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From: Christian Leber (christian_at_[hidden])
Date: 2006-12-08 06:35:27

On Fri, Dec 08, 2006 at 04:11:04PM +0530, krishna chaitanya wrote:

> I learnt from a reliable source that MPI uses the services
> provided by TCP/IP or infiniband.

Did you hear that from a whistle-blower?

> Suppose that there is a bottle-neck in
> the TCP/IP layer itself, how will optimization of MPI calls really help?

Bottleneck is usually a fuzzy term.

Collective calls basically means for example that you tell MPI:
"send this to all nodes"
instead of
for(i=0;i<number_of_nodes;i++) "send this to node i"

Therefore you don't have serialization of the tasks and the MPI layer
could do optmizations.
For example the connection network could have a way to broadcast or at
least sending could be interleaved.

Christian Leber