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author Chris Cannam <cannam@all-day-breakfast.com>
date Wed, 20 Mar 2013 15:35:50 +0000
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3 <title>How Many Threads to Use? - FFTW 3.3.3</title>
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58 <h3 class="section">5.3 How Many Threads to Use?</h3>
59
60 <p><a name="index-number-of-threads-339"></a>There is a fair amount of overhead involved in synchronizing threads,
61 so the optimal number of threads to use depends upon the size of the
62 transform as well as on the number of processors you have.
63
64 <p>As a general rule, you don't want to use more threads than you have
65 processors. (Using more threads will work, but there will be extra
66 overhead with no benefit.) In fact, if the problem size is too small,
67 you may want to use fewer threads than you have processors.
68
69 <p>You will have to experiment with your system to see what level of
70 parallelization is best for your problem size. Typically, the problem
71 will have to involve at least a few thousand data points before threads
72 become beneficial. If you plan with <code>FFTW_PATIENT</code>, it will
73 automatically disable threads for sizes that don't benefit from
74 parallelization.
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