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Subject: Re: [OMPI devel] MPI Message Communication over TCP/IP
From: pranav jadhav (pranavjadhav_at_[hidden])
Date: 2009-04-26 03:39:30


Thanks Jeff and Tim for providing the details about the layered structure of

OpenMPI library source code. The document you sent on Xen based VM
communication for HEC clusters is indeed good and covered the extensive
details about the BTL components.It helped me a lot in understanding the
working of BTL layer.Thanks once again :)


On Sat, Apr 25, 2009 at 10:05 AM, Timothy Hayes <hayesti_at_[hidden]> wrote:

> I uploaded it to
> I'm not sure if it's any good or even if it's 100% accurate; but if someone
> gets any use out of it, that would be good.
> Tim
> 2009/4/17 Jeff Squyres <jsquyres_at_[hidden]>
> On Apr 16, 2009, at 11:38 AM, Timothy Hayes wrote:
>> From what I understand MPI_Send will hit 3 separate layers of code before
>>> reaching the socket file descriptors you've found. The PML (Point to Point
>>> Messaging Layer) is a layer that bridges the MPI semantics from the
>>> underlying point to point communications. The standard PML implementation is
>>> called 'ob1' which is what indirectly calls the code you found. MPI_Send
>>> should go through pml_isend() or pml_send() which will request a BTL (Byte
>>> Transfer Layer) modules from the BML (BTL Management Layer) and invoke the
>>> BTL's btl_prepare_src() or btl_alloc() functions before calling the
>>> btl_send(). It becomes clearer when you step through it all with a debugger
>>> though ;-)
>>> If you're interested, I've recently implemented a BTL component of my own
>>> and am now writing up a report on the process. It will be ready next week,
>>> so if you think it might be useful, just let me know.
>> Ooohh... that would be positively yummy! We can even host/link to that on
>> :-)
>> --
>> Jeff Squyres
>> Cisco Systems
>> _______________________________________________
>> devel mailing list
>> devel_at_[hidden]
> _______________________________________________
> devel mailing list
> devel_at_[hidden]

Pranav Jadhav
Graduate Student
Computer Science Department
Stony Brook University