SUMMARYThis research addresses a high-speed computation method for the Kleene star of the weighted adjacency matrix in a max-plus algebraic system. We focus on systems whose precedence constraints are represented by a directed acyclic graph and implement it on a Cell Broadband Engine TM (CBE) processor. Since the resulting matrix gives the longest travel times between two adjacent nodes, it is often utilized in scheduling problem solvers for a class of discrete event systems. This research, in particular, attempts to achieve a speedup by using two approaches: parallelization and SIMDization (Single Instruction, Multiple Data), both of which can be accomplished by a CBE processor. The former refers to a parallel computation using multiple cores, while the latter is a method whereby multiple elements are computed by a single instruction. Using the implementation on a Sony PlayStation 3 TM equipped with a CBE processor, we found that the SIMDization is effective regardless of the system's size and the number of processor cores used. We also found that the scalability of using multiple cores is remarkable especially for systems with a large number of nodes. In a numerical experiment where the number of nodes is 2000, we achieved a speedup of 20 times compared with the method without the above techniques. key words: directed acyclic graph, max-plus algebra, scheduling, parallel processing, vector processing, Cell Broadband Engine
IntroductionThis research aims to develop a fast computation method for the representation matrix in a state-space representation in max-plus algebra [1], [2]. This approach is often used in solvers for a class of scheduling problems. Specifically, we focus on quickly calculating the transition matrix, which requires a high computation load using this approach. For the computation, we use a processor called the Cell Broadband Engine (CBE) [3]-[6], which has instructions for vector operations and parallel processing.The features of the class of focused systems are: (1) parallel execution of multiple tasks, (2) synchronization of multiple tasks, and (3) no-concurrency between the previous or succeeding job. Such systems can also be explained as repetitive discrete event systems in which a number of jobs are processed sequentially using the same facilities in FIFO order. We assume that the precedence relationships of the system are described by a Directed Acyclic Graph (DAG). The behavior of this class can be represented by a pair of simple equations in max-plus algebra, called the state-space representation. Since this is similar to the representation in modern control theory, a number of research developments Manuscript received October 30, 2009. Manuscript revised January 29, 2010. † The author is with Nagaoka University of Technology, Nagaoka-shi, 940-2188 Japan.a) E-mail: hgoto@kjs.nagaokaut.ac.jp DOI: 10.1587/transinf.E93. D.1798 in modern control theory have been applied to various kinds of scheduling problems [7]- [9]. The state-space representation consists of a pair of state ...