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Current fftw source
author Chris Cannam
date Tue, 18 Oct 2016 13:40:26 +0100
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78 <a name="How-Many-Threads-to-Use_003f-1"></a>
79 <h3 class="section">5.3 How Many Threads to Use?</h3>
80
81 <a name="index-number-of-threads"></a>
82 <p>There is a fair amount of overhead involved in synchronizing threads,
83 so the optimal number of threads to use depends upon the size of the
84 transform as well as on the number of processors you have.
85 </p>
86 <p>As a general rule, you don&rsquo;t want to use more threads than you have
87 processors. (Using more threads will work, but there will be extra
88 overhead with no benefit.) In fact, if the problem size is too small,
89 you may want to use fewer threads than you have processors.
90 </p>
91 <p>You will have to experiment with your system to see what level of
92 parallelization is best for your problem size. Typically, the problem
93 will have to involve at least a few thousand data points before threads
94 become beneficial. If you plan with <code>FFTW_PATIENT</code>, it will
95 automatically disable threads for sizes that don&rsquo;t benefit from
96 parallelization.
97 <a name="index-FFTW_005fPATIENT-3"></a>
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