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

George Bosilca bosilca at [hidden]
Thu Jan 31 11:58:59 CST 2008 

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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