On Jul 18, 2007, at 12:25 PM, Pedro Petrovitch wrote:
> Hi, I've read in a book that in some implementations (didnt
> mentioned one)
> the regular send (MPI_Send) is implemented using the synchronous
> one. Is
> that true for LAM-MPI?
It depends on the size of the message. Short messages are sent
eagerly (pending available buffering) and therefore do not require an
ACK from the receiver; long messages use a rendezvous protocol to
avoid excess resource consumption at the receiver.
Synchronous sends *always* use a rendezvous protocol, regardless of
length.
> Also is there any change in this aspect from the
> version 7.0.6 to 7.1.1?
No.
> What I know now is that the synchronous send only
> starts when a matching receive is executed while the basic one
> starts as
> soon as possible but does not finish until the matching receive is
> called,
> is that true? Thanks for the patience.
The only thing that MPI guarantees about MPI_SSEND is that it will
not return until the buffer is available for re-use and a matching
receive has been posted.
The only thing that MPI guarantees about MPI_SEND is that it will
return when the buffer is available for re-use.
--
Jeff Squyres
Cisco Systems
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