[mpi3-coll] [Mpi-forum] MPI_Comm_create_group Meeting

Bronis R. de Supinski bronis at llnl.gov
Wed Dec 7 21:00:11 CST 2011


I think it would be good to create a companion ticket to make
MPI_Intercomm_create use the tag space. We should get that
ticket ready now (I expect it is just a few lines of change)
so that it will be in MPI 3.0, assuming ticket 286 passes.

Anyway, please change:

"new intracommunicator, newcomm, whose communication group is defined by 
the group argument."


"new intracommunicator, newcomm, for which the group argument defines
the communication group."

Also, please change:

"to order calls and/or use different tag arguments"


"to order calls and/or to use differenttag arguments"


On Wed, 7 Dec 2011, Jim Dinan wrote:

> Hi All,
> I've updated the text with feedback from the last meeting, adding text
> to define a collective tag space.  Please take a look at the ticket286
> edits in the attached PDF and send any feedback.
> Also, I'd like to have another conference call early next week to
> discuss and get ready for a reading in January.  Please fill in your
> availability on the doodle poll:
> http://www.doodle.com/yx5b2f5f5hwc2qzq
> Thanks,
>  ~Jim.
> On 11/8/11 3:57 PM, James Dinan wrote:
>> 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.
>> Best,
>> ~Jim.
>> 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.
>> Tasks:
>> * Jim will work on a revision of the text that follows the above semantics.
>> * 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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