[mvapich-discuss] Fwd: Completion of non-blocking collective MPI_Iallgather

[pramod kumbhar]

Could someone provide any suggestion on this?

Thanks.

---------- Forwarded message ----------
From: Kumbhar Pramod Shivaji <pramod.kumbhar at epfl.ch>
Date: Mon, Jan 26, 2015 at 6:02 PM
Subject: [mvapich-discuss] Completion of non-blocking collective
MPI_Iallgather
To: "mvapich-discuss at cse.ohio-state.edu" <mvapich-discuss at cse.ohio-state.edu
>


 Hello All,

 I am looking into mpi non-blocking collectives (specifically
mpi_iallgather & mpi_iallgatherv)
and wondering about the internal completion / progress of these routines.
To explain, I have following
pseudo example:

 MPI_Iallgather(…&req)        *  // this called by all ranks at the same
time*
...
while( i < 4) {

           compute(…);   // compute for few seconds
          MPI_Test(…&flag, &req);                               *   // Can
I expect this flag to be true? i.e. operation is completed here at some
point?*
          i++;
}
….
MPI_Wait(&req);   * // I see that MPI_Iallgather is getting finished when
everyone calls MPI_Wait at this point, why?*


 I was running this test example on single node with 8 mpi ranks. I see
that MPI_Test is always returning false. With
compute() function of two seconds, I expect MPI_Iallgather to finish
quickly. But instead mpi_iallgather is completed
at MPI_Wait(). See attached sample trace of the program.

 Could anyone point out possible cause of this behaviour? It will be great
help.


 Regards,
Pramod

 MVAPICH 2 version: 2.0
Configure command:  /configure --with-slurm
 --with-slurm-include=slurm/default/include
--with-slurm-lib=slurm/default/lib  --with-pm=none --with-pmi=slurm
--enable-threads=multiple --enable-shared --enable-sharedlibs=gcc
--enable-fc --enable-cxx --with-mpe --enable-rdma-cm --enable-fast
--enable-smpcoll --with-hwloc --enable-xrc --with-device=ch3:mrail
--with-rdma=gen2 --enable-cuda --with-cuda=/usr/local/cuda-5.0
--with-cuda-include=/usr/local/cuda-5.0/include
--with-cuda-lib=/usr/local/cuda-5.0/lib64 --enable-g=dbg --enable-debuginfo
CC=gcc CXX=g++ FC=gfortran F77=gfortran




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