Message Passing Interface: Difference between revisions

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{{Expand section|date=June 2008}}

The key aspect is "the ability of an MPI process to participate in the creation of new MPI processes or to establish communication with MPI processes that have been started separately." The MPI-2 specification describes three main interfaces by which MPI processes can dynamically establish communications, <code>MPI_Comm_spawn</code>, <code>MPI_Comm_accept</code>/<code>MPI_Comm_connect</code> and <code>MPI_Comm_join</code>. The <code>MPI_Comm_spawn</code> interface allows an MPI process to spawn a number of instances of the named MPI process. The newly spawned set of MPI processes form a new <code>MPI_COMM_WORLD</code> intracommunicator but can communicate with the parent and the intercommunicator the function returns. <code>MPI_Comm_spawn_multiple</code> is an alternate interface that allows the different instances spawned to be different binaries with different arguments.<ref name="Gropp99adv-p7">{{harvnb |Gropp |Lusk |SkjellumSkjelling |19991999b |p=7 }}</ref>

===I/O===

{{Expand section|date=June 2008}}

The parallel I/O feature is sometimes called MPI-IO,<ref name="Gropp99adv-pp5-6">{{harvnb |Gropp |Lusk |Skjelling |19991999b |pp=5–6 }}</ref> and refers to a set of functions designed to abstract I/O management on distributed systems to MPI, and allow files to be easily accessed in a patterned way using the existing derived datatype functionality.

The little research that has been done on this feature indicates that it may not be trivial to get high performance gains by using MPI-IO. For example, an implementation of sparse [[Matrix multiplication|matrix-vector multiplications]] using the MPI I/O library shows a general behavior of minor performance gain, but these results are inconclusive.<ref>{{cite web|url=http://marcovan.hulten.org/report.pdf|title=Sparse matrix-vector multiplications using the MPI I/O library}}</ref> It was not