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2 <head>
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3 <title>FFTW MPI Performance Tips - FFTW 3.3.3</title>
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4 <meta http-equiv="Content-Type" content="text/html">
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5 <meta name="description" content="FFTW 3.3.3">
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7 <link title="Top" rel="start" href="index.html#Top">
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8 <link rel="up" href="Distributed_002dmemory-FFTW-with-MPI.html#Distributed_002dmemory-FFTW-with-MPI" title="Distributed-memory FFTW with MPI">
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9 <link rel="prev" href="Avoiding-MPI-Deadlocks.html#Avoiding-MPI-Deadlocks" title="Avoiding MPI Deadlocks">
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10 <link rel="next" href="Combining-MPI-and-Threads.html#Combining-MPI-and-Threads" title="Combining MPI and Threads">
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11 <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
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12 <!--
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13 This manual is for FFTW
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14 (version 3.3.3, 25 November 2012).
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15
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16 Copyright (C) 2003 Matteo Frigo.
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17
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18 Copyright (C) 2003 Massachusetts Institute of Technology.
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19
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20 Permission is granted to make and distribute verbatim copies of
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21 this manual provided the copyright notice and this permission
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22 notice are preserved on all copies.
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23
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24 Permission is granted to copy and distribute modified versions of
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25 this manual under the conditions for verbatim copying, provided
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26 that the entire resulting derived work is distributed under the
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27 terms of a permission notice identical to this one.
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28
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29 Permission is granted to copy and distribute translations of this
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30 manual into another language, under the above conditions for
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31 modified versions, except that this permission notice may be
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32 stated in a translation approved by the Free Software Foundation.
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45 --></style>
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46 </head>
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47 <body>
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48 <div class="node">
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49 <a name="FFTW-MPI-Performance-Tips"></a>
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50 <p>
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51 Next: <a rel="next" accesskey="n" href="Combining-MPI-and-Threads.html#Combining-MPI-and-Threads">Combining MPI and Threads</a>,
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52 Previous: <a rel="previous" accesskey="p" href="Avoiding-MPI-Deadlocks.html#Avoiding-MPI-Deadlocks">Avoiding MPI Deadlocks</a>,
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53 Up: <a rel="up" accesskey="u" href="Distributed_002dmemory-FFTW-with-MPI.html#Distributed_002dmemory-FFTW-with-MPI">Distributed-memory FFTW with MPI</a>
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54 <hr>
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55 </div>
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56
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57 <h3 class="section">6.10 FFTW MPI Performance Tips</h3>
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58
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59 <p>In this section, we collect a few tips on getting the best performance
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60 out of FFTW's MPI transforms.
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61
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62 <p>First, because of the 1d block distribution, FFTW's parallelization is
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63 currently limited by the size of the first dimension.
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64 (Multidimensional block distributions may be supported by a future
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65 version.) More generally, you should ideally arrange the dimensions so
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66 that FFTW can divide them equally among the processes. See <a href="Load-balancing.html#Load-balancing">Load balancing</a>.
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67 <a name="index-block-distribution-423"></a><a name="index-load-balancing-424"></a>
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68
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69 <p>Second, if it is not too inconvenient, you should consider working
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70 with transposed output for multidimensional plans, as this saves a
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71 considerable amount of communications. See <a href="Transposed-distributions.html#Transposed-distributions">Transposed distributions</a>.
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72 <a name="index-transpose-425"></a>
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73
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74 <p>Third, the fastest choices are generally either an in-place transform
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75 or an out-of-place transform with the <code>FFTW_DESTROY_INPUT</code> flag
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76 (which allows the input array to be used as scratch space). In-place
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77 is especially beneficial if the amount of data per process is large.
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78 <a name="index-FFTW_005fDESTROY_005fINPUT-426"></a>
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79
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80 <p>Fourth, if you have multiple arrays to transform at once, rather than
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81 calling FFTW's MPI transforms several times it usually seems to be
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82 faster to interleave the data and use the advanced interface. (This
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83 groups the communications together instead of requiring separate
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84 messages for each transform.)
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85
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86 <!-- -->
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87 </body></html>
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88
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