[mpich-discuss] Mpich2's behavior when too many messages are sent

[Matthieu Dorier]

Thank you both for your answer!

Matthieu

----- Mail original -----
> De: "Darius Buntinas" <buntinas at mcs.anl.gov>
> À: discuss at mpich.org
> Envoyé: Mardi 27 Novembre 2012 15:49:15
> Objet: Re: [mpich-discuss] Mpich2's behavior when too many messages are	sent
> 
> The MPI standard allows an implementation to run out of resources, so
> MPICH is compliant here :-). As Jeff mentioned it is a "quality of
> implementation" issue and some implementations might be able to
> handle it better than others.  Simply queuing the sends on the
> sender side can lead to deadlocks, so something trickier is needed
> (imagine that the receiver posts a blocking receive with tag A
> followed by a million receives with tag B, and the sender sends a
> million messages with tag B then one message with tag A.  If we
> queue the messages at the sender, the receiver will never receive
> the message with tag A and the program deadlocks).
> 
> We've seen such "flow-control" problems before (some in out test
> suite), and generally the solution is to add some sort of
> synchronization in the application, e.g., to an Ssend (or Issend so
> long as you wait on the requests often enough) once in a while to
> let the receiver catch up.
> 
> -d
> 
> On Nov 27, 2012, at 2:50 AM, Matthieu Dorier wrote:
> 
> > Hello,
> > 
> > I have a program that include two processes, one is doing a lot of
> > MPI_Isend, the other one loops, receives the messages using
> > MPI_Irecv and treats them.
> > I'd like to know what the MPI-2 standard says, and what Mpich2
> > does, if the first process is too fast and the second process
> > cannot keep up with the number of messages sent. Is the first
> > process supposed to eventually block, waiting for the messages to
> > be received, or will the application crashes?
> > 
> > Thanks
> > 
> > Matthieu Dorier
> > PhD student at ENS Cachan Brittany and IRISA
> > http://people.irisa.fr/Matthieu.Dorier
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