[Mpi3-hybridpm] Reminder for the hybrid telecon tomorrow

Mon Apr 22 11:42:05 CDT 2013

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

-- 
Jeff Squyres
jsquyres at cisco.com
For corporate legal information go to: http://www.cisco.com/web/about/doing_business/legal/cri/