Ubuntu Manpage: mpi - LAM/MPI implementation

Provided by: lam-runtime_7.1.4-7.1build2_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).

   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

LAM 7.1.4                                          July, 2007                                             mpi(7)

NAME

DESCRIPTION

LAM Extensions to MPI

SEE ALSO