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Add FFTW3
author Chris Cannam
date Wed, 20 Mar 2013 15:35:50 +0000
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+<html lang="en">
+<head>
+<title>FFTW MPI Performance Tips - FFTW 3.3.3</title>
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+<link rel="up" href="Distributed_002dmemory-FFTW-with-MPI.html#Distributed_002dmemory-FFTW-with-MPI" title="Distributed-memory FFTW with MPI">
+<link rel="prev" href="Avoiding-MPI-Deadlocks.html#Avoiding-MPI-Deadlocks" title="Avoiding MPI Deadlocks">
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+<!--
+This manual is for FFTW
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+Copyright (C) 2003 Matteo Frigo.
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+Copyright (C) 2003 Massachusetts Institute of Technology.
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+<div class="node">
+<a name="FFTW-MPI-Performance-Tips"></a>
+<p>
+Next:&nbsp;<a rel="next" accesskey="n" href="Combining-MPI-and-Threads.html#Combining-MPI-and-Threads">Combining MPI and Threads</a>,
+Previous:&nbsp;<a rel="previous" accesskey="p" href="Avoiding-MPI-Deadlocks.html#Avoiding-MPI-Deadlocks">Avoiding MPI Deadlocks</a>,
+Up:&nbsp;<a rel="up" accesskey="u" href="Distributed_002dmemory-FFTW-with-MPI.html#Distributed_002dmemory-FFTW-with-MPI">Distributed-memory FFTW with MPI</a>
+<hr>
+</div>
+
+<h3 class="section">6.10 FFTW MPI Performance Tips</h3>
+
+<p>In this section, we collect a few tips on getting the best performance
+out of FFTW's MPI transforms.
+
+   <p>First, because of the 1d block distribution, FFTW's parallelization is
+currently limited by the size of the first dimension. 
+(Multidimensional block distributions may be supported by a future
+version.) More generally, you should ideally arrange the dimensions so
+that FFTW can divide them equally among the processes. See <a href="Load-balancing.html#Load-balancing">Load balancing</a>. 
+<a name="index-block-distribution-423"></a><a name="index-load-balancing-424"></a>
+
+   <p>Second, if it is not too inconvenient, you should consider working
+with transposed output for multidimensional plans, as this saves a
+considerable amount of communications.  See <a href="Transposed-distributions.html#Transposed-distributions">Transposed distributions</a>. 
+<a name="index-transpose-425"></a>
+
+   <p>Third, the fastest choices are generally either an in-place transform
+or an out-of-place transform with the <code>FFTW_DESTROY_INPUT</code> flag
+(which allows the input array to be used as scratch space).  In-place
+is especially beneficial if the amount of data per process is large. 
+<a name="index-FFTW_005fDESTROY_005fINPUT-426"></a>
+
+   <p>Fourth, if you have multiple arrays to transform at once, rather than
+calling FFTW's MPI transforms several times it usually seems to be
+faster to interleave the data and use the advanced interface.  (This
+groups the communications together instead of requiring separate
+messages for each transform.)
+
+<!--  -->
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+