Open MPI main development repository (BSD license)
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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) 2004-2007 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) 2006-2007 Cisco Systems, Inc. All rights reserved. Copyright (c) 2006-2007 Voltaire, Inc. All rights reserved. Copyright (c) 2006-2007 Sun Microsystems, Inc. All rights reserved. Copyright (c) 2007 Myricom, Inc. All rights reserved. $COPYRIGHT$ Additional copyrights may follow $HEADER$ =========================================================================== 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): users@open-mpi.org devel@open-mpi.org 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 -- joe@example.com is considered different than joe@mycomputer.example.com!). Visit these pages to subscribe to the lists: http://www.open-mpi.org/mailman/listinfo.cgi/users http://www.open-mpi.org/mailman/listinfo.cgi/devel 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 (19 September 2007): - 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 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 Open MPI installation must be in your PATH on all nodes (and potentially LD_LIBRARY_PATH, if libmpi is a shared library), unless using the --prefix or --enable-mpirun-prefix-by-default functionality (see below). - LAM/MPI-like mpirun notation of "C" and "N" is not yet supported. - Striping MPI messages across multiple networks is supported (and happens automatically when multiple networks are available), but needs performance tuning. - The run-time systems that are currently supported are: - rsh / ssh - BProc versions 3 and 4 with LSF - LoadLeveler - PBS Pro, Open PBS, Torque - SLURM - XGrid - Cray XT-3 and XT-4 - Sun N1 Grid Engine (N1GE) 6 and open source Grid Engine - 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. - Systems that have been tested are: - Linux, 32 bit, with gcc - Linux, 64 bit (x86), with gcc - OS X (10.4), 32 and 64 bit (i386, PPC, PPC64, x86_64), with gcc - Solaris 10 updates 2 and 3, SPARC and AMD, 32 and 64 bit, with Sun Studio 10 and 11 - Other systems have been lightly (but not fully tested): - Other compilers on Linux, 32 and 64 bit - Other 64 bit platforms (e.g., Linux on PPC64) - 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 ..." - Open MPI does not support the Sparc v8 CPU target, which is the default on Sun Solaris. The v8plus (32 bit) or v9 (64 bit) targets must be used to build Open MPI on Solaris. This can be done by including a flag in CFLAGS, CXXFLAGS, FFLAGS, and FCFLAGS, -xarch=v8plus for the Sun compilers, -mv8plus for GCC. - 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. - 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. - Open MPI will build bindings suitable for all common forms of Fortran 77 compiler symbol mangling on platforms that support it (e.g., Linux). On platforms that do not support weak symbols (e.g., OS X), Open MPI will build Fortran 77 bindings just for the compiler that Open MPI was configured with. Hence, on platforms that support it, if you configure Open MPI with a Fortran 77 compiler that uses one symbol mangling scheme, you can successfully compile and link MPI Fortran 77 applications with a Fortran 77 compiler that uses a different symbol mangling scheme. NOTE: For platforms that support the multi-Fortran-compiler bindings (i.e., weak symbols are supported), due to limitations in the MPI standard and in Fortran compilers, it is not possible to hide these differences in all cases. Specifically, the following two cases may not be portable between different Fortran compilers: 1. The C constants MPI_F_STATUS_IGNORE and MPI_F_STATUSES_IGNORE will only compare properly to Fortran applications that were created with Fortran compilers that that use the same name-mangling scheme as the Fortran compiler that Open MPI was configured with. 2. Fortran compilers may have different values for the logical .TRUE. constant. As such, any MPI function that uses the Fortran LOGICAL type may only get .TRUE. values back that correspond to the the .TRUE. value of the Fortran compiler that Open MPI was configured with. Note that some Fortran compilers allow forcing .TRUE. to be 1 and .FALSE. to be 0. For example, the Portland Group compilers provide the "-Munixlogical" option, and Intel compilers (version >= 8.) provide the "-fpscomp logicals" option. You can use the ompi_info command to see the Fortran compiler that Open MPI was configured with. - 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_THREAD_MULTIPLE support is included, but is only lightly tested. It likely does not work for thread-intensive applications. - Asynchronous message passing progress using threads can be turned on with the --enable-progress-threads option to configure. Asynchronous message passing progress is only supported for TCP, shared memory, and Myrinet/GM. Myrinet/GM has only been lightly tested. - The XGrid support is experimental - see the Open MPI FAQ and this post on the Open MPI user's mailing list for more information: http://www.open-mpi.org/community/lists/users/2006/01/0539.php - 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). - Older mVAPI-based InfiniBand drivers (Mellanox VAPI) are no longer supported. Please use an older version of Open MPI (1.2 series or earlier) if you need mVAPI support. - The use of fork() with 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). More complete support will be included in a future release of Open MPI (see the OFED 1.2 distribution for details). - The Fortran 90 MPI bindings can now be built in one of three sizes using --with-mpi-f90-size=SIZE (see description below). These sizes reflect the number of MPI functions included in the "mpi" Fortran 90 module and therefore which functions will be subject to strict type checking. All functions not included in the Fortran 90 module can still be invoked from F90 applications, but will fall back to Fortran-77 style checking (i.e., little/none). - trivial: Only includes F90-specific functions from MPI-2. This means overloaded versions of MPI_SIZEOF for all the MPI-supported F90 intrinsic types. - small (default): All the functions in "trivial" plus all MPI functions that take no choice buffers (meaning buffers that are specified by the user and are of type (void*) in the C bindings -- generally buffers specified for message passing). Hence, functions like MPI_COMM_RANK are included, but functions like MPI_SEND are not. - medium: All the functions in "small" plus all MPI functions that take one choice buffer (e.g., MPI_SEND, MPI_RECV, ...). All one-choice-buffer functions have overloaded variants for each of the MPI-supported Fortran intrinsic types up to the number of dimensions specified by --with-f90-max-array-dim (default value is 4). Increasing the size of the F90 module (in order from trivial, small, and medium) will generally increase the length of time required to compile user MPI applications. Specifically, "trivial"- and "small"-sized F90 modules generally allow user MPI applications to be compiled fairly quickly but lose type safety for all MPI functions with choice buffers. "medium"-sized F90 modules generally take longer to compile user applications but provide greater type safety for MPI functions. Note that MPI functions with two choice buffers (e.g., MPI_GATHER) are not currently included in Open MPI's F90 interface. Calls to these functions will automatically fall through to Open MPI's F77 interface. A "large" size that includes the two choice buffer MPI functions is possible in future versions of Open MPI. - Starting with Open MPI v1.2, there are two MPI network models available: "ob1" and "cm". "ob1" uses the familiar BTL components for each supported network. "cm" introduces MTL 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 and iWARP - Loopback (send-to-self) - Myrinet: GM and MX - Portals - Shared memory - TCP - uDAPL - "cm" supports a smaller number of networks (and they cannot be used together), but may provide better better overall MPI performance: - Myrinet MX (not GM) - InfiniPath PSM - Portals Open MPI will, by default, choose to use "cm" if it finds a cm-supported network at run-time. Users can force the use of ob1 if desired by setting the "pml" MCA parameter at run-time: shell$ mpirun --mca pml ob1 ... *** JMS need more verbiage here about cm? - The MX support is shared between the 2 internal devices, the MTL and the BTL. MTL stands for Message Transport Layer, while BTL stands for Byte Transport Layer. 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 MX, PSM or Portals, natively implement highly-optimized two-sided communication semantics. To leverage these capabilities, Open MPI provides the MTL interface 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 message length, internal resources and other parameters specific to the interconnect used. However, Open MPI cannot currently use multiple MTL modules at once. In the case of the MX MTL, self and 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. In the case of the BTL, MCA parameters allow Open MPI to use our own shared memory and self device for increased 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, more specifically when using multiple interconnects at the same time (including TCP), transferring non contiguous data-types or when using the DR PML. =========================================================================== Building Open MPI ----------------- 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: --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. --with-gm=<directory> Specify the directory where the GM libraries and header files are located. This enables GM support in Open MPI. --with-gm-libdir=<directory> Look in directory for the GM libraries. By default, Open MPI will look in <gm directory>/lib and <gm directory>/lib64, which covers most cases. This option is only needed for special configurations. --with-mx=<directory> Specify the directory where the MX libraries and header files are located. This enables MX support in Open MPI. --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-openib=<directory> Specify the directory where the OpenFabrics (previously known as OpenIB) libraries and header files are located. This enables OpenFabrics support in Open MPI (both InfiniBand and iWARP). --with-openib-libdir=<directory> Look in directory for the OpenFabrics 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-psm=<directory> Specify the directory where the QLogic PSM library and header files are located. This enables InfiniPath support in Open MPI. --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-udapl=<directory> Specify the directory where the UDAPL libraries and header files are located. This enables UDAPL support in Open MPI. Note that UDAPL support is disabled by default on Linux; the --with-udapl flag must be specified in order to enable it. --with-udapl-libdir=<directory> Look in directory for the UDAPL libraries. By default, Open MPI will look in <udapl directory>/lib and <udapl directory>/lib64, which covers most cases. This option is only needed for special configurations. --with-tm=<directory> Specify the directory where the TM libraries and header files are located. This enables PBS / Torque support in Open MPI. --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 (both support for MPI_THREAD_MULTIPLE and asynchronous progress) 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-threads and/or --enable-progress-threads. --enable-mpi-threads Allows the MPI thread level MPI_THREAD_MULTIPLE. See --with-threads; this is currently disabled by default. --enable-progress-threads Allows asynchronous progress in some transports. See --with-threads; this is currently disabled by default. --disable-mpi-cxx Disable building the C++ MPI bindings. Note that this does *not* disable the C++ checks during configure; some of Open MPI's tools are written in C++ and therefore require a C++ compiler to be built. --disable-mpi-cxx-seek Disable the MPI::SEEK_* constants. Due to a problem with the MPI-2 specification, these constants can conflict with system-level SEEK_* constants. Open MPI attempts to work around this problem, but the workaround may fail in some esoteric situations. The --disable-mpi-cxx-seek switch disables Open MPI's workarounds (and therefore the MPI::SEEK_* constants will be unavailable). --disable-mpi-f77 Disable building the Fortran 77 MPI bindings. --disable-mpi-f90 Disable building the Fortran 90 MPI bindings. Also related to the --with-f90-max-array-dim and --with-mpi-f90-size options. --with-mpi-f90-size=<SIZE> Three sizes of the MPI F90 module can be built: trivial (only a handful of MPI-2 F90-specific functions are included in the F90 module), small (trivial + all MPI functions that take no choice buffers), and medium (small + all MPI functions that take 1 choice buffer). This parameter is only used if the F90 bindings are enabled. --with-f90-max-array-dim=<DIM> The F90 MPI bindings are strictly typed, even including the number of dimensions for arrays for MPI choice buffer parameters. Open MPI generates these bindings at compile time with a maximum number of dimensions as specified by this parameter. The default value is 4. --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. --disable-shared By default, libmpi is 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 --disable-shared; enabling static libraries and disabling shared libraries are two independent options. --enable-static Build libmpi as a static library, 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. --enable-sparse-groups Enable the usage of sparse groups. This would save memory significantly especially if you are creating large communicators. (Disabled by default) 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 F77 - Fortran 77 compiler to use FFLAGS - Compile flags to pass to the Fortran 77 compiler FC - Fortran 90 compiler to use FCFLAGS - Compile flags to pass to the Fortran 90 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) For example: shell$ ./configure CC=mycc CXX=myc++ F77=myf77 F90=myf90 ... 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 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 rsh/ssh-based logins will be able to find the Open MPI executables. =========================================================================== 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. Changing the values of these parameters is explained in the "The Modular Component Architecture (MCA)" section, below. =========================================================================== Compiling Open MPI Applications ------------------------------- Open MPI provides "wrapper" compilers that should be used for compiling MPI applications: C: mpicc C++: mpiCC (or mpic++ if your filesystem is case-insensitive) Fortran 77: mpif77 Fortran 90: mpif90 For example: shell$ mpicc hello_world_mpi.c -o hello_world_mpi -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. =========================================================================== Running Open MPI Applications ----------------------------- Open MPI supports both mpirun and mpiexec (they are exactly equivalent). 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 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 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 an interactive SLURM job with 8 processors: shell$ srun -n 8 -A shell$ mpirun a.out The above command will 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)". =========================================================================== 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 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 io - MPI-2 I/O mpool - Memory pooling mtl - Matching transport layer, used for MPI point-to-point messages on some types of networks osc - MPI-2 one-sided communications pml - MPI point-to-point management layer rcache - Memory registration cache topo - MPI topology routines Back-end run-time environment component frameworks: --------------------------------------------------- errmgr - RTE error manager gpr - General purpose registry iof - I/O forwarding ns - Name server odls - OpenRTE daemon local launch subsystem oob - Out of band messaging pls - Process launch system ras - Resource allocation system rds - Resource discovery system rmaps - Resource mapping system rmgr - Resource manager rml - RTE message layer schema - Name schemas sds - Startup / discovery service smr - State-of-health monitoring subsystem Miscellaneous frameworks: ------------------------- backtrace - Debugging call stack backtrace support maffinity - Memory affinity memory - Memory subsystem hooks memcpy - Memopy copy support memory - Memory management hooks paffinity - Processor affinity 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 MPI to send bytes across underlying networks. The tcp btl, for example, sends messages across TCP-based networks; the gm btl sends messages across GM Myrinet-based 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 all the parameters (and default values) for the tcp btl component. 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 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. =========================================================================== 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! 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 When submitting bug reports to either list, 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/ Make today an Open MPI day!