<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> <title>Design Philosophy</title> <link rel="stylesheet" href="../../../doc/src/boostbook.css" type="text/css"> <meta name="generator" content="DocBook XSL Stylesheets V1.75.2"> <link rel="home" href="../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset"> <link rel="up" href="../mpi.html" title="Chapter 12. Boost.MPI"> <link rel="prev" href="python.html" title="Python Bindings"> <link rel="next" href="performance.html" title="Performance Evaluation"> </head> <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> <table cellpadding="2" width="100%"><tr> <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../boost.png"></td> <td align="center"><a href="../../../index.html">Home</a></td> <td align="center"><a href="../../../libs/libraries.htm">Libraries</a></td> <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> <td align="center"><a href="../../../more/index.htm">More</a></td> </tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="python.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../mpi.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="performance.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> </div> <div class="section"> <div class="titlepage"><div><div><h2 class="title" style="clear: both"> <a name="mpi.design"></a> Design Philosophy</h2></div></div></div> <p> The design philosophy of the Parallel MPI library is very simple: be both convenient and efficient. MPI is a library built for high-performance applications, but it's FORTRAN-centric, performance-minded design makes it rather inflexible from the C++ point of view: passing a string from one process to another is inconvenient, requiring several messages and explicit buffering; passing a container of strings from one process to another requires an extra level of manual bookkeeping; and passing a map from strings to containers of strings is positively infuriating. The Parallel MPI library allows all of these data types to be passed using the same simple <code class="computeroutput"><span class="identifier">send</span><span class="special">()</span></code> and <code class="computeroutput"><span class="identifier">recv</span><span class="special">()</span></code> primitives. Likewise, collective operations such as <code class="computeroutput"><a class="link" href="../boost/mpi/reduce.html" title="Function reduce">reduce()</a></code> allow arbitrary data types and function objects, much like the C++ Standard Library would. </p> <p> The higher-level abstractions provided for convenience must not have an impact on the performance of the application. For instance, sending an integer via <code class="computeroutput"><span class="identifier">send</span></code> must be as efficient as a call to <code class="computeroutput"><span class="identifier">MPI_Send</span></code>, which means that it must be implemented by a simple call to <code class="computeroutput"><span class="identifier">MPI_Send</span></code>; likewise, an integer <code class="computeroutput"><a class="link" href="../boost/mpi/reduce.html" title="Function reduce">reduce()</a></code> using <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">plus</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span></code> must be implemented with a call to <code class="computeroutput"><span class="identifier">MPI_Reduce</span></code> on integers using the <code class="computeroutput"><span class="identifier">MPI_SUM</span></code> operation: anything less will impact performance. In essence, this is the "don't pay for what you don't use" principle: if the user is not transmitting strings, s/he should not pay the overhead associated with strings. </p> <p> Sometimes, achieving maximal performance means foregoing convenient abstractions and implementing certain functionality using lower-level primitives. For this reason, it is always possible to extract enough information from the abstractions in Boost.MPI to minimize the amount of effort required to interface between Boost.MPI and the C MPI library. </p> </div> <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> <td align="left"></td> <td align="right"><div class="copyright-footer">Copyright © 2005-2007 Douglas Gregor, Matthias Troyer, Trustees of Indiana University<p> Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top"> http://www.boost.org/LICENSE_1_0.txt </a>) </p> </div></td> </tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="python.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../mpi.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="performance.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> </div> </body> </html>