Sharif Digital Repository

This paper introduces an analytical method for approximating the performance of a firm real-time system consisting of a number of parallel infinite-capacity single-server queues. The service discipline for the individual queues is earliest-deadline-first (EDF). Real-time jobs with exponentially distributed relative deadlines arrive according to a Poisson process. Jobs either all have deadlines until the beginning of service or deadlines until the end of service. Upon arrival, a job joins a queue according to a state-dependent stationary policy, where the state of the system is the number of jobs in each queue. Migration among the queues is not allowed. An important performance measure to... 

This paper presents the performance analysis of several best-known partitioning scheduling algorithms in real-time and fault-tolerant multiprocessor systems. To do this, multiple versions of tasks are executed on different processors. Both static and dynamic scheduling algorithms are analyzed. In the case of static scheduling algorithms, rate-monotonic (RM) scheduling policy is considered. In the dynamic scheduling algorithms, the scheduling policies are rate-monotonic and earliest-deadline-first (EDF). Partitioning scheduling algorithms which are studied here are heuristic algorithms that are formed by combining any of the bin-packing algorithms with any of the schedulability conditions for... 

This paper introduces an analytical method for approximating the performance of a two-class priority M/M/1 system. The prioritized class-1 jobs are real-time, served either with the preemptive or non-preemptive Earliest- Deadline- First (EDF) policy and can preempt the non real-time class-2 jobs. The preempted service of the class-2 job is resumed from the time in instances where no class-1 job is in the system. The service discipline of class-2 jobs is FCFS. The required mean service times may depend on the class of the jobs. The real-time jobs have exponentially distributed relative deadlines until the end of service. The system is approximated by a Markovian model in the long run, which... 

The general approach to fault tolerance in uniprocessor systems is to maintain enough time redundancy in the schedule so that any task instance can be re-executed in presence of faults during the execution. In this paper a scheme is presented to add enough and efficient time redundancy to the Earliest-Deadline-First (EDF) scheduling policy for periodic real-time tasks. This scheme can be used to tolerate transient faults during the execution of tasks. We describe a recovery scheme which can be used to re-execute tasks in the event of transient faults and discuss conditions that must be met by any such recovery scheme. For performance evaluation of this idea a tool is developed. © 2007 IEEE  

This paper presents a comprehensive comparison between job-level dynamic scheduling algorithms on real-time multiprocessor environments using simulation. Earliest Deadline First (EDF) and Least Laxity First (LLF) are two well-known and extensively applied dynamic scheduling algorithms which have been proved to be optimal on uniprocessor systems. However, neither is shown to be optimal on multiprocessors. Many researches have already been done on aforementioned algorithms, but to the best of our knowledge, none of which has compared the efficiency of the two algorithms under similar conditions. Perhaps the main reason is that LLF algorithm is fully dynamic and impractical to implement. In... 

This paper introduces an analytical method to approximate the fraction of jobs missing their deadlines in a soft real-time system when the earliest-deadline-first (EDF) scheduling policy is used. In the system, jobs either all have deadlines until the beginning of service (DBS) and are non-preemptive, or have deadlines until the end of service (DES) and are preemptive. In the former case, the system is represented by an M/M/m/EDF+G model, i.e., a multi-sever queue with Poisson arrival, exponential service, and generally distributed relative deadlines. In the latter case, it is represented by an M/M/1/EDF+G model, i.e., a single-server queue with the same specifications as before. EDF is... 

Two main objectives in designing real-time embedded systems are high reliability and low power consumption. Hardware replication (e.g., standby-sparing) can provide high reliability while keeping the power consumption under control. In this paper, we consider a standby-sparing system where the main tasks on primary cores are scheduled by our proposed peak-power-aware earliest-deadline-first policy while the backup tasks on spare cores are scheduled by our proposed peak-power-aware earliest-deadline-late policy to meet the chip thermal design power (TDP) constraint. These policies provide the best opportunity to shift the task executions as much as possible to minimize execution overlaps... 

Power consumption, performance and reliability are the most important parameters in modern safety-critical distributed real-time embedded systems. This paper evaluates and compares different schedulability conditions in faulttolerant Rate-Monotonic (RM) and Earliest-Deadline-First (EDF) algorithms, with respect to their power efficiency. The primary-backup scheme is used to implement fault tolerance in the algorithms. To evaluate the algorithms, a software tool is developed that can simulate an embedded system consisting of n processors and m periodic tasks. The results show that depending on the different schedulability conditions, the EDF algorithm implemented with the Best-Fit policy is... 

On-time delivery of network flows is crucial to ensure the quality of service of deadline-constrained applications. Today, real time applications have various uses in multimedia communications, the Internet of Things (IoT), and 5G (5th generation mobile network) technology. In Software Defined Network (SDN) architecture, the controller has a global view of the network. Hence, it is possible to enrich the features of the controller and/or forwarding devices to support real time communication. In this paper, we propose a firm real time software-defined approach (FRT-SDN) for real time communication and present a novel solution for the real time forwarding/routing of time-sensitive applications...