The Experts below are selected from a list of 4161 Experts worldwide ranked by ideXlab platform
Chris Walshaw - One of the best experts on this subject based on the ideXlab platform.
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multiphase Mesh Partitioning for parallel computational mechanics codes
International Conference on Computational Science, 2002Co-Authors: Chris Walshaw, Mark Cross, K. McmanusAbstract:We consider the load-balancing problems which arise from parallel scientific codes containing multiple computational phases, or loops over subsets of the data, which are separated by global synchronisation points. We motivate, derive and describe the implementation of an approach which we refer to as the multiphase Mesh Partitioning strategy to address such issues. The technique is tested on example Meshes containing multiple computational phases and it is demonstrated that our method can achieve high quality partitions where a standard Mesh Partitioning approach fails.
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International Conference on Computational Science (2) - Multiphase Mesh Partitioning for Parallel Computational Mechanics Codes
Lecture Notes in Computer Science, 2002Co-Authors: Chris Walshaw, Mark Cross, K. McmanusAbstract:We consider the load-balancing problems which arise from parallel scientific codes containing multiple computational phases, or loops over subsets of the data, which are separated by global synchronisation points. We motivate, derive and describe the implementation of an approach which we refer to as the multiphase Mesh Partitioning strategy to address such issues. The technique is tested on example Meshes containing multiple computational phases and it is demonstrated that our method can achieve high quality partitions where a standard Mesh Partitioning approach fails.
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Multilevel Mesh Partitioning for heterogeneous communication networks
Future Generation Computer Systems, 2001Co-Authors: Chris Walshaw, Mark CrossAbstract:Multilevel algorithms are a successful class of optimisation techniques which address the Mesh Partitioning problem for distributing unstructured Meshes onto parallel computers. They usually combine a graph contraction algorithm together with a local optimisation method which refines the partition at each graph level. To date these algorithms have been used almost exclusively to minimise the cut edge weight in the graph with the aim of minimising the parallel communication overhead, but recently there has been a perceived need to take into account the communications network of the parallel machine. For example the increasing use of SMP clusters (systems of multiprocessor compute nodes with very fast intra-node communications but relatively slow inter-node networks) suggest the use of hierarchical network models. Indeed this requirement is exacerbated in the early experiments with meta-computers (multiple supercomputers combined together, in extreme cases over inter-continental networks). In this paper therefore, we modify a multilevel algorithm in order to minimise a cost function based on a model of the communications network. Several network models and variants of the algorithm are tested and we establish that it is possible to successfully guide the optimisation to reflect the chosen architecture.
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Multiphase Mesh Partitioning
Applied Mathematical Modelling, 2000Co-Authors: Chris Walshaw, Mark Cross, K. McmanusAbstract:We consider the load-balancing problems which arise from parallel scientific codes containing multiple computational phases, or loops over subsets of the data, which are separated by global synchronisation points. We motivate, derive and describe the implementation of an approach which we refer to as the multiphase Mesh Partitioning strategy to address such issues. The technique is tested on several examples of Meshes, both real and artificial, containing multiple computational phases and it is demonstrated that our method can achieve high quality partitions where a standard Mesh Partitioning approach fails.
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Mesh Partitioning: A Multilevel Balancing and Refinement Algorithm
SIAM Journal on Scientific Computing, 2000Co-Authors: Chris Walshaw, Mark CrossAbstract:Multilevel algorithms are a successful class of optimization techniques which addresses the Mesh Partitioning problem. They usually combine a graph contraction algorithm together with a local optimization method which refines the partition at each graph level. In this paper we present an enhancement of the technique which uses imbalance to achieve higher quality partitions. We also present a formulation of the Kernighan--Lin partition optimization algorithm which incorporates load-balancing. The resulting algorithm is tested against a different but related state-of-the-art partitioner and shown to provide improved results.
Mark Cross - One of the best experts on this subject based on the ideXlab platform.
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multiphase Mesh Partitioning for parallel computational mechanics codes
International Conference on Computational Science, 2002Co-Authors: Chris Walshaw, Mark Cross, K. McmanusAbstract:We consider the load-balancing problems which arise from parallel scientific codes containing multiple computational phases, or loops over subsets of the data, which are separated by global synchronisation points. We motivate, derive and describe the implementation of an approach which we refer to as the multiphase Mesh Partitioning strategy to address such issues. The technique is tested on example Meshes containing multiple computational phases and it is demonstrated that our method can achieve high quality partitions where a standard Mesh Partitioning approach fails.
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International Conference on Computational Science (2) - Multiphase Mesh Partitioning for Parallel Computational Mechanics Codes
Lecture Notes in Computer Science, 2002Co-Authors: Chris Walshaw, Mark Cross, K. McmanusAbstract:We consider the load-balancing problems which arise from parallel scientific codes containing multiple computational phases, or loops over subsets of the data, which are separated by global synchronisation points. We motivate, derive and describe the implementation of an approach which we refer to as the multiphase Mesh Partitioning strategy to address such issues. The technique is tested on example Meshes containing multiple computational phases and it is demonstrated that our method can achieve high quality partitions where a standard Mesh Partitioning approach fails.
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Multilevel Mesh Partitioning for heterogeneous communication networks
Future Generation Computer Systems, 2001Co-Authors: Chris Walshaw, Mark CrossAbstract:Multilevel algorithms are a successful class of optimisation techniques which address the Mesh Partitioning problem for distributing unstructured Meshes onto parallel computers. They usually combine a graph contraction algorithm together with a local optimisation method which refines the partition at each graph level. To date these algorithms have been used almost exclusively to minimise the cut edge weight in the graph with the aim of minimising the parallel communication overhead, but recently there has been a perceived need to take into account the communications network of the parallel machine. For example the increasing use of SMP clusters (systems of multiprocessor compute nodes with very fast intra-node communications but relatively slow inter-node networks) suggest the use of hierarchical network models. Indeed this requirement is exacerbated in the early experiments with meta-computers (multiple supercomputers combined together, in extreme cases over inter-continental networks). In this paper therefore, we modify a multilevel algorithm in order to minimise a cost function based on a model of the communications network. Several network models and variants of the algorithm are tested and we establish that it is possible to successfully guide the optimisation to reflect the chosen architecture.
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Multiphase Mesh Partitioning
Applied Mathematical Modelling, 2000Co-Authors: Chris Walshaw, Mark Cross, K. McmanusAbstract:We consider the load-balancing problems which arise from parallel scientific codes containing multiple computational phases, or loops over subsets of the data, which are separated by global synchronisation points. We motivate, derive and describe the implementation of an approach which we refer to as the multiphase Mesh Partitioning strategy to address such issues. The technique is tested on several examples of Meshes, both real and artificial, containing multiple computational phases and it is demonstrated that our method can achieve high quality partitions where a standard Mesh Partitioning approach fails.
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Mesh Partitioning: A Multilevel Balancing and Refinement Algorithm
SIAM Journal on Scientific Computing, 2000Co-Authors: Chris Walshaw, Mark CrossAbstract:Multilevel algorithms are a successful class of optimization techniques which addresses the Mesh Partitioning problem. They usually combine a graph contraction algorithm together with a local optimization method which refines the partition at each graph level. In this paper we present an enhancement of the technique which uses imbalance to achieve higher quality partitions. We also present a formulation of the Kernighan--Lin partition optimization algorithm which incorporates load-balancing. The resulting algorithm is tested against a different but related state-of-the-art partitioner and shown to provide improved results.
F Schlimbach - One of the best experts on this subject based on the ideXlab platform.
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multilevel Mesh Partitioning for optimising aspect ratio
International Conference on Parallel Processing, 1999Co-Authors: Chris Walshaw, Mark Cross, Ralf Diekmann, F SchlimbachAbstract:Mesh Partitioning problem. They usually combine a graph contraction algorithm together with a local optimisation method which refines the partition at each graph level To date these algorithms have been used almost exclusively to minimise the cut-edge weight, however it has been shown that for certain classes of solution algorithm, the convergence of the solver is strongly influenced by the subdomain aspect ratio. In this paper therefore, we modify the multilevel algorithms in order to optimise a cost function based on aspect ratio. Several variants of the algorithms are tested and shown to provide excellent results. -
VECPAR - Multilevel Mesh Partitioning for Optimising Aspect Ratio
Vector and Parallel Processing – VECPAR’98, 1999Co-Authors: Chris Walshaw, Mark Cross, Ralf Diekmann, F SchlimbachAbstract:Multilevel algorithms are a successful class of optimisation techniques which address the Mesh Partitioning problem. They usually combine a graph contraction algorithm together with a local optimisation method which refines the partition at each graph level. To date these algorithms have been used almost exclusively to minimise the cut-edge weight, however it has been shown that for certain classes of solution algorithm, the convergence of the solver is strongly influenced by the subdomain aspect ratio. In this paper therefore, we modify the multilevel algorithms in order to optimise a cost function based on aspect ratio. Several variants of the algorithms are tested and shown to provide excellent results.
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Multilevel Mesh Partitioning for Optimizing Domain Shape
The International Journal of High Performance Computing Applications, 1999Co-Authors: Chris Walshaw, Mark Cross, Ralf Diekmann, F SchlimbachAbstract:Multilevel algorithms are a successful class of optimization techniques that address the Mesh Partitioning problem for mapping Meshes onto parallel computers. They usually combine a graph contraction algorithm together with a lo-cal optimization method that refines the partition at each graph level. To date, these algorithms have been used al-most exclusively to minimize the cut-edge weight in the graph with the aim of minimizing the parallel communication overhead. However, it has been shown that for certain classes of problems, the convergence of the underlying solution algorithm is strongly influenced by the shape or aspect ratio of the subdomains. Therefore, in this paper, the authors modify the multilevel algorithms to optimize a cost function based on the aspect ratio. Several variants of the algorithms are tested and shown to provide excellent results.
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aspect radio for Mesh Partitioning
European Conference on Parallel Processing, 1998Co-Authors: Ralf Diekmann, Robert Preis, F Schlimbach, Chris WalshawAbstract:This paper deals with the measure of Aspect Ratio for Mesh Partitioning and gives hints why, for certain solvers, the Aspect Ratio of partitions plays an important role. We define and rate different kinds of Aspect Ratio, present a new center-based Partitioning method which optimizes this measure implicitly and rate several existing Partitioning methods and tools under the criterion of Aspect Ratio.
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Euro-Par - Aspect Radio for Mesh Partitioning
Euro-Par’98 Parallel Processing, 1998Co-Authors: Ralf Diekmann, Robert Preis, F Schlimbach, Chris WalshawAbstract:This paper deals with the measure of Aspect Ratio for Mesh Partitioning and gives hints why, for certain solvers, the Aspect Ratio of partitions plays an important role. We define and rate different kinds of Aspect Ratio, present a new center-based Partitioning method which optimizes this measure implicitly and rate several existing Partitioning methods and tools under the criterion of Aspect Ratio.
Guillaume Houzeaux - One of the best experts on this subject based on the ideXlab platform.
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Parallel SFC-based Mesh Partitioning and load balancing
arXiv: Computational Physics, 2020Co-Authors: R. Borrell, Guillermo Oyarzun, Damien Dosimont, Guillaume HouzeauxAbstract:Modern supercomputers allow the simulation of complex phenomena with increased accuracy. Eventually, this requires finer geometric discretizations with larger numbers of Mesh elements. In this context, and extrapolating to the Exascale paradigm, Meshing operations such as generation, adaptation or partition, become a critical bottleneck within the simulation workflow. In this paper, we focus on Mesh Partitioning. In particular, we present some improvements carried out on an in-house parallel Mesh partitioner based on the Hilbert Space-Filling Curve. Additionally, taking advantage of its performance, we present the application of the SFC-based Partitioning for dynamic load balancing. This method is based on the direct monitoring of the imbalance at runtime and the subsequent re-Partitioning of the Mesh. The target weights for the optimized partitions are evaluated using a least-squares approximation considering all measurements from previous iterations. In this way, the final partition corresponds to the average performance of the computing devices engaged.
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parallel sfc based Mesh Partitioning and load balancing
2019 IEEE ACM 10th Workshop on Latest Advances in Scalable Algorithms for Large-Scale Systems (ScalA), 2019Co-Authors: R. Borrell, Guillermo Oyarzun, Damien Dosimont, Guillaume HouzeauxAbstract:Modern supercomputers allow the simulation of complex phenomena with increased accuracy. Eventually, this requires finer geometric discretizations with larger numbers of Mesh elements. In this context, and extrapolating to the Exascale paradigm, Meshing operations such as generation, adaptation or partition, become a critical issue within the simulation workflow. In this paper, we focus on Mesh Partitioning. In particular, we present some improvements carried out on an in-house parallel Mesh partitioner based on the Hilbert Space-Filling Curve. Additionally, taking advantage of its performance, we present the application of the SFC-based Partitioning for dynamic load balancing. This method is based on the direct monitoring of the imbalance at runtime and the subsequent re-Partitioning of the Mesh. The target weights for the optimized partitions are evaluated using a least-squares approximation considering all measurements from previous iterations. In this way, the final partition corresponds to the average performance of the computing devices engaged.
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ScalA@SC - Parallel SFC-based Mesh Partitioning and load balancing
2019 IEEE ACM 10th Workshop on Latest Advances in Scalable Algorithms for Large-Scale Systems (ScalA), 2019Co-Authors: R. Borrell, Guillermo Oyarzun, Damien Dosimont, Guillaume HouzeauxAbstract:Modern supercomputers allow the simulation of complex phenomena with increased accuracy. Eventually, this requires finer geometric discretizations with larger numbers of Mesh elements. In this context, and extrapolating to the Exascale paradigm, Meshing operations such as generation, adaptation or partition, become a critical issue within the simulation workflow. In this paper, we focus on Mesh Partitioning. In particular, we present some improvements carried out on an in-house parallel Mesh partitioner based on the Hilbert Space-Filling Curve. Additionally, taking advantage of its performance, we present the application of the SFC-based Partitioning for dynamic load balancing. This method is based on the direct monitoring of the imbalance at runtime and the subsequent re-Partitioning of the Mesh. The target weights for the optimized partitions are evaluated using a least-squares approximation considering all measurements from previous iterations. In this way, the final partition corresponds to the average performance of the computing devices engaged.
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Parallel Mesh Partitioning based on space filling curves
Computers & Fluids, 2018Co-Authors: R. Borrell, J.c. Cajas, Daniel Mira, Ahmed Taha, Seid Koric, Mariano Vázquez, Guillaume HouzeauxAbstract:Abstract Larger supercomputers allow the simulation of more complex phenomena with increased accuracy. Eventually this requires finer and thus also larger geometric discretizations. In this context, and extrapolating to the Exascale paradigm, Meshing operations such as generation, deformation, adaptation/regeneration or partition/load balance, become a critical issue within the simulation workflow. In this paper we focus on Mesh Partitioning. In particular, we present a fast and scalable geometric partitioner based on Space Filling Curves (SFC), as an alternative to the standard graph Partitioning approach. We have avoided any computing or memory bottleneck in the algorithm, while we have imposed that the solution achieved is independent (discounting rounding off errors) of the number of parallel processes used to compute it. The performance of the SFC-based partitioner presented has been demonstrated using up to 4096 CPU-cores in the Blue Waters supercomputer.
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Parallel Mesh Partitioning in Alya
2015Co-Authors: Antoni Artigues, Guillaume HouzeauxAbstract:The Alya System is the BSC simulation code for multi-physics problems [1]. It is based on a Variational Multiscale Finite Element Method for unstructured Meshes. Work distribution is achieved by Partitioning the original Mesh into subdomains (subMeshes). This pre-partition step has until now been done in serial by only one process, using the metis library [2]. This is a huge bottleneck when larger Meshes with millions of elements have to be partitioned. This is due to the data not fitting in the memory of a single computing node and in the cases where the data does fit; Alya takes too long in the Partitioning step. In this document we explain the tasks done to design, implement and test a new parallel Partitioning algorithm for Alya. In this algorithm a subset of the workers, is in charge of partition the Mesh in parallel, using the parmetis library [3]. Partitioning workers, load consecutive parts of the main Mesh, with a parallel space Partitioning bin structure [4], capable of obtaining the adjacent boundary elements of their respective subMeshes. With this local Mesh, each of the Partitioning workers is able to create its local element adjacency graph and to partition the Mesh. We have validated our new algorithm using a Navier-Stokes problem on a small cube Mesh of 1000 elements. Then we performed a scalability test on a 30M element Mesh to check if the time to partition the Mesh is reduced proportionally with the number of Partitioning workers. We have also done a comparison between metis and parmetis, the balancing of the element distribution among the domains, to test how the use of many Partitioning workers to partition the Mesh affects the scalability of Alya. We have noticed in these tests that it’s better to use fewer Partitioning workers to partition the Mesh. Finally we have two sections explaining the results and the future work that has to be done in order to finalise and improve the parallel partition algorithm.
Charbel Farhat - One of the best experts on this subject based on the ideXlab platform.
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top domdec a software tool for Mesh Partitioning and parallel processing
Computing Systems in Engineering, 1995Co-Authors: Charbel Farhat, Stéphane Lanteri, Horst D. SimonAbstract:Abstract TOP/DOMDEC is an interactive software package for Mesh Partitioning and parallel processing. It offers several state-of-the-art graph decomposition algorithms in a user friendly environment. Generated Mesh partitions can be smoothed and optimized for minimum interface and maximum load balance using one of several non-deterministic optimization algorithms. TOP/DOMDEC also provides real-time means for assessing a priori the quality of a Mesh partition and discriminating between different Partitioning algorithms. The user interface includes high speed three-dimensional graphics, an interprocessor communication simulator for today's massively parallel systems, and an output function with parallel I/O data structures. In this paper, we describe the basic features of TOP/DOMDEC and highlight their application to the parallel solution of computational fluid and solid mechanics problems.
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Mesh Partitioning for implicit computations via iterative domain decomposition: Impact and optimization of the subdomain aspect ratio
International Journal for Numerical Methods in Engineering, 1995Co-Authors: Charbel Farhat, Nathan Maman, Gregory W. BrownAbstract:Optimal domain decomposition methods have emerged as powerful iterative algorithms for parallel implicit computations. Their key preprocessing step is Mesh Partitioning, where research has focused so far on the automatic generation of load-balanced subdomains with minimum interface nodes. In this paper, we emphasize the importance of the subdomain aspect ratio as a Mesh Partitioning factor, and highlight its impact an the convergence rate of an optimal domain decomposition based iterative method. We also present a fast optimization algorithm for improving the aspect ratio of existing Mesh partitions, and illustrate it with several examples from fluid dynamics and structural mechanics applications. For a stiffened shell problem decomposed by the optimal Recursive Spectral Bisection scheme and solved by the FETI method, this optimization algorithm is shown to improve the solution time by a factor equal to 1.54 and to restore numerical scalability.
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TOP/DOMDEC—A software tool for Mesh Partitioning and parallel processing
Computing Systems in Engineering, 1995Co-Authors: Charbel Farhat, Stéphane Lanteri, Horst D. SimonAbstract:Abstract TOP/DOMDEC is an interactive software package for Mesh Partitioning and parallel processing. It offers several state-of-the-art graph decomposition algorithms in a user friendly environment. Generated Mesh partitions can be smoothed and optimized for minimum interface and maximum load balance using one of several non-deterministic optimization algorithms. TOP/DOMDEC also provides real-time means for assessing a priori the quality of a Mesh partition and discriminating between different Partitioning algorithms. The user interface includes high speed three-dimensional graphics, an interprocessor communication simulator for today's massively parallel systems, and an output function with parallel I/O data structures. In this paper, we describe the basic features of TOP/DOMDEC and highlight their application to the parallel solution of computational fluid and solid mechanics problems.
