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| <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. |
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| <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. |
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| <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>) |
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