[mpich-discuss] Message Protocols

[Marcelo Tomim]

Hello MPI users,

I have the results of some point-to-point benchmarks on MPICH2 library 
and I have been having a hard time to interpret them.
The test is based on paired Send and Recv routines, similar to ping-pong 
tests. One specific detail I have been wondering about is the fact that 
for large messages (larger than 128kB, i.e., rendezvous protocol), the 
overhead for sending is much smaller that the overhead for receiving. I 
was expecting them to be close to one another, based on the fact that 
the receiver has to acknowledge to the sender that the message has been 
successfully received. There must be a flaw in this reasoning, but I don 
not where it is.
Could any one help me with that or indicate me a document which 
explains, in detail, all the message protocols (short, eager and 
rendezvous) employed in the MPICH2 implementation?

Thank you all very much for your attention.

Regards,
Marcelo Tomim.