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Add null config files
author Chris Cannam <cannam@all-day-breakfast.com>
date Mon, 02 Mar 2020 14:03:47 +0000
parents 7867fa7e1b6b
children
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cannam@127 3 <!-- This manual is for FFTW
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cannam@127 6 Copyright (C) 2003 Matteo Frigo.
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cannam@127 25 <title>FFTW 3.3.5: How Many Threads to Use?</title>
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cannam@127 75 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@127 76 </div>
cannam@127 77 <hr>
cannam@127 78 <a name="How-Many-Threads-to-Use_003f-1"></a>
cannam@127 79 <h3 class="section">5.3 How Many Threads to Use?</h3>
cannam@127 80
cannam@127 81 <a name="index-number-of-threads"></a>
cannam@127 82 <p>There is a fair amount of overhead involved in synchronizing threads,
cannam@127 83 so the optimal number of threads to use depends upon the size of the
cannam@127 84 transform as well as on the number of processors you have.
cannam@127 85 </p>
cannam@127 86 <p>As a general rule, you don&rsquo;t want to use more threads than you have
cannam@127 87 processors. (Using more threads will work, but there will be extra
cannam@127 88 overhead with no benefit.) In fact, if the problem size is too small,
cannam@127 89 you may want to use fewer threads than you have processors.
cannam@127 90 </p>
cannam@127 91 <p>You will have to experiment with your system to see what level of
cannam@127 92 parallelization is best for your problem size. Typically, the problem
cannam@127 93 will have to involve at least a few thousand data points before threads
cannam@127 94 become beneficial. If you plan with <code>FFTW_PATIENT</code>, it will
cannam@127 95 automatically disable threads for sizes that don&rsquo;t benefit from
cannam@127 96 parallelization.
cannam@127 97 <a name="index-FFTW_005fPATIENT-3"></a>
cannam@127 98 </p>
cannam@127 99
cannam@127 100
cannam@127 101
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