Traditional interprocess communication requires cooperation and synchronization between sender and receiver. MPI-2’s new remote memory access features allow one process to update or interrogate the memory of another, hence the name one-sided communication. Here’s a hands-on guide.
While Parallel Virtual Machine (PVM) and other applications programming interfaces are still available and in widespread use, the Message Passing Interface (MPI) has become the preferred programming interface for data exchange in most new parallel scientific applications. The MPI-2 standard was released in 1997 and implementations of the standard are beginning to become widely available.
Both MPICH (http://www-unix.mcs.anl.gov/mpi/mpich/) and LAM/MPI (http://www.lam-mpi.org/) — the two most popular MPI implementations for Linux clusters — comply fully with the MPI-1.2 standard, which is described in the MPI-2 standards document. Moreover, both implementations now support subsets of the new MPI-2 features. LAM/MPI includes support in its regular 7.0.x versions, whereas a completely new implementation of MPICH, called MPICH2, provides early support for many MPI-2 features.
Installation and testing instructions for both of these implementations (LAM/MPI 7.0.6 and MPICH2 beta 0.96p2) and a short MPI-2 program demonstrating one-sided communication were included in the August 2004 “Extreme Linux” column. In the September “Extreme Linux” column, MPI-2’s new process creation and management features were discussed and demonstrated using a manager/worker program example.
This month, let’s look at MPI-2’s new remote memory access (RMA) capabilities, usually called one-sided communications, because only one process needs to issue a send or receive call to achieve the communication. This scheme can simplify programming in cases where the memory locations that must be updated or interrogated are known on only one side of a communicating pair of processes.
One-Sided Communication
Traditionally, the parameters…
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