[mpi-21] Ballot 4 - MPI_THREAD_FUNNELED - was Re: Attending, topics, etc

Thu Jan 31 10:09:17 CST 2008

Sorry Rich,

but MPI 2.0 has defined "main thread", and not less!

The open question was only, who is responsible for guaranteing this.

Dicks text is fine:
>> MPI_THREAD_FUNNELED The process may be multi-threaded, but the application
>> must insure that only the main thread makes MPI calls.

My first proposal
>>>> > >   MPI_THREAD_FUNNELED The process may be multi-threaded, but only
>>>> > >   the main thread will make MPI calls (all MPI calls are "funneled"
>>>> > >   to the main thread, e.g., by using the OpenMP directive "master"
>>>> > >   in the application program).
has the advantage, that "main thread" is defined by refering to
the OpenMP-Standard where "OpenMP master thread" is defined (and not "main").

We can combine this to: 
  MPI_THREAD_FUNNELED The process may be multi-threaded, but the application
  must insure that only the main thread makes MPI calls, e.g., by using the
  OpenMP directive "master".

(This clearly tells that OpenMP single directive is not enough.)

Best regards
Rolf

On Thu, 31 Jan 2008 10:50:35 -0500
 Richard Graham <rlgraham_at_[hidden]> wrote:
>Why restrict this to a standard specified thread (main thread), why not word
>it
> as a singe thread, and let the app decide what thread this is, based on
>what
> ever criteria it wants to use to select this thread ?
>
>Rich
>
>
>On 1/31/08 10:27 AM, "Richard Treumann" <treumann_at_[hidden]> wrote:
>
>> How about::
>> MPI_THREAD_FUNNELED The process may be multi-threaded, but the application
>> must insure that only the main thread makes MPI calls.
>> 
>> 
>> Dick Treumann  -  MPI Team/TCEM
>> IBM Systems & Technology Group
>> Dept 0lva / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601
>> Tele (845) 433-7846         Fax (845) 433-8363
>> 
>> 
>> mpi-21-bounces_at_[hidden] wrote on 01/31/2008 09:44:08 AM:
>> 
>>> > A simpler change which would seem to achieve the desired clarification
>>> > would be :- 
>>> > 
>>> >    MPI_THREAD_FUNNELED The process may be multi-threaded, but only the
>>> > main          
>>> >    thread is allowed to make MPI calls.
>>> > 
>>> > (and you could add
>>> >    If other threads make MPI calls the behavior is undefined.
>>> >  if you want to be verbose about it).
>>> > 
>>> > -- Jim
>>> > 
>>> > James Cownie <james.h.cownie_at_[hidden]>
>>> > SSG/DPD/PAT
>>> > Tel: +44 117 9071438
>>> > 
>>> > 
>>> > 
>>> > 
>>>> > > -----Original Message-----
>>>> > > From: mpi-21-bounces_at_[hidden] [mailto:mpi-21-bounces_at_[hidden]]
>>> > On
>>>> > > Behalf Of Rolf Rabenseifner
>>>> > > Sent: 31 January 2008 14:31
>>>> > > To: mpi-21_at_[hidden]
>>>> > > Subject: [mpi-21] Ballot 4 - MPI_THREAD_FUNNELED - was Re: Attending,
>>>> > > topics, etc
>>>> > > 
>>>> > > This is a proposal for MPI 2.1, Ballot 4.
>>>> > > 
>>>> > > I'm asking especially
>>>> > >   Greg Lindahl,
>>>> > > the participants of the email-discussion in 2007, to review this
>>> > proposal.
>>>> > > 
>>>> > > This is a follow up to:
>>>> > >   Which thread is the funneled thread?
>>>> > >   in http://www.cs.uiuc.edu/homes/wgropp/projects/parallel/MPI/mpi-
>>>> > > errata/index.html
>>>> > > with mail discussion in
>>>> > >   http://www.cs.uiuc.edu/homes/wgropp/projects/parallel/MPI/mpi-
>>>> > > errata/discuss/funneled/
>>>> > > ___________________________________
>>>> > > 
>>>> > > Proposal:
>>>> > > MPI-2.0 Sect. 8.7.3, MPI_Init_thread, page 196, lines 25-26 read:
>>>> > > 
>>>> > >   MPI_THREAD_FUNNELED The process may be multi-threaded, but only
>>>> > >   the main thread will make MPI calls (all MPI calls are "funneled"
>>>> > >   to the main thread).
>>>> > > 
>>>> > > but should read:
>>>> > > 
>>>> > >   MPI_THREAD_FUNNELED The process may be multi-threaded, but only
>>>> > >   the main thread will make MPI calls (all MPI calls are "funneled"
>>>> > >   to the main thread, e.g., by using the OpenMP directive "master"
>>>> > >   in the application program).
>>>> > > ___________________________________
>>>> > > Rationale for this clarification from the email from Greg Lindahl:
>>>> > >   The existing document doesn't make it clear that
>>>> > >   the MPI user has to funnel the calls to the main thread;
>>>> > >   it's not the job of the MPI library. I have seen multiple
>>>> > >   MPI users confused by this issue, and when I first read
>>>> > >   this section, I was confused by it, too.
>>>> > > ___________________________________
>>>> > > 
>>>> > > 
>>>> > > Best regards
>>>> > > Rolf
>>>> > > 
>>>> > > 
>>>> > > 
>>>> > > 
>>>> > > Dr. Rolf Rabenseifner . . . . . . . . . .. email rabenseifner_at_[hidden]
>>>> > > High Performance Computing Center (HLRS) . phone ++49(0)711/685-65530
>>>> > > University of Stuttgart . . . . . . . . .. fax ++49(0)711 / 685-65832
>>>> > > Head of Dpmt Parallel Computing . . . www.hlrs.de/people/rabenseifner
>>>> > > Nobelstr. 19, D-70550 Stuttgart, Germany . (Office: Allmandring 30)
>>>> > > _______________________________________________
>>>> > > mpi-21 mailing list
>>>> > > mpi-21_at_[hidden]
>>>> > > http://lists.cs.uiuc.edu/mailman/listinfo/mpi-21
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>> 
>> 
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>

Dr. Rolf Rabenseifner . . . . . . . . . .. email rabenseifner_at_[hidden]
High Performance Computing Center (HLRS) . phone ++49(0)711/685-65530
University of Stuttgart . . . . . . . . .. fax ++49(0)711 / 685-65832
Head of Dpmt Parallel Computing . . . www.hlrs.de/people/rabenseifner
Nobelstr. 19, D-70550 Stuttgart, Germany . (Office: Allmandring 30)