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Current fftw source
author Chris Cannam <cannam@all-day-breakfast.com>
date Tue, 18 Oct 2016 13:40:26 +0100
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cannam@127 3 <!-- This manual is for FFTW
cannam@127 4 (version 3.3.5, 30 July 2016).
cannam@127 5
cannam@127 6 Copyright (C) 2003 Matteo Frigo.
cannam@127 7
cannam@127 8 Copyright (C) 2003 Massachusetts Institute of Technology.
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cannam@127 24 <head>
cannam@127 25 <title>FFTW 3.3.5: Distributed-memory FFTW with MPI</title>
cannam@127 26
cannam@127 27 <meta name="description" content="FFTW 3.3.5: Distributed-memory FFTW with MPI">
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cannam@127 70
cannam@127 71 <body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
cannam@127 72 <a name="Distributed_002dmemory-FFTW-with-MPI"></a>
cannam@127 73 <div class="header">
cannam@127 74 <p>
cannam@127 75 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>
cannam@127 76 </div>
cannam@127 77 <hr>
cannam@127 78 <a name="Distributed_002dmemory-FFTW-with-MPI-1"></a>
cannam@127 79 <h2 class="chapter">6 Distributed-memory FFTW with MPI</h2>
cannam@127 80 <a name="index-MPI"></a>
cannam@127 81
cannam@127 82 <a name="index-parallel-transform-1"></a>
cannam@127 83 <p>In this chapter we document the parallel FFTW routines for parallel
cannam@127 84 systems supporting the MPI message-passing interface. Unlike the
cannam@127 85 shared-memory threads described in the previous chapter, MPI allows
cannam@127 86 you to use <em>distributed-memory</em> parallelism, where each CPU has
cannam@127 87 its own separate memory, and which can scale up to clusters of many
cannam@127 88 thousands of processors. This capability comes at a price, however:
cannam@127 89 each process only stores a <em>portion</em> of the data to be
cannam@127 90 transformed, which means that the data structures and
cannam@127 91 programming-interface are quite different from the serial or threads
cannam@127 92 versions of FFTW.
cannam@127 93 <a name="index-data-distribution"></a>
cannam@127 94 </p>
cannam@127 95
cannam@127 96 <p>Distributed-memory parallelism is especially useful when you are
cannam@127 97 transforming arrays so large that they do not fit into the memory of a
cannam@127 98 single processor. The storage per-process required by FFTW&rsquo;s MPI
cannam@127 99 routines is proportional to the total array size divided by the number
cannam@127 100 of processes. Conversely, distributed-memory parallelism can easily
cannam@127 101 pose an unacceptably high communications overhead for small problems;
cannam@127 102 the threshold problem size for which parallelism becomes advantageous
cannam@127 103 will depend on the precise problem you are interested in, your
cannam@127 104 hardware, and your MPI implementation.
cannam@127 105 </p>
cannam@127 106 <p>A note on terminology: in MPI, you divide the data among a set of
cannam@127 107 &ldquo;processes&rdquo; which each run in their own memory address space.
cannam@127 108 Generally, each process runs on a different physical processor, but
cannam@127 109 this is not required. A set of processes in MPI is described by an
cannam@127 110 opaque data structure called a &ldquo;communicator,&rdquo; the most common of
cannam@127 111 which is the predefined communicator <code>MPI_COMM_WORLD</code> which
cannam@127 112 refers to <em>all</em> processes. For more information on these and
cannam@127 113 other concepts common to all MPI programs, we refer the reader to the
cannam@127 114 documentation at <a href="http://www.mcs.anl.gov/research/projects/mpi/">the MPI home
cannam@127 115 page</a>.
cannam@127 116 <a name="index-MPI-communicator"></a>
cannam@127 117 <a name="index-MPI_005fCOMM_005fWORLD"></a>
cannam@127 118 </p>
cannam@127 119
cannam@127 120 <p>We assume in this chapter that the reader is familiar with the usage
cannam@127 121 of the serial (uniprocessor) FFTW, and focus only on the concepts new
cannam@127 122 to the MPI interface.
cannam@127 123 </p>
cannam@127 124 <table class="menu" border="0" cellspacing="0">
cannam@127 125 <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">
cannam@127 126 </td></tr>
cannam@127 127 <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">
cannam@127 128 </td></tr>
cannam@127 129 <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">
cannam@127 130 </td></tr>
cannam@127 131 <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">
cannam@127 132 </td></tr>
cannam@127 133 <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">
cannam@127 134 </td></tr>
cannam@127 135 <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">
cannam@127 136 </td></tr>
cannam@127 137 <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">
cannam@127 138 </td></tr>
cannam@127 139 <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">
cannam@127 140 </td></tr>
cannam@127 141 <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">
cannam@127 142 </td></tr>
cannam@127 143 <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">
cannam@127 144 </td></tr>
cannam@127 145 <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">
cannam@127 146 </td></tr>
cannam@127 147 <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">
cannam@127 148 </td></tr>
cannam@127 149 <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">
cannam@127 150 </td></tr>
cannam@127 151 </table>
cannam@127 152
cannam@127 153 <hr>
cannam@127 154 <div class="header">
cannam@127 155 <p>
cannam@127 156 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>
cannam@127 157 </div>
cannam@127 158
cannam@127 159
cannam@127 160
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cannam@127 162 </html>