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