[Mpi3-hybridpm] Reminder for the hybrid telecon tomorrow

Jim Dinan dinan at mcs.anl.gov
Fri Apr 19 14:06:51 CDT 2013


Another issue that ought to consider is that MPI currently can only be 
initialized/finalized once.  This requirement breaks the "MPI is a 
library" semantic and leads to some of the nastiness Jeff S. mentioned 
below.  I think we should re-evaluate if this restriction is really 
required, or if it's just convenient for implementers.

Another suggestion on this front -- Why not modify the semantics of 
MPI_Init to match what we want?

MPI_Init:

  - Always THREAD_MULTIPLE
  - Always a thread safe call
  - Ref-counted
  - Can be used to initialize/finalize MPI multiple times
  - Cannot be combined with MPI_Init_thread

If apps really care about getting rid of threading overhead, then they 
should use MPI_Init_thread() and use the thread level argument to give a 
performance hint.

  ~Jim.

On 4/19/13 1:11 PM, Jeff Squyres (jsquyres) wrote:
> Points to think about for the Monday teleconf...
>
> With regards to ref-counted MPI_INIT / MPI_FINALIZE (https://svn.mpi-forum.org/trac/mpi-forum-web/ticket/302):
>
> PROBLEMS IT SOLVES:
> - multiple, separate libraries in a single process needing access to MPI
>    ==> works best when all entities call MPI_INIT* at the beginning of time, work for a "long" period of time, and then call MPI_FINALIZE at the end of time (i.e., there's no race condition -- see below)
>
> PROBLEMS IT DOES NOT SOLVE:
> - Implementation not providing MPI_THREAD_MULTIPLE support (e.g., if the separate libraries are in different threads and someone already initialized MPI with THREAD_SINGLE, other threads can't know if it's safe to call MPI_INIT* or not)
> - The "finalize" problem (i.e., can't guarantee to know if MPI has been finalized or not -- there's a race between calling MPI_FINALIZED, seeing that MPI is not finalized, and then calling MPI_INIT)
>
> PROBLEMS IT CREATES:
> - Will need to change the definition of "main thread"
> - Possibly also need to change the definitions of MPI_THREAD_SERIALIZED and MPI_THREAD_FUNNELED
>
> OPEN QUESTIONS:
> - Do we still need to keep the restriction that the thread that initializes MPI is the same thread that finalizes MPI?
> - Should we allow re-initialization?  This effectively solves some (but not all) of the problems that have been discussed, but probably opens a new can of worms...
>
>
>
> On Apr 12, 2013, at 8:27 AM, Pavan Balaji <balaji at mcs.anl.gov> wrote:
>
>> All,
>>
>> Jim and I will be late for the April 22nd meeting.  So we decided to
>> move the endpoints discussion to the telecon after this one.
>>
>> I chatted with Jeff Squyres yesterday.  He'll be driving the April 22nd
>> telecon to discuss more details on the ref-counted init/finalize issue.
>> He'll be sending out some notes before the call for discussion.
>>
>> Thanks,
>>
>> -- Pavan
>>
>> On 04/08/2013 11:47 AM US Central Time, Pavan Balaji wrote:
>>>
>>> The next call will be on April 22nd, 11am central.  Same telecon number.
>>>
>>> -- Pavan
>>>
>>> On 04/08/2013 11:42 AM US Central Time, Jim Dinan wrote:
>>>> Meeting notes are on the wiki:
>>>>
>>>> https://svn.mpi-forum.org/trac/mpi-forum-web/wiki/MPI3Hybrid/notes-2013-04-08
>>>>
>>>>
>>>> ~Jim.
>>>>
>>>> On 4/7/13 12:45 PM, Pavan Balaji wrote:
>>>>> All,
>>>>>
>>>>> This is a reminder that we'll have our hybrid telecon tomorrow at 11am.
>>>>>   Here's the telecon information:
>>>>>
>>>>> International dial-in number: 1-719-234-7800
>>>>> Domestic dial-in number: 1-888-850-4523
>>>>> Participant Passcode: 314159
>>>>>
>>>>> The main item we'll be discussing is Jeff Squyres' ref-count proposal.
>>>>>
>>>>> https://svn.mpi-forum.org/trac/mpi-forum-web/ticket/302
>>>>>
>>>>>   -- Pavan
>>>>>
>>>> _______________________________________________
>>>> Mpi3-hybridpm mailing list
>>>> Mpi3-hybridpm at lists.mpi-forum.org
>>>> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi3-hybridpm
>>>
>>
>> --
>> Pavan Balaji
>> http://www.mcs.anl.gov/~balaji
>
>



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