviour of the real-time software running on a given platform. It is obtained by assigning execution times to the transitions of the abstract model. A necessary condition for implementability is time-safety, that is, any (timed) execution sequence of the physical model is also an execution sequence of the abstract model. Time-safety simply means that the platform is fast enough to meet the timing requirements. As execution times of actions are not known exactly, time-safety is checked for the worst-case execution times of actions by making an assumption of time-robustness: time-safety is preserved when the speed of the execution platform increases.We show that, as a rule, physical models are not time-robust, and that time-determinism is a sufficient condition for time-robustness. For a given piece of real-time software and an execution platform corresponding to a time-robust model, we define an execution engine that coordinates the execution of the application software so that it meets its timing constraints. Furthermore, in the case of non-robustness, the execution engine can detect violations of time-safety and stop execution.We have implemented the execution engine for BIP programs with real-time constraints and validated the implementation method for two case studies. The experimental results for a module of a robotic application show that the CPU utilisation and the size of the model are reduced compared with existing implementations. The experimental results for an adaptive video encoder also show that a lack of time-robustness may seriously degrade the performance for increasing platform execution speed.

On the Competitiveness of Online Real-Time Scheduling with Rate of Progress Guarantees

2003 ◽  
Vol 14 (03) ◽  
pp. 359-370 ◽  
Author(s):  
Michael A. Palis
Keyword(s):  
Real Time ◽  
Task Scheduling ◽  
Competitive Ratio ◽  
Scheduling Algorithm ◽  
Real Time Systems ◽  
Real Time Scheduling ◽  
Qos Guarantees ◽  
Time Scheduling ◽  
Time Systems

This paper investigates the task scheduling problem in the oontext of reservation-based real-time systems that provide quality of service (QoS) guarantees. In such a system, each incoming task specifies a rate of progress requirement on the task's execution that must be met by the system in order for the computation to be deeemed usable. A new metric, called granularity, is introduced that quantifies both the maximum slowdown and the variance in execution rate that the task allows. This metric generalizes the stretch metric used in recent research on task scheduling. An online preemptive scheduling algorithm is presented that achieves a competitive ratio of g(1 - r) for every set of tasks with maximum rate r and minimum granularity g. This result generalizes a previous result based on the stretch metric that showed that a competitive ratio of (1 - r) is achievable for the case when g = 1.

Reconfiguration of Synchronous Real-Time Operating System

2013 ◽  
Vol 2 (1) ◽  
pp. 114-132 ◽  
Author(s):  
Hamza Gharsellaoui ◽  
Mohamed Khalgui ◽  
Samir Ben Ahmed
Keyword(s):  
Real Time ◽  
Systems Engineering ◽  
Scheduling Algorithm ◽  
User Requirements ◽  
Real Time Systems ◽  
Real Time Scheduling ◽  
Temporal Properties ◽  
Time Scheduling ◽  
Run Time ◽  
Time Systems

Real-time scheduling is the theoretical basis of real-time systems engineering. Earliest Deadline first (EDF) is an optimal scheduling algorithm for uniprocessor real-time systems. The paper deals with Reconfigurable Uniprocessor embedded Real-Time Systems classically implemented by different OS tasks that the authors suppose independent, synchronous and periodic to meet functional and temporal properties described in user requirements. They define two forms of automatic reconfigurations which are applied at run-time: Addition-Remove of tasks or just modifications of their temporal parameters: WCET and/or Periods. The authors define a new semantic of the reconfiguration where a crucial criterion to consider is the automatic improvement of the system’s feasibility at run-time by using an Intelligent Agent that automatically checks the system’s feasibility after any reconfiguration scenario to verify if all tasks meet the required deadlines. To handle all possible reconfiguration solutions, the authors propose an agent-based architecture that applies automatic reconfigurations to re-obtain the system’s feasibility and satisfy user requirements. Therefore, they developed the tool RT-Reconfiguration to support these contributions that they apply on the running example system and the authors apply the Real-Time Simulator, Cheddar to check the whole system behavior and evaluate the performance of the algorithm. They present simulations of this architecture where the agent that implemented is evaluated.

Performance Analysis of Preemptive Based Uniprocessor Scheduling

2016 ◽  
Vol 6 (4) ◽  
pp. 1489 ◽  
Author(s):  
M Shanmugasundaram ◽  
R Kumar ◽  
Harish M Kittur
Keyword(s):  
Performance Analysis ◽  
Response Time ◽  
Real Time ◽  
Time Constraints ◽  
Real Time Systems ◽  
Real Time Scheduling ◽  
Analysis Methodology ◽  
Time Scheduling ◽  
Time Systems ◽  
Uniprocessor Scheduling

All the real-time systems are bound with response time constraints, or else, there is a risk of  severe consequences, which includes failure. The System will fail when not able to meet the requirements according to the specifications. The problem of real-time scheduling is very vast, ranging from uni-processor to complicated-multiprocessor. In this paper, we have compared the performance of real-time tasks that should be scheduled properly, to get optimum performance. Analysis methodology and the concept of optimization leads to the design of appropriate scheduling. We have done  the analysis among RM and EDF algorithm that are important for scheduling in uni-processor.

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