[Mpi3-hybridpm] Reminder for the hybrid telecon tomorrow

[Jim Dinan]

I think the new semantics for MPI_Init() would be backward compatible, 
but we could also add a new routine: MPI_Init_awesome().  :)

On 4/22/13 11:42 AM, Jeff Squyres (jsquyres) wrote:
> Sayantan and I talked about this on the phone today.  It seems like re-initialization might be a good idea, but a good first step might be asking all the hardware/software vendors if there's a technical reason they don't allow re-initialzation today (other than "because it's not required by MPI").  I.e., I think that some API's/networks (like PSM) don't allow re-initialization -- is there a technical reason for that, or is it just an overcome-able software limitation?
>
> I'm not a big fan of re-defining the default behavior of MPI_INIT, however -- I think there might be a big impact on legacy applications.
>
>
>
> On Apr 19, 2013, at 3:06 PM, Jim Dinan <dinan at mcs.anl.gov> wrote:
>
>> 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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>
>