= Description = 

MPI-START is an abstration layer that offers a unique interface to start
MPI jobs with different MPI implementations.

= Installation = 

Normally users do not need to install MPI-Start. However if they want to use it in a site without an existing installation, the recommendation is to create a tarball installation that can be transfered in the input sandbox of the job.

In order to create a tarball installation, [[http://devel.ifca.es/hg/mpi-start|get the source code]] and do the following:

{{{
$ make tarball
}}}

This will create a mpi-start-X.Y.Z.tar.gz (with X.Y.Z being the version of MPI-Start) that contains all that is needed for the execution of jobs. In your job script unpack the tarball and set the `I2G_MPI_START` environment variable to `$PWD/bin/mpi-start`.

= Usage =

All necessary information of the mpi-start program are provided via
environment  variables. A user has to set the below specified variables
before executing mpi-start.

== Environment Variables ==

 - `I2G_MPI_APPLICATION` 
   The application binary to execute.

 - `I2G_MPI_APPLICATION_ARGS` 
   The command line parameters for the application

 - `I2G_MPI_TYPE`
   The name of the MPI implementation to use. So far defined values :
   - openmpi
   - pacx-mpi (Check RunningPacxMpi for details on how to run this kind of jobs)
   - mpich
   - mpich2
   - lam

 - `I2G_MPI_VERSION`
   Specifies the version of the MPI implementation specified by
   I2G_MPI_TYPE. If not specified the default version will be used.

 - `I2G_MPI_PRE_RUN_HOOK`
   This variable can be set to a script which must define the
   pre_run_hook function. This function will be called after the MPI
   support has been established and before the internal pre-run
  hooks. This hook can be used to prepare input data or compile the
  program.

 - `I2G_MPI_POST_RUN_HOOK`
  This variable can be set to a script which must define the
  post_run_hook function. This function will be called after the
  mpirun has finished.

== EGEE Environment ==

mpi-start supports the EGEE environment variable schema for specifing
the local MPI installations. For the latest specification of the EGEE
environment specification refer to :

[[http://www.grid.ie/mpi/wiki]]

==Debugging== 

For debugging purpose the `I2G_MPI_START_DEBUG` variable can be set to 1
to enable the debugging output. The `I2G_MPI_START_VERBOSE` variable can be set to 1 to turn on the additional output.

The variable `I2G_MPI_START_TRACE` can be set to 1 to trace every operation that is performed by mpi-start (goes to stderr).

== Hooks ==

The Hooks framework opens the possibility of customizing the behavior of MPI-Start. Users can provide their own hooks to perform any pre (e.g. compilation of binaries, data fetching) or post (e.g. storage of application results, clean-up) actions needed for the execution of their application. The [[/HooksFramework|Hooks Framework]] page describes in detail the framework and how to create user hooks.

== Other Environment Variables ==

This section list other environment variables that affect to the MPI-Start execution but are not so frequently used:

 - `I2G_MPI_APPLICATION_STDIN`
  Standard input file to use.

 - `I2G_MPI_APPLICATION_STDOUT`
  Standard output file to use.

 - `I2G_MPI_FILE_DIST`
  File distribution method to use (see [[/HooksFramework|Hooks Framework]])

== Examples ==
=== Simple Job ===

{{{#!highlight sh
#!/bin/sh
# IMPORTANT : This example script execute a 
#             non-mpi program with Open MPI
#
export I2G_MPI_APPLICATION=/bin/hostname
export I2G_MPI_TYPE=openmpi

$I2G_MPI_START
}}}

=== Job with user specified hooks ===

{{{#!highlight sh
#!/bin/sh
#
# MPI_START_SHARED_FS can be used to figure out if the current working
# is located on a shared file system or not. (1=yes, 0=no);
#
# The "mpi_start_foreach_host" function takes as parameter the name of 
# another function that will be called for each host in the machine as 
# first parameter. 
# - For each host the callback function will be called exactly once, 
#   independent how often the host appears in the machinefile.
# - The callback function will also be called for the local host.

# create the pre-run hook
cat > pre_run_hook.sh << EOF
pre_run_hook () {
    echo "pre run hook called "
    # - download data
    # - compile program

    if [ "x\$MPI_START_SHARED_FS" = "x0" ] ; then
        echo "If we need a shared file system we can return -1 to abort" 
        # return -1
    fi

    return 0
}
EOF

# create the post-run hook 
cat > post_run_hook.sh << EOF
# the first paramter is the name of a host in the 
my_copy () {
    CMD="scp . \$1:\$PWD/mydata.1"
    echo \$CMD
    #\$CMD
    # upload data
}

post_run_hook () {
    echo "post_run_hook called"
    if [ "x\$MPI_START_SHARED_FS" = "x0" ] ; then
        echo "gather output from remote hosts"
        mpi_start_foreach_host my_copy
    fi
    return 0
}
EOF

export I2G_MPI_APPLICATION=mpi_sleep
export I2G_MPI_APPLICATION_ARGS=0
export I2G_MPI_TYPE=openmpi
export I2G_MPI_PRE_RUN_HOOK=./pre_run_hook.sh
export I2G_MPI_POST_RUN_HOOK=./post_run_hook.sh

$I2G_MPI_START
}}}

= Using MPI-Start with grid middleware =
== gLite ==

[[http://glite.web.cern.ch/glite/|gLite]] uses the WMS software for submitting jobs to the different available resources. The WMS gets a job description in the JDL language and performs the selection and actual submission of the job into the resources on behalf of the user. The following sections describe how to submit a job using the WMS.
 
=== Basic Job Submission ===

Jobs are described with the [[https://edms.cern.ch/document/590869/1|JDL language]]. Most relevant attributes for parallel job submission are:
 * `CPUNumber`: number of processes to allocate.
 * `Requirements`: requirements of the job, will allow to force the selection of sites with MPI-Start support.

The following example shows a job that will use 6 processes and it is executed with Open MPI. The `requirements` attribute makes the WMS to select sites that publish that they support MPI-Start and Open MPI.

{{{
JobType       = Normal;
CPUNumber     = 6;
Executable    = "starter.sh";
Arguments     = "OPENMPI hello_bin hello arguments";
InputSandbox  = {"starter.sh", "hello_bin"};
OutputSandbox = {"std.out", "std.err"};
StdOutput     = "std.out";
StdError      = "std.err";
Requirements  = member("MPI-START", other.GlueHostApplicationSoftwareRunTimeEnvironment) 
                && member("OPENMPI", other.GlueHostApplicationSoftwareRunTimeEnvironment);
}}}

The `Executable` attribute is a script that will invoke MPI-Start with the correct options for the execution of the user's application. We propose a generic wrapper that can be used for any application and MPI flavour that gets in the `Arguments` attribute:
 * Name of MPI-Start execution environment (I2G_MPI_FLAVOUR variable), in the example: OPENMPI
 * Name of user binary, in the example: hello_bin
 * Arguments for the user binary, in the example: hello arguments

This is the content of the wrapper:
{{{#!highlight sh
#!/bin/bash
# Pull in the arguments.
MPI_FLAVOR=$1

MPI_FLAVOR_LOWER=`echo $MPI_FLAVOR | tr '[:upper:]' '[:lower:]'`
export I2G_MPI_TYPE=$MPI_FLAVOR_LOWER

shift
export I2G_MPI_APPLICATION=$1

shift
export I2G_MPI_APPLICATION_ARGS=$*
 
# Touch the executable, and make sure it's executable.
touch $I2G_MPI_APPLICATION
chmod +x $I2G_MPI_APPLICATION
 
# Invoke mpi-start.
$I2G_MPI_START
}}}

User needs to include this wrapper in the `InputSandbox` of the JDL (`starter.sh`) and set it as the `Executable` of the job. Submission is performed as any other gLite job:

{{{
$ glite-wms-job-submit -a hello-mpi.sh

Connecting to the service https://gridwms01.ifca.es:7443/glite_wms_wmproxy_server


====================== glite-wms-job-submit Success ======================

The job has been successfully submitted to the WMProxy
Your job identifier is:

https://gridwms01.ifca.es:9000/8jG3MUNRm-ol7BqhFP5Crg

==========================================================================
}}}

Once the job is finished, the output can be retrieved:
{{{
$ glite-wms-job-output https://gridwms01.ifca.es:9000/8jG3MUNRm-ol7BqhFP5Crg

Connecting to the service https://gridwms01.ifca.es:7443/glite_wms_wmproxy_server	
  
================================================================================	

			JOB GET OUTPUT OUTCOME

Output sandbox files for the job:
https://gridwms01.ifca.es:9000/8jG3MUNRm-ol7BqhFP5Crg
have been successfully retrieved and stored in the directory:
/gpfs/csic_projects/grid/tmp/jobOutput/enol_8jG3MUNRm-ol7BqhFP5Crg	
  
================================================================================	
  

$ cat /gpfs/csic_projects/grid/tmp/jobOutput/enol_8jG3MUNRm-ol7BqhFP5Crg/std.*
Hello world from gcsic054wn. Process 3 of 6
Hello world from gcsic054wn. Process 1 of 6
Hello world from gcsic054wn. Process 2 of 6
Hello world from gcsic054wn. Process 0 of 6
Hello world from gcsic055wn. Process 4 of 6
Hello world from gcsic055wn. Process 5 of 6
}}}

=== Modifying MPI-Start behavior ===

MPI-Start behavior can be customized by setting different environment variables (see  [#Usage usage section] for a complete list). If using the generic wrapper, one easy way of customizing MPI-Start execution is using the `Environment` attribute of the JDL. The following JDL adds debugging to the previous example by setting the `I2G_MPI_START_VERBOSE` and `I2G_MPI_START_DEBUG` variables to 1:
{{{
JobType       = Normal;
CPUNumber     = 6;
Executable    = "starter.sh";
Arguments     = "OPENMPI hello_bin hello arguments";
InputSandbox  = {"starter.sh", "hello_bin"};
OutputSandbox = {"std.out", "std.err"};
StdOutput     = "std.out";
StdError      = "std.err";
Requirements  = member("MPI-START", other.GlueHostApplicationSoftwareRunTimeEnvironment) 
                && member("OPENMPI", other.GlueHostApplicationSoftwareRunTimeEnvironment);
Environment   = {"I2G_MPI_START_VERBOSE=1", "I2G_MPI_START_DEBUG=1"};
}}}

Use of hooks (see [[HooksFramework|Hooks Framework]]) is also possible using this mechanism. If the user has a file with the MPI-Start hooks called `hooks.sh`, the following JDL would add it to the execution (notice that the file is also added in the `InputSandbox`): 

{{{
JobType       = Normal;
CPUNumber     = 6;
Executable    = "starter.sh";
Arguments     = "OPENMPI hello_bin hello arguments";
InputSandbox  = {"starter.sh", "hello_bin", "hooks.sh"};
OutputSandbox = {"std.out", "std.err"};
StdOutput     = "std.out";
StdError      = "std.err";
Requirements  = member("MPI-START", other.GlueHostApplicationSoftwareRunTimeEnvironment) 
                && member("OPENMPI", other.GlueHostApplicationSoftwareRunTimeEnvironment);
Environment   = {"I2G_MPI_PRE_RUN_HOOK=hooks.sh", "I2G_MPI_POST_RUN_HOOK=hooks.sh"};
}}}