One difference is that putting a blocking send before the irecv is a classic "unsafe" MPI program. It depends on eager send buffering to complete the MPI_Send so the MPI_Irecv can be posted. The example with MPI_Send first would be allowed to hang.
The original program is correct and safe MPI. Dick Treumann - MPI Team IBM Systems & Technology Group Dept X2ZA / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601 Tele (845) 433-7846 Fax (845) 433-8363 users-boun...@open-mpi.org wrote on 02/05/2009 05:48:34 AM: > [image removed] > > Re: [OMPI users] MPI_Test bug? > > Gabriele Fatigati > > to: > > Open MPI Users > > 02/05/2009 05:49 AM > > Sent by: > > users-boun...@open-mpi.org > > Please respond to Open MPI Users > > Hi Jody, > thanks four your quick reply. But what's the difference? > > 2009/2/5 jody <jody....@gmail.com>: > > Hi Gabriele > > > > Shouldn't you reverse the order of your send and recv from > > MPI_Irecv(buffer_recv, bufferLen, MPI_INT, recv_to, tag, > > MPI_COMM_WORLD, &request); > > MPI_Send(buffer_send, bufferLen, MPI_INT, send_to, tag, MPI_COMM_WORLD); > > > > to > > > > MPI_Send(buffer_send, bufferLen, MPI_INT, send_to, tag, MPI_COMM_WORLD); > > MPI_Irecv(buffer_recv, bufferLen, MPI_INT, recv_to, tag, > > MPI_COMM_WORLD, &request); > > > > ? > > Jody > > > > On Thu, Feb 5, 2009 at 11:37 AM, Gabriele Fatigati > <g.fatig...@cineca.it> wrote: > >> Dear OpenMPI developer, > >> i have found a very strange behaviour of MPI_Test. I'm using OpenMPI > >> 1.2 over Infiniband interconnection net. > >> > >> I've tried to implement net check with a series of MPI_Irecv and > >> MPI_Send beetwen processors, testing with MPI_Wait the end of Irecv. > >> For strange reasons, i've noted that, when i launch the test in one > >> node, it works well. If i launch over 2 or more procs over different > >> nodes, MPI_Test fails many time before to tell that the IRecv is > >> finished. > >> > >> I've tried that it fails also after one minutes, with very small > >> buffer( less than eager limit). It's impossible that the communication > >> is pending after one minutes, with 10 integer sended. To solve this, > >> I need to implement a loop over MPI_Test, and only after 3 or 4 > >> MPI_Test it returns that IRecv finished successful. Is it possible > >> that MPI_Test needs to call many time also if the communication is > >> already finished? > >> > >> In attach you have my simple C test program. > >> > >> Thanks in advance. > >> > >> -- > >> Ing. Gabriele Fatigati > >> > >> Parallel programmer > >> > >> CINECA Systems & Tecnologies Department > >> > >> Supercomputing Group > >> > >> Via Magnanelli 6/3, Casalecchio di Reno (BO) Italy > >> > >> www.cineca.it Tel: +39 051 6171722 > >> > >> g.fatigati [AT] cineca.it > >> > >> _______________________________________________ > >> users mailing list > >> us...@open-mpi.org > >> http://www.open-mpi.org/mailman/listinfo.cgi/users > >> > > _______________________________________________ > > users mailing list > > us...@open-mpi.org > > http://www.open-mpi.org/mailman/listinfo.cgi/users > > > > > > > > -- > Ing. Gabriele Fatigati > > Parallel programmer > > CINECA Systems & Tecnologies Department > > Supercomputing Group > > Via Magnanelli 6/3, Casalecchio di Reno (BO) Italy > > www.cineca.it Tel: +39 051 6171722 > > g.fatigati [AT] cineca.it > _______________________________________________ > users mailing list > us...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/users
