Provided by: lam-runtime_7.1.4-7.2_amd64 
NAME
mpi - LAM/MPI implementation
DESCRIPTION
LAM features a full implementation of Message Passing Interface (MPI) 1 standard with many
features included from the MPI-2 standard.
Compliant applications are source code portable between LAM and any other implementation
of MPI. In addition to meeting the standard in a high quality manner, LAM offers
extensive monitoring capabilities to support debugging. Monitoring happens on two levels.
LAM has the hooks to allow a snapshot of process and message status to be taken at any
time during an application run. The status includes all aspects of synchronization plus
datatype map / signature, communicator group membership and message contents. On the
second level, the MPI library is instrumented to produce a cumulative record of
communication, which can be visualized either at runtime or post-mortem.
LAM/MPI features the ability to change its underlying message transport mechanism, as well
as pass tunable parameters to different components in LAM/MPI at run-time -- without the
need to recompile or relink user MPI applications. This provides great flexibility for
both developers of MPI software as well as researchers investigating MPI performance.
This modual framework is called the System Services Interface (SSI), and is responsible
for much of the back-end functionality in LAM/MPI.
Another strength of this MPI implementation is the movement of non-blocking communication
requests, including those that result from buffered sends. This is the real challenge of
implementing MPI; everything else is mostly a straight forward wrapping of an underlying
communication mechanism. LAM allows messages to be buffered on the source end in any
state of progression, including partially transmitted packets. This capability leads to
great portability and robustness.
User Information
Users are strongly encouraged to read the LAM/MPI User's Guide that is included with the
LAM/MPI distribution, and is provided on the main LAM/MPI web site (http://www.lam-
mpi.org/).
Up-to-Date Information
The LAM home page can be found on the World Wide Web at: http://www.lam-mpi.org/. It
should be consulted for the most current information about LAM, as well as updates,
patches, etc.
MPI Communication
The sophisticated message advancing engine at the heart of the MPI library uses only a
handful of routines to drive the underlying communication system. Runtime flags decide
which message passing engine module is used, so recompilation of user programs is not
necessary.
The different message passing engines are commonly referred to as "Request Progression
Interface" (RPI) modules. The LAM/MPI distribution includes multiple RPI modules; see the
lamssi_rpi(7) man page for more details.
One notable module uses LAM's network message-passing subsystem, including its buffer
daemon. In this "daemon" mode, LAM's extensive monitoring features are fully available.
Although the "daemon" mode typically incurrs higher latency than the "native" RPI modules,
applications that can utilize latency-hiding techniques may experience greater performance
due to the daemon-mode's ability to exhibit true asynchronous message passing.
Guaranteed Envelope Resources
Applications may fail, legitimately, on some implementations but not others due to an
escape hatch in the MPI Standard called "resource limitations". Most resources are
managed locally and it is easy for an implementation to provide a helpful error code
and/or message when a resource is exhausted. Buffer space for message envelopes is often
a remote resource (as in LAM) which is difficult to manage. An overflow may not be
reported (as in some other implementations) to the process that caused the overflow.
Moreover, interpretation of the MPI guarantee on message progress may confuse the
debugging of an application that actually died on envelope overflow.
LAM has a property called "Guaranteed Envelope Resources" (GER) which serves two purposes.
It is a promise from the implementation to the application that a minimum amount of
envelope buffering will be available to each process pair. Secondly, it ensures that the
producer of messages that overflows this resource will be throttled or cited with an error
as necessary.
A minimum GER is configured when LAM is built. The MPI library uses a protocol to ensure
GER when running in daemon mode. The default C2C mode (TCP/IP) does not use a protocol,
because process-pair protection is provided by TCP/IP itself. Errors are only reported to
the receiving process in C2C mode. An option to mpirun(1) disables GER.
Input and Output
The MPI standard does not specify standard I/O functionality. LAM does not interfere with
the I/O capabilities of the underlying system but it does make special provisions for
remote terminal I/O using the ANSI/POSIX routines. See mpirun(1) and tstdio(3).
LAM now includes the ROMIO distribution for MPI-2 file input and output. If ROMIO support
is compiled into LAM, the functionality from Chapter 9 of the MPI-2 standard is provided.
ROMIO has some important limitations under LAM; the User's Guide in the LAM distribution
should be consulted before writing MPI programs that use MPI I/O.
Dynamic Processes
LAM includes an implementation of MPI-2 dynamic process creation.
LAM Extensions to MPI
Debugging Aids
LAM includes the MPI-2 functionality for naming opaque types. Support for the Etnus
TotalView parallel debugger is also provided; see the User's Guide for more details.
Additionally, LAM provides the capability to launch non-MPI programs on remote nodes.
This includes shell scripts, debuggers, etc. As long as an MPI program is eventually
launched (as a child, grandchild, etc.), LAM can handle executing as many intermediate
programs as necessary. This can greatly help debugging and logging of user programs.
Trace Generation
To avoid being swamped with trace data from a long running application, LAM supplies
collective operations to turn the tap on and off. See MPIL_Trace_on(2) and
MPIL_Trace_off(2).
Asynchronous Signals
LAM has an signal handling package which mirrors but does not interfere with POSIX signal
handling. An MPI extension routine delivers a signal to a process. See MPIL_Signal(2).
SEE ALSO
Overview of Commands and Libraries
introu(1), introc(2), INTROF(2)
System Services Interface (SSI)
lamssi(7), lamssi_boot(7), lamssi_coll(7), lamssi_rpi(7)
Starting / Stopping LAM
recon(1), lamboot(1), lamhalt(1), lamnodes(1), lamwipe(1), tping(1), lamgrow(1),
lamshrink(1)
Compiling MPI Applications
mpicc(1), mpiCC(1), mpif77(1)
Running MPI Applications
mpirun(1), lamclean(1)
Running Non-MPI Applications
lamexec(1)
Monitoring MPI Applications
mpitask(1)
Unloading MPI Trace Data
lamtrace(1)
Reference Documents
"LAM/MPI Installation Guide"
included in the LAM/MPI distribution and available on http://www.lam-mpi.org/
"LAM/MPI User's Guide"
included in the LAM/MPI distribution and available on http://www.lam-mpi.org/
"LAM Frequently Asked Questions"
at http://www.lam-mpi.org/faq/
"MPI Primer / Developing with LAM", Ohio Supercomputer Center
"MPI: A Message-Passing Interface Standard", Message-Passing Interface Forum, version 1.1
at http://www.mpi-forum.org/
"MPI-2: Extensions to the Message Passing Interface", Message Passing Interface Forum,
version 2.0
at http://www.mpi-forum.org/
MPI Quick Tutorials
"LAM/MPI ND User Guide / Introduction"
"MPI: It's Easy to Get Started"
"MPI: Everyday Datatypes"
"MPI: Everyday Collective Communication"
at http://www.lam-mpi.org/mpi/tutorials/lam/
Guaranteed Envelope Resources
"Robust MPI Message Delivery Through Guaranteed Resources",
MPI Developer's Conference, 1995