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date Fri, 07 Feb 2020 11:51:13 +0000
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Chris@82 4 (version 3.3.8, 24 May 2018).
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Chris@82 6 Copyright (C) 2003 Matteo Frigo.
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Chris@82 25 <title>FFTW 3.3.8: Distributed-memory FFTW with MPI</title>
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Chris@82 69
Chris@82 70 <body lang="en">
Chris@82 71 <a name="Distributed_002dmemory-FFTW-with-MPI"></a>
Chris@82 72 <div class="header">
Chris@82 73 <p>
Chris@82 74 Next: <a href="Calling-FFTW-from-Modern-Fortran.html#Calling-FFTW-from-Modern-Fortran" accesskey="n" rel="next">Calling FFTW from Modern Fortran</a>, Previous: <a href="Multi_002dthreaded-FFTW.html#Multi_002dthreaded-FFTW" accesskey="p" rel="prev">Multi-threaded FFTW</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
Chris@82 75 </div>
Chris@82 76 <hr>
Chris@82 77 <a name="Distributed_002dmemory-FFTW-with-MPI-1"></a>
Chris@82 78 <h2 class="chapter">6 Distributed-memory FFTW with MPI</h2>
Chris@82 79 <a name="index-MPI"></a>
Chris@82 80
Chris@82 81 <a name="index-parallel-transform-1"></a>
Chris@82 82 <p>In this chapter we document the parallel FFTW routines for parallel
Chris@82 83 systems supporting the MPI message-passing interface. Unlike the
Chris@82 84 shared-memory threads described in the previous chapter, MPI allows
Chris@82 85 you to use <em>distributed-memory</em> parallelism, where each CPU has
Chris@82 86 its own separate memory, and which can scale up to clusters of many
Chris@82 87 thousands of processors. This capability comes at a price, however:
Chris@82 88 each process only stores a <em>portion</em> of the data to be
Chris@82 89 transformed, which means that the data structures and
Chris@82 90 programming-interface are quite different from the serial or threads
Chris@82 91 versions of FFTW.
Chris@82 92 <a name="index-data-distribution"></a>
Chris@82 93 </p>
Chris@82 94
Chris@82 95 <p>Distributed-memory parallelism is especially useful when you are
Chris@82 96 transforming arrays so large that they do not fit into the memory of a
Chris@82 97 single processor. The storage per-process required by FFTW&rsquo;s MPI
Chris@82 98 routines is proportional to the total array size divided by the number
Chris@82 99 of processes. Conversely, distributed-memory parallelism can easily
Chris@82 100 pose an unacceptably high communications overhead for small problems;
Chris@82 101 the threshold problem size for which parallelism becomes advantageous
Chris@82 102 will depend on the precise problem you are interested in, your
Chris@82 103 hardware, and your MPI implementation.
Chris@82 104 </p>
Chris@82 105 <p>A note on terminology: in MPI, you divide the data among a set of
Chris@82 106 &ldquo;processes&rdquo; which each run in their own memory address space.
Chris@82 107 Generally, each process runs on a different physical processor, but
Chris@82 108 this is not required. A set of processes in MPI is described by an
Chris@82 109 opaque data structure called a &ldquo;communicator,&rdquo; the most common of
Chris@82 110 which is the predefined communicator <code>MPI_COMM_WORLD</code> which
Chris@82 111 refers to <em>all</em> processes. For more information on these and
Chris@82 112 other concepts common to all MPI programs, we refer the reader to the
Chris@82 113 documentation at <a href="http://www.mcs.anl.gov/research/projects/mpi/">the MPI home
Chris@82 114 page</a>.
Chris@82 115 <a name="index-MPI-communicator"></a>
Chris@82 116 <a name="index-MPI_005fCOMM_005fWORLD"></a>
Chris@82 117 </p>
Chris@82 118
Chris@82 119 <p>We assume in this chapter that the reader is familiar with the usage
Chris@82 120 of the serial (uniprocessor) FFTW, and focus only on the concepts new
Chris@82 121 to the MPI interface.
Chris@82 122 </p>
Chris@82 123 <table class="menu" border="0" cellspacing="0">
Chris@82 124 <tr><td align="left" valign="top">&bull; <a href="FFTW-MPI-Installation.html#FFTW-MPI-Installation" accesskey="1">FFTW MPI Installation</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
Chris@82 125 </td></tr>
Chris@82 126 <tr><td align="left" valign="top">&bull; <a href="Linking-and-Initializing-MPI-FFTW.html#Linking-and-Initializing-MPI-FFTW" accesskey="2">Linking and Initializing MPI FFTW</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
Chris@82 127 </td></tr>
Chris@82 128 <tr><td align="left" valign="top">&bull; <a href="2d-MPI-example.html#g_t2d-MPI-example" accesskey="3">2d MPI example</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
Chris@82 129 </td></tr>
Chris@82 130 <tr><td align="left" valign="top">&bull; <a href="MPI-Data-Distribution.html#MPI-Data-Distribution" accesskey="4">MPI Data Distribution</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
Chris@82 131 </td></tr>
Chris@82 132 <tr><td align="left" valign="top">&bull; <a href="Multi_002ddimensional-MPI-DFTs-of-Real-Data.html#Multi_002ddimensional-MPI-DFTs-of-Real-Data" accesskey="5">Multi-dimensional MPI DFTs of Real Data</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
Chris@82 133 </td></tr>
Chris@82 134 <tr><td align="left" valign="top">&bull; <a href="Other-Multi_002ddimensional-Real_002ddata-MPI-Transforms.html#Other-Multi_002ddimensional-Real_002ddata-MPI-Transforms" accesskey="6">Other Multi-dimensional Real-data MPI Transforms</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
Chris@82 135 </td></tr>
Chris@82 136 <tr><td align="left" valign="top">&bull; <a href="FFTW-MPI-Transposes.html#FFTW-MPI-Transposes" accesskey="7">FFTW MPI Transposes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
Chris@82 137 </td></tr>
Chris@82 138 <tr><td align="left" valign="top">&bull; <a href="FFTW-MPI-Wisdom.html#FFTW-MPI-Wisdom" accesskey="8">FFTW MPI Wisdom</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
Chris@82 139 </td></tr>
Chris@82 140 <tr><td align="left" valign="top">&bull; <a href="Avoiding-MPI-Deadlocks.html#Avoiding-MPI-Deadlocks" accesskey="9">Avoiding MPI Deadlocks</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
Chris@82 141 </td></tr>
Chris@82 142 <tr><td align="left" valign="top">&bull; <a href="FFTW-MPI-Performance-Tips.html#FFTW-MPI-Performance-Tips">FFTW MPI Performance Tips</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
Chris@82 143 </td></tr>
Chris@82 144 <tr><td align="left" valign="top">&bull; <a href="Combining-MPI-and-Threads.html#Combining-MPI-and-Threads">Combining MPI and Threads</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
Chris@82 145 </td></tr>
Chris@82 146 <tr><td align="left" valign="top">&bull; <a href="FFTW-MPI-Reference.html#FFTW-MPI-Reference">FFTW MPI Reference</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
Chris@82 147 </td></tr>
Chris@82 148 <tr><td align="left" valign="top">&bull; <a href="FFTW-MPI-Fortran-Interface.html#FFTW-MPI-Fortran-Interface">FFTW MPI Fortran Interface</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
Chris@82 149 </td></tr>
Chris@82 150 </table>
Chris@82 151
Chris@82 152 <hr>
Chris@82 153 <div class="header">
Chris@82 154 <p>
Chris@82 155 Next: <a href="Calling-FFTW-from-Modern-Fortran.html#Calling-FFTW-from-Modern-Fortran" accesskey="n" rel="next">Calling FFTW from Modern Fortran</a>, Previous: <a href="Multi_002dthreaded-FFTW.html#Multi_002dthreaded-FFTW" accesskey="p" rel="prev">Multi-threaded FFTW</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
Chris@82 156 </div>
Chris@82 157
Chris@82 158
Chris@82 159
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