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105 lines
4.6 KiB
HTML
105 lines
4.6 KiB
HTML
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- This manual is for FFTW
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(version 3.3.10, 10 December 2020).
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Copyright (C) 2003 Matteo Frigo.
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Copyright (C) 2003 Massachusetts Institute of Technology.
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Permission is granted to make and distribute verbatim copies of this
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manual provided the copyright notice and this permission notice are
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preserved on all copies.
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Permission is granted to copy and distribute modified versions of this
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manual under the conditions for verbatim copying, provided that the
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entire resulting derived work is distributed under the terms of a
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permission notice identical to this one.
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Permission is granted to copy and distribute translations of this manual
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into another language, under the above conditions for modified versions,
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except that this permission notice may be stated in a translation
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approved by the Free Software Foundation. -->
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<!-- Created by GNU Texinfo 6.7, http://www.gnu.org/software/texinfo/ -->
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<title>FFTW MPI Performance Tips (FFTW 3.3.10)</title>
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<meta name="description" content="FFTW MPI Performance Tips (FFTW 3.3.10)">
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<meta name="keywords" content="FFTW MPI Performance Tips (FFTW 3.3.10)">
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<meta name="distribution" content="global">
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<meta name="Generator" content="makeinfo">
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<link href="index.html" rel="start" title="Top">
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<link href="Concept-Index.html" rel="index" title="Concept Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Distributed_002dmemory-FFTW-with-MPI.html" rel="up" title="Distributed-memory FFTW with MPI">
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<link href="Combining-MPI-and-Threads.html" rel="next" title="Combining MPI and Threads">
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<link href="Avoiding-MPI-Deadlocks.html" rel="prev" title="Avoiding MPI Deadlocks">
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</head>
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<body lang="en">
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<span id="FFTW-MPI-Performance-Tips"></span><div class="header">
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<p>
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Next: <a href="Combining-MPI-and-Threads.html" accesskey="n" rel="next">Combining MPI and Threads</a>, Previous: <a href="Avoiding-MPI-Deadlocks.html" accesskey="p" rel="prev">Avoiding MPI Deadlocks</a>, Up: <a href="Distributed_002dmemory-FFTW-with-MPI.html" accesskey="u" rel="up">Distributed-memory FFTW with MPI</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<span id="FFTW-MPI-Performance-Tips-1"></span><h3 class="section">6.10 FFTW MPI Performance Tips</h3>
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<p>In this section, we collect a few tips on getting the best performance
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out of FFTW’s MPI transforms.
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</p>
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<p>First, because of the 1d block distribution, FFTW’s parallelization is
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currently limited by the size of the first dimension.
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(Multidimensional block distributions may be supported by a future
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version.) More generally, you should ideally arrange the dimensions so
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that FFTW can divide them equally among the processes. See <a href="Load-balancing.html">Load balancing</a>.
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<span id="index-block-distribution-2"></span>
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<span id="index-load-balancing-1"></span>
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</p>
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<p>Second, if it is not too inconvenient, you should consider working
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with transposed output for multidimensional plans, as this saves a
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considerable amount of communications. See <a href="Transposed-distributions.html">Transposed distributions</a>.
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<span id="index-transpose-3"></span>
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</p>
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<p>Third, the fastest choices are generally either an in-place transform
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or an out-of-place transform with the <code>FFTW_DESTROY_INPUT</code> flag
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(which allows the input array to be used as scratch space). In-place
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is especially beneficial if the amount of data per process is large.
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<span id="index-FFTW_005fDESTROY_005fINPUT-1"></span>
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</p>
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<p>Fourth, if you have multiple arrays to transform at once, rather than
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calling FFTW’s MPI transforms several times it usually seems to be
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faster to interleave the data and use the advanced interface. (This
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groups the communications together instead of requiring separate
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messages for each transform.)
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</p>
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</body>
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</html>
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