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Add FFTW 3.3.8 source, and a Linux build
author Chris Cannam
date Tue, 19 Nov 2019 14:52:55 +0000
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3 <!-- This manual is for FFTW
4 (version 3.3.8, 24 May 2018).
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6 Copyright (C) 2003 Matteo Frigo.
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8 Copyright (C) 2003 Massachusetts Institute of Technology.
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25 <title>FFTW 3.3.8: FFTW MPI Performance Tips</title>
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35 <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
36 <link href="Distributed_002dmemory-FFTW-with-MPI.html#Distributed_002dmemory-FFTW-with-MPI" rel="up" title="Distributed-memory FFTW with MPI">
37 <link href="Combining-MPI-and-Threads.html#Combining-MPI-and-Threads" rel="next" title="Combining MPI and Threads">
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71 <a name="FFTW-MPI-Performance-Tips"></a>
72 <div class="header">
73 <p>
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> &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>
75 </div>
76 <hr>
77 <a name="FFTW-MPI-Performance-Tips-1"></a>
78 <h3 class="section">6.10 FFTW MPI Performance Tips</h3>
79
80 <p>In this section, we collect a few tips on getting the best performance
81 out of FFTW&rsquo;s MPI transforms.
82 </p>
83 <p>First, because of the 1d block distribution, FFTW&rsquo;s parallelization is
84 currently limited by the size of the first dimension.
85 (Multidimensional block distributions may be supported by a future
86 version.) More generally, you should ideally arrange the dimensions so
87 that FFTW can divide them equally among the processes. See <a href="Load-balancing.html#Load-balancing">Load balancing</a>.
88 <a name="index-block-distribution-2"></a>
89 <a name="index-load-balancing-1"></a>
90 </p>
91
92 <p>Second, if it is not too inconvenient, you should consider working
93 with transposed output for multidimensional plans, as this saves a
94 considerable amount of communications. See <a href="Transposed-distributions.html#Transposed-distributions">Transposed distributions</a>.
95 <a name="index-transpose-3"></a>
96 </p>
97
98 <p>Third, the fastest choices are generally either an in-place transform
99 or an out-of-place transform with the <code>FFTW_DESTROY_INPUT</code> flag
100 (which allows the input array to be used as scratch space). In-place
101 is especially beneficial if the amount of data per process is large.
102 <a name="index-FFTW_005fDESTROY_005fINPUT-1"></a>
103 </p>
104
105 <p>Fourth, if you have multiple arrays to transform at once, rather than
106 calling FFTW&rsquo;s MPI transforms several times it usually seems to be
107 faster to interleave the data and use the advanced interface. (This
108 groups the communications together instead of requiring separate
109 messages for each transform.)
110 </p>
111
112
113
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