[Mpi-forum] MPI_Comm_create_group Meeting

James Dinan dinan at mcs.anl.gov
Tue Nov 8 15:57:47 CST 2011

Hi All,

Notes from yesterday's meeting are attached.  Please note that we are 
moving all future discussion of this ticket to the mpi3-coll mailing list.


In attendance:

Adam Moody, David Goodell, Jim Dinan, Pavan Balaji, Fab Tiller, Bronis 
de Supinski, Jeff Hammond

Item 1: Name of the routine.

We decided to stick with MPI_Comm_create group as the best way of 
matching the MPI_CLASS_ACTION_SUBSET naming convention.

Item 2: Tag versus color.

We decided to use a tag, which is defined to be in a collective tag 
space that is distinct from the point-to-point tag space.  The 
collective tag will follow all MPI tag semantics, however it will not 
conflict with any point-to-point tags (including MPI_ANY_TAG).  This 
essentially exposes the expected implementation in the standard, 
providing more flexible semantics to the user.  In addition, it allows 
an implementation to make more efficient use of the tag space by 
defining tag conflicts across tagged collective operations (currently 
only MPI_Intercomm_create and MPI_Comm_create_group, but we could define 
others in the future).

In a separate ticket, we can update MPI_Intercomm_create to specify that 
its tag is also in the collective tag space.  This will be backward 
compatible, but will make MPI_Intercomm_create considerably easier to 
use because its tags will no longer conflict with point-to-point operations.


  * Jim will work on a revision of the text that follows the above 

  * The group will reconvene after Thanksgiving to review new text.

  * The group will move discussion to the collectives mailing list.

On 11/4/11 11:07 AM, James Dinan wrote:
> Based on the doodle poll, it looks like Monday at 3pm CT will be the
> best time to meet. We'll use the hybrid WG telecon bridge:
> Domestic dial number: 866-654-6744
> International dial number: 517-308-8226
> Passcode: 6086006
> See you then,
> ~Jim.
> On 11/1/11 2:33 PM, James Dinan wrote:
>> Hi All,
>> I would like to form a group to review the MPI_Comm_create_group()
>> proposal (#286) for a formal reading at the next Forum meeting. If you
>> are interested in joining the discussion, could you please fill in your
>> availability for a one hour conference call next week:
>> http://www.doodle.com/9tganzq2hqiqy7kt
>> We have a couple issues to discuss:
>> 1.) The name of the function: MPI_Comm_create_group,
>> MPI_Group_comm_create, MPI_Comm_create_from_group, ...
>> 2.) The tag argument: Should we use a tag or a "color" to establish a
>> safe communication conduit on the parent communicator. As discussed at
>> the Forum, using a tag could conflict with the use of MPI_ANY_TAG on the
>> parent communicator. A color would avoid this issue, however it could
>> complicate tag matching.
>> 3.) Changes to the text.
>> Thanks,
>> ~Jim.
>> PS- I've attached a copy of the current text with comments from the
>> formal reading at the last Forum meeting (in Acrobat: Comments ->
>> Comments View -> Show Comments List for the full list).
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