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From: John Robinson (jr_at_[hidden])
Date: 2006-05-26 09:31:30


Jeff,

How about writing applications that use the OMPI plugins as-is? Suppose
I want to write an application that makes use of generic byte-movement
operations. Is it feasible to write my applicaiton to use a btl plugin?

- my apologies in advance if this is well covered in the docs you
mention - just slap me down ;-).

thanks,
/jr

---
Jeff Squyres (jsquyres) wrote:
> Open MPI is based on a component architecture, where plugins are used
> for various types of back-end functionality.
> 
> For MPI point-to-point communication, there are three types of plugins
> that are used:
> 
> - pml: Point to Point Messaging Layer (what is directly invoked behind
> MPI_SEND and friends).  This layer understands MPI semantics.
> - btl: Byte Transfer Layer (lowest layer "network driver" for
> communicating across specific networks).  This layer is completely
> MPI-agnostic; it just pushes bytes between endpoints (usually
> processes).
> - bml: BTL Management Layer (for loading, unloading, and generally
> run-time managing multiple BTL plugins).
> 
> Note that previous generations of Open MPI used "ptl" plugins instead of
> "btl" plugins.
> 
> I would suggest reading the "Open MPI: A Flexible High Performance MPI"
> paper on the Open MPI web site (see the "Publications" section) to get
> an overview of the OB1 pml plugin.  It describes the basis and top-level
> design of how the pml, bml, and btls interact at run-time.  Also read
> "InfiniBand Scalability in Open MPI" (also in the publications section).
> It is much more recent and, although somewhat IB-specific, also gives a
> good overview of how things work.  Finally, look at the MPI Developer's
> Workshop slides.  They probably provide the best description of what is
> happening for point-to-point messaging (there's whole sections devoted
> to this).
> 
> If you simply want to implement a new network driver (e.g., raw
> ethernet), you will want to write a new BTL plugin.  If you want to play
> with various scheduling policies, you probably want to modify / write a
> new PML plugin.  This code is not well documented other than comments in
> the code and the description of the plugin interfaces; your best bet is
> to ask questions here on the mailing list.
> 
> I strongly recommend working with a Subversion checkout -- things have
> changed since the 1.0 release.  See http://www.open-mpi.org/svn/ for
> details on getting a subversion checkout.
> 
> Within the code base, you'll be working within the ompi/ tree (the MPI
> layer).  You'll find the MPI C API bindings in ompi/mpi/c/*.c (e.g.,
> MPI_SEND is in ompi/mpi/c/send.c).  Also in ompi/ is the mca/ directory
> which, in turn, has subdirectories for each kind of plugin (a.k.a.
> "frameworks"), so you'll see subdirectories for pml/ and bml/ and btl/.
> In each framework's directory are subdirectories for each plugin (a.k.a.
> "components").  So you'll see ompi/mca/pml/ob1 (code for the ob1 PML
> plugin), ompi/mca/bml/r2 (code for the r2 BML plugin), ompi/mca/btl/tcp
> (code for the tcp BTL plugin), etc.
> 
> This is probably enough to get you started.  Let us know what your next
> questions are.
> 
> 
> 
> 
>>-----Original Message-----
>>From: users-bounces_at_[hidden] 
>>[mailto:users-bounces_at_[hidden]] On Behalf Of Mahesh Barve
>>Sent: Tuesday, May 23, 2006 1:24 AM
>>To: users_at_[hidden]
>>Subject: [OMPI users] Help regarding send/recv code
>>
>>Hi,
>> I am a novice to openmpi. Just managed to get openmpi
>>running on my system. 
>> I would like to modify the code for send and recv.
>>The target lower level device will be ethernet and
>>infiniband. I would like to know the files/functions 
>>to look for. Could you please guide me in this. 
>> thanks,
>>-Mahesh 
>> 
>>
>>
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