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From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2007-03-29 17:48:49

On Mar 29, 2007, at 2:34 PM, pooja_at_[hidden] wrote:

> I am Pooja and I am doing a project in my High performance
> computing lab.
> In this project I need to find the internal state chnages of
> Openmpi.For
> eg:When does MPi_send is used how does messages are actually send
> and how
> does control messages are send.

This is a fairly complex question; the chain of events from MPI_SEND
down to when the message actually hits the wire is long and complex.
Control messages for the MPI layer are dependent upon which device is
being used (in the case of the MPI layer, this device is called the
Byte Transfer Layer (BTL)). For example, the TCP device sends
entirely different control messages then the openib/InfiniBand device.

Which ones are you interested in?

We have a paper describing the MPI long message protocols over RDMA
interconnects here:
hpc-protocols. It doesn't explicitly describe the control messages,
but it does give you an idea of what protocols are used and you can
infer at least some of the control messages from that (there are
others dealing with network credit management, connection
establishment, etc.).

There are also slides from a workshop that we gave in 2005 about the
internals of Open MPI:
workshop-2006/. These also don't speak specifically about the
control messages that are sent, but there's a starting point for
understanding the overall system.

Jeff Squyres
Cisco Systems