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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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25 <title>FFTW 3.3.8: How Many Threads to Use?</title>
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71 <a name="How-Many-Threads-to-Use_003f"></a>
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73 <p>
74 Next: <a href="Thread-safety.html#Thread-safety" accesskey="n" rel="next">Thread safety</a>, Previous: <a href="Usage-of-Multi_002dthreaded-FFTW.html#Usage-of-Multi_002dthreaded-FFTW" accesskey="p" rel="prev">Usage of Multi-threaded FFTW</a>, Up: <a href="Multi_002dthreaded-FFTW.html#Multi_002dthreaded-FFTW" accesskey="u" rel="up">Multi-threaded FFTW</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="How-Many-Threads-to-Use_003f-1"></a>
78 <h3 class="section">5.3 How Many Threads to Use?</h3>
79
80 <a name="index-number-of-threads"></a>
81 <p>There is a fair amount of overhead involved in synchronizing threads,
82 so the optimal number of threads to use depends upon the size of the
83 transform as well as on the number of processors you have.
84 </p>
85 <p>As a general rule, you don&rsquo;t want to use more threads than you have
86 processors. (Using more threads will work, but there will be extra
87 overhead with no benefit.) In fact, if the problem size is too small,
88 you may want to use fewer threads than you have processors.
89 </p>
90 <p>You will have to experiment with your system to see what level of
91 parallelization is best for your problem size. Typically, the problem
92 will have to involve at least a few thousand data points before threads
93 become beneficial. If you plan with <code>FFTW_PATIENT</code>, it will
94 automatically disable threads for sizes that don&rsquo;t benefit from
95 parallelization.
96 <a name="index-FFTW_005fPATIENT-3"></a>
97 </p>
98
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