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Message Passing Interface (MPI) FAQ Shane Hebert, firstname.lastname@example.org Last modified: Tues Jan 13 13:58:32 1997 This is the list of Frequently Asked Questions about the MPI (Message Passing Interface) standard, a set of library functions for message passing. For a list of the latest changes to this document, see sec- tion ``What's New?''. Comments on the FAQ are welcome. See question ``Formats'' for details of where to get the PostScript, Emacs Info, HTML, and text versions of this document. 1. Introduction and General Information This FAQ attempts to answer basic questions regarding MPI. Pointers to further information on MPI are included for those wishing to know more. 1.1. What is MPI? MPI stands for Message Passing Interface. The goal of MPI, simply stated, is to develop a widely used standard for writing message- passing programs. As such the interface attempts to establish a practical, portable, efficient, and flexible standard for message passing. In designing MPI the MPI Forum sought to make use of the most attractive features of a number of existing message passing systems, rather than selecting one of them and adopting it as the standard. Thus, MPI has been strongly influenced by work at the IBM T. J. Watson Research Center, Intel's NX/2, Express, nCUBE's Vertex, p4, and PARMACS. Other important contributions have come from Zipcode, Chimp, PVM, Chameleon, and PICL. The main advantages of establishing a message-passing standard are portability and ease-of-use. In a distributed memory communication environment in which the higher level routines and/or abstractions are build upon lower level message passing routines the benefits of standardization are particularly apparent. Furthermore, the definition of a message passing standard provides vendors with a clearly defined base set of routines that they can implement efficiently, or in some cases provide hardware support for, thereby enhancing scalability. Source: MPI Document - <http://www.mpi- forum.org/docs/mpi-11-html/mpi-report.html>. 1.2. What is the MPI Forum? Message Passing Interface Forum The Message Passing Interface Forum (MPIF), with participation from over 40 organizations, met from November 1992 to April 1994 to discuss and define a set of library interface standards for message passing. Version 1.0 of the standard was released on May 5, 1994. Beginning in March, 1995, the MPIF reconvened to correct errors and make clarifications in the MPI document of May 5, 1994. These discussions resulted in Version 1.1 (dated June, 1995) which contained only minor changes from Version 1.0. MPI-2 meetings began April, 1995 and met every six weeks until April 25, 1997. At the end of that meeting, the entire MPI-2 Document was unanimously accepted by all voting institutions. For more information on the MPI-2 process, see the section on the MPI-2 effort (Section ``MPI-2''). The MPIF is not sanctioned or supported by any official standards organization. Source: MPI Document - <http://www.mpi- forum.org/docs/mpi-11-html/mpi-report.html>. 1.3. A Brief History of MPI The MPI standardization effort involved about 60 people from 40 organizations mainly from the United States and Europe. Most of the major vendors of concurrent computers were involved in MPI, along with researchers from universities, government laboratories, and industry. The standardization process began with the Workshop on Standards for Message Passing in a Distributed Memory Environment, sponsored by the Center for Research on Parallel Computing, held April 29-30, 1992, in Williamsburg, Virginia. At this workshop the basic features essential to a standard message passing interface were discussed, and a working group established to continue the standardization process. A preliminary draft proposal, known as MPI1 <ftp://netlib2.cs.utk.edu/mpi/mpi1.ps>, was put forward by Dongarra, Hempel, Hey, and Walker in November 1992, and a revised version was completed in February 1993. MPI1 embodied the main features that were identified at the Williamsburg workshop as being necessary in a message passing standard. Since MPI1 was primarily intended to promote discussion and ``get the ball rolling,'' it focused mainly on point- to-point communications. MPI1 brought to the forefront a number of important standardization issues, but did not include any collective communication routines and was not thread-safe. In November 1992, a meeting of the MPI working group was held in Minneapolis, at which it was decided to place the standardization process on a more formal footing, and to generally adopt the procedures and organization of the High Performance Fortran Forum. Subcommittees were formed for the major component areas of the standard, and an email discussion service established for each. In addition, the goal of producing a draft MPI standard by the Fall of 1993 was set. To achieve this goal the MPI working group met every 6 weeks for two days throughout the first 9 months of 1993, and presented the draft MPI standard at the Supercomputing 93 conference in November 1993. These meetings and the email discussion together constituted the MPI Forum, membership of which was and continues to be open to all members of the high performance computing community. Beginning in March, 1995, the MPIF reconvened to correct errors and make clarifications in the MPI document of May 5, 1994. These discussions resulted in Version 1.1 (dated June, 1995) which contained only minor changes from Version 1.0. MPI-2 meetings began April, 1995 and met every six weeks until April 25, 1997. At this meeting, the MPI-2 Document was unanimously accepted. For more information on the MPI-2 process, see the section on the MPI-2 effort (Section ``MPI-2''). Source: MPI Document - <http://www.mpi- forum.org/docs/mpi-11-html/mpi-report.html>. 1.4. The MPI-1 Document There are two versions of the MPI document: version 1.0 (dated May 5, 1994) and version 1.1 (dated June, 1995). o Version 1.1 (June 12, 1995) Version 1.1 (June 12, 1995) of the MPI Document is available on- line as HTML at <http://www.mpi-forum.org/docs/mpi-11-html/mpi- report.html>. It is also available as postscript from the following locations: o <http://www.mpi-forum.org/docs/mpi-11.ps> o <ftp://ftp.erc.msstate.edu/pub/mpi/docs/mpi-report1.1.ps> A compressed version of the postscript document is available from o <http://www.mpi-forum.org/docs/mpi-11.ps.Z> o <ftp://ftp.erc.msstate.edu/pub/mpi/docs/mpi-report1.1.ps.Z> o Version 1.0 (May 5, 1994) The official postscript version of the document can be obtained from netlib at ORNL by sending a mail message to email@example.com with the message "send mpi-report.ps from mpi". It may also be obtained by anonymous ftp from the following sites: o <ftp://netlib2.cs.utk.edu/mpi/mpi-report.ps> o <ftp://ftp.erc.msstate.edu/pub/mpi/docs/mpi-report.ps.Z> o <http://www.mpi-forum.org/docs/mpi-10.ps> o <http://www.mpi-forum.org/docs/mpi-10.ps.Z> 2. Online Resources 2.1. WWW Sites Official Message Passing Interface (MPI) Homepage <http://www.mpi- forum.org> MPI-Forum.Org is the official homesite of the MPI Forum and contains official Forum documents and the MPI Standard documents in a variety of formats. Argonne MPI Homepage <http://www.mcs.anl.gov/mpi> The Argonne National Lab MPI Homepage has a large collection of accumulated information about MPI, including pointers to implementations and tutorials by the site maintainers and others. Official MPICH Homepage <http://www.mcs.anl.gov/mpich> The Official MPICH Homepage has buttons for downloading MPICH in various forms, buglists, patchfiles, and other MPICH-related stuff. Australian National University <http://cap.anu.edu.au/cap/projects/mpi/mpi.html> The Australian National University site contains information on the implementation of MPI on the Fujitsu AP1000 multicomputer located at the Australian National University as well as various links to other MPI information. Mississippi State University <http://www.erc.msstate.edu/mpi/> Contains pointers to MPI resources on the Web, pointers to implementations, pointers to tutorials, pointers to libraries, and other things. Home site of the MPI FAQ. MPI-2 Mailing List Archives <http://www.mpi- forum.org/archives/mail/mail.html> The MPI-Forum web page now contains the mail archive of the MPI-2 Forum mailing lists. Netlib <http://www.netlib.org/mpi/> Netlib has a fairly large repository of MPI information. It contains such items as the original MPI1 proposal and minutes from several of the MPI Forum meetings. Oak Ridge National Laboratory <http://www.epm.ornl.gov/~walker/mpi/> Oak Ridge maintains a well-organized resource center for MPI- related materials. Notre Dame LAM <http://www.mpi.nd.edu/lam> Notre Dame is now the home location for information about LAM, one of the public domain MPI implementations. MPI Validation Suite <http://www.ssd.intel.com/mpi.html> Intel's "MPI Validation Suite" is now available to the public. To download a copy, please visit the site above. 2.2. Newsgroup An MPI-specific newsgroup, comp.parallel.mpi was created by a vote of 506 to 14. The RFD for comp.parallel.mpi was originally posted to comp.parallel, comp.parallel.pvm, and news.announce.newgroups on April 4, 1994. The CFV was issued June 15, 1994. The voting results, RFD, and CFV can be retrieved by anonymous ftp from ftp.erc.msstate.edu as pub/mpi/newsgroup/result, pub/mpi/newsgroup/rfd and pub/mpi/newsgroup/cfv. 2.3. Implementations Many of the MPI WWW pages have information about the various MPI implementations. The Ohio Supercomputing Center is attempting to maintain a comprehensive list of implementations at <http://www.lsc.nd.edu/MPI/>. Information such as the supplier, current version, help contact, etc. can be found there. 3. MPI-2 3.1. MPI-2 Status It was decided at the final MPI-1 meeting (Feb. 1994) that plans for extending MPI should wait until people have had some experience with the current version of MPI. The MPI Forum held a BOF session at Supercomputing '94 to discuss the possibility of an MPI-2 effort. A decision was made to begin MPI-2 meetings in April of 1995. These meetings were held approximately every six weeks until October 11, 1997. After that meeting, the customary two month public comment period was initiated. At SuperComputing'96 (held in Pittsburgh, PA), the document was 'unveiled'. Meetings began again in January, 1997 and continued approximately every six weeks until April 25, 1997. At this meeting, the MPI-2 Document was unanimously accepted by the voting institutions. The MPI-2 Document is viewable as HTML <http://www.mpi-forum.org/docs/mpi-20-html/mpi2-report.html> or downloadable as compressed postscript <http://www.mpi- forum.org/docs/mpi-20.ps.Z> or downloadable as uncompressed postscript <http://www.mpi-forum.org/docs/mpi-20.ps>. 3.2. What features are included in MPI-2? There are several major subsections of functionality addressed in the MPI-2 Standard. o Miscellaneous Topics o Dynamic Process Management o One-Sided Communication o Extended Collective Operations o External Interfaces o Parallel I/O o Language Bindings (C++ and Fortran-90) The I/O subcommittee was added after the MPI-2 process began. There were several other sections of the MPI-2 Document that were present during some form of the process that were removed from the document and placed in the Journal of Development (JOD). This document, which is also downloadable from the web site <http://www.mpi- forum.org/docs/mpi-20-jod.ps> was created so that ideas that were interesting but either were either of unknown value or weren't mature would not be lost and would be documented. One chapter on Real-Time MPI which was placed in the JOD but developed into a standards body of its own. This body has a web page located at <http://www.mpirt.org>. 3.3. What mailing lists were being used for MPI-2? If you wanted to participate in the discussion of a particular MPI-2 topic, send mail to firstname.lastname@example.org containing: subscribe <list-name> <your email address> The current mailing lists include: email@example.com MPI Forum discussion list, all comments welcome firstname.lastname@example.org MPI forum meeting attendees list mpi-dynamic MPI Forum discussion list for dynamic process management mpi-1sided MPI Forum discussion list for one-sided communication mpi-coll MPI Forum discussion list for collective operations mpi-external MPI Forum discussion list for external interfaces mpi-bind MPI Forum discussion list for C++ and Fortran-90 bindings mpi-realtime MPI Forum discussion list for real-time extensions mpi-io MPI Forum discussion list for I/O 3.4. Where are the MPI-2 mailing lists archived? The MPI-2 mailing lists are archived using hypermail. These archived mailing lists can be retrieved from <http://www.mpi- forum.org/archives/mail/mail.html>. 3.5. Where is the current MPI-2 document? The MPI-2 Document can be viewed as HTML as <http://www.mpi- forum.org/docs/mpi-20-html/mpi2-report.html> or can be downloaded in compressed postscript form as <http://www.mpi- forum.org/docs/mpi-20.ps.Z> or as uncompressed postscript form as <http://www.mpi-forum.org/docs/mpi-20.ps>. 3.6. Where can I find out more about MPI-2? More information on MPI-2 is available from <http://www.erc.msstate.edu/mpi/mpi2.html> and <http://www.mpi- forum.org>. These sites contain information about minutes from MPI-2 meetings, votes, etc. 3.7. What is MPI/RT? In the form of the MPI Forums, MPI/RT is a standards effort to design an MPI for Real-Time programming. This Forum meets approximately every six weeks to: o Create integrated messaging, scheduling, and parallel programming API together with syntax and semantics to support the emerging computational hierarchies of node architectures and gigabit/s networks efficiently. o Expand the horizons of performance-portable real-time programming o Support multiple real-time paradigms o Enhance the performance of Messaging over MPI-1 and MPI-2 o Catalyze a new generation of portable parallel applications that require or benefit from the explicit use of time 3.8. Where can I find out more about MPI/RT? The MPI/RT Forum has a web site <http://www.mpirt.org>. 4. Administrative Information and Acknowledgments 4.1. Recent changes to the FAQ o Added references to MPI/RT. o Changed the content of the FAQ to reflect the current status of MPI. o Changed the format of the FAQ. 4.2. Formats in which this FAQ is Available This document is available as ASCII text, an Emacs Info document, PostScript, and HTML. It is also available on the world wide web (WWW) at <http://www.erc.msstate.edu/mpi/mpi-faq.html> or at <http://www.cis.ohio-state.edu/hypertext/faq/usenet/mpi-faq/faq.html> The text, Emacs Info, HTML, and Postscript versions are generated automatically by Linuxdoc-SGML, a text-formating package based on SGML used by Linux Documentation Project. Information on Linuxdoc-SGML can be found at <http://www.informatik.tu-muenchen.de/~schwarz/linuxdoc- sgml/>. The output files mpi-faq.txt, mpi-faq.info, mpi-faq.html, mpi-faq.ps, and mpi-faq.sgml are available at <ftp://ftp.erc.msstate.edu/pub/mpi/faq>. A tarfile (mpi- faq.source.tar.gz) also is available which contains all of these files. 4.3. Where can I get a copy of this FAQ? In addition to finding it in those places listed in question ``Formats'', the text version is posted monthly to comp.parallel.mpi, news.answers, and comp.answers. The text version is also available through anonymous ftp from <ftp://rtfm.mit.edu/pub/usenet/news.answers/> and <ftp://ftp.erc.msstate.edu/pub/mpi/faq/mpi-faq.txt> or those without FTP access can send e-mail to email@example.com with "send usenet/news.answers/mpi-faq" in the message body. You can also get a postscript verion from <ftp://ftp.erc.msstate.edu/pub/mpi/faq/mpi- faq.ps> 4.4. Disclaimer and Copyright Note that this document is provided as is. The information in it is not warranted to be correct; you use it at your own risk.