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Current fftw source
author Chris Cannam
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: 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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72 <a name="FFTW-MPI-Performance-Tips"></a>
73 <div class="header">
74 <p>
75 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>
76 </div>
77 <hr>
78 <a name="FFTW-MPI-Performance-Tips-1"></a>
79 <h3 class="section">6.10 FFTW MPI Performance Tips</h3>
80
81 <p>In this section, we collect a few tips on getting the best performance
82 out of FFTW&rsquo;s MPI transforms.
83 </p>
84 <p>First, because of the 1d block distribution, FFTW&rsquo;s parallelization is
85 currently limited by the size of the first dimension.
86 (Multidimensional block distributions may be supported by a future
87 version.) More generally, you should ideally arrange the dimensions so
88 that FFTW can divide them equally among the processes. See <a href="Load-balancing.html#Load-balancing">Load balancing</a>.
89 <a name="index-block-distribution-2"></a>
90 <a name="index-load-balancing-1"></a>
91 </p>
92
93 <p>Second, if it is not too inconvenient, you should consider working
94 with transposed output for multidimensional plans, as this saves a
95 considerable amount of communications. See <a href="Transposed-distributions.html#Transposed-distributions">Transposed distributions</a>.
96 <a name="index-transpose-3"></a>
97 </p>
98
99 <p>Third, the fastest choices are generally either an in-place transform
100 or an out-of-place transform with the <code>FFTW_DESTROY_INPUT</code> flag
101 (which allows the input array to be used as scratch space). In-place
102 is especially beneficial if the amount of data per process is large.
103 <a name="index-FFTW_005fDESTROY_005fINPUT-1"></a>
104 </p>
105
106 <p>Fourth, if you have multiple arrays to transform at once, rather than
107 calling FFTW&rsquo;s MPI transforms several times it usually seems to be
108 faster to interleave the data and use the advanced interface. (This
109 groups the communications together instead of requiring separate
110 messages for each transform.)
111 </p>
112
113
114
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