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Add FFTW 3.3.8 source, and a Linux build
author Chris Cannam <cannam@all-day-breakfast.com>
date Tue, 19 Nov 2019 14:52:55 +0000
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cannam@167 1 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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cannam@167 3 <!-- This manual is for FFTW
cannam@167 4 (version 3.3.8, 24 May 2018).
cannam@167 5
cannam@167 6 Copyright (C) 2003 Matteo Frigo.
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cannam@167 8 Copyright (C) 2003 Massachusetts Institute of Technology.
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cannam@167 24 <head>
cannam@167 25 <title>FFTW 3.3.8: How Many Threads to Use?</title>
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cannam@167 36 <link href="Multi_002dthreaded-FFTW.html#Multi_002dthreaded-FFTW" rel="up" title="Multi-threaded FFTW">
cannam@167 37 <link href="Thread-safety.html#Thread-safety" rel="next" title="Thread safety">
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cannam@167 69
cannam@167 70 <body lang="en">
cannam@167 71 <a name="How-Many-Threads-to-Use_003f"></a>
cannam@167 72 <div class="header">
cannam@167 73 <p>
cannam@167 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>
cannam@167 75 </div>
cannam@167 76 <hr>
cannam@167 77 <a name="How-Many-Threads-to-Use_003f-1"></a>
cannam@167 78 <h3 class="section">5.3 How Many Threads to Use?</h3>
cannam@167 79
cannam@167 80 <a name="index-number-of-threads"></a>
cannam@167 81 <p>There is a fair amount of overhead involved in synchronizing threads,
cannam@167 82 so the optimal number of threads to use depends upon the size of the
cannam@167 83 transform as well as on the number of processors you have.
cannam@167 84 </p>
cannam@167 85 <p>As a general rule, you don&rsquo;t want to use more threads than you have
cannam@167 86 processors. (Using more threads will work, but there will be extra
cannam@167 87 overhead with no benefit.) In fact, if the problem size is too small,
cannam@167 88 you may want to use fewer threads than you have processors.
cannam@167 89 </p>
cannam@167 90 <p>You will have to experiment with your system to see what level of
cannam@167 91 parallelization is best for your problem size. Typically, the problem
cannam@167 92 will have to involve at least a few thousand data points before threads
cannam@167 93 become beneficial. If you plan with <code>FFTW_PATIENT</code>, it will
cannam@167 94 automatically disable threads for sizes that don&rsquo;t benefit from
cannam@167 95 parallelization.
cannam@167 96 <a name="index-FFTW_005fPATIENT-3"></a>
cannam@167 97 </p>
cannam@167 98
cannam@167 99
cannam@167 100
cannam@167 101 </body>
cannam@167 102 </html>