Mercurial > hg > batch-feature-extraction-tool
diff Lib/fftw-3.2.1/doc/html/.svn/text-base/FFTW-MPI-Wisdom.html.svn-base @ 15:585caf503ef5 tip
Tidy up for ROLI
| author | Geogaddi\David <d.m.ronan@qmul.ac.uk> |
|---|---|
| date | Tue, 17 May 2016 18:50:19 +0100 |
| parents | 636c989477e7 |
| children |
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--- a/Lib/fftw-3.2.1/doc/html/.svn/text-base/FFTW-MPI-Wisdom.html.svn-base Wed May 04 11:02:59 2016 +0100 +++ /dev/null Thu Jan 01 00:00:00 1970 +0000 @@ -1,132 +0,0 @@ -<html lang="en"> -<head> -<title>FFTW MPI Wisdom - FFTW 3.2alpha3</title> -<meta http-equiv="Content-Type" content="text/html"> -<meta name="description" content="FFTW 3.2alpha3"> -<meta name="generator" content="makeinfo 4.8"> -<link title="Top" rel="start" href="index.html#Top"> -<link rel="up" href="Distributed_002dmemory-FFTW-with-MPI.html#Distributed_002dmemory-FFTW-with-MPI" title="Distributed-memory FFTW with MPI"> -<link rel="prev" href="FFTW-MPI-Transposes.html#FFTW-MPI-Transposes" title="FFTW MPI Transposes"> -<link rel="next" href="Avoiding-MPI-Deadlocks.html#Avoiding-MPI-Deadlocks" title="Avoiding MPI Deadlocks"> -<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> -<!-- -This manual is for FFTW -(version 3.2alpha3, 14 August 2007). - -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"> -<p> -<a name="FFTW-MPI-Wisdom"></a> -Next: <a rel="next" accesskey="n" href="Avoiding-MPI-Deadlocks.html#Avoiding-MPI-Deadlocks">Avoiding MPI Deadlocks</a>, -Previous: <a rel="previous" accesskey="p" href="FFTW-MPI-Transposes.html#FFTW-MPI-Transposes">FFTW MPI Transposes</a>, -Up: <a rel="up" accesskey="u" href="Distributed_002dmemory-FFTW-with-MPI.html#Distributed_002dmemory-FFTW-with-MPI">Distributed-memory FFTW with MPI</a> -<hr> -</div> - -<h3 class="section">6.8 FFTW MPI Wisdom</h3> - -<p><a name="index-wisdom-380"></a><a name="index-saving-plans-to-disk-381"></a> -FFTW's “wisdom” facility (see <a href="Words-of-Wisdom_002dSaving-Plans.html#Words-of-Wisdom_002dSaving-Plans">Words of Wisdom-Saving Plans</a>) can -be used to save MPI plans as well as to save uniprocessor plans. -However, for MPI there are several unavoidable complications. - - <p>First, the MPI standard does not guarantee that every process can -perform file I/O (at least, not using C stdio routines)—only the -process of rank <code>MPI_IO</code> can in general (unless <code>MPI_IO == -MPI_ANY_SOURCE</code>). (In practice, <code>MPI_IO</code> is commonly assumed to -be zero, i.e. at least process 0 can perform I/O, since otherwise a -single-process run could not perform I/O.) So, if we want to export -the wisdom from a single process to a file, we must first export the -wisdom to a string, then send it to process 0, then write it to a -file. -<a name="index-MPI_005fIO-382"></a><a name="index-MPI_005fANY_005fSOURCE-383"></a> -Second, in principle we may want to have separate wisdom for every -process, since in general the processes may run on different hardware -even for a single MPI program. However, in practice FFTW's MPI code -is designed for the case of homogeneous hardware (see <a href="Load-balancing.html#Load-balancing">Load balancing</a>), and in this case it is convenient to use the same wisdom -for every process. Thus, we need a mechanism to synchronize the wisdom. - - <p>To address both of these problems, FFTW provides the following two -functions: - -<pre class="example"> void fftw_mpi_broadcast_wisdom(MPI_Comm comm); - void fftw_mpi_gather_wisdom(MPI_Comm comm); -</pre> - <p><a name="index-fftw_005fmpi_005fgather_005fwisdom-384"></a><a name="index-fftw_005fmpi_005fbroadcast_005fwisdom-385"></a> -Given a communicator <code>comm</code>, <code>fftw_mpi_broadcast_wisdom</code> -will broadcast the wisdom from process 0 to all other processes. -Conversely, <code>fftw_mpi_gather_wisdom</code> will collect wisdom from all -processes onto process 0. (If the plans created for the same problem -by different processes are not the same, <code>fftw_mpi_gather_wisdom</code> -will arbitrarily choose one of the plans.) Both of these functions -may result in suboptimal plans for different processes if the -processes are running on non-identical hardware. Both of these -functions are <em>collective</em> calls, which means that they must be -executed by all processes in the communicator. -<a name="index-collective-function-386"></a> -So, for example, a typical code snippet to import wisdom from a file -and use it on all processes would be: - -<pre class="example"> { - int rank; - FILE *f; - - fftw_mpi_init(); - MPI_Comm_rank(MPI_COMM_WORLD, &rank); - if (rank == 0 && (f = fopen("mywisdom", "r"))) { - fftw_import_wisdom_from_file(f); - fclose(f); - } - fftw_mpi_broadcast_wisdom(MPI_COMM_WORLD); - } -</pre> - <p>(Note that we must call <code>fftw_mpi_init</code> before importing any -wisdom that might contain MPI plans.) Similarly, a typical code -snippet to export wisdom from all processes to a file is: -<a name="index-fftw_005fmpi_005finit-387"></a> -<pre class="example"> { - int rank; - FILE *f; - - fftw_mpi_gather_wisdom(MPI_COMM_WORLD); - MPI_Comm_rank(MPI_COMM_WORLD, &rank); - if (rank == 0 && (f = fopen("mywisdom", "w"))) { - fftw_export_wisdom_to_file(f); - fclose(f); - } - } -</pre> - <!-- --> -</body></html> -