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README
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Copyright (c) 2004-2007 The Trustees of Indiana University and Indiana
University Research and Technology
Corporation. All rights reserved.
Copyright (c) 2004-2007 The University of Tennessee and The University
of Tennessee Research Foundation. All rights
reserved.
Copyright (c) 2004-2008 High Performance Computing Center Stuttgart,
University of Stuttgart. All rights reserved.
Copyright (c) 2004-2007 The Regents of the University of California.
All rights reserved.
Copyright (c) 2006-2020 Cisco Systems, Inc. All rights reserved.
Copyright (c) 2006-2011 Mellanox Technologies. All rights reserved.
Copyright (c) 2006-2012 Oracle and/or its affiliates. All rights reserved.
Copyright (c) 2007 Myricom, Inc. All rights reserved.
Copyright (c) 2008-2018 IBM Corporation. All rights reserved.
Copyright (c) 2010 Oak Ridge National Labs. All rights reserved.
Copyright (c) 2011 University of Houston. All rights reserved.
Copyright (c) 2013-2020 Intel, Inc. All rights reserved.
Copyright (c) 2015 NVIDIA Corporation. All rights reserved.
Copyright (c) 2017-2018 Los Alamos National Security, LLC. All rights
reserved.
Copyright (c) 2017 Research Organization for Information Science
and Technology (RIST). All rights reserved.
Copyright (c) 2020 Google, LLC. All rights reserved.
$COPYRIGHT$
Additional copyrights may follow
$HEADER$
===========================================================================
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:
https://www.open-mpi.org/community/help/
The best way to report bugs, send comments, or ask questions is to
sign up on the user's and/or developer's mailing list (for user-level
and developer-level questions; when in doubt, send to the user's
list):
Because of spam, only subscribers are allowed to post to these lists
(ensure that you subscribe with and post from exactly the same e-mail
address -- [email protected] is considered different than
[email protected]!). Visit these pages to subscribe to the
lists:
https://lists.open-mpi.org/mailman/listinfo/users
https://lists.open-mpi.org/mailman/listinfo/devel
Thanks for your time.
===========================================================================
Much, much more information is also available in the Open MPI FAQ:
https://www.open-mpi.org/faq/
===========================================================================
Quick start
-----------
In many cases, Open MPI can be built and installed by simply
indicating the installation directory on the command line:
$ tar xf openmpi-<version>.tar.bz2
$ cd openmpi-<version>
$ ./configure --prefix=<path> |& tee config.out
...lots of output...
$ make -j 8 |& tee make.out
...lots of output...
$ make install |& tee install.out
...lots of output...
Note that there are many, many configuration options to the
"./configure" step. Some of them may be needed for your particular
environmnet; see below for desciptions of the options available.
If your installation prefix path is not writable by a regular user,
you may need to use sudo or su to run the "make install" step. For
example:
$ sudo make install |& tee install.out
[sudo] password for jsquyres: <enter your password here>
...lots of output...
Finally, note that VPATH builds are fully supported. For example:
$ tar xf openmpi-<version>.tar.bz2
$ cd openmpi-<version>
$ mkdir build
$ cd build
$ ../configure --prefix=<path> |& tee config.out
...etc.
The rest of this README file contains:
- General release notes about Open MPI, including information about
platform, compiler, and run-time support, MPI and OpenSHMEM
functionality, network support, and MPI extensions.
- Detailed information on building and installing Open MPI.
- Open MPI version and library numbering policies, including how those
are related to backwards compatibility guarantees.
- Information on how to both query and validate your Open MPI
installation.
- Description of Open MPI extensions.
- Examples showing how to compile and run Open MPI applications.
- Summary information on the various plugin frameworks inside Open
MPI and OpenSHMEM.
===========================================================================
The following abbreviated list of release notes applies to this code
base as of this writing (April 2020):
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 "OpenSHMEM"
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/
This OpenSHMEM implementation will only work in Linux environments
with a restricted set of supported networks.
- 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 -- Libfabric 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
(https://www.open-mpi.org/).
- 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
- PBS Pro, Torque
- Platform LSF (tested with v9.1.1 and later)
- SLURM
- Cray XE, XC, and XK
- Oracle Grid Engine (OGE) 6.1, 6.2 and open source Grid Engine
- Systems that have been tested are:
- Linux (various flavors/distros), 64 bit (x86, ppc, aarch64),
with gcc (>=4.8.x+), clang (>=3.6.0), Absoft (fortran), Intel,
and Portland (*)
- macOS (10.14-10.15), 64 bit (x86_64) with XCode compilers
(*) Be sure to read the Compiler Notes, below.
- Other systems have been lightly (but not fully) tested:
- Linux (various flavors/distros), 32 bit, with gcc
- Cygwin 32 & 64 bit with gcc
- ARMv6, ARMv7
- Other 64 bit platforms.
- OpenBSD. Requires configure options --enable-mca-no-build=patcher
and --disable-dlopen with this release.
- Problems have been reported when building Open MPI on FreeBSD 11.1
using the clang-4.0 system compiler. A workaround is to build
Open MPI using the GNU compiler.
- Open MPI has taken some steps towards Reproducible Builds
(https://reproducible-builds.org/). Specifically, Open MPI's
"configure" and "make" process, by default, records some
system-specific information such as the hostname where Open MPI was
built and the username who built it. If you desire a Reproducible
Build, set the $USER and $HOSTNAME environment variables before
invoking "configure" and "make", and Open MPI will use those values
instead of invoking "whoami" and/or "hostname", respectively.
Platform Notes
--------------
- N/A
Compiler Notes
--------------
- Open MPI requires a C99-capable compiler to build.
- On platforms other than x86-64, ARM, and PPC, Open MPI requires a
compiler that either supports C11 atomics or the GCC "__atomic"
atomics (i.e., GCC >= v4.7.2).
- 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.
- Users have reported issues with older versions of the Fortran PGI
compiler suite when using Open MPI's (non-default) --enable-debug
configure option. Per the above advice of using the most recent
version of a compiler series, the Open MPI team recommends using the
latest version of the PGI suite, and/or not using the --enable-debug
configure option. If it helps, here's what we have found with some
(not comprehensive) testing of various versions of the PGI compiler
suite:
pgi-8 : NO known good version with --enable-debug
pgi-9 : 9.0-4 known GOOD
pgi-10: 10.0-0 known GOOD
pgi-11: NO known good version with --enable-debug
pgi-12: 12.10 known BAD with -m32, but known GOOD without -m32
(and 12.8 and 12.9 both known BAD with --enable-debug)
pgi-13: 13.9 known BAD with -m32, 13.10 known GOOD without -m32
pgi-15: 15.10 known BAD with -m32
- Similarly, there is a known Fortran PGI compiler issue with long
source directory path names that was resolved in 9.0-4 (9.0-3 is
known to be broken in this regard).
- Open MPI does not support the PGI compiler suite on OS X or MacOS.
See issues below for more details:
https://github.com/open-mpi/ompi/issues/2604
https://github.com/open-mpi/ompi/issues/2605
- OpenSHMEM Fortran bindings do not support the `no underscore` Fortran
symbol convention. IBM's xlf compilers build in that mode by default.
As such, IBM's xlf compilers cannot build/link the OpenSHMEM Fortran
bindings by default. A workaround is to pass FC="xlf -qextname" at
configure time to force a trailing underscore. See the issue below
for more details:
https://github.com/open-mpi/ompi/issues/3612
- MPI applications that use the mpi_f08 module on PowerPC platforms
(tested ppc64le) will likely experience runtime failures if:
- they are using a GNU linker (ld) version after v2.25.1 and before v2.28,
-and-
- they compiled with PGI (tested 17.5) or XL (tested v15.1.5) compilers.
This was noticed on Ubuntu 16.04 which uses the 2.26.1 version of ld by
default. However, this issue impacts any OS using a version of ld noted
above. This GNU linker regression will be fixed in version 2.28.
Below is a link to the GNU bug on this issue:
https://sourceware.org/bugzilla/show_bug.cgi?id=21306
The XL compiler will include a fix for this issue in a future release.
- 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.
- On OpenBSD/i386, if you configure with
--enable-mca-no-build=patcher, you will also need to add
--disable-dlopen. Otherwise, odd crashes can occur
nondeterministically.
- 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 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. GCC may
require either "-m32" or "-mcpu=v9 -m32", depending on GCC version.
- 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.
- 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.
- 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.
- It has been reported that Pathscale 5.0.5 and 6.0.527 compilers
give an internal compiler error when trying to Open MPI.
- As of July 2017, the Pathscale compiler suite apparently has no
further commercial support, and it does not look like there will be
further releases. Any issues discovered regarding building /
running Open MPI with the Pathscale compiler suite therefore may not
be able to be resolved.
- 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 OpenSHMEM wrapper compiler: mpifort and oshfort,
*** respectively. 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.
********************************************************************
********************************************************************
As a direct result, it is STRONGLY recommended that you specify a
Fortran compiler that uses file suffixes to determine Fortran code
layout (e.g., free form vs. fixed). For example, with some versions
of the IBM XLF compiler, it is preferable to use FC=xlf instead of
FC=xlf90, because xlf will automatically determine the difference
between free form and fixed Fortran source code.
However, many Fortran compilers allow specifying additional
command-line arguments to indicate which Fortran dialect to use.
For example, if FC=xlf90, you may need to use "mpifort --qfixed ..."
to compile fixed format Fortran source files.
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 OpenSHMEM specification, there is only one Fortran OpenSHMEM
binding provided:
- shmem.fh: All Fortran OpenSHMEM programs **should** include
'shmem.fh', and Fortran OpenSHMEM programs that use constants
defined by OpenSHMEM **MUST** include 'shmem.fh'.
The following notes apply to the above-listed Fortran bindings:
- All Fortran compilers support the mpif.h/shmem.fh-based bindings,
with one exception: the MPI_SIZEOF interfaces will only be present
when Open MPI is built with a Fortran compiler that support the
INTERFACE keyword and ISO_FORTRAN_ENV. Most notably, this
excludes the GNU Fortran compiler suite before version 4.9.
- The level of support provided by the mpi module is based on your
Fortran compiler.
If Open MPI is built with a non-GNU Fortran compiler, or if Open
MPI is built with the GNU Fortran compiler >= v4.9, all MPI
subroutines will be prototyped in the mpi module. All calls to
MPI subroutines will therefore have their parameter types checked
at compile time.
If Open MPI is built with an old gfortran (i.e., < v4.9), a
limited "mpi" module will be built. Due to the limitations of
these compilers, and per guidance from the MPI-3 specification,
all MPI subroutines with "choice" buffers are specifically *not*
included in the "mpi" module, and their parameters will not be
checked at compile time. 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.).
Similar to the mpif.h interface, MPI_SIZEOF is only supported on
Fortran compilers that support INTERFACE and ISO_FORTRAN_ENV.
- The mpi_f08 module has been tested with the Intel Fortran compiler
and gfortran >= 4.9. Other modern Fortran compilers likely also
work.
Many older Fortran compilers do not provide enough modern Fortran
features to support the mpi_f08 module. For example, gfortran <
v4.9 does provide enough support for the mpi_f08 module.
You can examine the output of the following command to see all
the Fortran features that are/are not enabled in your Open MPI
installation:
shell$ ompi_info | grep -i fort
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 MPI Component
Architecture (MCA) 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" parameter 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-3 functionality is supported.
- Note that starting with Open MPI v4.0.0, prototypes for several
legacy MPI-1 symbols that were deleted in the MPI-3.0 specification
(which was published in 2012) are no longer available by default in
mpi.h. Specifically, several MPI-1 symbols were deprecated in the
1996 publishing of the MPI-2.0 specification. These deprecated
symbols were eventually removed from the MPI-3.0 specification in
2012.
The symbols that now no longer appear by default in Open MPI's mpi.h
are:
- MPI_Address (replaced by MPI_Get_address)
- MPI_Errhandler_create (replaced by MPI_Comm_create_errhandler)
- MPI_Errhandler_get (replaced by MPI_Comm_get_errhandler)
- MPI_Errhandler_set (replaced by MPI_Comm_set_errhandler)
- MPI_Type_extent (replaced by MPI_Type_get_extent)
- MPI_Type_hindexed (replaced by MPI_Type_create_hindexed)
- MPI_Type_hvector (replaced by MPI_Type_create_hvector)
- MPI_Type_lb (replaced by MPI_Type_get_extent)
- MPI_Type_struct (replaced by MPI_Type_create_struct)
- MPI_Type_ub (replaced by MPI_Type_get_extent)
- MPI_LB (replaced by MPI_Type_create_resized)
- MPI_UB (replaced by MPI_Type_create_resized)
- MPI_COMBINER_HINDEXED_INTEGER
- MPI_COMBINER_HVECTOR_INTEGER
- MPI_COMBINER_STRUCT_INTEGER
- MPI_Handler_function (replaced by MPI_Comm_errhandler_function)
Although these symbols are no longer prototyped in mpi.h, they
are still present in the MPI library in Open MPI v4.0.x. This
enables legacy MPI applications to link and run successfully with
Open MPI v4.0.x, even though they will fail to compile.
*** Future releases of Open MPI beyond the v4.0.x series may
remove these symbols altogether.
*** The Open MPI team STRONGLY encourages all MPI application
developers to stop using these constructs that were first
deprecated over 20 years ago, and finally removed from the MPI
specification in MPI-3.0 (in 2012).
*** The Open MPI FAQ (https://www.open-mpi.org/faq/) contains
examples of how to update legacy MPI applications using these
deleted symbols to use the "new" symbols.
All that being said, if you are unable to immediately update your
application to stop using these legacy MPI-1 symbols, you can
re-enable them in mpi.h by configuring Open MPI with the
--enable-mpi1-compatibility flag.
- Rank reordering support is available using the TreeMatch library. It
is activated for the graph and dist_graph communicator topologies.
- 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 is supported with some exceptions.
The following PMLs support MPI_THREAD_MULTIPLE:
- cm (see list (1) of supported MTLs, below)
- ob1 (see list (2) of supported BTLs, below)
- ucx
(1) The cm PML and the following MTLs support MPI_THREAD_MULTIPLE:
- ofi (Libfabric)
- portals4
(2) The ob1 PML and the following BTLs support MPI_THREAD_MULTIPLE:
- self
- sm
- smcuda
- tcp
- ugni
- usnic
- vader (shared memory)
Currently, MPI File operations are not thread safe even if MPI is
initialized for MPI_THREAD_MULTIPLE support.
- 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 application via (e.g., via -lompitrace) will automatically
output to stderr when some MPI functions are invoked:
shell$ cd examples/
shell$ mpicc hello_c.c -o hello_c -lompitrace
shell$ mpirun -np 1 hello_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. Pull requests on github.com
would be greatly appreciated.
OpenSHMEM Functionality and Features
------------------------------------
- All OpenSHMEM-1.3 functionality is supported.
MPI Collectives
---------------
- The "cuda" coll component provides CUDA-aware support for the
reduction type collectives with GPU buffers. This component is only
compiled into the library when the library has been configured with
CUDA-aware support. It intercepts calls to the reduction
collectives, copies the data to staging buffers if GPU buffers, then
calls underlying collectives to do the work.
OpenSHMEM 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
OpenSHMEM collective operations.
Network Support
---------------
- There are several main MPI network models available: "ob1", "cm",
and "ucx". "ob1" uses BTL ("Byte Transfer Layer")
components for each supported network. "cm" uses MTL ("Matching
Transport Layer") components for each supported network. "ucx" uses
the OpenUCX transport.
- "ob1" supports a variety of networks that can be used in
combination with each other:
- OpenFabrics: InfiniBand, iWARP, and RoCE
- Loopback (send-to-self)
- Shared memory
- TCP
- SMCUDA
- Cisco usNIC
- uGNI (Cray Gemini, Aries)
- vader (XPMEM, Linux CMA, Linux KNEM, and copy-in/copy-out shared
memory)
- "cm" supports a smaller number of networks (and they cannot be
used together), but may provide better overall MPI performance:
- Intel Omni-Path PSM2
- Intel True Scale PSM (QLogic InfiniPath)
- OpenFabrics Interfaces ("libfabric" tag matching)
- Portals 4
- UCX is the Unified Communication X (UCX) communication library
(https://www.openucx.org/). This is an open-source project
developed in collaboration between industry, laboratories, and
academia to create an open-source production grade communication
framework for data centric and high-performance applications. The
UCX library can be downloaded from repositories (e.g.,
Fedora/RedHat yum repositories). The UCX library is also part of
Mellanox OFED and Mellanox HPC-X binary distributions.
UCX currently supports:
- OpenFabrics Verbs (including InfiniBand and RoCE)
- Cray's uGNI
- TCP
- Shared memory
- NVIDIA CUDA drivers
While users can manually select any of the above transports at run
time, Open MPI will select a default transport as follows:
1. If InfiniBand devices are available, use the UCX PML.
2. If PSM, PSM2, or other tag-matching-supporting Libfabric
transport devices are available (e.g., Cray uGNI), use the "cm"
PML and a single appropriate corresponding "mtl" module.
3. Otherwise, use the ob1 PML and one or more appropriate "btl"
modules.
Users can override Open MPI's default selection algorithms and force
the use of a specific transport if desired by setting the "pml" MCA
parameter (and potentially the "btl" and/or "mtl" MCA parameters) at
run-time:
shell$ mpirun --mca pml ob1 --mca btl [comma-delimted-BTLs] ...
or
shell$ mpirun --mca pml cm --mca mtl [MTL] ...
or
shell$ mpirun --mca pml ucx ...
- The main OpenSHMEM network model is "ucx"; it interfaces directly
with UCX.
- In prior versions of Open MPI, InfiniBand and RoCE support was
provided through the openib BTL and ob1 PML plugins. Starting with
Open MPI 4.0.0, InfiniBand support through the openib plugin is both
deprecated and superseded by the ucx PML component. The openib BTL
was removed in Open MPI v5.0.0.
While the openib BTL depended on libibverbs, the UCX PML depends on
the UCX library.
Once installed, Open MPI can be built with UCX support by adding
--with-ucx to the Open MPI configure command. Once Open MPI is
configured to use UCX, the runtime will automatically select the UCX
PML if one of the supported networks is detected (e.g., InfiniBand).
It's possible to force using UCX in the mpirun or oshrun command
lines by specifying any or all of the following mca parameters:
"--mca pml ucx" for MPI point-to-point operations, "--mca spml ucx"
for OpenSHMEM support, and "--mca osc ucx" for MPI RMA (one-sided)
operations.
- 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 Libfabric API
stack, this BTL is specific to Cisco usNIC devices.
- uGNI is a Cray library for communicating over the Gemini and Aries
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:
https://lwn.net/Articles/343351/
- The use of fork() with OpenFabrics-based networks (i.e., the UCX
PML) 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.
- Linux "knem" support is used when the "vader" or "sm" (shared
memory) BTLs are 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 https://knem.gforge.inria.fr/ for details on Knem.
- Linux Cross-Memory Attach (CMA) or XPMEM is used by the vader
shared-memory BTL when the CMA/XPMEM libraries are installedm,
respectively. Linux CMA and XPMEM are similar (but different)
mechanisms for Open MPI to utilize single-copy semantics for shared
memory.
Open MPI Extensions
-------------------
- An MPI "extensions" framework is included in Open MPI, 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:
- pcollreq: Provides routines for persistent collective communication
operations and persistent neighborhood collective communication
operations, which are planned to be included in the next MPI
Standard after MPI-3.1 as of Nov. 2018. The function names are
prefixed with MPIX_ instead of MPI_, like MPIX_Barrier_init,
because they are not standardized yet. Future versions of Open MPI
will switch to the MPI_ prefix once the MPI Standard which includes
this feature is published. See their man page for more details.
- shortfloat: Provides MPI datatypes MPIX_C_FLOAT16, MPIX_SHORT_FLOAT,
MPIX_SHORT_FLOAT, and MPIX_CXX_SHORT_FLOAT_COMPLEX if corresponding
language types are available. See ompi/mpiext/shortfloat/README.txt
for details.
- affinity: Provides the OMPI_Affinity_str() a string indicating the
resources which a process is bound. For more details, see its man
page.
- cuda: When the library is compiled with CUDA-aware support, it
provides two things. First, a macro
MPIX_CUDA_AWARE_SUPPORT. Secondly, the function
MPIX_Query_cuda_support that can be used to query for support.
- example: A non-functional extension; its only purpose is to
provide an example for how to create other extensions.
===========================================================================
Building Open MPI
-----------------
If you have checked out a DEVELOPER'S COPY of Open MPI (i.e., you
cloned from Git), you really need to read the HACKING file before
attempting to build Open MPI. Really.
If you have downloaded a tarball, then things are much simpler.
Open MPI uses a traditional configure script paired with "make" to
build. Typical installs can be of the pattern:
shell$ ./configure [...options...]
shell$ make [-j N] all install
(use an integer value of N for parallel builds)
There are many available configure options (see "./configure --help"
for a full list); a summary of the more commonly used ones is included
below.
NOTE: if you are building Open MPI on a network filesystem, the
machine you on which you are building *must* be
time-synchronized with the file server. Specifically: Open
MPI's build system *requires* accurate filesystem timestamps.
If your "make" output includes warning about timestamps in the
future or runs GNU Automake, Autoconf, and/or Libtool, this is
*not normal*, and you may have an invalid build. Ensure that
the time on your build machine is synchronized with the time on
your file server, or build on a local filesystem. Then remove
the Open MPI source directory and start over (e.g., by
re-extracting the Open MPI tarball).
Note that for many of Open MPI's --with-<foo> options, Open MPI will,
by default, search for header files and/or libraries for <foo>. If
the relevant files are found, Open MPI will built support for <foo>;
if they are not found, Open MPI will skip building support for <foo>.
However, if you specify --with-<foo> on the configure command line and
Open MPI is unable to find relevant support for <foo>, configure will
assume that it was unable to provide a feature that was specifically
requested and will abort so that a human can resolve out the issue.
Additionally, if a search directory is specified in the form
--with-<foo>=<dir>, Open MPI will:
1. Search for <foo>'s header files in <dir>/include.
2. Search for <foo>'s library files:
2a. If --with-<foo>-libdir=<libdir> was specified, search in
<libdir>.
2b. Otherwise, search in <dir>/lib, and if they are not found
there, search again in <dir>/lib64.
3. If both the relevant header files and libraries are found:
3a. Open MPI will build support for <foo>.
3b. If the root path where the <foo> libraries are found is neither
"/usr" nor "/usr/local", Open MPI will compile itself with
RPATH flags pointing to the directory where <foo>'s libraries
are located. Open MPI does not RPATH /usr/lib[64] and
/usr/local/lib[64] because many systems already search these
directories for run-time libraries by default; adding RPATH for
them could have unintended consequences for the search path
ordering.
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, Open MPI and OpenSHMEM build shared libraries, 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 MPI and OpenSHMEM 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/OpenSHMEM application and cannot be overridden at
run-time.
"runpath": the location of the Open MPI libraries is hard-coded into
the MPI/OpenSHMEM 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/OpenSHMEM 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.
If you would like to keep the rpath option, but not enable runpath
a different configure option is avalabile
--disable-wrapper-runpath.
--enable-dlopen
Build all of Open MPI's components as standalone Dynamic Shared
Objects (DSO's) that are loaded at run-time (this is the default).
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.
--disable-show-load-errors-by-default
Set the default value of the mca_base_component_show_load_errors MCA
variable: the --enable form of this option sets the MCA variable to
true, the --disable form sets the MCA variable to false. The MCA
mca_base_component_show_load_errors variable can still be overridden
at run time via the usual MCA-variable-setting mechanisms; this
configure option simply sets the default value.
The --disable form of this option is intended for Open MPI packagers
who tend to enable support for many different types of networks and
systems in their packages. For example, consider a packager who
includes support for both the FOO and BAR networks in their Open MPI
package, both of which require support libraries (libFOO.so and
libBAR.so). If an end user only has BAR hardware, they likely only
have libBAR.so available on their systems -- not libFOO.so.
Disabling load errors by default will prevent the user from seeing