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1 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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2 <html>
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3 <!-- This manual is for FFTW
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4 (version 3.3.5, 30 July 2016).
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5
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6 Copyright (C) 2003 Matteo Frigo.
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7
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8 Copyright (C) 2003 Massachusetts Institute of Technology.
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9
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10 Permission is granted to make and distribute verbatim copies of this
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11 manual provided the copyright notice and this permission notice are
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12 preserved on all copies.
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13
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14 Permission is granted to copy and distribute modified versions of this
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15 manual under the conditions for verbatim copying, provided that the
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16 entire resulting derived work is distributed under the terms of a
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17 permission notice identical to this one.
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18
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19 Permission is granted to copy and distribute translations of this manual
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20 into another language, under the above conditions for modified versions,
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21 except that this permission notice may be stated in a translation
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22 approved by the Free Software Foundation. -->
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23 <!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
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24 <head>
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25 <title>FFTW 3.3.5: Distributed-memory FFTW with MPI</title>
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26
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27 <meta name="description" content="FFTW 3.3.5: Distributed-memory FFTW with MPI">
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28 <meta name="keywords" content="FFTW 3.3.5: Distributed-memory FFTW with MPI">
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33 <link href="index.html#Top" rel="start" title="Top">
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34 <link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index">
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35 <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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36 <link href="index.html#Top" rel="up" title="Top">
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37 <link href="FFTW-MPI-Installation.html#FFTW-MPI-Installation" rel="next" title="FFTW MPI Installation">
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38 <link href="Thread-safety.html#Thread-safety" rel="prev" title="Thread safety">
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65 -->
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66 </style>
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67
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68
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69 </head>
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70
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71 <body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
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72 <a name="Distributed_002dmemory-FFTW-with-MPI"></a>
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73 <div class="header">
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74 <p>
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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> [<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>
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76 </div>
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77 <hr>
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78 <a name="Distributed_002dmemory-FFTW-with-MPI-1"></a>
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79 <h2 class="chapter">6 Distributed-memory FFTW with MPI</h2>
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80 <a name="index-MPI"></a>
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81
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82 <a name="index-parallel-transform-1"></a>
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83 <p>In this chapter we document the parallel FFTW routines for parallel
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84 systems supporting the MPI message-passing interface. Unlike the
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85 shared-memory threads described in the previous chapter, MPI allows
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86 you to use <em>distributed-memory</em> parallelism, where each CPU has
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87 its own separate memory, and which can scale up to clusters of many
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88 thousands of processors. This capability comes at a price, however:
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89 each process only stores a <em>portion</em> of the data to be
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90 transformed, which means that the data structures and
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91 programming-interface are quite different from the serial or threads
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92 versions of FFTW.
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93 <a name="index-data-distribution"></a>
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94 </p>
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95
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96 <p>Distributed-memory parallelism is especially useful when you are
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97 transforming arrays so large that they do not fit into the memory of a
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98 single processor. The storage per-process required by FFTW’s MPI
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99 routines is proportional to the total array size divided by the number
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100 of processes. Conversely, distributed-memory parallelism can easily
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101 pose an unacceptably high communications overhead for small problems;
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102 the threshold problem size for which parallelism becomes advantageous
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103 will depend on the precise problem you are interested in, your
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104 hardware, and your MPI implementation.
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105 </p>
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106 <p>A note on terminology: in MPI, you divide the data among a set of
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107 “processes” which each run in their own memory address space.
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108 Generally, each process runs on a different physical processor, but
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109 this is not required. A set of processes in MPI is described by an
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110 opaque data structure called a “communicator,” the most common of
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111 which is the predefined communicator <code>MPI_COMM_WORLD</code> which
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112 refers to <em>all</em> processes. For more information on these and
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113 other concepts common to all MPI programs, we refer the reader to the
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114 documentation at <a href="http://www.mcs.anl.gov/research/projects/mpi/">the MPI home
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115 page</a>.
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116 <a name="index-MPI-communicator"></a>
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117 <a name="index-MPI_005fCOMM_005fWORLD"></a>
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118 </p>
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119
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120 <p>We assume in this chapter that the reader is familiar with the usage
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121 of the serial (uniprocessor) FFTW, and focus only on the concepts new
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122 to the MPI interface.
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123 </p>
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124 <table class="menu" border="0" cellspacing="0">
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125 <tr><td align="left" valign="top">• <a href="FFTW-MPI-Installation.html#FFTW-MPI-Installation" accesskey="1">FFTW MPI Installation</a>:</td><td> </td><td align="left" valign="top">
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126 </td></tr>
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127 <tr><td align="left" valign="top">• <a href="Linking-and-Initializing-MPI-FFTW.html#Linking-and-Initializing-MPI-FFTW" accesskey="2">Linking and Initializing MPI FFTW</a>:</td><td> </td><td align="left" valign="top">
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128 </td></tr>
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129 <tr><td align="left" valign="top">• <a href="2d-MPI-example.html#g_t2d-MPI-example" accesskey="3">2d MPI example</a>:</td><td> </td><td align="left" valign="top">
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130 </td></tr>
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131 <tr><td align="left" valign="top">• <a href="MPI-Data-Distribution.html#MPI-Data-Distribution" accesskey="4">MPI Data Distribution</a>:</td><td> </td><td align="left" valign="top">
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132 </td></tr>
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133 <tr><td align="left" valign="top">• <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> </td><td align="left" valign="top">
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134 </td></tr>
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135 <tr><td align="left" valign="top">• <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> </td><td align="left" valign="top">
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136 </td></tr>
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137 <tr><td align="left" valign="top">• <a href="FFTW-MPI-Transposes.html#FFTW-MPI-Transposes" accesskey="7">FFTW MPI Transposes</a>:</td><td> </td><td align="left" valign="top">
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138 </td></tr>
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139 <tr><td align="left" valign="top">• <a href="FFTW-MPI-Wisdom.html#FFTW-MPI-Wisdom" accesskey="8">FFTW MPI Wisdom</a>:</td><td> </td><td align="left" valign="top">
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140 </td></tr>
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141 <tr><td align="left" valign="top">• <a href="Avoiding-MPI-Deadlocks.html#Avoiding-MPI-Deadlocks" accesskey="9">Avoiding MPI Deadlocks</a>:</td><td> </td><td align="left" valign="top">
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142 </td></tr>
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143 <tr><td align="left" valign="top">• <a href="FFTW-MPI-Performance-Tips.html#FFTW-MPI-Performance-Tips">FFTW MPI Performance Tips</a>:</td><td> </td><td align="left" valign="top">
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144 </td></tr>
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145 <tr><td align="left" valign="top">• <a href="Combining-MPI-and-Threads.html#Combining-MPI-and-Threads">Combining MPI and Threads</a>:</td><td> </td><td align="left" valign="top">
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146 </td></tr>
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147 <tr><td align="left" valign="top">• <a href="FFTW-MPI-Reference.html#FFTW-MPI-Reference">FFTW MPI Reference</a>:</td><td> </td><td align="left" valign="top">
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148 </td></tr>
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149 <tr><td align="left" valign="top">• <a href="FFTW-MPI-Fortran-Interface.html#FFTW-MPI-Fortran-Interface">FFTW MPI Fortran Interface</a>:</td><td> </td><td align="left" valign="top">
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150 </td></tr>
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151 </table>
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152
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153 <hr>
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154 <div class="header">
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155 <p>
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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> [<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>
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157 </div>
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158
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159
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160
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161 </body>
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162 </html>
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