[Mpi3-hybridpm] Reminder for the hybrid telecon tomorrow

Mon Apr 22 17:09:16 CDT 2013

Would we actually specify what "not being initialized" anymore means, except that users are no longer allowed to call MPI routines before they call MPI_Init again? If so, the impact on the implementation should be minimal, since it could just keep MPI "alive" under the hood.

Martin

On Apr 22, 2013, at 12:08 PM, Jim Dinan <dinan at mcs.anl.gov> wrote:

> 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
>>>> 
>>>> 
>>> _______________________________________________
>>> Mpi3-hybridpm mailing list
>>> Mpi3-hybridpm at lists.mpi-forum.org
>>> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi3-hybridpm
>> 
>> 
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________________________________________________________________________
Martin Schulz, schulzm at llnl.gov, http://people.llnl.gov/schulzm
CASC @ Lawrence Livermore National Laboratory, Livermore, USA