[mpich-discuss] MPI Implementation on 1 module

[Gulshan Singh]

What is available:
I have full access to the module that I wish to implement MPI in. However I
do not have access to source code of other modules, only object files of all
the modules are available for me to do linking.

workflow/pipeline?
I do not completely understand this question but the software calls certain
number of modules one after another depending upon the problem to be solved.
The modules are called one after another. Each module that is called
provides some results to the next module.

move on?
Yes exactly right. Need to launch MPI-enhanced subroutine/module, wait until
it is done. And move on to next next without even knowing that the
computation was done in parallel of serial.

Resources allocation is not a problem; the software will have n number of
processors to itself whenever needed. This is accomplished by requesting n
processors for the entire run time.

Additional Question:
I have source code of one module and object files of all other modules. The
object files were created using ifort (Intel Fortran). The MPI-enhanced
object file I am creating is using MPIF90. Does linking these two type of
object files is a problem? Do I need to create all object files using MPIF90
or ifort object files will work?

Gulshan

On Tue, Dec 14, 2010 at 4:51 AM, Nicolas Rosner <nrosner at gmail.com> wrote:

> Hello Gulshan,
>
> I'm assuming you meant more or less the following:
>
>  - you have a program spanning multiple compilation units and/or libs
>      and
>  - you would like to MPI-enable just one of said units or modules
>      and
>  - any necessary IPC/comm/sync between the MPI-ized unit and the rest
>    is addressed by separate mechanisms (other than MPI)
>
> If so, sure, as long as you have the source code for that particular unit
> or module, you should be able to limit any MPI compile/link-dependency of
> your system to the one module that actually uses MPI calls.
>
>
> > There are more than 10 modules in the software we are trying to modify to
> > improve the speed. We know that the most time is taken by only one
> module.
>
> Do these modules map to sequential stages of a workflow/pipeline? Is that
> one module one such stage? Is it currently invoked in a call-return way?
>
>
> > So MPI starts when the particular module is called and
> > the MPI collapses as soon as the computation in the module is finished.
>
> What you describe sounds essentially like a sequential program that, at
> some point --or perhaps every now and then-- needs to launch a parallel,
> MPI-enhanced subroutine/subprocess, wait until it's done, then move on..?
>
> If so, this is certainly possible, assuming your resource allocation
> plays along (ie the machines are always there for you when you need them,
> etc).
>
> HTH, just guessing; good luck!  N.
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