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.

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