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diff src/fftw-3.3.3/doc/html/How-Many-Threads-to-Use_003f.html @ 95:89f5e221ed7b
Add FFTW3
| author | Chris Cannam <cannam@all-day-breakfast.com> |
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| date | Wed, 20 Mar 2013 15:35:50 +0000 |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/src/fftw-3.3.3/doc/html/How-Many-Threads-to-Use_003f.html Wed Mar 20 15:35:50 2013 +0000 @@ -0,0 +1,79 @@ +<html lang="en"> +<head> +<title>How Many Threads to Use? - FFTW 3.3.3</title> +<meta http-equiv="Content-Type" content="text/html"> +<meta name="description" content="FFTW 3.3.3"> +<meta name="generator" content="makeinfo 4.13"> +<link title="Top" rel="start" href="index.html#Top"> +<link rel="up" href="Multi_002dthreaded-FFTW.html#Multi_002dthreaded-FFTW" title="Multi-threaded FFTW"> +<link rel="prev" href="Usage-of-Multi_002dthreaded-FFTW.html#Usage-of-Multi_002dthreaded-FFTW" title="Usage of Multi-threaded FFTW"> +<link rel="next" href="Thread-safety.html#Thread-safety" title="Thread safety"> +<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> +<!-- +This manual is for FFTW +(version 3.3.3, 25 November 2012). + +Copyright (C) 2003 Matteo Frigo. + +Copyright (C) 2003 Massachusetts Institute of Technology. + + Permission is granted to make and distribute verbatim copies of + this manual provided the copyright notice and this permission + notice are preserved on all copies. + + Permission is granted to copy and distribute modified versions of + this manual under the conditions for verbatim copying, provided + that the entire resulting derived work is distributed under the + terms of a permission notice identical to this one. + + Permission is granted to copy and distribute translations of this + manual into another language, under the above conditions for + modified versions, except that this permission notice may be + stated in a translation approved by the Free Software Foundation. + --> +<meta http-equiv="Content-Style-Type" content="text/css"> +<style type="text/css"><!-- + pre.display { font-family:inherit } + pre.format { font-family:inherit } + pre.smalldisplay { font-family:inherit; font-size:smaller } + pre.smallformat { font-family:inherit; font-size:smaller } + pre.smallexample { font-size:smaller } + pre.smalllisp { font-size:smaller } + span.sc { font-variant:small-caps } + span.roman { font-family:serif; font-weight:normal; } + span.sansserif { font-family:sans-serif; font-weight:normal; } +--></style> +</head> +<body> +<div class="node"> +<a name="How-Many-Threads-to-Use%3f"></a> +<a name="How-Many-Threads-to-Use_003f"></a> +<p> +Next: <a rel="next" accesskey="n" href="Thread-safety.html#Thread-safety">Thread safety</a>, +Previous: <a rel="previous" accesskey="p" href="Usage-of-Multi_002dthreaded-FFTW.html#Usage-of-Multi_002dthreaded-FFTW">Usage of Multi-threaded FFTW</a>, +Up: <a rel="up" accesskey="u" href="Multi_002dthreaded-FFTW.html#Multi_002dthreaded-FFTW">Multi-threaded FFTW</a> +<hr> +</div> + +<h3 class="section">5.3 How Many Threads to Use?</h3> + +<p><a name="index-number-of-threads-339"></a>There is a fair amount of overhead involved in synchronizing threads, +so the optimal number of threads to use depends upon the size of the +transform as well as on the number of processors you have. + + <p>As a general rule, you don't want to use more threads than you have +processors. (Using more threads will work, but there will be extra +overhead with no benefit.) In fact, if the problem size is too small, +you may want to use fewer threads than you have processors. + + <p>You will have to experiment with your system to see what level of +parallelization is best for your problem size. Typically, the problem +will have to involve at least a few thousand data points before threads +become beneficial. If you plan with <code>FFTW_PATIENT</code>, it will +automatically disable threads for sizes that don't benefit from +parallelization. +<a name="index-FFTW_005fPATIENT-340"></a> +<!-- --> + + </body></html> +