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From: Marcelo Stival (marstival_at_[hidden])
Date: 2006-08-29 15:13:45


OK, I really thank u ... !

How to verify the value for "first_fragment" param?
I tried "ompi_info --param btl tcp", but I can't found this one.
(openmpi 1.1.1b)

One more "deep inside" question (next time, to the right list..:P)
I suppose that the progress thread will be used just for rendezvous...
(and non-blocking)
But, it will be used for non-blocking synchronous short messages?
OK, that's rendezvous too.
However, the use of progress-thread depends on the condition used to
start or not the progress thread inside MPI.
(btl tcp over Ethernet)

Marcelo

On 8/29/06, George Bosilca <bosilca_at_[hidden]> wrote:
> Well, you post the question on the user mailing list. Therefore, I
> give you a user answer. If you want to know how do we implemented
> deep inside, then the answer is different.
>
> Short messages even on synchronous mode are sent using the rendez-
> vous protocol (sic). Except that our rendez-vous protocol transport
> some data. How much data, that depend on the network and it can be
> modified via an MCA parameter (first_fragment).
>
> In all the cases the for the synchronous send we will wait for an ack
> from the remote side before marking the request as completed at the
> sender. In fact, internally it happens exactly how you described in
> your email.
>
> george.
>
> On Aug 29, 2006, at 1:32 PM, Marcelo Stival wrote:
>
> > 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
> >>
> >> _______________________________________________
> >> users mailing list
> >> users_at_[hidden]
> >> http://www.open-mpi.org/mailman/listinfo.cgi/users
> >>
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> "Half of what I say is meaningless; but I say it so that the other
> half may reach you"
> Kahlil Gibran
>
>
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