openmpi/README

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===========================================================================

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extra information as possible.  This web page details all the
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Thanks for your time.

===========================================================================

Much, much more information is also available in the Open MPI FAQ:

    http://www.open-mpi.org/faq/

===========================================================================

The following abbreviated list of release notes applies to this code
base as of this writing (22 February 2012):

General notes
-------------

- Open MPI now includes two public software layers: MPI and OpenSHMEM.
  Throughout this document, references to Open MPI implicitly include 
  both of these layers. When distinction between these two layers is 
  necessary, we will reference them as the "MPI" and "OSHMEM" layers
  respectively. 
  
  OpenSHMEM is a collaborative effort between academia, industry, 
  and the U.S. Government to create a specification for a 
  standardized API for parallel programming in the Partitioned 
  Global Address Space (PGAS.) For more information about the OpenSHMEM
  project, including access to the current OpenSHMEM specification, 
  please visit:

     http://openshmem.org/
  
  The OpenSHMEM implementation contained herein is provided by 
  Mellanox Technologies Inc. made possible by the support and patient 
  guidance of the Open MPI community. This implementation attempts 
  to be portable, to allow it to be deployed in multiple environments, 
  and to be a starting point for optimizations targeted to particular 
  hardware platforms. However, until other network vendors and/or 
  institutions contribute platform specific optimizations, this 
  implementation will most likely provide optimal performance on Mellanox
  hardware and software stacks.   

- Open MPI includes support for a wide variety of supplemental
  hardware and software package.  When configuring Open MPI, you may
  need to supply additional flags to the "configure" script in order
  to tell Open MPI where the header files, libraries, and any other
  required files are located.  As such, running "configure" by itself
  may not include support for all the devices (etc.) that you expect,
  especially if their support headers / libraries are installed in
  non-standard locations.  Network interconnects are an easy example
  to discuss -- Myrinet and OpenFabrics networks, for example, both
  have supplemental headers and libraries that must be found before
  Open MPI can build support for them.  You must specify where these
  files are with the appropriate options to configure.  See the
  listing of configure command-line switches, below, for more details.

- The majority of Open MPI's documentation is here in this file, the
  included man pages, and on the web site FAQ
  (http://www.open-mpi.org/).  This will eventually be supplemented
  with cohesive installation and user documentation files.

- Note that Open MPI documentation uses the word "component"
  frequently; the word "plugin" is probably more familiar to most
  users.  As such, end users can probably completely substitute the
  word "plugin" wherever you see "component" in our documentation.
  For what it's worth, we use the word "component" for historical
  reasons, mainly because it is part of our acronyms and internal API
  function calls.

- The run-time systems that are currently supported are:
  - rsh / ssh
  - LoadLeveler
  - PBS Pro, Torque
  - Platform LSF (v7.0.2 and later)
  - SLURM
  - Cray XT-3, XT-4, and XT-5
  - Oracle Grid Engine (OGE) 6.1, 6.2 and open source Grid Engine

- Systems that have been tested are:
  - Linux (various flavors/distros), 32 bit, with gcc
  - Linux (various flavors/distros), 64 bit (x86), with gcc, Absoft,
    Intel, and Portland (*)
  - OS X (10.6, 10.7, 10.8, 10.9), 32 and 64 bit (x86_64), with gcc and
    Absoft compilers (*)

  (*) Be sure to read the Compiler Notes, below.

- Other systems have been lightly (but not fully tested):
  - Cygwin 32 & 64 bit with gcc
  - ARMv4, ARMv5, ARMv6, ARMv7 (when using non-inline assembly; only
    ARMv7 is fully supported when -DOMPI_DISABLE_INLINE_ASM is used).
  - Other 64 bit platforms (e.g., Linux on PPC64)
  - Oracle Solaris 10 and 11, 32 and 64 bit (SPARC, i386, x86_64),
    with Oracle Solaris Studio 12.2 and 12.3

Compiler Notes
--------------

- Mixing compilers from different vendors when building Open MPI
  (e.g., using the C/C++ compiler from one vendor and the Fortran
  compiler from a different vendor) has been successfully employed by
  some Open MPI users (discussed on the Open MPI user's mailing list),
  but such configurations are not tested and not documented.  For
  example, such configurations may require additional compiler /
  linker flags to make Open MPI build properly.

- In general, the latest versions of compilers of a given vendor's
  series have the least bugs.  We have seen cases where Vendor XYZ's
  compiler version A.B fails to compile Open MPI, but version A.C
  (where C>B) works just fine.  If you run into a compile failure, you
  might want to double check that you have the latest bug fixes and
  patches for your compiler.

- On NetBSD-6 (at least AMD64 and i386), and possibly on OpenBSD,
  libtool misidentifies properties of f95/g95, leading to obscure
  compile-time failures if used to build Open MPI.  You can work
  around this issue by ensuring that libtool will not use f95/g95
  (e.g., by specifying FC=<some_other_compiler>, or otherwise ensuring
  a different Fortran compiler will be found earlier in the path than
  f95/g95), or by disabling the Fortran MPI bindings with
  --disable-mpi-fortran.

- Absoft 11.5.2 plus a service pack from September 2012 (which Absoft
  says is available upon request), or a version later than 11.5.2
  (e.g., 11.5.3), is required to compile the new Fortran mpi_f08
  module.

- Open MPI does not support the Sparc v8 CPU target.  However,
  as of Solaris Studio 12.1,  and later compilers, one should not 
  specify -xarch=v8plus or -xarch=v9.  The use of the options
  -m32 and -m64 for producing 32 and 64 bit targets, respectively,
  are now preferred by the Solaris Studio compilers.

- It has been noticed that if one uses CXX=sunCC, in which sunCC
  is a link in the Solaris Studio compiler release, that the OMPI 
  build system has issue with sunCC and does not build libmpi_cxx.so.
  Therefore  the make install fails.  So we suggest that one should
  use CXX=CC, which works, instead of CXX=sunCC.

- If one tries to build OMPI on Ubuntu with Solaris Studio using the C++
  compiler and the -m32 option, you might see a warning:

    CC: Warning: failed to detect system linker version, falling back to
    custom linker usage

  And the build will fail.  One can overcome this error by either 
  setting LD_LIBRARY_PATH to the location of the 32 bit libraries (most
  likely /lib32), or giving LDFLAGS="-L/lib32 -R/lib32" to the configure
  command.  Officially, Solaris Studio is not supported on Ubuntu Linux
  distributions, so additional problems might be incurred.

- The Solaris Studio 12.2 compilers may have a problem compiling
  VampirTrace on some Linux platforms.  You can either upgrade to a
  later version of the Solaris Studio compilers (e.g., 12.3 does not
  have this problem), or disable building VampirTrace.

- Open MPI does not support the gccfss compiler (GCC For SPARC
  Systems; a now-defunct compiler project from Sun).

- At least some versions of the Intel 8.1 compiler seg fault while
  compiling certain Open MPI source code files.  As such, it is not
  supported.

- The Intel 9.0 v20051201 compiler on IA64 platforms seems to have a
  problem with optimizing the ptmalloc2 memory manager component (the
  generated code will segv).  As such, the ptmalloc2 component will
  automatically disable itself if it detects that it is on this
  platform/compiler combination.  The only effect that this should
  have is that the MCA parameter mpi_leave_pinned will be inoperative.

- It has been reported that the Intel 9.1 and 10.0 compilers fail to
  compile Open MPI on IA64 platforms.  As of 12 Sep 2012, there is
  very little (if any) testing performed on IA64 platforms (with any
  compiler).  Support is "best effort" for these platforms, but it is
  doubtful that any effort will be expended to fix the Intel 9.1 /
  10.0 compiler issuers on this platform.

- Early versions of the Intel 12.1 Linux compiler suite on x86_64 seem
  to have a bug that prevents Open MPI from working.  Symptoms
  including immediate segv of the wrapper compilers (e.g., mpicc) and
  MPI applications.  As of 1 Feb 2012, if you upgrade to the latest
  version of the Intel 12.1 Linux compiler suite, the problem will go
  away.

- Early versions of the Portland Group 6.0 compiler have problems
  creating the C++ MPI bindings as a shared library (e.g., v6.0-1).
  Tests with later versions show that this has been fixed (e.g.,
  v6.0-5).

- The Portland Group compilers prior to version 7.0 require the
  "-Msignextend" compiler flag to extend the sign bit when converting
  from a shorter to longer integer.  This is is different than other
  compilers (such as GNU).  When compiling Open MPI with the Portland
  compiler suite, the following flags should be passed to Open MPI's
  configure script:

  shell$ ./configure CFLAGS=-Msignextend CXXFLAGS=-Msignextend \
	--with-wrapper-cflags=-Msignextend \
	--with-wrapper-cxxflags=-Msignextend ...

  This will both compile Open MPI with the proper compile flags and
  also automatically add "-Msignextend" when the C and C++ MPI wrapper
  compilers are used to compile user MPI applications.

- Using the MPI C++ bindings with older versions of the Pathscale
  compiler on some platforms is an old issue that seems to be a
  problem when Pathscale uses a back-end GCC 3.x compiler. Here's a
  proposed solution from the Pathscale support team (from July 2010):

      The proposed work-around is to install gcc-4.x on the system and
      use the pathCC -gnu4 option. Newer versions of the compiler (4.x
      and beyond) should have this fixed, but we'll have to test to
      confirm it's actually fixed and working correctly.

  We don't anticipate that this will be much of a problem for Open MPI
  users these days (our informal testing shows that not many users are
  still using GCC 3.x).  Contact Pathscale support if you continue to
  have problems with Open MPI's C++ bindings.

- Using the Absoft compiler to build the MPI Fortran bindings on Suse
  9.3 is known to fail due to a Libtool compatibility issue.

- MPI Fortran API support has been completely overhauled since the
  Open MPI v1.5/v1.6 series.  

  ********************************************************************
  ********************************************************************
  *** There is now only a single Fortran MPI wrapper compiler and 
  *** a single Fortran OSHMEM wrapper compiler:
  *** mpifort, and oshfort.  mpif77 and mpif90 still exist, but they 
  *** are symbolic links to mpifort.
  ********************************************************************
  *** Similarly, Open MPI's configure script only recognizes the FC
  *** and FCFLAGS environment variables (to specify the Fortran
  *** compiler and compiler flags, respectively).  The F77 and FFLAGS
  *** environment variables are IGNORED.
  ********************************************************************
  ********************************************************************

  You can use either ompi_info or oshmem_info to see with which Fortran 
  compiler Open MPI was configured and compiled. 

  There are up to three sets of Fortran MPI bindings that may be
  provided depending on your Fortran compiler):

  - mpif.h: This is the first MPI Fortran interface that was defined
    in MPI-1.  It is a file that is included in Fortran source code.
    Open MPI's mpif.h does not declare any MPI subroutines; they are
    all implicit.

  - mpi module: The mpi module file was added in MPI-2.  It provides
    strong compile-time parameter type checking for MPI subroutines.

  - mpi_f08 module: The mpi_f08 module was added in MPI-3.  It
    provides many advantages over the mpif.h file and mpi module.  For
    example, MPI handles have distinct types (vs. all being integers).
    See the MPI-3 document for more details.

    *** The mpi_f08 module is STRONGLY is recommended for all new MPI
        Fortran subroutines and applications.  Note that the mpi_f08
        module can be used in conjunction with the other two Fortran
        MPI bindings in the same application (only one binding can be
        used per subroutine/function, however).  Full interoperability
        between mpif.h/mpi module and mpi_f08 module MPI handle types
        is provided, allowing mpi_f08 to be used in new subroutines in
        legacy MPI applications.

  Per the OSHMEM specification, there is only one Fortran OSHMEM binding 
  provided:

  - shmem.fh: All Fortran OpenSHMEM programs **should** include 'shmem.fh',
    and Fortran OSHMEM programs that use constants defined by OpenSHMEM
    **MUST** include 'shmem.fh'. 


  The following notes apply to the above-listed Fortran bindings:

  - The mpi_f08 module is new and has been tested with the Intel
    Fortran compiler.  Other modern Fortran compilers may also work
    (but are, as yet, currently untested).  It is expected that this
    support will mature over time.

    As of v4.9, the GNU Fortran compiler (gfortran) is *not* supported
    with the mpi_f08 module (gfortran lacks some necessary modern
    Fortran features, sorry).

  - All Fortran compilers support the mpif.h/shmem.fh-based bindings.

  - If Open MPI is built with a non-gfortran compiler or with gfortran
    >=v4.9, all MPI subroutines will be prototyped in the mpi module,
    meaning that all calls to MPI subroutines will have their parameter
    types checked at compile time.

  - If Open MPI is built with gfortran <v4.9, it will compile a
    limited "mpi" module -- not all MPI subroutines will be prototyped
    due to both poor design of the mpi module in the MPI-2
    specification and a lack of features in older versions of
    gfortran.

    Specifically, all MPI subroutines with no "choice" buffers are
    prototyped and will receive strong parameter type checking at
    run-time (e.g., MPI_INIT, MPI_COMM_RANK, etc.).

    MPI subroutines with one choice buffer (e.g., MPI_SEND) are
    prototyped for all intrinsic Fortran types for scalars and ranks 1
    through 4 (the --with-gfortran-max-array-dim configure switch can
    be used to increase the max array rank supported to up to 7).

    MPI subroutines with two choice buffers (e.g., MPI_GATHER) are
    *not* prototyped.  These subroutines can still be called in MPI
    applications; they just will not receive strong parameter type
    checking.


General Run-Time Support Notes
------------------------------

- The Open MPI installation must be in your PATH on all nodes (and
  potentially LD_LIBRARY_PATH (or DYLD_LIBRARY_PATH), if libmpi/libshmem 
  is a shared library), unless using the --prefix or
  --enable-mpirun-prefix-by-default functionality (see below).

- Open MPI's run-time behavior can be customized via MCA ("MPI
  Component Architecture") parameters (see below for more information
  on how to get/set MCA parameter values).  Some MCA parameters can be
  set in a way that renders Open MPI inoperable (see notes about MCA
  parameters later in this file).  In particular, some parameters have
  required options that must be included.

  - If specified, the "btl" parameter must include the "self"
    component, or Open MPI will not be able to deliver messages to the
    same rank as the sender.  For example: "mpirun --mca btl tcp,self
    ..."
  - If specified, the "btl_tcp_if_exclude" paramater must include the
    loopback device ("lo" on many Linux platforms), or Open MPI will
    not be able to route MPI messages using the TCP BTL.  For example:
    "mpirun --mca btl_tcp_if_exclude lo,eth1 ..."

- Running on nodes with different endian and/or different datatype
  sizes within a single parallel job is supported in this release.
  However, Open MPI does not resize data when datatypes differ in size
  (for example, sending a 4 byte MPI_DOUBLE and receiving an 8 byte
  MPI_DOUBLE will fail).


MPI Functionality and Features
------------------------------

- All MPI-2.2 and most MPI-3 functionality is supported.

- When using MPI deprecated functions, some compilers will emit
  warnings.  For example:

  shell$ cat deprecated_example.c
  #include <mpi.h>
  void foo(void) {
      MPI_Datatype type;
      MPI_Type_struct(1, NULL, NULL, NULL, &type);
  }
  shell$ mpicc -c deprecated_example.c
  deprecated_example.c: In function 'foo':
  deprecated_example.c:4: warning: 'MPI_Type_struct' is deprecated (declared at /opt/openmpi/include/mpi.h:1522)
  shell$

- MPI_THREAD_MULTIPLE support is included, but is only lightly tested.
  It likely does not work for thread-intensive applications.  Note
  that *only* the MPI point-to-point communication functions for the
  BTL's listed here are considered thread safe.  Other support
  functions (e.g., MPI attributes) have not been certified as safe
  when simultaneously used by multiple threads.
  - tcp
  - sm
  - self

  Note that Open MPI's thread support is in a fairly early stage; the
  above devices may *work*, but the latency is likely to be fairly
  high.  Specifically, efforts so far have concentrated on
  *correctness*, not *performance* (yet).

- MPI_REAL16 and MPI_COMPLEX32 are only supported on platforms where a
  portable C datatype can be found that matches the Fortran type
  REAL*16, both in size and bit representation.

- The "libompitrace" library is bundled in Open MPI and is installed
  by default (it can be disabled via the --disable-libompitrace
  flag).  This library provides a simplistic tracing of select MPI
  function calls via the MPI profiling interface.  Linking it in to
  your appliation via (e.g., via -lompitrace) will automatically
  output to stderr when some MPI functions are invoked:

  shell$ mpicc hello_world.c -o hello_world -lompitrace
  shell$ mpirun -np 1 hello_world.c
  MPI_INIT: argc 1
  Hello, world, I am 0 of 1
  MPI_BARRIER[0]: comm MPI_COMM_WORLD
  MPI_FINALIZE[0]
  shell$

  Keep in mind that the output from the trace library is going to
  stderr, so it may output in a slightly different order than the
  stdout from your application.

  This library is being offered as a "proof of concept" / convenience
  from Open MPI.  If there is interest, it is trivially easy to extend
  it to printf for other MPI functions.  Patches and/or suggestions
  would be greatfully appreciated on the Open MPI developer's list.

- ROMIO is not supported on OpenBSD.  You will need to specify the
  --disable-io-romio flag to configure when building on OpenBSD.


OSHMEM Functionality and Features
------------------------------

- All OpenSHMEM-1.0 functionality is supported.


MPI Collectives
-----------

- The "hierarch" coll component (i.e., an implementation of MPI
  collective operations) attempts to discover network layers of
  latency in order to segregate individual "local" and "global"
  operations as part of the overall collective operation.  In this
  way, network traffic can be reduced -- or possibly even minimized
  (similar to MagPIe).  The current "hierarch" component only
  separates MPI processes into on- and off-node groups.

  Hierarch has had sufficient correctness testing, but has not
  received much performance tuning.  As such, hierarch is not
  activated by default -- it must be enabled manually by setting its
  priority level to 100:

    mpirun --mca coll_hierarch_priority 100 ...

  We would appreciate feedback from the user community about how well
  hierarch works for your applications.

- The "fca" coll component: the Mellanox Fabric Collective Accelerator
  (FCA) is a solution for offloading collective operations from the
  MPI process onto Mellanox QDR InfiniBand switch CPUs and HCAs.


- The "ML" coll component is an implementation of MPI collective 
  operations that takes advantage of communication hierarchies 
  in modern systems. A ML collective operation is implemented by 
  combining multiple independently progressing collective primitives 
  implemented over different communication hierarchies, hence a ML 
  collective operation is also reffered to as a hierarchical collective 
  operation. The number of collective primitives that are included in a 
  ML collective operation is a function of subgroups(hierarchies). 
  Typically, MPI processes in a single communication hierarchy such as 
  CPU socket, node, or subnet are grouped together into a single subgroup
  (hierarchy). The number of subgroups are configurable at runtime, 
  and each different collective operation could be configured to have 
  a different of number of subgroups.

  The component frameworks and components used by\required for a 
  "ML" collective operation.

  Frameworks: 
  * "sbgp" - Provides functionality for grouping processes into subgroups
  * "bcol" - Provides collective primitives optimized for a particular 
           communication hierarchy

  Components:
  * sbgp components     - Provides grouping functionality over a CPU socket
                          ("basesocket"), shared memory ("basesmuma"), 
                          Mellanox's ConnectX HCA ("ibnet"), and other 
                          interconnects supported by PML ("p2p")

  * BCOL components     - Provides optimized collective primitives for 
                          shared memory ("basesmuma"), Mellanox's ConnectX 
                          HCA ("iboffload"), and other interconnects supported 
                          by PML ("ptpcoll")

  * "ofacm"             - Provides connection manager functionality for
                          InfiniBand communications
  * "verbs"             - Provides commonly used verbs utilities
  * "netpatterns"       - Provides an implementation of algorithm patterns 
  * "commpatterns"      - Provides collectives for bootstrap
   

OSHMEM Collectives
-----------

- The "fca" scoll component: the Mellanox Fabric Collective Accelerator
  (FCA) is a solution for offloading collective operations from the
  MPI process onto Mellanox QDR InfiniBand switch CPUs and HCAs.

- The "basic" scoll component: Reference implementation of all OSHMEM 
  collective operations.


Network Support
---------------

- There are two MPI network models available: "ob1", and "cm". "ob1"
  uses BTL ("Byte Transfer Layer") components for each supported network.
  "cm" uses MTL ("Matching Tranport Layer") components for each supported
  network.

  - "ob1" supports a variety of networks that can be used in
    combination with each other (per OS constraints; e.g., there are
    reports that the GM and OpenFabrics kernel drivers do not operate
    well together):

    - OpenFabrics: InfiniBand, iWARP, and RoCE
    - Loopback (send-to-self)
    - Myrinet MX and Open-MX
    - Portals4
    - Shared memory
    - TCP
    - Intel Phi SCIF
    - SMCUDA
    - SCTP
    - Cisco usNIC
    - uGNI (Cray Gemini, Ares)
    - vader (XPMEM)

  - "cm" supports a smaller number of networks (and they cannot be
    used together), but may provide better overall MPI performance:

    - Myrinet MX and Open-MX
    - InfiniPath PSM
    - Mellanox MXM
    - Portals4

    Open MPI will, by default, choose to use "cm" when the InfiniPath
    PSM or the Mellanox MXM MTL can be used.  Otherwise, "ob1" will be
    used and the corresponding BTLs will be selected. Users can force
    the use of ob1 or cm if desired by setting the "pml" MCA parameter
    at run-time:

      shell$ mpirun --mca pml ob1 ...
      or
      shell$ mpirun --mca pml cm ...

- Similarly, there are two OSHMEM network models available: "yoda", and "ikrit". "yoda"
  also uses the BTL components for many supported network. "ikrit" interfaces directly with 
  Mellanox MXM.

  - "yoda" supports a variety of networks that can be used:
    
    - OpenFabrics: InfiniBand, iWARP, and RoCE
    - Loopback (send-to-self)
    - Shared memory
    - TCP

  - "ikrit" only supports Mellanox MXM. 
 
- MXM is the Mellanox Messaging Accelerator library utilizing a full range of IB
  transports to provide the following messaging services to the upper
  level MPI/OSHMEM libraries:

  - Usage of all available IB transports 
  - Native RDMA support
  - Progress thread
  - Shared memory communication
  - Hardware-assisted reliability

- The usnic BTL is support for Cisco's usNIC device ("userspace NIC")
  on Cisco UCS servers with the Virtualized Interface Card (VIC).
  Although the usNIC is accessed via the OpenFabrics / Verbs API
  stack, this BTL is specific to the Cisco usNIC device.

- uGNI is a Cray library for communicating over the Gemini and Ares
  interconnects.

- The OpenFabrics Enterprise Distribution (OFED) software package v1.0
  will not work properly with Open MPI v1.2 (and later) due to how its
  Mellanox InfiniBand plugin driver is created.  The problem is fixed
  OFED v1.1 (and later).

- Better memory management support is available for OFED-based
  transports using the "ummunotify" Linux kernel module.  OFED memory
  managers are necessary for better bandwidth when re-using the same
  buffers for large messages (e.g., benchmarks and some applications).
  
  Unfortunately, the ummunotify module was not accepted by the Linux
  kernel community (and is still not distributed by OFED).  But it
  still remains the best memory management solution for MPI
  applications that used the OFED network transports.  If Open MPI is
  able to find the <linux/ummunotify.h> header file, it will build
  support for ummunotify and include it by default.  If MPI processes
  then find the ummunotify kernel module loaded and active, then their
  memory managers (which have been shown to be problematic in some
  cases) will be disabled and ummunotify will be used.  Otherwise, the
  same memory managers from prior versions of Open MPI will be used.
  The ummunotify Linux kernel module can be downloaded from:

    http://lwn.net/Articles/343351/

- The use of fork() with OpenFabrics-based networks (i.e., the openib
  BTL) is only partially supported, and only on Linux kernels >=
  v2.6.15 with libibverbs v1.1 or later (first released as part of
  OFED v1.2), per restrictions imposed by the OFED network stack.

- Myrinet MX (and Open-MX) support is shared between the 2 internal
  devices, the MTL and the BTL.  The design of the BTL interface in
  Open MPI assumes that only naive one-sided communication
  capabilities are provided by the low level communication layers.
  However, modern communication layers such as Myrinet MX, InfiniPath
  PSM, or Portals4, natively implement highly-optimized two-sided
  communication semantics.  To leverage these capabilities, Open MPI
  provides the "cm" PML and corresponding MTL components to transfer
  messages rather than bytes.  The MTL interface implements a shorter
  code path and lets the low-level network library decide which
  protocol to use (depending on issues such as message length,
  internal resources and other parameters specific to the underlying
  interconnect).  However, Open MPI cannot currently use multiple MTL
  modules at once.  In the case of the MX MTL, process loopback and
  on-node shared memory communications are provided by the MX library.
  Moreover, the current MX MTL does not support message pipelining
  resulting in lower performances in case of non-contiguous
  data-types.

  The "ob1" PML and BTL components use Open MPI's internal
  on-node shared memory and process loopback devices for high
  performance.  The BTL interface allows multiple devices to be used
  simultaneously.  For the MX BTL it is recommended that the first
  segment (which is as a threshold between the eager and the
  rendezvous protocol) should always be at most 4KB, but there is no
  further restriction on the size of subsequent fragments.

  The MX MTL is recommended in the common case for best performance on
  10G hardware when most of the data transfers cover contiguous memory
  layouts.  The MX BTL is recommended in all other cases, such as when
  using multiple interconnects at the same time (including TCP), or
  transferring non contiguous data-types.

- Linux "knem" support is used when the "sm" (shared memory) BTL is
  compiled with knem support (see the --with-knem configure option)
  and the knem Linux module is loaded in the running kernel.  If the
  knem Linux kernel module is not loaded, the knem support is (by
  default) silently deactivated during Open MPI jobs.

  See http://runtime.bordeaux.inria.fr/knem/ for details on Knem.

- XPMEM is used by the vader shared-memory BTL when the XPMEM
  libraries are installed. XPMEM allows Open MPI to map pages from
  other processes into the current process' memory space. This
  allows single-copy semantics for shared memory without the need
  for a system call.

Open MPI Extensions
-------------------

- An MPI "extensions" framework has been added (but is not enabled by
  default).  See the "Open MPI API Extensions" section below for more
  information on compiling and using MPI extensions.

- The following extensions are included in this version of Open MPI:

  - affinity: Provides the OMPI_Affinity_str() routine on retrieving
    a string that contains what resources a process is bound to.  See
    its man page for more details.
  - cr: Provides routines to access to checkpoint restart routines.
    See ompi/mpiext/cr/mpiext_cr_c.h for a listing of availble
    functions.
  - example: A non-functional extension; its only purpose is to
    provide an example for how to create other extensions.

===========================================================================

Building Open MPI
-----------------

Building Open MPI implies building both the MPI and OpenSHMEM libraries, as
such, configure flags that are neither MPI or OSHMEM specific in their names
should be regarded as applicable to both libraries. Some pairs of MPI and 
OSHMEM specific switches may be mutually exclusive e.g. passing both 

    --disable-mpi-fortran --enable-oshmem-fortran 

will cause configure to abort since the OSHMEM Fortran bindings are dependent 
upon the MPI bindings being built. 

Open MPI uses a traditional configure script paired with "make" to
build.  Typical installs can be of the pattern:

---------------------------------------------------------------------------
shell$ ./configure [...options...]
shell$ make all install
---------------------------------------------------------------------------

There are many available configure options (see "./configure --help"
for a full list); a summary of the more commonly used ones follows:

INSTALLATION OPTIONS

--prefix=<directory>
  Install Open MPI into the base directory named <directory>.  Hence,
  Open MPI will place its executables in <directory>/bin, its header
  files in <directory>/include, its libraries in <directory>/lib, etc.

--disable-shared
  By default, libmpi and libshmem are built as a shared library, and 
  all components are built as dynamic shared objects (DSOs). This 
  switch disables this default; it is really only useful when used with
  --enable-static.  Specifically, this option does *not* imply
  --enable-static; enabling static libraries and disabling shared
  libraries are two independent options.

--enable-static
  Build libmpi and libshmem as static libraries, and statically link in all
  components.  Note that this option does *not* imply
  --disable-shared; enabling static libraries and disabling shared
  libraries are two independent options.

  Be sure to read the description of --without-memory-manager, below;
  it may have some effect on --enable-static.

--disable-wrapper-rpath

  By default, the wrapper compilers (e.g., mpicc) will enable "rpath"
  support in generated executables on systems that support it.  That
  is, they will include a file reference to the location of Open MPI's
  libraries in the application executable itself.  This means that
  the user does not have to set LD_LIBRARY_PATH to find Open MPI's
  libraries (e.g., if they are installed in a location that the
  run-time linker does not search by default).

  On systems that utilize the GNU ld linker, recent enough versions
  will actually utilize "runpath" functionality, not "rpath".  There
  is an important difference between the two:

  "rpath": the location of the Open MPI libraries is hard-coded into
      the MPI/OSHMEM application and cannot be overridden at run-time.
  "runpath": the location of the Open MPI libraries is hard-coded into
      the MPI/OSHMEM application, but can be overridden at run-time by
      setting the LD_LIBRARY_PATH environment variable.

  For example, consider that you install Open MPI vA.B.0 and
  compile/link your MPI/OSHMEM application against it.  Later, you install
  Open MPI vA.B.1 to a different installation prefix (e.g.,
  /opt/openmpi/A.B.1 vs. /opt/openmpi/A.B.0), and you leave the old
  installation intact.

  In the rpath case, your MPI application will always use the
  libraries from your A.B.0 installation.  In the runpath case, you
  can set the LD_LIBRARY_PATH environment variable to point to the
  A.B.1 installation, and then your MPI application will use those
  libraries.  

  Note that in both cases, however, if you remove the original A.B.0
  installation and set LD_LIBRARY_PATH to point to the A.B.1
  installation, your application will use the A.B.1 libraries.

  This rpath/runpath behavior can be disabled via
  --disable-wrapper-rpath.

--enable-dlopen
  Build all of Open MPI's components as standalone Dynamic Shared
  Objects (DSO's) that are loaded at run-time.  The opposite of this
  option, --disable-dlopen, causes two things: 

  1. All of Open MPI's components will be built as part of Open MPI's
     normal libraries (e.g., libmpi).  
  2. Open MPI will not attempt to open any DSO's at run-time.

  Note that this option does *not* imply that OMPI's libraries will be
  built as static objects (e.g., libmpi.a).  It only specifies the
  location of OMPI's components: standalone DSOs or folded into the
  Open MPI libraries.  You can control whether Open MPI's libraries
  are build as static or dynamic via --enable|disable-static and
  --enable|disable-shared.

--with-platform=FILE
  Load configure options for the build from FILE.  Options on the
  command line that are not in FILE are also used.  Options on the
  command line and in FILE are replaced by what is in FILE.

NETWORKING SUPPORT / OPTIONS

--with-fca=<directory>
  Specify the directory where the Mellanox FCA library and
  header files are located.  

  FCA is the support library for Mellanox QDR switches and HCAs.

--with-knem=<directory>
  Specify the directory where the knem libraries and header files are
  located.  This option is generally only necessary if the knem headers
  and libraries are not in default compiler/linker search paths.

  knem is a Linux kernel module that allows direct process-to-process
  memory copies (optionally using hardware offload), potentially
  increasing bandwidth for large messages sent between messages on the
  same server.  See http://runtime.bordeaux.inria.fr/knem/ for
  details.

--with-mx=<directory>
  Specify the directory where the MX libraries and header files are
  located.  This option is generally only necessary if the MX headers
  and libraries are not in default compiler/linker search paths.

  MX is the support library for Myrinet-based networks.  An open
  source software package named Open-MX provides the same
  functionality on Ethernet-based clusters (Open-MX can provide
  MPI performance improvements compared to TCP messaging).

--with-mx-libdir=<directory>
  Look in directory for the MX libraries.  By default, Open MPI will
  look in <mx directory>/lib and <mx directory>/lib64, which covers
  most cases.  This option is only needed for special configurations.

--with-mxm=<directory>
  Specify the directory where the Mellanox MXM library and header
  files are located.  This option is generally only necessary if the
  MXM headers and libraries are not in default compiler/linker search
  paths.

  MXM is the support library for Mellanox Network adapters.

--with-mxm-libdir=<directory>
  Look in directory for the MXM libraries.  By default, Open MPI will
  look in <mxm directory>/lib and <mxm directory>/lib64, which covers
  most cases.  This option is only needed for special configurations.

--with-verbs=<directory>
  Specify the directory where the verbs (also know as OpenFabrics, and
  previously known as OpenIB) libraries and header files are located.
  This option is generally only necessary if the verbs headers and
  libraries are not in default compiler/linker search paths.

  "OpenFabrics" refers to operating system bypass networks, such as
  InfiniBand, usNIC, iWARP, and RoCE (aka "IBoIP").

--with-verbs-libdir=<directory>
  Look in directory for the verbs libraries.  By default, Open
  MPI will look in <openib directory>/lib and <openib
  directory>/lib64, which covers most cases.  This option is only
  needed for special configurations.

--with-openib=<directory>
  DEPRECATED synonym for --with-verbs.

--with-openib-libdir=<directory>
  DEPRECATED synonym for --with-verbs-libdir.

--with-portals4=<directory>
  Specify the directory where the Portals4 libraries and header files
  are located.  This option is generally only necessary if the Portals4
  headers and libraries are not in default compiler/linker search
  paths.

  Portals4 is the support library for Cray interconnects, but is also
  available on other platforms (e.g., there is a Portals4 library
  implemented over regular TCP).

--with-portals4-libdir=<libdir>
  Location of libraries to link with for Portals4 support.

--with-portals4-max-md-size=SIZE
--with-portals4-max-va-size=SIZE
  Set configuration values for Portals 4

--with-psm=<directory>
  Specify the directory where the QLogic InfiniPath PSM library and
  header files are located.  This option is generally only necessary
  if the InfiniPath headers and libraries are not in default
  compiler/linker search paths.

  PSM is the support library for QLogic InfiniPath network adapters.

--with-psm-libdir=<directory>
  Look in directory for the PSM libraries.  By default, Open MPI will
  look in <psm directory>/lib and <psm directory>/lib64, which covers
  most cases.  This option is only needed for special configurations.

--with-sctp=<directory>
  Specify the directory where the SCTP libraries and header files are
  located.  This option is generally only necessary if the SCTP headers
  and libraries are not in default compiler/linker search paths.

  SCTP is a special network stack over Ethernet networks.

--with-sctp-libdir=<directory>
  Look in directory for the SCTP libraries.  By default, Open MPI will
  look in <sctp directory>/lib and <sctp directory>/lib64, which covers
  most cases.  This option is only needed for special configurations.

--with-scif=<dir>
  Look in directory for Intel SCIF support libraries

RUN-TIME SYSTEM SUPPORT

--enable-mpirun-prefix-by-default
  This option forces the "mpirun" command to always behave as if
  "--prefix $prefix" was present on the command line (where $prefix is
  the value given to the --prefix option to configure).  This prevents
  most rsh/ssh-based users from needing to modify their shell startup
  files to set the PATH and/or LD_LIBRARY_PATH for Open MPI on remote
  nodes.  Note, however, that such users may still desire to set PATH
  -- perhaps even in their shell startup files -- so that executables
  such as mpicc and mpirun can be found without needing to type long
  path names.  --enable-orterun-prefix-by-default is a synonym for
  this option.

--enable-sensors
  Enable internal sensors (default: disabled)

--enable-orte-static-ports
   Enable orte static ports for tcp oob. (default: enabled)

--with-alps
  Force the building of for the Cray Alps run-time environment.  If
  Alps support cannot be found, configure will abort.

--with-cray-pmi-ext
  Include Cray PMI2 extensions.

--with-loadleveler
  Force the building of LoadLeveler scheduler support.  If LoadLeveler
  support cannot be found, configure will abort.

--with-lsf=<directory>
  Specify the directory where the LSF libraries and header files are
  located.  This option is generally only necessary if the LSF headers
  and libraries are not in default compiler/linker search paths.

  LSF is a resource manager system, frequently used as a batch
  scheduler in HPC systems.

  NOTE: If you are using LSF version 7.0.5, you will need to add
        "LIBS=-ldl" to the configure command line.  For example:

            ./configure LIBS=-ldl --with-lsf ...

        This workaround should *only* be needed for LSF 7.0.5.

--with-lsf-libdir=<directory>
  Look in directory for the LSF libraries.  By default, Open MPI will
  look in <lsf directory>/lib and <lsf directory>/lib64, which covers
  most cases.  This option is only needed for special configurations.

--with-pmi
  Build PMI support (by default, it is not built).  If PMI support
  cannot be found, configure will abort. If the pmi2.h header is found 
  in addition to pmi.h, then support for PMI2 will be built. 

--with-slurm
  Force the building of SLURM scheduler support.  If SLURM support
  cannot be found, configure will abort.

--with-sge
  Specify to build support for the Oracle Grid Engine (OGE) resource
  manager and/or the open Grid Engine.  OGE support is disabled by
  default; this option must be specified to build OMPI's OGE support.

  The Oracle Grid Engine (OGE) and open Grid Engine packages are
  resource manager systems, frequently used as a batch scheduler in
  HPC systems.

--with-tm=<directory>
  Specify the directory where the TM libraries and header files are
  located.  This option is generally only necessary if the TM headers
  and libraries are not in default compiler/linker search paths.

  TM is the support library for the Torque and PBS Pro resource
  manager systems, both of which are frequently used as a batch
  scheduler in HPC systems.

MISCELLANEOUS SUPPORT LIBRARIES

--with-blcr=<directory>
  Specify the directory where the Berkeley Labs Checkpoint / Restart
  (BLCR) libraries and header files are located.  This option is
  generally only necessary if the BLCR headers and libraries are not
  in default compiler/linker search paths.

  This option is only meaningful if the --with-ft option is also used
  to active Open MPI's fault tolerance behavior.

--with-blcr-libdir=<directory>
  Look in directory for the BLCR libraries.  By default, Open MPI will
  look in <blcr directory>/lib and <blcr directory>/lib64, which
  covers most cases.  This option is only needed for special
  configurations.

--with-dmtcp=<directory>
  Specify the directory where the Distributed MultiThreaded
  Checkpointing (DMTCP) libraries and header files are located.  This
  option is generally only necessary if the DMTCP headers and
  libraries are not in default compiler/linker search paths.

  This option is only meaningful if the --with-ft option is also used
  to active Open MPI's fault tolerance behavior.

--with-dmtcp-libdir=<directory>
  Look in directory for the DMTCP libraries.  By default, Open MPI
  will look in <dmtcp directory>/lib and <dmtcp directory>/lib64,
  which covers most cases.  This option is only needed for special
  configurations.

--with-esmtp=<directory>
  Specify the directory where the libESMTP libraries and header files are
  located.  This option is generally only necessary of the libESMTP
  headers and libraries are not included in the default
  compiler/linker search paths.

  libESMTP is a support library for sending e-mail.

--with-ftb=<directory>
  Specify the directory where the Fault Tolerant Backplane (FTB)
  libraries and header files are located.  This option is generally
  only necessary if the BLCR headers and libraries are not in default
  compiler/linker search paths.

--with-ftb-libdir=<directory>
  Look in directory for the FTB libraries.  By default, Open MPI will
  look in <ftb directory>/lib and <ftb directory>/lib64, which covers
  most cases.  This option is only needed for special configurations.

--with-hwloc=<location>
  Build hwloc support.  If <location> is "internal", Open MPI's
  internal copy of hwloc is used.  If <location> is "external", Open
  MPI will search in default locations for an hwloc installation.
  Finally, if <location> is a directory, that directory will be
  searched for a valid hwloc installation, just like other
  --with-FOO=<directory> configure options.

  hwloc is a support library that provides processor and memory
  affinity information for NUMA platforms.

--with-hwloc-libdir=<directory>
  Look in directory for the hwloc libraries.  This option is only
  usable when building Open MPI against an external hwloc
  installation.  Just like other --with-FOO-libdir configure options,
  this option is only needed for special configurations.

--disable-hwloc-pci
  Disable building hwloc's PCI device-sensing capabilities.  On some
  platforms (e.g., SusE 10 SP1, x86-64), the libpci support library is
  broken.  Open MPI's configure script should usually detect when
  libpci is not usable due to such brokenness and turn off PCI
  support, but there may be cases when configure mistakenly enables
  PCI support in the presence of a broken libpci.  These cases may
  result in "make" failing with warnings about relocation symbols in
  libpci.  The --disable-hwloc-pci switch can be used to force Open
  MPI to not build hwloc's PCI device-sensing capabilities in these
  cases.

  Similarly, if Open MPI incorrectly decides that libpci is broken,
  you can force Open MPI to build hwloc's PCI device-sensing
  capabilities by using --enable-hwloc-pci.

  hwloc can discover PCI devices and locality, which can be useful for
  Open MPI in assigning message passing resources to MPI processes.

--with-libltdl[=VALUE]
  This option specifies where to find the GNU Libtool libltdl support
  library.  The following VALUEs are permitted:

    internal:    Use Open MPI's internal copy of libltdl.
    external:    Use an external libltdl installation (rely on default
                 compiler and linker paths to find it)
    <no value>:  Same as "internal".
    <directory>: Specify the location of a specific libltdl
                 installation to use

  By default (or if --with-libltdl is specified with no VALUE), Open
  MPI will build and use the copy of libltdl that it has in its source
  tree.  However, if the VALUE is "external", Open MPI will look for
  the relevant libltdl header file and library in default compiler /
  linker locations.  Or, VALUE can be a directory tree where the
  libltdl header file and library can be found.  This option allows
  operating systems to include Open MPI and use their default libltdl
  installation instead of Open MPI's bundled libltdl.

  Note that this option is ignored if --disable-dlopen is specified.

--disable-libompitrace
  Disable building the simple "libompitrace" library (see note above
  about libompitrace)

--with-valgrind=<directory>
  Directory where the valgrind software is installed.  If Open MPI
  finds Valgrind's header files, it will include support for
  Valgrind's memory-checking debugger.  

  Specifically, it will eliminate a lot of false positives from
  running Valgrind on MPI applications.

--disable-vt
  Disable building VampirTrace.

MPI FUNCTIONALITY

--with-mpi-param-check(=value)
  "value" can be one of: always, never, runtime.  If --with-mpi-param
  is not specified, "runtime" is the default.  If --with-mpi-param
  is specified with no value, "always" is used.  Using
  --without-mpi-param-check is equivalent to "never".

  - always: the parameters of MPI functions are always checked for
    errors 
  - never: the parameters of MPI functions are never checked for
    errors 
  - runtime: whether the parameters of MPI functions are checked
    depends on the value of the MCA parameter mpi_param_check
    (default: yes).

--with-threads=value
  Since thread support is only partially tested, it is disabled by
  default.  To enable threading, use "--with-threads=posix".  This is
  most useful when combined with --enable-mpi-thread-multiple.

--enable-mpi-thread-multiple
  Allows the MPI thread level MPI_THREAD_MULTIPLE.  See
  --with-threads; this is currently disabled by default. Enabling
  this feature will automatically --enable-opal-multi-threads.

--enable-opal-multi-threads
  Enables thread lock support in the OPAL and ORTE layers. Does
  not enable MPI_THREAD_MULTIPLE - see above option for that feature.
  This is currently disabled by default.

--enable-mpi-cxx
  Enable building the C++ MPI bindings.  The MPI C++ bindings were
  deprecated in MPI-2.2 and deleted in MPI-3.0.  Open MPI no longer
  builds its C++ bindings by default.  It is likely that the C++
  bindings will be removed from Open MPI at some point in the future.

  Note that disabling building the C++ bindings does *not* disable all
  C++ checks during configure.

--enable-mpi-java
  Enable building of an EXPERIMENTAL Java MPI interface (disabled by
  default).  You may also need to specify --with-jdk-dir,
  --with-jdk-bindir, and/or --with-jdk-headers.  See README.JAVA.txt
  for details.

  Note that this Java interface is INCOMPLETE (meaning: it does not
  support all MPI functionality) and LIKELY TO CHANGE.  The Open MPI
  developers would very much like to hear your feedback about this
  interface.  See README.JAVA.txt for more details.

--disable-mpi-fortran
  Disable building the Fortran MPI bindings. Mutually exclusive to 
  --enable-oshmem-fortran.

--disable-oshmem-fortran
  Disable building the Fortran OSHMEM bindings.

--enable-mpi-ext(=<list>)
  Enable Open MPI's non-portable API extensions.  If no <list> is
  specified, all of the extensions are enabled.

  See "Open MPI API Extensions", below, for more details.

--with-io-romio-flags=flags
  Pass flags to the ROMIO distribution configuration script.  This
  option is usually only necessary to pass
  parallel-filesystem-specific preprocessor/compiler/linker flags back
  to the ROMIO system.

--enable-sparse-groups
  Enable the usage of sparse groups. This would save memory
  significantly especially if you are creating large
  communicators. (Disabled by default)

--without-memory-manager
  Disable building Open MPI's memory manager.  Open MPI's memory
  manager is usually built on Linux based platforms, and is generally
  only used for optimizations with some OpenFabrics-based networks (it
  is not *necessary* for OpenFabrics networks, but some performance
  loss may be observed without it).

  However, it may be necessary to disable the memory manager in order
  to build Open MPI statically.

--with-ft=TYPE
  Specify the type of fault tolerance to enable.  Options: LAM
  (LAM/MPI-like), cr (Checkpoint/Restart).  Fault tolerance support is
  disabled unless this option is specified.

--enable-peruse 
  Enable the PERUSE MPI data analysis interface.

--enable-heterogeneous
  Enable support for running on heterogeneous clusters (e.g., machines
  with different endian representations).  Heterogeneous support is
  disabled by default because it imposes a minor performance penalty.

--with-wrapper-cflags=<cflags>
--with-wrapper-cxxflags=<cxxflags>
--with-wrapper-fflags=<fflags>
--with-wrapper-fcflags=<fcflags>
--with-wrapper-ldflags=<ldflags>
--with-wrapper-libs=<libs>
  Add the specified flags to the default flags that used are in Open
  MPI's "wrapper" compilers (e.g., mpicc -- see below for more
  information about Open MPI's wrapper compilers).  By default, Open
  MPI's wrapper compilers use the same compilers used to build Open
  MPI and specify an absolute minimum set of additional flags that are
  necessary to compile/link MPI/OSHMEM applications. These configure options
  give system administrators the ability to embed additional flags in
  OMPI's wrapper compilers (which is a local policy decision).  The
  meanings of the different flags are:

  <cflags>: Flags passed by the mpicc wrapper to the C compiler
  <cxxflags>: Flags passed by the mpic++ wrapper to the C++ compiler
  <fcflags>: Flags passed by the mpifort wrapper to the Fortran compiler
  <ldflags>: Flags passed by all the wrappers to the linker
  <libs>: Flags passed by all the wrappers to the linker

  There are other ways to configure Open MPI's wrapper compiler
  behavior; see the Open MPI FAQ for more information.

There are many other options available -- see "./configure --help".

Changing the compilers that Open MPI uses to build itself uses the
standard Autoconf mechanism of setting special environment variables
either before invoking configure or on the configure command line.
The following environment variables are recognized by configure:

CC          - C compiler to use
CFLAGS      - Compile flags to pass to the C compiler
CPPFLAGS    - Preprocessor flags to pass to the C compiler

CXX         - C++ compiler to use
CXXFLAGS    - Compile flags to pass to the C++ compiler
CXXCPPFLAGS - Preprocessor flags to pass to the C++ compiler

FC          - Fortran compiler to use
FCFLAGS     - Compile flags to pass to the Fortran compiler

LDFLAGS     - Linker flags to pass to all compilers
LIBS        - Libraries to pass to all compilers (it is rarely
              necessary for users to need to specify additional LIBS)

PKG_CONFIG  - Path to the pkg-config utility

For example:

  shell$ ./configure CC=mycc CXX=myc++ FC=myfortran ...

*** NOTE: We generally suggest using the above command line form for
    setting different compilers (vs. setting environment variables and
    then invoking "./configure").  The above form will save all
    variables and values in the config.log file, which makes
    post-mortem analysis easier when problems occur.

Note that if you intend to compile Open MPI with a "make" other than
the default one in your PATH, then you must either set the $MAKE
environment variable before invoking Open MPI's configure script, or
pass "MAKE=your_make_prog" to configure.  For example:

  shell$ ./configure MAKE=/path/to/my/make ...

This could be the case, for instance, if you have a shell alias for
"make", or you always type "gmake" out of habit.  Failure to tell
configure which non-default "make" you will use to compile Open MPI
can result in undefined behavior (meaning: don't do that).

Note that you may also want to ensure that the value of
LD_LIBRARY_PATH is set appropriately (or not at all) for your build
(or whatever environment variable is relevant for your operating
system).  For example, some users have been tripped up by setting to
use a non-default Fortran compiler via FC, but then failing to set
LD_LIBRARY_PATH to include the directory containing that non-default
Fortran compiler's support libraries.  This causes Open MPI's
configure script to fail when it tries to compile / link / run simple
Fortran programs.

It is required that the compilers specified be compile and link
compatible, meaning that object files created by one compiler must be
able to be linked with object files from the other compilers and
produce correctly functioning executables.

Open MPI supports all the "make" targets that are provided by GNU
Automake, such as:

all       - build the entire Open MPI package
install   - install Open MPI
uninstall - remove all traces of Open MPI from the $prefix
clean     - clean out the build tree

Once Open MPI has been built and installed, it is safe to run "make
clean" and/or remove the entire build tree.

VPATH and parallel builds are fully supported.

Generally speaking, the only thing that users need to do to use Open
MPI is ensure that <prefix>/bin is in their PATH and <prefix>/lib is
in their LD_LIBRARY_PATH.  Users may need to ensure to set the PATH
and LD_LIBRARY_PATH in their shell setup files (e.g., .bashrc, .cshrc)
so that non-interactive rsh/ssh-based logins will be able to find the
Open MPI executables.

===========================================================================

Open MPI Version Numbers and Binary Compatibility
-------------------------------------------------

Open MPI has two sets of version numbers that are likely of interest
to end users / system administrator:

    * Software version number
    * Shared library version numbers

Both are described below, followed by a discussion of application
binary interface (ABI) compatibility implications.

Software Version Number
-----------------------

Open MPI's version numbers are the union of several different values:
major, minor, release, and an optional quantifier.

  * Major: The major number is the first integer in the version string
    (e.g., v1.2.3). Changes in the major number typically indicate a
    significant change in the code base and/or end-user
    functionality. The major number is always included in the version
    number.

  * Minor: The minor number is the second integer in the version
    string (e.g., v1.2.3). Changes in the minor number typically
    indicate a incremental change in the code base and/or end-user
    functionality. The minor number is always included in the version
    number. Starting with Open MPI v1.3.0, the minor release number
    took on additional significance (see this wiki page for more
    details):

    o Even minor release numbers are part of "super-stable"
      release series (e.g., v1.4.0). Releases in super stable series
      are well-tested, time-tested, and mature. Such releases are
      recomended for production sites. Changes between subsequent
      releases in super stable series are expected to be fairly small.
    o Odd minor release numbers are part of "feature" release
      series (e.g., 1.3.7). Releases in feature releases are
      well-tested, but they are not necessarily time-tested or as
      mature as super stable releases. Changes between subsequent
      releases in feature series may be large.

  * Release: The release number is the third integer in the version
    string (e.g., v1.2.3). Changes in the release number typically
    indicate a bug fix in the code base and/or end-user
    functionality. If the release number is 0, it is omitted from the
    version number (e.g., v1.2 has a release number of 0).

  * Quantifier: Open MPI version numbers sometimes have an arbitrary
    string affixed to the end of the version number. Common strings
    include:

    o aX: Indicates an alpha release. X is an integer indicating
      the number of the alpha release (e.g., v1.2.3a5 indicates the
      5th alpha release of version 1.2.3).
    o bX: Indicates a beta release. X is an integer indicating
      the number of the beta release (e.g., v1.2.3b3 indicates the 3rd
      beta release of version 1.2.3).
    o rcX: Indicates a release candidate. X is an integer
      indicating the number of the release candidate (e.g., v1.2.3rc4
      indicates the 4th release candidate of version 1.2.3).
    o rV or hgV: Indicates the Subversion / Mercurial repository
      number string that the release was made from (V is usually an
      integer for Subversion releases and usually a string for
      Mercurial releases). Although all official Open MPI releases are
      tied to a single, specific Subversion or Mercurial repository
      number (which can be obtained from the ompi_info command), only
      some releases have the Subversion / Mercurial repository number
      in the version number. Development snapshot tarballs, for
      example, have the Subversion repository included in the version
      to reflect that they are a development snapshot of an upcoming
      release (e.g., v1.2.3r1234 indicates a development snapshot of
      version 1.2.3 corresponding to Subversion repository number
      1234). 

    Quantifiers may be mixed together -- for example v1.2.3rc7r2345
    indicates a development snapshot of an upcoming 7th release
    candidate for version 1.2.3 corresponding to Subversion repository
    number 2345.

Shared Library Version Number
-----------------------------

Open MPI started using the GNU Libtool shared library versioning
scheme with the release of v1.3.2.

NOTE: Only official releases of Open MPI adhere to this versioning
      scheme. "Beta" releases, release candidates, and nightly
      tarballs, developer snapshots, and Subversion/Mercurial snapshot
      tarballs likely will all have arbitrary/meaningless shared
      library version numbers.

For deep voodoo technical reasons, only the MPI API libraries were
versioned until Open MPI v1.5 was released (i.e., libmpi*so --
libopen-rte.so or libopen-pal.so were not versioned until v1.5).
Please see https://svn.open-mpi.org/trac/ompi/ticket/2092 for more
details.

NOTE: This policy change will cause an ABI incompatibility between MPI
      applications compiled/linked against the Open MPI v1.4 series;
      such applications will not be able to upgrade to the Open MPI
      v1.5 series without re-linking.  Sorry folks!

The GNU Libtool official documentation details how the versioning
scheme works.  The quick version is that the shared library versions
are a triple of integers: (current,revision,age), or "c:r:a".  This
triple is not related to the Open MPI software version number.  There
are six simple rules for updating the values (taken almost verbatim
from the Libtool docs):

 1. Start with version information of "0:0:0" for each shared library.

 2. Update the version information only immediately before a public
    release of your software. More frequent updates are unnecessary,
    and only guarantee that the current interface number gets larger
    faster.

 3. If the library source code has changed at all since the last
    update, then increment revision ("c:r:a" becomes "c:r+1:a").

 4. If any interfaces have been added, removed, or changed since the
    last update, increment current, and set revision to 0.

 5. If any interfaces have been added since the last public release,
    then increment age.

 6. If any interfaces have been removed since the last public release,
    then set age to 0.

Here's how we apply those rules specifically to Open MPI:

 1. The above rules do not apply to MCA components (a.k.a. "plugins");
    MCA component .so versions stay unspecified.

 2. The above rules apply exactly as written to the following
    libraries starting with Open MPI version v1.5 (prior to v1.5,
    libopen-pal and libopen-rte were still at 0:0:0 for reasons
    discussed in bug ticket #2092
    https://svn.open-mpi.org/trac/ompi/ticket/2092):

    * libopen-rte
    * libopen-pal
    * libmca_common_*

 3. The following libraries use a slightly modified version of the
    above rules: rules 4, 5, and 6 only apply to the official MPI
    interfaces (functions, global variables).  The rationale for this
    decision is that the vast majority of our users only care about
    the official/public MPI interfaces; we therefore want the .so
    version number to reflect only changes to the official MPI API.
    Put simply: non-MPI API / internal changes to the
    MPI-application-facing libraries are irrelevant to pure MPI
    applications.

    * libmpi
    * libmpi_mpifh
    * libmpi_usempi_tkr
    * libmpi_usempi_ignore_tkr
    * libmpi_usempif08
    * libmpi_cxx

 4. Note, however, that libmpi.so can have its "revision" number
    incremented if libopen-rte or libopen-pal change (because these
    two libraries are wholly included in libmpi.so).  Specifically:
    the revision will change, but since we have defined that the only
    relevant API interface in libmpi.so is the official MPI API,
    updates to libopen-rte and libopen-pal do not change the "current"
    or "age" numbers of libmpi.so.

Application Binary Interface (ABI) Compatibility
------------------------------------------------

Open MPI provided forward application binary interface (ABI)
compatibility for MPI applications starting with v1.3.2.  Prior to
that version, no ABI guarantees were provided.  

NOTE: Prior to v1.3.2, subtle and strange failures are almost
      guaranteed to occur if applications were compiled and linked
      against shared libraries from one version of Open MPI and then
      run with another.  The Open MPI team strongly discourages making
      any ABI assumptions before v1.3.2.

Starting with v1.3.2, Open MPI provides forward ABI compatibility in
all versions of a given feature release series and its corresponding
super stable series.  For example, on a single platform, an MPI
application linked against Open MPI v1.3.2 shared libraries can be
updated to point to the shared libraries in any successive v1.3.x or
v1.4 release and still work properly (e.g., via the LD_LIBRARY_PATH
environment variable or other operating system mechanism).

For the v1.7 series, this means that all releases of v1.7.x and v1.8.x
will be ABI compatible, per the above definition.

Note that in v1.5.4, a fix was applied to the "large" size of the "use
mpi" F90 MPI bindings module: two of MPI_SCATTERV's parameters had the
wrong type and were corrected.  Note that this fix *only* applies if
Open MPI was configured with a Fortran 90 compiler and the
--with-mpi-f90-size=large configure option.

However, in order to preserve the ABI with respect to prior v1.5.x
releases, the old/incorrect MPI_SCATTERV interface was preserved in
1.5.5 and all 1.6.x releases.  A new/corrected interface was added
(note that Fortran 90 has function overloading, similar to C++; hence,
both the old and new interface can be accessed via "call
MPI_Scatterv(...)").

The incorrect interface was removed in Open MPI v1.7.

To be clear: applications that use the old/incorrect MPI_SCATTERV
binding will no longer be able to compile properly (*).  Developers
must fix their applications or use an older version of Open MPI.

(*) Note that using this incorrect MPI_SCATTERV interface will not be
    recongized in v1.7 if you are using gfortran (as of gfortran
    v4.8).

    This is because gfortran <=v4.8 does not (yet) have the support
    Open MPI needs for its new, full-featured "mpi" and "mpi_f08"
    modules.  Hence, Open MPI falls back to the same "mpi" module from
    the v1.6 series, but the "large" size of that module -- which
    contains the MPI_SCATTERV interface -- been disabled because it is
    broken.  Further, this "large" sized (old) "mpi" module has been
    deemed unworthy of fixing because it has been wholly replaced by a
    new, full-featured "mpi" module.  We anticipate supporting
    gfortran in the new, full-featured module in the future.

Open MPI reserves the right to break ABI compatibility at new feature
release series.  For example, the same MPI application from above
(linked against Open MPI v1.3.2 shared libraries) will *not* work with
Open MPI v1.5 shared libraries.

===========================================================================

Checking Your Open MPI Installation
-----------------------------------

The "ompi_info" command can be used to check the status of your Open
MPI installation (located in <prefix>/bin/ompi_info).  Running it with
no arguments provides a summary of information about your Open MPI
installation.   

Note that the ompi_info command is extremely helpful in determining
which components are installed as well as listing all the run-time
settable parameters that are available in each component (as well as
their default values).

The following options may be helpful:

--all       Show a *lot* of information about your Open MPI
            installation. 
--parsable  Display all the information in an easily
            grep/cut/awk/sed-able format.
--param <framework> <component>
            A <framework> of "all" and a <component> of "all" will
            show all parameters to all components.  Otherwise, the
            parameters of all the components in a specific framework,
            or just the parameters of a specific component can be
            displayed by using an appropriate <framework> and/or
            <component> name.
--level <level>
            Show MCA parameters up to level <level> (<level> defaults
            to 1 if not specified; 9 is the maximum value).  Use
            "ompi_info --param <framework> <component> --level 9" to
            see *all* MCA parameters for a given component.  See "The
            Modular Component Architecture (MCA)" section, below, for
            a fuller explanation.

Changing the values of these parameters is explained in the "The
Modular Component Architecture (MCA)" section, below.

When verifying a new Open MPI installation, we recommend running six 
tests:

1. Use "mpirun" to launch a non-MPI program (e.g., hostname or uptime)
   across multiple nodes.

2. Use "mpirun" to launch a trivial MPI program that does no MPI
   communication (e.g., the hello_c program in the examples/ directory
   in the Open MPI distribution).

3. Use "mpirun" to launch a trivial MPI program that sends and
   receives a few MPI messages (e.g., the ring_c program in the
   examples/ directory in the Open MPI distribution).

4. Use "oshrun" to launch a non-OSHMEM program across multiple nodes.
   
5. Use "oshrun" to launch a trivial MPI program that does no OSHMEM
   communication (e.g., hello_shmem.c program in the examples/ directory
   in the Open MPI distribution.)

6. Use "oshrun" to launch a trivial OSHMEM program that puts and gets
   a few messages. (e.g., the ring_shmem.c in the examples/ directory
   in the Open MPI distribution.)

If you can run all six of these tests successfully, that is a good
indication that Open MPI built and installed properly.

===========================================================================

Open MPI API Extensions
-----------------------

Open MPI contains a framework for extending the MPI API that is
available to applications.  Each extension is usually a standalone set of
functionality that is distinct from other extensions (similar to how
Open MPI's plugins are usually unrelated to each other).  These
extensions provide new functions and/or constants that are available
to MPI applications.

WARNING: These extensions are neither standard nor portable to other
MPI implementations!

Compiling the extensions
------------------------

Open MPI extensions are not enabled by default; they must be enabled
by Open MPI's configure script.  The --enable-mpi-ext command line
switch accepts a comma-delimited list of extensions to enable, or, if
it is specified without a list, all extensions are enabled.

Since extensions are meant to be used by advanced users only, this
file does not document which extensions are available or what they
do.  Look in the ompi/mpiext/ directory to see the extensions; each
subdirectory of that directory contains an extension.  Each has a
README file that describes what it does.

Using the extensions
--------------------

To reinforce the fact that these extensions are non-standard, you must
include a separate header file after <mpi.h> to obtain the function
prototypes, constant declarations, etc.  For example:

-----
#include <mpi.h>
#if defined(OPEN_MPI) && OPEN_MPI
#include <mpi-ext.h>
#endif

int main() {
    MPI_Init(NULL, NULL);

#if defined(OPEN_MPI) && OPEN_MPI
    {
        char ompi_bound[OMPI_AFFINITY_STRING_MAX];
        char current_binding[OMPI_AFFINITY_STRING_MAX];
        char exists[OMPI_AFFINITY_STRING_MAX];
        OMPI_Affinity_str(OMPI_AFFINITY_LAYOUT_FMT, ompi_bound,
                          current_bindings, exists);
    }
#endif
    MPI_Finalize();
    return 0;
}
-----

Notice that the Open MPI-specific code is surrounded by the #if
statement to ensure that it is only ever compiled by Open MPI.  

The Open MPI wrapper compilers (mpicc and friends) should
automatically insert all relevant compiler and linker flags necessary
to use the extensions.  No special flags or steps should be necessary
compared to "normal" MPI applications.

===========================================================================

Compiling Open MPI Applications
-------------------------------

Open MPI provides "wrapper" compilers that should be used for
compiling MPI and OSHMEM applications:

C:          mpicc, oshcc
C++:        mpiCC, oshCC (or mpic++ if your filesystem is case-insensitive)
Fortran:    mpifort, oshfort

For example:

  shell$ mpicc hello_world_mpi.c -o hello_world_mpi -g
  shell$

For OSHMEM applications:

  shell$ oshcc hello_shmem.c -o hello_shmem -g
  shell$ 

All the wrapper compilers do is add a variety of compiler and linker
flags to the command line and then invoke a back-end compiler.  To be
specific: the wrapper compilers do not parse source code at all; they
are solely command-line manipulators, and have nothing to do with the
actual compilation or linking of programs.  The end result is an MPI
executable that is properly linked to all the relevant libraries.

Customizing the behavior of the wrapper compilers is possible (e.g.,
changing the compiler [not recommended] or specifying additional
compiler/linker flags); see the Open MPI FAQ for more information.

Alternatively, starting in the Open MPI v1.5 series, Open MPI also
installs pkg-config(1) configuration files under $libdir/pkgconfig.
If pkg-config is configured to find these files, then compiling /
linking Open MPI programs can be performed like this:

  shell$ gcc hello_world_mpi.c -o hello_world_mpi -g \
              `pkg-config ompi-c --cflags --libs`
  shell$

Open MPI supplies multiple pkg-config(1) configuration files; one for
each different wrapper compiler (language):

------------------------------------------------------------------------
ompi       Synonym for "ompi-c"; Open MPI applications using the C
           MPI bindings
ompi-c     Open MPI applications using the C MPI bindings
ompi-cxx   Open MPI applications using the C or C++ MPI bindings
ompi-fort  Open MPI applications using the Fortran MPI bindings
------------------------------------------------------------------------

The following pkg-config(1) configuration files *may* be installed,
depending on which command line options were specified to Open MPI's
configure script.  They are not necessary for MPI applications, but
may be used by applications that use Open MPI's lower layer support
libraries.

orte:       Open MPI Run-Time Environment applicaions
opal:       Open Portable Access Layer applications

===========================================================================

Running Open MPI Applications
-----------------------------

Open MPI supports both mpirun and mpiexec (they are exactly
equivalent) to launch MPI applications.  For example:

  shell$ mpirun -np 2 hello_world_mpi
  or
  shell$ mpiexec -np 1 hello_world_mpi : -np 1 hello_world_mpi

are equivalent.  Some of mpiexec's switches (such as -host and -arch)
are not yet functional, although they will not error if you try to use
them.  

The rsh launcher (which defaults to using ssh) accepts a -hostfile
parameter (the option "-machinefile" is equivalent); you can specify a
-hostfile parameter indicating an standard mpirun-style hostfile (one
hostname per line):

  shell$ mpirun -hostfile my_hostfile -np 2 hello_world_mpi

If you intend to run more than one process on a node, the hostfile can
use the "slots" attribute.  If "slots" is not specified, a count of 1
is assumed.  For example, using the following hostfile:

---------------------------------------------------------------------------
node1.example.com
node2.example.com
node3.example.com slots=2
node4.example.com slots=4
---------------------------------------------------------------------------

  shell$ mpirun -hostfile my_hostfile -np 8 hello_world_mpi

will launch MPI_COMM_WORLD rank 0 on node1, rank 1 on node2, ranks 2
and 3 on node3, and ranks 4 through 7 on node4.

Other starters, such as the resource manager / batch scheduling
environments, do not require hostfiles (and will ignore the hostfile
if it is supplied).  They will also launch as many processes as slots
have been allocated by the scheduler if no "-np" argument has been
provided.  For example, running a SLURM job with 8 processors:

  shell$ salloc -n 8 mpirun a.out

The above command will reserve 8 processors and run 1 copy of mpirun,
which will, in turn, launch 8 copies of a.out in a single
MPI_COMM_WORLD on the processors that were allocated by SLURM.

Note that the values of component parameters can be changed on the
mpirun / mpiexec command line.  This is explained in the section
below, "The Modular Component Architecture (MCA)".

Open MPI supports oshrun to launch OSHMEM applications. For example:

   shell$ oshrun -np 2 hello_world_oshmem

OSHMEM applications may also be launched directly by resource managers such as
SLURM. For example, when OMPI is configured --with-pmi and --with-slurm one may
launch OSHMEM applications via srun

   shell$ srun -N 2 hello_world_oshmem 


===========================================================================

The Modular Component Architecture (MCA)

The MCA is the backbone of Open MPI -- most services and functionality
are implemented through MCA components.  Here is a list of all the
component frameworks in Open MPI:

---------------------------------------------------------------------------

MPI component frameworks:
-------------------------

allocator - Memory allocator
bcol      - Base collective operations
bml       - BTL management layer
btl       - MPI point-to-point Byte Transfer Layer, used for MPI
            point-to-point messages on some types of networks
coll      - MPI collective algorithms
crcp      - Checkpoint/restart coordination protocol
dpm       - MPI-2 dynamic process management
fbtl      - file byte transfer layer: abstraction for individual 
            read/write operations for OMPIO
fcoll     - collective read and write operations for MPI I/O
fs        - file system functions for MPI I/O
io        - MPI-2 I/O
mpool     - Memory pooling
mtl       - Matching transport layer, used for MPI point-to-point
            messages on some types of networks
op        - Back end computations for intrinsic MPI_Op operators
osc       - MPI-2 one-sided communications
pml       - MPI point-to-point management layer
pubsub    - MPI-2 publish/subscribe management
rcache    - Memory registration cache
rte       - Run-time environment operations
sbgp      - Collective operation sub-group
sharedfp  - shared file pointer operations for MPI I/O
topo      - MPI topology routines
vprotocol - Protocols for the "v" PML

OSHMEM component frameworks:
-------------------------

atomic    - OSHMEM atomic operations
memheap   - OSHMEM memory allocators that support the 
            PGAS memory model
scoll     - OSHMEM collective operations
spml      - OSHMEM "pml-like" layer: supports one-sided,
            point-to-point operations 
 

Back-end run-time environment (RTE) component frameworks:
---------------------------------------------------------

dfs       - Distributed filesystem
errmgr    - RTE error manager
ess       - RTE environment-specfic services
filem     - Remote file management
grpcomm   - RTE group communications
iof       - I/O forwarding
odls      - OpenRTE daemon local launch subsystem
oob       - Out of band messaging
plm       - Process lifecycle management
ras       - Resource allocation system
rmaps     - Resource mapping system
rml       - RTE message layer
routed    - Routing table for the RML
sensor    - Software and hardware health monitoring
snapc     - Snapshot coordination
sstore    - Distributed scalable storage
state     - RTE state machine

Miscellaneous frameworks:
-------------------------

backtrace   - Debugging call stack backtrace support
compress    - Compression algorithms
crs         - Checkpoint and restart service
db          - Internal database support
event       - Event library (libevent) versioning support
hwloc       - Hardware locality (hwloc) versioning support
if          - OS IP interface support
installdirs - Installation directory relocation services
memchecker  - Run-time memory checking
memcpy      - Memopy copy support
memory      - Memory management hooks
pstat       - Process status
shmem       - Shared memory support (NOT related to OSHMEM)
timer       - High-resolution timers

---------------------------------------------------------------------------

Each framework typically has one or more components that are used at
run-time.  For example, the btl framework is used by the MPI layer to
send bytes across different types underlying networks.  The tcp btl,
for example, sends messages across TCP-based networks; the openib btl
sends messages across OpenFabrics-based networks; the MX btl sends
messages across Myrinet MX / Open-MX networks.

Each component typically has some tunable parameters that can be
changed at run-time.  Use the ompi_info command to check a component
to see what its tunable parameters are.  For example:

  shell$ ompi_info --param btl tcp

shows a some of parameters (and default values) for the tcp btl
component.  

Note that ompi_info only shows a small number a component's MCA
parameters by default.  Each MCA parameter has a "level" value from 1
to 9, corresponding to the MPI-3 MPI_T tool interface levels.  In Open
MPI, we have interpreted these nine levels as three groups of three:

 1. End user / basic
 2. End user / detailed
 3. End user / all

 4. Application tuner / basic
 5. Application tuner / detailed
 6. Application tuner / all

 7. MPI/OSHMEM developer / basic
 8. MPI/OSHMEM developer / detailed
 9. MPI/OSHMEM developer / all

Here's how the three sub-groups are defined:

 1. End user: Generally, these are parameters that are required for
    correctness, meaning that someone may need to set these just to
    get their MPI/OSHMEM application to run correctly. 
 2. Application tuner: Generally, these are parameters that can be
    used to tweak MPI application performance.
 3. MPI/OSHMEM developer: Parameters that either don't fit in the other two,
    or are specifically intended for debugging / development of Open
    MPI itself.

Each sub-group is broken down into three classifications:

 1. Basic: For parameters that everyone in this category will want to
    see.
 2. Detailed: Parameters that are useful, but you probably won't need
    to change them often.
 3. All: All other parameters -- probably including some fairly
    esoteric parameters.

To see *all* available parameters for a given component, specify that
ompi_info should use level 9:

  shell$ ompi_info --param btl tcp --level 9

These values can be overridden at run-time in several ways.  At
run-time, the following locations are examined (in order) for new
values of parameters:

1. <prefix>/etc/openmpi-mca-params.conf

   This file is intended to set any system-wide default MCA parameter
   values -- it will apply, by default, to all users who use this Open
   MPI installation.  The default file that is installed contains many
   comments explaining its format.

2. $HOME/.openmpi/mca-params.conf

   If this file exists, it should be in the same format as
   <prefix>/etc/openmpi-mca-params.conf.  It is intended to provide
   per-user default parameter values.

3. environment variables of the form OMPI_MCA_<name> set equal to a
   <value>

   Where <name> is the name of the parameter.  For example, set the
   variable named OMPI_MCA_btl_tcp_frag_size to the value 65536
   (Bourne-style shells):

   shell$ OMPI_MCA_btl_tcp_frag_size=65536
   shell$ export OMPI_MCA_btl_tcp_frag_size

4. the mpirun/oshrun command line: --mca <name> <value>
 
   Where <name> is the name of the parameter.  For example:

   shell$ mpirun --mca btl_tcp_frag_size 65536 -np 2 hello_world_mpi

These locations are checked in order.  For example, a parameter value
passed on the mpirun command line will override an environment
variable; an environment variable will override the system-wide
defaults.

Each component typically activates itself when relavant.  For example,
the MX component will detect that MX devices are present and will
automatically be used for MPI communications.  The SLURM component
will automatically detect when running inside a SLURM job and activate
itself.  And so on.

Components can be manually activated or deactivated if necessary, of
course.  The most common components that are manually activated,
deactivated, or tuned are the "BTL" components -- components that are
used for MPI point-to-point communications on many types common
networks. 

For example, to *only* activate the TCP and "self" (process loopback)
components are used for MPI communications, specify them in a
comma-delimited list to the "btl" MCA parameter:

   shell$ mpirun --mca btl tcp,self hello_world_mpi

To add shared memory support, add "sm" into the command-delimited list
(list order does not matter):
    
   shell$ mpirun --mca btl tcp,sm,self hello_world_mpi

To specifically deactivate a specific component, the comma-delimited
list can be prepended with a "^" to negate it:

   shell$ mpirun --mca btl ^tcp hello_mpi_world

The above command will use any other BTL component other than the tcp
component.

===========================================================================

Common Questions
----------------

Many common questions about building and using Open MPI are answered
on the FAQ:

    http://www.open-mpi.org/faq/

===========================================================================

Got more questions?
-------------------

Found a bug?  Got a question?  Want to make a suggestion?  Want to
contribute to Open MPI?  Please let us know!

When submitting questions and problems, be sure to include as much
extra information as possible.  This web page details all the
information that we request in order to provide assistance:

     http://www.open-mpi.org/community/help/

User-level questions and comments should generally be sent to the
user's mailing list (users@open-mpi.org).  Because of spam, only
subscribers are allowed to post to this list (ensure that you
subscribe with and post from *exactly* the same e-mail address --
joe@example.com is considered different than
joe@mycomputer.example.com!).  Visit this page to subscribe to the
user's list:

     http://www.open-mpi.org/mailman/listinfo.cgi/users

Developer-level bug reports, questions, and comments should generally
be sent to the developer's mailing list (devel@open-mpi.org).  Please
do not post the same question to both lists.  As with the user's list,
only subscribers are allowed to post to the developer's list.  Visit
the following web page to subscribe:

     http://www.open-mpi.org/mailman/listinfo.cgi/devel

Make today an Open MPI day!