Papers by V. V. Dimakopoulos
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Parallel Processing Letters, Dec 20, 2022
Auto-scoping in OpenMP has been proposed as a means for relieving the programmer from the non-tri... more Auto-scoping in OpenMP has been proposed as a means for relieving the programmer from the non-trivial effort of identifying the data sharing attributes of variables used within code regions that produce concurrency, such as parallel and task constructs. In this work we reconsider autoscoping on parallel constructs, including combined parallel-worksharing constructs. We first show that the current implementations do not always scope variables correctly in the presence of nested parallel constructs. We then proceed to extend the set of rules that guide the autoscoping decisions so as to handle nested constructs successfully. We also discuss how this functionality is implemented in the OMPi source-to-source OpenMP compiler.
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The advent of distributed-memory multiprocessors has spawned an increasing amount of research in ... more The advent of distributed-memory multiprocessors has spawned an increasing amount of research in information dissemination problems. Given a network of processors (or nodes) where some of them own pieces of information, the problem is to spread the information to a group of recipients using the links of the network. The term 'collective communications' has been coined to signify the fact that such problems involve more than two nodes. Multinode broadcasting, an important collective communication problem, involves simultaneous broadcastings from all the nodes in a network. We present algorithms for the minimum-time solution of the problem in packet-switched networks that follow the single-port model. In particular, we construct a general algorithm for the solution of the problem in arbitrary multidimensional networks and provide conditions that ensure its optimality
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Παράλληλα Συστήματα και Προγραμματισμός [ΠΑΝEΠΙΣΤΗΜΙΟ ΙΩΑΝΝΙΝΩΝ, ΣΧΟΛΗ ΘEΤΙΚΩΝ EΠΙΣΤΗΜΩΝ, ΤΜΗΜΑ Μ... more Παράλληλα Συστήματα και Προγραμματισμός [ΠΑΝEΠΙΣΤΗΜΙΟ ΙΩΑΝΝΙΝΩΝ, ΣΧΟΛΗ ΘEΤΙΚΩΝ EΠΙΣΤΗΜΩΝ, ΤΜΗΜΑ ΜΗΧΑΝΙΚΩΝ ΗΛEΚΤΡΟΝΙΚΩΝ ΥΠΟΛΟΓΙΣΤΩΝ ΚΑΙ ΠΛΗΡΟΦΟΡΙΚΗΣ]
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Παράλληλα Συστήματα και Προγραμματισμός [ΠΑΝEΠΙΣΤΗΜΙΟ ΙΩΑΝΝΙΝΩΝ, ΣΧΟΛΗ ΘEΤΙΚΩΝ EΠΙΣΤΗΜΩΝ, ΤΜΗΜΑ Μ... more Παράλληλα Συστήματα και Προγραμματισμός [ΠΑΝEΠΙΣΤΗΜΙΟ ΙΩΑΝΝΙΝΩΝ, ΣΧΟΛΗ ΘEΤΙΚΩΝ EΠΙΣΤΗΜΩΝ, ΤΜΗΜΑ ΜΗΧΑΝΙΚΩΝ ΗΛEΚΤΡΟΝΙΚΩΝ ΥΠΟΛΟΓΙΣΤΩΝ ΚΑΙ ΠΛΗΡΟΦΟΡΙΚΗΣ]
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Workshop Proceedings of the 51st International Conference on Parallel Processing
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Parallel Computing, 2022
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Cornell University - arXiv, May 21, 2022
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Lecture Notes in Computer Science, 2012
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Fat trees are built around complete b-ary trees but have processing nodes only at the leaf level ... more Fat trees are built around complete b-ary trees but have processing nodes only at the leaf level and may have different branch capacities in different levels. In this paper we study the communication capabilities of binary fat trees (including the simple binary tree) with respect to five major communication operations: broadcasting, multinode broadcasting, scattering, gathering and total exchange. We present and analyse optimal and nearly optimal algorithms for the five operations.
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We examine the hamiltonicity of the cartesian product P = G1 × G2 of two graphs G1, G2. We provid... more We examine the hamiltonicity of the cartesian product P = G1 × G2 of two graphs G1, G2. We provide necessary and/or sufficient conditions for P to be hamiltonian, depending on the hamiltonian properties of G1 and G2, with corresponding constructions. We also prove a conjecture by Batagelj and Pisanski related to the ‘cyclic hamiltonicity ’ of a graph.
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Hypercycles is a class of multidimensional multiprocessor interconnection networks which includes... more Hypercycles is a class of multidimensional multiprocessor interconnection networks which includes hypercubes, toruses, rings and other related topologies. In this paper we consider the one-to-all communication problem for the general class of hypercycles. We present a nonredundant broadcasting algorithm which is completed in the minimum number of steps. The algorithm is given in distributed form, directly suggesting an efficient hardware implementation. 1. Introduction 1 1. Introduction In a multiprocessor, one-to-all communication involves sending a message from a root node to all the other nodes through the underlying interconnection network. Such a communication primitive is necessary for system-level maintenance as well as for a big number of parallel applications, such as linear algebra algorithms [1]. A number of network topologies have been suggested for the interconnection between the processors. Hypercycles [8, 6] is a class of multidimensional graphs that includes such w...
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In this paper we consider the problem of total exchange (or multi-scattering) in the context of l... more In this paper we consider the problem of total exchange (or multi-scattering) in the context of linear arrays and rings. Such a communication mode occurs when each node has a distinct message to send to every other node in the network. The problem has been studied extensively, although no optimal algorithm has been proposed for the two networks of interest. We present simple algorithms for the two topologies and prove their optimality. 1
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We present a general solution to the total exchange communication problem for any homogeneous mul... more We present a general solution to the total exchange communication problem for any homogeneous multi-dimensional network under the all-port assumption. More specifically, we consider cartesian product networks where every dimension is the same graph (e.g. hypercubes, square meshes, n-ary d-cubes) and where each node is able to communicate simultaneously with all its neighbors. We show that if we are given an algorithm for a single n-node dimension which requires T steps, we can construct an algorithm for d-dimensions and running time of n d−1 T steps, which is provably optimal for many popular topologies. Our scheme, in effect, generalizes the total exchange algorithm given by Bertsekas et al [1] for the hypercubes and complements our theory [7] for the single-port model.
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Papers by V. V. Dimakopoulos