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

Thu Jan 31 13:13:17 CST 2008

See MPI_IS_THREAD_MAIN on page 198.  The definition of "main thread" is
there.  Maybepage 198 is not the best place for a definition of a term that
is used on page 196 but the standard does provide one.

I am reluctant to mention OpenMP in the context of defining
MPI_THREAD_FUNNELED because then we would need to discuss other ways an
application could become multi threaded too.

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 12:58:59 PM:

> What is the definition of a "main thread" ? The OpenMP example is
> still vague.
>
> I think we should clarify what we expect the "main thread" to be. From
> my perspective, this "main thread" is the one that called the
> MPI_Init_thread function, as the MPI library is then allowed to attach
> some kind of private key(s) to it (pthread_key_create).
>
>    Thanks,
>      george.
>
> On Jan 31, 2008, at 11:09 AM, Rolf Rabenseifner wrote:
>
> > 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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> >>
> >
> >
> >
> > 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)
> > _______________________________________________
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> Treumann/Poughkeepsie/IBM]
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