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From: Marcelo Stival (marstival_at_[hidden])
Date: 2006-08-29 13:32:43


Thanks for your replay...

Let me be a little insistent... :P

I read (I don't remember where...) that an specific implementation
could send messages with synchronous comm mode... eagerly!
I think it still conform to the standard if the operation completes
just after the ack from the receiver.

The MPI_Ssend() could send a short message eagerly and wait for the
ack... (to satisfy the semantics of synchronous send)

Well, if it's possible.... I want to know if the OPENMPI
implementation (with BTL TCP over Ethernet) uses different protocols
for short/long when synchronous ...
(or it will be always rendezvous... as stated before)

Thanks
Marcelo

On 8/29/06, George Bosilca <bosilca_at_[hidden]> wrote:
> On Tue, 29 Aug 2006, Marcelo Stival wrote:
>
> > Hi,
> >
> > I have 2 questions related to short/long message protocols...
> >
> > 1) When using synchronous comm mode, short messages (<64kB) still be
> > transferred eagerly?
>
> Depend. 64Kb is not the limits between the eager and rendez-vous protocol.
> In fact it depend on the underlying network that get activated. Anyway,
> for this particular question this limit between the eager and rendez-vous
> protocol does not matter. Synchronous is alway a rendez-vous protocol as
> specified in the MPI standard.
>
> > And larger messages will be transferred using rendezvous...?
>
> That's always the case even for non synchronous operations.
>
> >
> > 2) When the progress-thread (tcp btl) will be applied?
> > Just for long messages? Does it affect synchronous short messages sends?
>
> The behavior will be the same with or without threads.
>
> Thanks,
> george.
>
>
> "We must accept finite disappointment, but we must never lose infinite
> hope."
> Martin Luther King
>
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