Scheduling and Allocation in Multiprocessor Systems

The problem of allocation has always been one of the fundamental issues of building applications in multiprocessor systems. For real-time applications, the allocation problem should directly address the issues of task and communication scheduling. In this context, the allocation of tasks has to fully utilize the available processors and the scheduling of tasks has to meet the specified timing constraints. Clearly, the execution of tasks under the allocation and schedule has to satisfy the precedence, resources, and synchronization constraints. Traditionally time constraints for real-time tasks have been specified in terms of ready time and deadlines. Many application tasks have relative timing constraints in which the constraints for the execution of a task are defined in terms of the actual execution instances of prior tasks. In this dissertation we consider the allocation and scheduling problem of the periodic tasks with relative timing requirements. We take a time-based scheduling approach to generate a multiprocessor schedule for a set of periodic tasks. A simulated annealing algorithm is developed as the overall search algorithm for a feasible solution. Our results show that the algorithm performs well and finds feasible allocation and scheduling. We also investigate how to exploit the replication technique to increase the schedulability and performance of the systems. In this dissertation, we adopt the computation model in which each task may have more than one copy and a task may start its execution after receiving necessary data from a copy of each of its predecessors. Based on this model, replication techniques are developed to increase the schedulability of the applications in real-time systems and to reduce the execution cost of the applications in non-real-time systems

Real-time and fault tolerance in distributed control software

Closed loop control systems typically contain multitude of spatially distributed sensors and actuators operated simultaneously. So those systems are parallel and distributed in their essence. But mapping this parallelism onto the given distributed hardware architecture, brings in some additional requirements: safe multithreading, optimal process allocation, real-time scheduling of bus and network resources. Nowadays, fault tolerance methods and fast even online reconfiguration are becoming increasingly important. All those often conflicting requirements, make design and implementation of real-time distributed control systems an extremely difficult task, that requires substantial knowledge in several areas of control and computer science. Although many design methods have been proposed so far, none of them had succeeded to cover all important aspects of the problem at hand. [1] Continuous increase of production in embedded market, makes a simple and natural design methodology for real-time systems needed more then ever

Formal and Informal Methods for Multi-Core Design Space Exploration

We propose a tool-supported methodology for design-space exploration for embedded systems. It provides means to define high-level models of applications and multi-processor architectures and evaluate the performance of different deployment (mapping, scheduling) strategies while taking uncertainty into account. We argue that this extension of the scope of formal verification is important for the viability of the domain.Comment: In Proceedings QAPL 2014, arXiv:1406.156

Reservation-Based Federated Scheduling for Parallel Real-Time Tasks

This paper considers the scheduling of parallel real-time tasks with arbitrary-deadlines. Each job of a parallel task is described as a directed acyclic graph (DAG). In contrast to prior work in this area, where decomposition-based scheduling algorithms are proposed based on the DAG-structure and inter-task interference is analyzed as self-suspending behavior, this paper generalizes the federated scheduling approach. We propose a reservation-based algorithm, called reservation-based federated scheduling, that dominates federated scheduling. We provide general constraints for the design of such systems and prove that reservation-based federated scheduling has a constant speedup factor with respect to any optimal DAG task scheduler. Furthermore, the presented algorithm can be used in conjunction with any scheduler and scheduling analysis suitable for ordinary arbitrary-deadline sporadic task sets, i.e., without parallelism