Mercurial > hg > sv-dependency-builds

annotate src/fftw-3.3.5/doc/html/Cycle-Counters.html @ 42:2cd0e3b3e1fd

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
Current fftw source
author Chris Cannam
date Tue, 18 Oct 2016 13:40:26 +0100
parents
children
rev   line source
Chris@42 1 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
Chris@42 2 <html>
Chris@42 3 <!-- This manual is for FFTW
Chris@42 4 (version 3.3.5, 30 July 2016).
Chris@42 5
Chris@42 6 Copyright (C) 2003 Matteo Frigo.
Chris@42 7
Chris@42 8 Copyright (C) 2003 Massachusetts Institute of Technology.
Chris@42 9
Chris@42 10 Permission is granted to make and distribute verbatim copies of this
Chris@42 11 manual provided the copyright notice and this permission notice are
Chris@42 12 preserved on all copies.
Chris@42 13
Chris@42 14 Permission is granted to copy and distribute modified versions of this
Chris@42 15 manual under the conditions for verbatim copying, provided that the
Chris@42 16 entire resulting derived work is distributed under the terms of a
Chris@42 17 permission notice identical to this one.
Chris@42 18
Chris@42 19 Permission is granted to copy and distribute translations of this manual
Chris@42 20 into another language, under the above conditions for modified versions,
Chris@42 21 except that this permission notice may be stated in a translation
Chris@42 22 approved by the Free Software Foundation. -->
Chris@42 23 <!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
Chris@42 24 <head>
Chris@42 25 <title>FFTW 3.3.5: Cycle Counters</title>
Chris@42 26
Chris@42 27 <meta name="description" content="FFTW 3.3.5: Cycle Counters">
Chris@42 28 <meta name="keywords" content="FFTW 3.3.5: Cycle Counters">
Chris@42 29 <meta name="resource-type" content="document">
Chris@42 30 <meta name="distribution" content="global">
Chris@42 31 <meta name="Generator" content="makeinfo">
Chris@42 32 <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
Chris@42 33 <link href="index.html#Top" rel="start" title="Top">
Chris@42 34 <link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index">
Chris@42 35 <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
Chris@42 36 <link href="Installation-and-Customization.html#Installation-and-Customization" rel="up" title="Installation and Customization">
Chris@42 37 <link href="Generating-your-own-code.html#Generating-your-own-code" rel="next" title="Generating your own code">
Chris@42 38 <link href="Installation-on-non_002dUnix-systems.html#Installation-on-non_002dUnix-systems" rel="prev" title="Installation on non-Unix systems">
Chris@42 39 <style type="text/css">
Chris@42 40 <!--
Chris@42 41 a.summary-letter {text-decoration: none}
Chris@42 42 blockquote.smallquotation {font-size: smaller}
Chris@42 43 div.display {margin-left: 3.2em}
Chris@42 44 div.example {margin-left: 3.2em}
Chris@42 45 div.indentedblock {margin-left: 3.2em}
Chris@42 46 div.lisp {margin-left: 3.2em}
Chris@42 47 div.smalldisplay {margin-left: 3.2em}
Chris@42 48 div.smallexample {margin-left: 3.2em}
Chris@42 49 div.smallindentedblock {margin-left: 3.2em; font-size: smaller}
Chris@42 50 div.smalllisp {margin-left: 3.2em}
Chris@42 51 kbd {font-style:oblique}
Chris@42 52 pre.display {font-family: inherit}
Chris@42 53 pre.format {font-family: inherit}
Chris@42 54 pre.menu-comment {font-family: serif}
Chris@42 55 pre.menu-preformatted {font-family: serif}
Chris@42 56 pre.smalldisplay {font-family: inherit; font-size: smaller}
Chris@42 57 pre.smallexample {font-size: smaller}
Chris@42 58 pre.smallformat {font-family: inherit; font-size: smaller}
Chris@42 59 pre.smalllisp {font-size: smaller}
Chris@42 60 span.nocodebreak {white-space:nowrap}
Chris@42 61 span.nolinebreak {white-space:nowrap}
Chris@42 62 span.roman {font-family:serif; font-weight:normal}
Chris@42 63 span.sansserif {font-family:sans-serif; font-weight:normal}
Chris@42 64 ul.no-bullet {list-style: none}
Chris@42 65 -->
Chris@42 66 </style>
Chris@42 67
Chris@42 68
Chris@42 69 </head>
Chris@42 70
Chris@42 71 <body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
Chris@42 72 <a name="Cycle-Counters"></a>
Chris@42 73 <div class="header">
Chris@42 74 <p>
Chris@42 75 Next: <a href="Generating-your-own-code.html#Generating-your-own-code" accesskey="n" rel="next">Generating your own code</a>, Previous: <a href="Installation-on-non_002dUnix-systems.html#Installation-on-non_002dUnix-systems" accesskey="p" rel="prev">Installation on non-Unix systems</a>, Up: <a href="Installation-and-Customization.html#Installation-and-Customization" accesskey="u" rel="up">Installation and Customization</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>
Chris@42 76 </div>
Chris@42 77 <hr>
Chris@42 78 <a name="Cycle-Counters-1"></a>
Chris@42 79 <h3 class="section">10.3 Cycle Counters</h3>
Chris@42 80 <a name="index-cycle-counter-1"></a>
Chris@42 81
Chris@42 82 <p>FFTW&rsquo;s planner actually executes and times different possible FFT
Chris@42 83 algorithms in order to pick the fastest plan for a given <em>n</em>. In
Chris@42 84 order to do this in as short a time as possible, however, the timer must
Chris@42 85 have a very high resolution, and to accomplish this we employ the
Chris@42 86 hardware <em>cycle counters</em> that are available on most CPUs.
Chris@42 87 Currently, FFTW supports the cycle counters on x86, PowerPC/POWER, Alpha,
Chris@42 88 UltraSPARC (SPARC v9), IA64, PA-RISC, and MIPS processors.
Chris@42 89 </p>
Chris@42 90 <a name="index-compiler-3"></a>
Chris@42 91 <p>Access to the cycle counters, unfortunately, is a compiler and/or
Chris@42 92 operating-system dependent task, often requiring inline assembly
Chris@42 93 language, and it may be that your compiler is not supported. If you are
Chris@42 94 <em>not</em> supported, FFTW will by default fall back on its estimator
Chris@42 95 (effectively using <code>FFTW_ESTIMATE</code> for all plans).
Chris@42 96 <a name="index-FFTW_005fESTIMATE-3"></a>
Chris@42 97 </p>
Chris@42 98 <p>You can add support by editing the file <code>kernel/cycle.h</code>; normally,
Chris@42 99 this will involve adapting one of the examples already present in order
Chris@42 100 to use the inline-assembler syntax for your C compiler, and will only
Chris@42 101 require a couple of lines of code. Anyone adding support for a new
Chris@42 102 system to <code>cycle.h</code> is encouraged to email us at <a href="mailto:fftw@fftw.org">fftw@fftw.org</a>.
Chris@42 103 </p>
Chris@42 104 <p>If a cycle counter is not available on your system (e.g. some embedded
Chris@42 105 processor), and you don&rsquo;t want to use estimated plans, as a last resort
Chris@42 106 you can use the <code>--with-slow-timer</code> option to <code>configure</code> (on
Chris@42 107 Unix) or <code>#define WITH_SLOW_TIMER</code> in <code>config.h</code> (elsewhere).
Chris@42 108 This will use the much lower-resolution <code>gettimeofday</code> function, or even
Chris@42 109 <code>clock</code> if the former is unavailable, and planning will be
Chris@42 110 extremely slow.
Chris@42 111 </p>
Chris@42 112 <hr>
Chris@42 113 <div class="header">
Chris@42 114 <p>
Chris@42 115 Next: <a href="Generating-your-own-code.html#Generating-your-own-code" accesskey="n" rel="next">Generating your own code</a>, Previous: <a href="Installation-on-non_002dUnix-systems.html#Installation-on-non_002dUnix-systems" accesskey="p" rel="prev">Installation on non-Unix systems</a>, Up: <a href="Installation-and-Customization.html#Installation-and-Customization" accesskey="u" rel="up">Installation and Customization</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>
Chris@42 116 </div>
Chris@42 117
Chris@42 118
Chris@42 119
Chris@42 120 </body>
Chris@42 121 </html>