Hi Persistence WG members,

We have a suggested change to the wording of the MPI Standard text that we will propose to the MPI Forum next week regarding persistent collective operations.

Once initialized,
persistent collective operations can be started in any order
independently of initialization order
+and the order can differ among ranks in the communicator

Most of this sentence already appears in our proposed text - the suggestion is to add the line beginning with “+”.

I think this is a good suggestion - we should make this point absolutely clear. We should word-smith the exact phrase (e.g. during the meeting later today?) and then include it in our formal reading next week by holding a “no-no” vote.

Cheers,
Dan.

Begin forwarded message:

From: KAWASHIMA Takahiro <notifications@github.com>
Subject: Re: [mpi-forum/mpi-standard] Persistent collectives 2017 (#29)
Date: 29 November 2017 at 06:09:20 GMT
To: mpi-forum/mpi-standard <mpi-standard@noreply.github.com>
Cc: Dan Holmes <dholmes@epcc.ed.ac.uk>, Mention <mention@noreply.github.com>
Reply-To: mpi-forum/mpi-standard <reply+00c7fc4ac57b95d8d1ec9f0842808776a6bf83a41aa2b15e92cf000000011636110f92a169ce0dd58755@reply.github.com>

@dholmes-epcc-ed-ac-uk,
With the existing text, I think many people can understand that it is saying (at least) "requests can be started using MPI_START or MPI_STARTALL in any order independently of initialization order", because of analogy to the point-to-point communication. So I think your suggested text is unnecessary.
But some people may not understand that it is also saying "the order of starting requests can differ among ranks in the communicator", because (1) the matching rule for persistent collective operations is different from the matching rule for point-to-point communication so that analogy to the point-to-point communication is not applied and (2) the order of nonblocking collective calls must be same among ranks in the communicator.

How about the sentence below? I'm not good at English. Please correct it if it is not good.

Once initialized,
persistent collective operations can be started in any order
independently of initialization order
and the order can differ among ranks in the communicator

If anyone else thinks the existing text is sufficient, I won't request the change. Probably my English reading skill is low.

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