Casiano Rodríguez

The OpenMP source code repository

The OpenMP source code repository (OmpSCR) is an infrastructure that we make available to the OpenMP community. It is based on a set of representative applications and it is supported by a Web site. The aim of this repository is to contribute to the knowledge and widespreading of OpenMP that in the recent times has become the standard tool for program developing in shared memory multiprocessor platforms. The discussions originated by the use of this framework defines the real needs of the users and developers community, and they leads the future of this project.

Efficient parallel LAN/WAN algorithms for optimization: the MALLBA project

The MALLBA project tackles the resolution of combinatorial optimization problems using generic algorithmic skeletons implemented in C++. A skeleton in the MALLBA library implements an optimization method in one of the three families of generic optimization techniques offered: exact, heuristic and hybrid. Moreover, for each of those methods, MALLBA provides three different implementations: sequential, parallel for Local Area Networks, and parallel for Wide Area Networks. This paper introduces the architecture of the MALLBA library, details some of the implemented skeletons, and offers computational results for some classical optimization problems to show the viability of our library. Among other conclusions, we claim that the design used to develop the optimization techniques included in the library is generic and efficient at the same time.

LLC: A PARALLEL SKELETAL LANGUAGE

The skeletal approach to the development of parallel applications has been revealed to be one of the most successful and has been widely explored in the recent years. The goal of this approach is to develop a methodology of parallel programming based on a restricted set of parallel constructs. This paper presents llc, a parallel skeletal language, the theoretical model that gives support to the language and a prototype implementation for its compiler. The language is based on directives, uses a C-like syntax and gives support to the most widely used skeletal constructs. llCoMP is a source to source compiler for the language built on top of MPI. We evaluate the performance of our prototype compiler using four different parallel architectures and three algorithms. We present the results obtained in both shared and distributed memory architectures. Our model guarantees the portability of the language to any platform and its simplicity greatly eases its implementation.

Integral knapsack problems: parallel algorithms and their implementations on distributed systems

The parallelization of the dynamic programming algorithm for the integral knapsack problem is approached from several perspectives. Two of them proceed by dividing the set of objects, while a third one proceeds by partitioning the set of capacities. Furthermore, we propose a new sequential algorithm and its parallelization by reducing the integral knapsack problem to a maximum path problem. The theoretical complexity analysis of the algorithms proves that for all the algorithms the product of the number of processors by the parallel time equals the corresponding sequential time. Computational results are presented both for transputer networks using occam and LAN using PVM. Although for many cases the best running times are obtained for the LAN, the speedup and the scalability are better for the transputer network.

Predicting the performance of parallel programs

This work presents a new approach to the relation between theoretical complexity models and performance analysis and tuning. The analysis of an algorithm produces a complexity function that gives an approach to the asymptotic number of operations performed by the algorithm. The time spent on these operations depends on the software-hardware platform being used. Usually such platforms are described, from the performance point of view, through a number of parameters. Those parameters are evaluated by a benchmarking program. Though for a given available platform, the algorithmic constants associated with the complexity formula can be computed using multidimensional linear regression, there is still the problem of predicting the performance when the platform is not available. We introduce the concept of Universal Instruction Class and derive from it a set of equations relating the values of the algorithmic constants with the platform parameters. Due to the hierarchical design of current memory systems, the performance behavior of most algorithms varies in a small number of large regions corresponding to small size, medium size and large size inputs. The constants involved in the complexity formula usually have different values for these regions. Assuming we have a complexity formula for the memory resources, it is possible to find a partition of the input size space and the different values of the algorithmic constants. This way, though the complexity formula is the same, the family of constants provides the adaptability of the formula to the different stationary uses of the memory.

Towards the automatic optimal mapping of pipeline algorithms

The assignment of computations to processors is a crucial factor determining the effectiveness of a parallel algorithm. The portability of parallel programs has involved lot of effort during the last decade. However, the performance of a parallel code suffers, in many cases, from inherent effects of the target architectures. The optimal mapping of a parallel program is strongly dependent on the granularity and network architecture. We focus on the problem of finding the optimal mapping of pipeline algorithms on a ring of processors. We propose an analytical model that allows an easy estimation of the parameters needed to obtain the mapping. The model can be introduced in a suitable tool to automatically produce this mapping. Both the accuracy of the model and the optimal efficiency of the algorithm found are contrasted on pipeline algorithms for the knapsack problem, for the resource allocation problem and for the path planning problem.

Design of parallel algorithms for the single resource allocation problem

Abstract Three new optimal parallel algorithms are presented for the single resource allocation problem. They run in the simplest networks: pipelines and rings. All of them have been implemented using PVM and MPI. Four representative platforms of the current state of parallel computing hardware were used for the experiences presented in this paper: the IBM SP2, the Cray T3E, the Silicon Origin 2000 and the Digital Alpha Server 8400. Computational results prove the good scalability of these three algorithms for practical cases.

2D cutting stock problem: a new parallel algorithm and bounds

This work introduces a set of important improvements in the resolution of the Two Dimensional Cutting Stock Problem. It presents a new heuristic enhancing existing ones, an original upper bound that lowers the upper bounds in the literature, and a parallel algorithm for distributed memory machines that achieves linear speedup. Many components of the algorithm are generic and can be ported to parallel branch and bound and A* skeletons. Among the new components there is a comprehensive mpi-compatible synchronization service which facilitates the writing of time-based balancing schemes.

Parallel skeletons for divide-and-conquer and branch-and-bound techniques

The article describes the parallel implementation of skeletons for the divide-and-conquer and branch-and-bound techniques. The user has to choose a paradigm and has to specify for it the type of the problem, the type of solution and the specific characteristics of the technique using the C++ programming language. This information is combined with the provided resolution skeleton to obtain a sequential program and a parallel program. The paper describes the parallel implementation of the skeletons using MPI. Computational results on a Linux-cluster of PCs, Cray T3E and Origin 3000 are presented.

A Skeleton for Parallel Dynamic Programming

The development of skeleton tools constitutes an alternative to cover the gap between current parallel architectures and sequential programmers. Its contruction involves formal models, paradigms and methologies. Based in the automata theory we have developed a formal model for Parallel Dynamic Programming over pipeline networks. This model makes up a paradigm which is the core of skeleton tools oriented to the Dynamic Programming Technique. Following the methodology coerced by the model, we present a tool that provides the user with the ability to obtain parallel programs adapted to the parallel architecture. The efficiency is contrasted on three current parallel platforms: Cray T3E, IBM SP2 and SG Origin 2000.