[mpich-discuss] Message Protocols

[Rajeev Thakur]

How are you measuring the overhead for receiving versus sending?

Rajeev 

> -----Original Message-----
> From: mpich-discuss-bounces at mcs.anl.gov 
> [mailto:mpich-discuss-bounces at mcs.anl.gov] On Behalf Of Marcelo Tomim
> Sent: Wednesday, April 29, 2009 7:31 PM
> To: mpich-discuss at mcs.anl.gov
> Subject: [mpich-discuss] Message Protocols
> 
> 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.
>