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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 3.3.8, 24 May 2018).
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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 6.3, http://www.gnu.org/software/texinfo/ -->
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24 <head>
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25 <title>FFTW 3.3.8: FFTW MPI Performance Tips</title>
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26
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27 <meta name="description" content="FFTW 3.3.8: FFTW MPI Performance Tips">
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28 <meta name="keywords" content="FFTW 3.3.8: FFTW MPI Performance Tips">
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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="Distributed_002dmemory-FFTW-with-MPI.html#Distributed_002dmemory-FFTW-with-MPI" rel="up" title="Distributed-memory FFTW with MPI">
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37 <link href="Combining-MPI-and-Threads.html#Combining-MPI-and-Threads" rel="next" title="Combining MPI and Threads">
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38 <link href="Avoiding-MPI-Deadlocks.html#Avoiding-MPI-Deadlocks" rel="prev" title="Avoiding MPI Deadlocks">
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64 -->
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65 </style>
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66
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67
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68 </head>
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69
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70 <body lang="en">
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71 <a name="FFTW-MPI-Performance-Tips"></a>
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72 <div class="header">
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73 <p>
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74 Next: <a href="Combining-MPI-and-Threads.html#Combining-MPI-and-Threads" accesskey="n" rel="next">Combining MPI and Threads</a>, Previous: <a href="Avoiding-MPI-Deadlocks.html#Avoiding-MPI-Deadlocks" accesskey="p" rel="prev">Avoiding MPI Deadlocks</a>, Up: <a href="Distributed_002dmemory-FFTW-with-MPI.html#Distributed_002dmemory-FFTW-with-MPI" 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#Concept-Index" title="Index" rel="index">Index</a>]</p>
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75 </div>
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76 <hr>
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77 <a name="FFTW-MPI-Performance-Tips-1"></a>
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78 <h3 class="section">6.10 FFTW MPI Performance Tips</h3>
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79
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80 <p>In this section, we collect a few tips on getting the best performance
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81 out of FFTW’s MPI transforms.
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82 </p>
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83 <p>First, because of the 1d block distribution, FFTW’s parallelization is
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84 currently limited by the size of the first dimension.
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85 (Multidimensional block distributions may be supported by a future
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86 version.) More generally, you should ideally arrange the dimensions so
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87 that FFTW can divide them equally among the processes. See <a href="Load-balancing.html#Load-balancing">Load balancing</a>.
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88 <a name="index-block-distribution-2"></a>
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89 <a name="index-load-balancing-1"></a>
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90 </p>
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91
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92 <p>Second, if it is not too inconvenient, you should consider working
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93 with transposed output for multidimensional plans, as this saves a
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94 considerable amount of communications. See <a href="Transposed-distributions.html#Transposed-distributions">Transposed distributions</a>.
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95 <a name="index-transpose-3"></a>
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96 </p>
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97
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98 <p>Third, the fastest choices are generally either an in-place transform
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99 or an out-of-place transform with the <code>FFTW_DESTROY_INPUT</code> flag
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100 (which allows the input array to be used as scratch space). In-place
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101 is especially beneficial if the amount of data per process is large.
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102 <a name="index-FFTW_005fDESTROY_005fINPUT-1"></a>
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103 </p>
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104
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105 <p>Fourth, if you have multiple arrays to transform at once, rather than
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106 calling FFTW’s MPI transforms several times it usually seems to be
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107 faster to interleave the data and use the advanced interface. (This
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108 groups the communications together instead of requiring separate
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109 messages for each transform.)
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110 </p>
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111
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112
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113
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114 </body>
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115 </html>
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