2008-01-01 02:12:45 UTC

Tags: accelerated computing, Cluster, CUDA, CUDA C/C, MPI, Multi-GPU, OpenACC 5 Comments MPI, the Message Passing Interface, is a standard API for communicating data via messages between distributed processes that is commonly used in HPC to build applications that can scale to multi-node computer clusters. Note that starting with Open MPI v4.0.0, prototypes for several legacy MPI-1 symbols that were deleted in the MPI-3.0 specification (which was published in 2012) are no longer available by default in mpi.h. Specifically, several MPI-1 symbols were deprecated in the 1996 publishing of the MPI-2.0 specification.

Greetings,
I'm trying to build the Salomé engineering simulation tool, and am

And mpi.h doesn't work either. – user2804865 Nov 13 '14 at 23:34 1 Program using the Message Passing Interface should be compiled by using something like mpicc main.c -o main or mpiCC main.cpp -o main.
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Changes in this release: See this page if you are upgrading from a prior major release series of Open MPI. It shows the Big Changes for which end users need to be aware. See the NEWS file for a more fine-grained listing of changes between each release and sub-release of the Open MPI v4.0 series.

having trouble compiling with OpenMPI. The full text of the error is at
http://lyre.mit.edu/~powell/salome-error . The crux of the problem can
be reproduced by trying to compile a C++ file with:
Test

extern 'C'
{
#include 'mpi.h'
}
At the end of mpi.h, the C++ headers get loaded while in extern C mode,
and the result is a vast list of errors.
It seems odd that one of the cplusplus variables is #defined while in
extern C mode, but that's what seems to be happening.
I see that it should be possible (and verified that it is possible) to
avoid this by using -DOMPI_SKIP_MPICXX. But something in me says that
shouldn't be necessary, that extern C code should only include C headers
and not C++ ones...
This is using Debian lenny (testing) with gcc 4.2.1-6.
Thanks,
-Adam

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This is a short introduction to the Message Passing Interface (MPI)designed to convey the fundamental operation and use of the interface.This introduction is designed for readers with some background programmingC, and should deliver enough information to allow readers towrite and run their own (very simple) parallel C programs using MPI.

There exists a version of this tutorial for Fortran programers calledIntroduction the the Message Passing Interface (MPI) using Fortran.

What is MPI?

MPI is a library of routines that can be used to create parallel programsin C or Fortran77. Standard C and Fortran include no constructs supporting parallelism so vendors have developed a variety of extensionsto allow users of those languages to build parallel applications.The result has been a spate of non-portable applications, and a needto retrain programmers for each platform upon which they work.

The MPI standard was developed to ameliorate these problems. It is alibrary that runs with standard C or Fortran programs, using commonly-available operating system services to create parallel processes and exchange information among these processes.

MPI is designed to allow users to create programs that can run efficientlyon most parallel architectures. The design process includedvendors (such as IBM, Intel, TMC, Cray, Convex, etc.), parallellibrary authors (involved in the development of PVM, Linda, etc.),and applications specialists. The final version for the draftstandard became available in May of 1994.

MPI can also support distributed program execution on heterogenoushardware. That is, you may run a program that starts processes onmultiple computer systems to work on the same problem. This is usefulwith a workstation farm.

Hello world

Here is the basic Hello world program in C using MPI:

If you compile hello.c with a command like

you will create an executable file called hello, which you canexecute by using the mpirun command as in the following sessionsegment:

When the program starts, it consists of only one process, sometimes calledthe 'parent', 'root', or 'master' process. When the routine MPI_Init executes within the root process, it causes the creation of 3 additional processes (to reach the number of processes (np) specified on the mpirun command line), sometimes called 'child' processes.

Each of the processes then continues executing separate versions of the hello world program. The next statement in every program isthe printf statement, and each process prints 'Hello world' as directed.Since terminal output from every program will be directed to thesame terminal, we see four lines saying 'Hello world'.

Identifying the separate processes

As written, we cannot tell which 'Hello world' line was printed bywhich process. To identify a process we need some sort of process ID and aroutine that lets a process find its own process ID.MPI assigns an integer to each process beginning with 0 for the parentprocess and incrementing each time a new process is created.A process ID is also called its 'rank'.

MPI also provides routines that let the process determine its process ID,as well as the number of processes that are have been created.

Here is an enhanced version of the Hello world program thatidentifies the process that writes each line of output:

When we run this program, each process identifies itself:

Note that the process numbers are not printed in ascending order.That is because the processes execute independently and executionorder was not controlled in any way. The programs may print their results in different orders each time they are run.

(To find out which Origin processors and memories areused to run a program you can turn on the MPI_DSM_VERBOSE environment variablewith 'export MPI_DSM_VERBOSE=ON', or equivalent.)

To let each process perform a different task, you can use a programstructure like:

Basic MPI communication routines

It is important to realize that separate processes share nomemory variables. They appear to be using the same variables, butthey are really using COPIES of any variable defined in the program.

As a result, these programs cannot communicate with each other byexchanging information in memory variables. Instead they may use anyof a large number of MPI communication routines. The two basicroutines are:

MPI_Send, to send a message to another process, and
MPI_Recv, to receive a message from another process.

The syntax of MPI_Send is:

data_to_send: variable of a C type that corresponds to the send_type supplied below
send_count: number of data elements to be sent (nonnegative int)
send_type: datatype of the data to be sent (one of the MPI datatype handles)
destination_ID: process ID of destination (int)
tag: message tag (int)
comm: communicator (handle)

Once a program calls MPI_Send, it blocks until the data transferhas taken place and the data_to_send variable can be safely reused. As a result, these routines provide a simplesynchronization service along with data exchange.

The syntax of MPI_Recv is:

received_data: variable of a C type that corresponds to the receive_type supplied below
receive_count: number of data elements expected (int)
receive_type: datatype of the data to be received (one of the MPI datatype handles)
sender_ID: process ID of the sending process (int)
tag: message tag (int)
comm: communicator (handle)
status: status struct (MPI_Status)

The receive_count, sender_ID, and tag values may bespecified so as to allow messages of unknown length, from several sources(MPI_ANY_SOURCE), or with various tag values (MPI_ANY_TAG).

The amount of information actually received can then be retrieved from the status variable, as with:

MPI_Recv blocks until the data transfer is complete and thereceived_data v

Mpi.h Dev C%2b%2b