Re: [Boost-users] mpi isend to group

Subject: Re: [Boost-users] mpi isend to group
From: Andreas Schäfer (gentryx_at_[hidden])
Date: 2012-12-29 17:32:38

Hi,

since you mention both, threads and MPI, I might add that the threading
support of most MPI implementations contains some caveats, to say the
least. It is certainly possible to emulate asynchronous collectives
either by isend/irecv (although that's really tough job given the
level of optimizations at hand in any major MPI implementation) or to
just use (possibly empty) synchronous broadcasts (as Riccardo
suggested). But to get a clearer picture I'd like to ask for some
details:

- Which MPI are you using?
- How many MPI processes do your jobs contain?
- Which threading level do you request via MPI_Thread_init()?
- How do you ensure asynchronous progress? (i.e.: mostly MPI will only
  send/receive data when some MPI function is being called. Unless
  e.g. MPI_Test is being polled or you MPI supports progress threads,
  the bulk of communication won't be carried out until you call MPI_Wait())

Cheers
-Andreas

 
On 15:15 Thu 27 Dec     , Philipp Kraus wrote:
> Hello,
> 
> I have got a problem to create a mpi::isend call. I have got a thread loop like:
> 
> while (thread_is_running)
> {
>       std::size_t id = 0;
>       if (!mpicom.rank())
>       {
>             try {
>                 id = getID();
>                 mpicom.isend(id)
>             } catch (...) { }
>      } else {
>         mpicom.ireceive(id);
>      }
>      
>     if (id > 0)
>     {
>            mpi::barrier();
>            do something with id
>     }
> 
>    boost::thread::yield();
> }
> 
> I would like to create a non-blocking communication over all nodes, so my node with rank 0
> checks if a dataset exists, if it exists, the id should be send to all other hosts. After all hosts
> reveived this id, they should start the calculation. The nodes must be synchronized before the
> "working part" is startet, but if there is no data send to the host, they should do nothing.
> 
> I don't know how to use isend to send a message to all hosts. I know only the mpi::any_source flag
> but I can not find an any_destination. IMHO the ireceive call must be written with iprobe like
> 
> if (boost::optional<mpi::status> l_status = mpicom.iprobe( 0, myTag ))
> {
> 	std::size_t id = 0;
>         mpicom.recv( l_status->source(), l_status->tag(), id )
> }
> 
> Is there a way to create a non-blocking group communication? How can I send if data exists, a message
> to all nodes and receive it on each node also with non-blocking communication?
> 
> Thanks for your help
> 
> Phil
> }
> 
> _______________________________________________
> Boost-users mailing list
> Boost-users_at_[hidden]
> http://lists.boost.org/mailman/listinfo.cgi/boost-users

-- 
==========================================================
Andreas Schäfer
HPC and Grid Computing
Chair of Computer Science 3
Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany
[phone]
PGP/GPG key via keyserver
http://www.libgeodecomp.org
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