1,296 research outputs found
Hierarchical QR factorization algorithms for multi-core cluster systems
This paper describes a new QR factorization algorithm which is especially designed for massively parallel platforms combining parallel distributed nodes, where a node is a multi-core processor. These platforms represent the present and the foreseeable future of high-performance computing. Our new QR factorization algorithm falls in the category of the tile algorithms which naturally enables good data locality for the sequential kernels executed by the cores (high sequential performance), low number of messages in a parallel distributed setting (small latency term), and fine granularity (high parallelism). Each tile algorithm is uniquely characterized by its sequence of reduction trees. In the context of a cluster of nodes, in order to minimize the number of inter-processor communications (aka, ''communication-avoiding''), it is natural to consider hierarchical trees composed of an ''inter-node'' tree which acts on top of ''intra-node'' trees. At the intra-node level, we propose a hierarchical tree made of three levels: (0) ''TS level'' for cache-friendliness, (1) ''low-level'' for decoupled highly parallel inter-node reductions, (2) ''domino level'' to efficiently resolve interactions between local reductions and global reductions. Our hierarchical algorithm and its implementation are flexible and modular, and can accommodate several kernel types, different distribution layouts, and a variety of reduction trees at all levels, both inter-node and intra-node. Numerical experiments on a cluster of multi-core nodes (i) confirm that each of the four levels of our hierarchical tree contributes to build up performance and (ii) build insights on how these levels influence performance and interact within each other. Our implementation of the new algorithm with the DAGUE scheduling tool significantly outperforms currently available QR factorization software for all matrix shapes, thereby bringing a new advance in numerical linear algebra for petascale and exascale platforms
QR Factorization of Tall and Skinny Matrices in a Grid Computing Environment
Previous studies have reported that common dense linear algebra operations do
not achieve speed up by using multiple geographical sites of a computational
grid. Because such operations are the building blocks of most scientific
applications, conventional supercomputers are still strongly predominant in
high-performance computing and the use of grids for speeding up large-scale
scientific problems is limited to applications exhibiting parallelism at a
higher level. We have identified two performance bottlenecks in the distributed
memory algorithms implemented in ScaLAPACK, a state-of-the-art dense linear
algebra library. First, because ScaLAPACK assumes a homogeneous communication
network, the implementations of ScaLAPACK algorithms lack locality in their
communication pattern. Second, the number of messages sent in the ScaLAPACK
algorithms is significantly greater than other algorithms that trade flops for
communication. In this paper, we present a new approach for computing a QR
factorization -- one of the main dense linear algebra kernels -- of tall and
skinny matrices in a grid computing environment that overcomes these two
bottlenecks. Our contribution is to articulate a recently proposed algorithm
(Communication Avoiding QR) with a topology-aware middleware (QCG-OMPI) in
order to confine intensive communications (ScaLAPACK calls) within the
different geographical sites. An experimental study conducted on the Grid'5000
platform shows that the resulting performance increases linearly with the
number of geographical sites on large-scale problems (and is in particular
consistently higher than ScaLAPACK's).Comment: Accepted at IPDPS10. (IEEE International Parallel & Distributed
Processing Symposium 2010 in Atlanta, GA, USA.
Taking advantage of hybrid systems for sparse direct solvers via task-based runtimes
The ongoing hardware evolution exhibits an escalation in the number, as well
as in the heterogeneity, of computing resources. The pressure to maintain
reasonable levels of performance and portability forces application developers
to leave the traditional programming paradigms and explore alternative
solutions. PaStiX is a parallel sparse direct solver, based on a dynamic
scheduler for modern hierarchical manycore architectures. In this paper, we
study the benefits and limits of replacing the highly specialized internal
scheduler of the PaStiX solver with two generic runtime systems: PaRSEC and
StarPU. The tasks graph of the factorization step is made available to the two
runtimes, providing them the opportunity to process and optimize its traversal
in order to maximize the algorithm efficiency for the targeted hardware
platform. A comparative study of the performance of the PaStiX solver on top of
its native internal scheduler, PaRSEC, and StarPU frameworks, on different
execution environments, is performed. The analysis highlights that these
generic task-based runtimes achieve comparable results to the
application-optimized embedded scheduler on homogeneous platforms. Furthermore,
they are able to significantly speed up the solver on heterogeneous
environments by taking advantage of the accelerators while hiding the
complexity of their efficient manipulation from the programmer.Comment: Heterogeneity in Computing Workshop (2014
Computing the eigenvalues of symmetric H2-matrices by slicing the spectrum
The computation of eigenvalues of large-scale matrices arising from finite
element discretizations has gained significant interest in the last decade.
Here we present a new algorithm based on slicing the spectrum that takes
advantage of the rank structure of resolvent matrices in order to compute m
eigenvalues of the generalized symmetric eigenvalue problem in operations, where is a small constant
Matrix Factorization at Scale: a Comparison of Scientific Data Analytics in Spark and C+MPI Using Three Case Studies
We explore the trade-offs of performing linear algebra using Apache Spark,
compared to traditional C and MPI implementations on HPC platforms. Spark is
designed for data analytics on cluster computing platforms with access to local
disks and is optimized for data-parallel tasks. We examine three widely-used
and important matrix factorizations: NMF (for physical plausability), PCA (for
its ubiquity) and CX (for data interpretability). We apply these methods to
TB-sized problems in particle physics, climate modeling and bioimaging. The
data matrices are tall-and-skinny which enable the algorithms to map
conveniently into Spark's data-parallel model. We perform scaling experiments
on up to 1600 Cray XC40 nodes, describe the sources of slowdowns, and provide
tuning guidance to obtain high performance
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