Scheduling Algorithms for Parallel Execution of Computer Programs

Computer Scienc

Programmation linéaire en nombres entiers pour l'ordonnancement cyclique sous contraintes de ressources

Un problème d'ordonnancement cyclique consiste à ordonner dans le temps l'exécution répétitive d'un ensemble d'opérations liées par des contraintes de précédence, en utilisant un nombre limité de ressources. Ces problèmes ont des applications immédiates dans les systèmes de production ou en informatique parallèle. Particulièrement, ils permettent de modéliser l'ensemble des contraintes de précédence et de ressource à prendre en compte pour l'ordonnancement d'instructions dans les processeurs de type VLIW (Very Long Instruction Word). Dans ce cas, une opération représente une instance d'une instruction dans un programme. L'ordonnancement d'instructions de boucles internes est connu sous le nom de pipeline logiciel. Le pipeline logiciel désigne une méthode efficace pour l'optimisation de boucles qui permet la réalisation en parallèle des opérations des différentes itérations de la boucle. Dans cette thèse, nous nous intéressons principalement au problème d'ordonnancement périodique qui est un cas particulier de l'ordonnancement cyclique et qui est également la base du pipeline logiciel. Le terme ordonnancement modulo désigne un ordonnancement périodique tel que l'allocation de ressources pour une opération donnée n'est pas modifiée d'une itération sur l'autre. Pour résoudre le problème, nous nous intéressons aux formulations de programmation linéaire en nombres entiers, et notamment à la résolution du problème par des techniques de séparation, évaluation, génération de colonnes, relaxation lagrangienne et des méthodes hybrides. En particulier, nous proposons des nouvelles formulations basées sur des variables binaires représentant l'exécution d'ensembles d'instructions en parallèle. Enfin, les méthodes développées ont été validées sur des jeux d'instances industrielles pour des processeurs de type VLIW.The resource-constrained modulo scheduling problem (RCMSP) is a general periodic cyclic scheduling problem, abstracted from the problem solved by compilers when optimizing inner loops at instruction level for very long instruction word parallel processors. Since solving the instruction scheduling problem at compilation phase in less time critical than for real time scheduling, integer linear programming (ILP) is a relevant technique for the RCMSP. In this work, we are interested in the methods based on the integer linear programming for the RCMSP. At first, we present a study of the two classic integer linear formulation for the RCMSP. A theoretical evidence of the equivalence between the classic formulations is shown in terms of linear programming (LP) relaxation. Secondly, based on the ILP formulations for the RCMSP, stronger formulations for the RCMSP derived from Dantzig-Wolfe decomposition are presented. In these formulations, the number of variables can be huge, for this reason, we proposed a column generation scheme to solve their LP relaxations. We propose also the heuristics methods based on the Lagragian relaxation and decomposed software pipelining. The heuristic methods search the transformation of the classic integer linear programming for the RCMSP for the performance improvement in the time for the search of solutions. All formulations are compared experimentally on problem instances generated from real data issued from the STMicroelectronics ST200 VLIW processor family

Scheduling techniques for packet routing, load, balancing and disk scheduling

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mathematics, 1997.Includes bibliographical references (p. 163-170).by Matthew Andrews.Ph.D

Task assignment in parallel processor systems

A generic object-oriented simulation platform is developed in order to conduct experiments on the performance of assignment schemes. The simulation platform, called Genesis, is generic in the sense that it can model the key parameters that describe a parallel system: the architecture, the program, the assignment scheme and the message routing strategy. Genesis uses as its basis a sound architectural representation scheme developed in the thesis. The thesis reports results from a number of experiments assessing the performance of assignment schemes using Genesis. The comparison results indicate that the new assignment scheme proposed in this thesis is a promising alternative to the work-greedy assignment schemes. The proposed scheme has a time-complexity less than those of the work-greedy schemes and achieves an average performance better than, or comparable to, those of the work-greedy schemes. To generate an assignment, some parameters describing the program model will be required. In many cases, accurate estimation of these parameters is hard. It is thought that inaccuracies in the estimation would lead to poor assignments. The thesis investigates this speculation and presents experimental evidence that shows such inaccuracies do not greatly affect the quality of the assignments

The Effect of Representations on Constraint Satisfaction Problems

Constraint Satisfaction is used in the solution of a wide variety of important problems such as frequency assignment, code analysis, and scheduling. It is apparent that the modelling process is key to the success of any constraint based technique, and much work has been done on the identification of good models [FJHM05]. One of the key choices made during the modelling process is the selection of a constraint representation with which to express the constraints [HS02]. Whilst practitioners will commonly use an implicit representation, most existing structural tractability results are defined for explicit representation. We address a well-known anomaly in structural tractability theory, that acyclic instances are tractable when expressed explicitly, but may not be when expressed implicitly, and show that there is a link between representation and tractability, We introduce the notion of interaction width in order to address this disconnect between theory and practice, and use this to define new tractable classes by applying existing structural tractability results to different constraint representations, We show that for a given succinct representation, a non-trivial class of instances with bounded interaction width can be transformed into an explicit representation in polynomial time 50 that existing structural tractability results may be applied, We compare our work to existing results Cor alternative succinct representutions and show that the tractable classes we have defined arc incomparable and novel, and can be used to deduce new tractable classes for SAT. 3EThOS - Electronic Theses Online ServiceGBUnited Kingdo