4,929 research outputs found
Hierarchical Dynamic Loop Self-Scheduling on Distributed-Memory Systems Using an MPI+MPI Approach
Computationally-intensive loops are the primary source of parallelism in
scientific applications. Such loops are often irregular and a balanced
execution of their loop iterations is critical for achieving high performance.
However, several factors may lead to an imbalanced load execution, such as
problem characteristics, algorithmic, and systemic variations. Dynamic loop
self-scheduling (DLS) techniques are devised to mitigate these factors, and
consequently, improve application performance. On distributed-memory systems,
DLS techniques can be implemented using a hierarchical master-worker execution
model and are, therefore, called hierarchical DLS techniques. These techniques
self-schedule loop iterations at two levels of hardware parallelism: across and
within compute nodes. Hybrid programming approaches that combine the message
passing interface (MPI) with open multi-processing (OpenMP) dominate the
implementation of hierarchical DLS techniques. The MPI-3 standard includes the
feature of sharing memory regions among MPI processes. This feature introduced
the MPI+MPI approach that simplifies the implementation of parallel scientific
applications. The present work designs and implements hierarchical DLS
techniques by exploiting the MPI+MPI approach. Four well-known DLS techniques
are considered in the evaluation proposed herein. The results indicate certain
performance advantages of the proposed approach compared to the hybrid
MPI+OpenMP approach
DART-MPI: An MPI-based Implementation of a PGAS Runtime System
A Partitioned Global Address Space (PGAS) approach treats a distributed
system as if the memory were shared on a global level. Given such a global view
on memory, the user may program applications very much like shared memory
systems. This greatly simplifies the tasks of developing parallel applications,
because no explicit communication has to be specified in the program for data
exchange between different computing nodes. In this paper we present DART, a
runtime environment, which implements the PGAS paradigm on large-scale
high-performance computing clusters. A specific feature of our implementation
is the use of one-sided communication of the Message Passing Interface (MPI)
version 3 (i.e. MPI-3) as the underlying communication substrate. We evaluated
the performance of the implementation with several low-level kernels in order
to determine overheads and limitations in comparison to the underlying MPI-3.Comment: 11 pages, International Conference on Partitioned Global Address
Space Programming Models (PGAS14
Design and Implementation of MPICH2 over InfiniBand with RDMA Support
For several years, MPI has been the de facto standard for writing parallel
applications. One of the most popular MPI implementations is MPICH. Its
successor, MPICH2, features a completely new design that provides more
performance and flexibility. To ensure portability, it has a hierarchical
structure based on which porting can be done at different levels. In this
paper, we present our experiences designing and implementing MPICH2 over
InfiniBand. Because of its high performance and open standard, InfiniBand is
gaining popularity in the area of high-performance computing. Our study focuses
on optimizing the performance of MPI-1 functions in MPICH2. One of our
objectives is to exploit Remote Direct Memory Access (RDMA) in Infiniband to
achieve high performance. We have based our design on the RDMA Channel
interface provided by MPICH2, which encapsulates architecture-dependent
communication functionalities into a very small set of functions. Starting with
a basic design, we apply different optimizations and also propose a
zero-copy-based design. We characterize the impact of our optimizations and
designs using microbenchmarks. We have also performed an application-level
evaluation using the NAS Parallel Benchmarks. Our optimized MPICH2
implementation achieves 7.6 s latency and 857 MB/s bandwidth, which are
close to the raw performance of the underlying InfiniBand layer. Our study
shows that the RDMA Channel interface in MPICH2 provides a simple, yet
powerful, abstraction that enables implementations with high performance by
exploiting RDMA operations in InfiniBand. To the best of our knowledge, this is
the first high-performance design and implementation of MPICH2 on InfiniBand
using RDMA support.Comment: 12 pages, 17 figure
POSH: Paris OpenSHMEM: A High-Performance OpenSHMEM Implementation for Shared Memory Systems
In this paper we present the design and implementation of POSH, an
Open-Source implementation of the OpenSHMEM standard. We present a model for
its communications, and prove some properties on the memory model defined in
the OpenSHMEM specification. We present some performance measurements of the
communication library featured by POSH and compare them with an existing
one-sided communication library. POSH can be downloaded from
\url{http://www.lipn.fr/~coti/POSH}. % 9 - 67Comment: This is an extended version (featuring the full proofs) of a paper
accepted at ICCS'1
Increasing the Efficiency of Sparse Matrix-Matrix Multiplication with a 2.5D Algorithm and One-Sided MPI
Matrix-matrix multiplication is a basic operation in linear algebra and an
essential building block for a wide range of algorithms in various scientific
fields. Theory and implementation for the dense, square matrix case are
well-developed. If matrices are sparse, with application-specific sparsity
patterns, the optimal implementation remains an open question. Here, we explore
the performance of communication reducing 2.5D algorithms and one-sided MPI
communication in the context of linear scaling electronic structure theory. In
particular, we extend the DBCSR sparse matrix library, which is the basic
building block for linear scaling electronic structure theory and low scaling
correlated methods in CP2K. The library is specifically designed to efficiently
perform block-sparse matrix-matrix multiplication of matrices with a relatively
large occupation. Here, we compare the performance of the original
implementation based on Cannon's algorithm and MPI point-to-point
communication, with an implementation based on MPI one-sided communications
(RMA), in both a 2D and a 2.5D approach. The 2.5D approach trades memory and
auxiliary operations for reduced communication, which can lead to a speedup if
communication is dominant. The 2.5D algorithm is somewhat easier to implement
with one-sided communications. A detailed description of the implementation is
provided, also for non ideal processor topologies, since this is important for
actual applications. Given the importance of the precise sparsity pattern, and
even the actual matrix data, which decides the effective fill-in upon
multiplication, the tests are performed within the CP2K package with
application benchmarks. Results show a substantial boost in performance for the
RMA based 2.5D algorithm, up to 1.80x, which is observed to increase with the
number of involved processes in the parallelization.Comment: In Proceedings of PASC '17, Lugano, Switzerland, June 26-28, 2017, 10
pages, 4 figure
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