mirror of
https://github.com/tildearrow/furnace.git
synced 2024-11-06 04:45:05 +00:00
159 lines
7.3 KiB
HTML
159 lines
7.3 KiB
HTML
|
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
||
|
|
<html>
|
||
|
|
<!-- This manual is for FFTW
|
||
|
|
(version 3.3.10, 10 December 2020).
|
||
|
|
|
||
|
|
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. -->
|
||
|
|
<!-- Created by GNU Texinfo 6.7, http://www.gnu.org/software/texinfo/ -->
|
||
|
|
<head>
|
||
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
|
||
|
|
<title>Combining MPI and Threads (FFTW 3.3.10)</title>
|
||
|
|
|
||
|
|
<meta name="description" content="Combining MPI and Threads (FFTW 3.3.10)">
|
||
|
|
<meta name="keywords" content="Combining MPI and Threads (FFTW 3.3.10)">
|
||
|
|
<meta name="resource-type" content="document">
|
||
|
|
<meta name="distribution" content="global">
|
||
|
|
<meta name="Generator" content="makeinfo">
|
||
|
|
<link href="index.html" rel="start" title="Top">
|
||
|
|
<link href="Concept-Index.html" rel="index" title="Concept Index">
|
||
|
|
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
|
||
|
|
<link href="Distributed_002dmemory-FFTW-with-MPI.html" rel="up" title="Distributed-memory FFTW with MPI">
|
||
|
|
<link href="FFTW-MPI-Reference.html" rel="next" title="FFTW MPI Reference">
|
||
|
|
<link href="FFTW-MPI-Performance-Tips.html" rel="prev" title="FFTW MPI Performance Tips">
|
||
|
|
<style type="text/css">
|
||
|
|
<!--
|
||
|
|
a.summary-letter {text-decoration: none}
|
||
|
|
blockquote.indentedblock {margin-right: 0em}
|
||
|
|
div.display {margin-left: 3.2em}
|
||
|
|
div.example {margin-left: 3.2em}
|
||
|
|
div.lisp {margin-left: 3.2em}
|
||
|
|
kbd {font-style: oblique}
|
||
|
|
pre.display {font-family: inherit}
|
||
|
|
pre.format {font-family: inherit}
|
||
|
|
pre.menu-comment {font-family: serif}
|
||
|
|
pre.menu-preformatted {font-family: serif}
|
||
|
|
span.nolinebreak {white-space: nowrap}
|
||
|
|
span.roman {font-family: initial; font-weight: normal}
|
||
|
|
span.sansserif {font-family: sans-serif; font-weight: normal}
|
||
|
|
ul.no-bullet {list-style: none}
|
||
|
|
-->
|
||
|
|
</style>
|
||
|
|
|
||
|
|
|
||
|
|
</head>
|
||
|
|
|
||
|
|
<body lang="en">
|
||
|
|
<span id="Combining-MPI-and-Threads"></span><div class="header">
|
||
|
|
<p>
|
||
|
|
Next: <a href="FFTW-MPI-Reference.html" accesskey="n" rel="next">FFTW MPI Reference</a>, Previous: <a href="FFTW-MPI-Performance-Tips.html" accesskey="p" rel="prev">FFTW MPI Performance Tips</a>, Up: <a href="Distributed_002dmemory-FFTW-with-MPI.html" accesskey="u" rel="up">Distributed-memory FFTW with MPI</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
|
||
|
|
</div>
|
||
|
|
<hr>
|
||
|
|
<span id="Combining-MPI-and-Threads-1"></span><h3 class="section">6.11 Combining MPI and Threads</h3>
|
||
|
|
<span id="index-threads-2"></span>
|
||
|
|
|
||
|
|
<p>In certain cases, it may be advantageous to combine MPI
|
||
|
|
(distributed-memory) and threads (shared-memory) parallelization.
|
||
|
|
FFTW supports this, with certain caveats. For example, if you have a
|
||
|
|
cluster of 4-processor shared-memory nodes, you may want to use
|
||
|
|
threads within the nodes and MPI between the nodes, instead of MPI for
|
||
|
|
all parallelization.
|
||
|
|
</p>
|
||
|
|
<p>In particular, it is possible to seamlessly combine the MPI FFTW
|
||
|
|
routines with the multi-threaded FFTW routines (see <a href="Multi_002dthreaded-FFTW.html">Multi-threaded FFTW</a>). However, some care must be taken in the initialization code,
|
||
|
|
which should look something like this:
|
||
|
|
</p>
|
||
|
|
<div class="example">
|
||
|
|
<pre class="example">int threads_ok;
|
||
|
|
|
||
|
|
int main(int argc, char **argv)
|
||
|
|
{
|
||
|
|
int provided;
|
||
|
|
MPI_Init_thread(&argc, &argv, MPI_THREAD_FUNNELED, &provided);
|
||
|
|
threads_ok = provided >= MPI_THREAD_FUNNELED;
|
||
|
|
|
||
|
|
if (threads_ok) threads_ok = fftw_init_threads();
|
||
|
|
fftw_mpi_init();
|
||
|
|
|
||
|
|
...
|
||
|
|
if (threads_ok) fftw_plan_with_nthreads(...);
|
||
|
|
...
|
||
|
|
|
||
|
|
MPI_Finalize();
|
||
|
|
}
|
||
|
|
</pre></div>
|
||
|
|
<span id="index-fftw_005fmpi_005finit-3"></span>
|
||
|
|
<span id="index-fftw_005finit_005fthreads-2"></span>
|
||
|
|
<span id="index-fftw_005fplan_005fwith_005fnthreads-1"></span>
|
||
|
|
|
||
|
|
<p>First, note that instead of calling <code>MPI_Init</code>, you should call
|
||
|
|
<code>MPI_Init_threads</code>, which is the initialization routine defined
|
||
|
|
by the MPI-2 standard to indicate to MPI that your program will be
|
||
|
|
multithreaded. We pass <code>MPI_THREAD_FUNNELED</code>, which indicates
|
||
|
|
that we will only call MPI routines from the main thread. (FFTW will
|
||
|
|
launch additional threads internally, but the extra threads will not
|
||
|
|
call MPI code.) (You may also pass <code>MPI_THREAD_SERIALIZED</code> or
|
||
|
|
<code>MPI_THREAD_MULTIPLE</code>, which requests additional multithreading
|
||
|
|
support from the MPI implementation, but this is not required by
|
||
|
|
FFTW.) The <code>provided</code> parameter returns what level of threads
|
||
|
|
support is actually supported by your MPI implementation; this
|
||
|
|
<em>must</em> be at least <code>MPI_THREAD_FUNNELED</code> if you want to call
|
||
|
|
the FFTW threads routines, so we define a global variable
|
||
|
|
<code>threads_ok</code> to record this. You should only call
|
||
|
|
<code>fftw_init_threads</code> or <code>fftw_plan_with_nthreads</code> if
|
||
|
|
<code>threads_ok</code> is true. For more information on thread safety in
|
||
|
|
MPI, see the
|
||
|
|
<a href="http://www.mpi-forum.org/docs/mpi-20-html/node162.htm">MPI and
|
||
|
|
Threads</a> section of the MPI-2 standard.
|
||
|
|
<span id="index-thread-safety-2"></span>
|
||
|
|
</p>
|
||
|
|
|
||
|
|
<p>Second, we must call <code>fftw_init_threads</code> <em>before</em>
|
||
|
|
<code>fftw_mpi_init</code>. This is critical for technical reasons having
|
||
|
|
to do with how FFTW initializes its list of algorithms.
|
||
|
|
</p>
|
||
|
|
<p>Then, if you call <code>fftw_plan_with_nthreads(N)</code>, <em>every</em> MPI
|
||
|
|
process will launch (up to) <code>N</code> threads to parallelize its transforms.
|
||
|
|
</p>
|
||
|
|
<p>For example, in the hypothetical cluster of 4-processor nodes, you
|
||
|
|
might wish to launch only a single MPI process per node, and then call
|
||
|
|
<code>fftw_plan_with_nthreads(4)</code> on each process to use all
|
||
|
|
processors in the nodes.
|
||
|
|
</p>
|
||
|
|
<p>This may or may not be faster than simply using as many MPI processes
|
||
|
|
as you have processors, however. On the one hand, using threads
|
||
|
|
within a node eliminates the need for explicit message passing within
|
||
|
|
the node. On the other hand, FFTW’s transpose routines are not
|
||
|
|
multi-threaded, and this means that the communications that do take
|
||
|
|
place will not benefit from parallelization within the node.
|
||
|
|
Moreover, many MPI implementations already have optimizations to
|
||
|
|
exploit shared memory when it is available, so adding the
|
||
|
|
multithreaded FFTW on top of this may be superfluous.
|
||
|
|
<span id="index-transpose-4"></span>
|
||
|
|
</p>
|
||
|
|
<hr>
|
||
|
|
<div class="header">
|
||
|
|
<p>
|
||
|
|
Next: <a href="FFTW-MPI-Reference.html" accesskey="n" rel="next">FFTW MPI Reference</a>, Previous: <a href="FFTW-MPI-Performance-Tips.html" accesskey="p" rel="prev">FFTW MPI Performance Tips</a>, Up: <a href="Distributed_002dmemory-FFTW-with-MPI.html" accesskey="u" rel="up">Distributed-memory FFTW with MPI</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
</body>
|
||
|
|
</html>
|