[mpich-discuss] nonblocking collectives, progress thread

[Jed Brown]

Pieter, you should pull the latest to get the fix for this ticket. I don't
know whether it could affect your current observations, but it could trip
you up anyway (depending on how your implementation works).

http://trac.mcs.anl.gov/projects/mpich2/ticket/1601

On Sat, Apr 7, 2012 at 02:42, Pieter Ghysels <pieter.ghysels at ua.ac.be>wrote:

> Ah, yes, sorry for the confusion. I am also overlapping the
> MPIX_Iallreduce with other (one-sided) MPI calls. But these calls are
> buried in the library I use, and I'm not so familiar with one sided
> communication. But I was told that there are no calls to MPI_Win_create
> or MPI_Win_free, except at the very beginning and end of the program.
>
> Is it possible to overlap different MPI calls like that?
>
> I configured MPICH2 with
> --enable-threads=runtime
> and initialized with
> MPI_Init_thread(argc, argv, MPI_THREAD_MULTIPLE, &thread_support);
>
>
> Pieter
>
> On Fri, 2012-04-06 at 19:27 -0500, Jeff Hammond wrote:
> > One way to implement nonblocking allreduce would be to use
> > MPI_Accumulate, so it doesn't seem entirely nuts.  I presume you know
> > the MPICH2 implementation of MPIX_Iallreduce does not use RMA...
> >
> > Jeff
> >
> > On Fri, Apr 6, 2012 at 6:24 PM, Rajeev Thakur <thakur at mcs.anl.gov>
> wrote:
> > > You mean your program doesn't call MPI_Win_create and MPI_win_free but
> Jumpshot shows them? No, that's not normal.
> > >
> > > Rajeev
> > >
> > > On Apr 6, 2012, at 3:14 PM, Pieter Ghysels wrote:
> > >
> > >> Dear,
> > >>
> > >> I'm replacing calls to MPI_Allreduce by calls to MPIX_Iallreduce.
> > >> I'm compiling with -mpe=mpilog and look at the communication pattern
> > >> with jumpshot. The MPI_Allreduce's are gone now of course, but
> > >> mpe/jumpshot does not show MPIX_Iallreduce. Instead, where the
> > >> MPI_Allreduce used to be, now a lot of time is being spent in
> > >> MPI_Win_create and MPI_Win_free, where before the MPI_Allreduce was
> > >> taking place. Is this normal?
> > >>
> > >> Can I configure MPICH2 to use a progress thread for the nonblocking
> > >> collectives, as in libNBC?
> > >> Do I have to use MPI_Init_thread()?
> > >>
> > >> Pieter
> > >>
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