From jedwards at ucar.edu Thu Dec 8 16:31:35 2022 From: jedwards at ucar.edu (Jim Edwards) Date: Thu, 8 Dec 2022 15:31:35 -0700 Subject: [Mpi-comments] Use of MPI_DATATYPE_NULL Message-ID: There seems to be some ambiguity in the standard with respect to usage of the MPI_DATATYPE_NULL variable. It would seem to me that if an MPI routine such as MPI_Send or MPI_ALLTOALLW has a data count argument of 0 then MPI_DATATYPE_NULL should be an acceptable value for the datatype. Here is a discussion from several years ago with openmpi developers. It references a discussion in the standards forum but I can no longer find it. http://lists.mpi-forum.org/mpi-forum/2016/01/3152.php Would it be possibly to clarify this case in the next iteration of the standard? -- Jim Edwards CESM Software Engineer National Center for Atmospheric Research Boulder, CO -------------- next part -------------- An HTML attachment was scrubbed... URL: From bosilca at icl.utk.edu Thu Dec 8 16:38:40 2022 From: bosilca at icl.utk.edu (George Bosilca) Date: Thu, 8 Dec 2022 17:38:40 -0500 Subject: [Mpi-comments] Use of MPI_DATATYPE_NULL In-Reply-To: References: Message-ID: You are correct. The MPI_DATATYPE_NULL is an acceptable datatype for cases where the target processor sends or receives no data. The standard uses MPI_DATATYPE_NULL in 2 instances (in example 5.23) to highlight no data movement, but fails to make a clear reference to the fact that this is an acceptable use. George. On Thu, Dec 8, 2022 at 5:31 PM Jim Edwards via mpi-comments < mpi-comments at lists.mpi-forum.org> wrote: > There seems to be some ambiguity in the standard with respect to usage of > the MPI_DATATYPE_NULL variable. > It would seem to me that if an MPI routine such as MPI_Send or > MPI_ALLTOALLW has a data count argument of 0 > then MPI_DATATYPE_NULL should be an acceptable value for the datatype. > Here is a discussion from several years > ago with openmpi developers. It references a discussion in the standards > forum but I can no longer find it. > > http://lists.mpi-forum.org/mpi-forum/2016/01/3152.php > > Would it be possibly to clarify this case in the next iteration of the > standard? > > > -- > Jim Edwards > > CESM Software Engineer > National Center for Atmospheric Research > Boulder, CO > _______________________________________________ > mpi-comments mailing list > mpi-comments at lists.mpi-forum.org > https://lists.mpi-forum.org/mailman/listinfo/mpi-comments > -------------- next part -------------- An HTML attachment was scrubbed... URL: From gilles at rist.or.jp Thu Dec 8 17:56:42 2022 From: gilles at rist.or.jp (gilles at rist.or.jp) Date: Fri, 09 Dec 2022 08:56:42 +0900 Subject: [Mpi-comments] Use of MPI_DATATYPE_NULL In-Reply-To: References: Message-ID: <20221208235642.00003162.0113@rist.or.jp> I have a different recollection. The link is broken, here is one that works for me https://lists.mpi-forum.org/pipermail/mpi-forum/2016-January/003152.html TL;DR from Bill Gropp: "The standard says that the null handles are invalid for input unless explicitly permitted. There?s no exemption for a datatype argument where the associated count is zero." IIRC there was no objection to updating the standard in order to allow this, but unless this has been completed, I am afraid MPI_DATATYPE_NULL is not a valid datatype here Gilles ----- Original Message ----- You are correct. The MPI_DATATYPE_NULL is an acceptable datatype for cases where the target processor sends or receives no data. The standard uses MPI_DATATYPE_NULL in 2 instances (in example 5.23) to highlight no data movement, but fails to make a clear reference to the fact that this is an acceptable use. George. On Thu, Dec 8, 2022 at 5:31 PM Jim Edwards via mpi-comments wrote: There seems to be some ambiguity in the standard with respect to usage of the MPI_DATATYPE_NULL variable. It would seem to me that if an MPI routine such as MPI_Send or MPI_ ALLTOALLW has a data count argument of 0 then MPI_DATATYPE_NULL should be an acceptable value for the datatype. Here is a discussion from several years ago with openmpi developers. It references a discussion in the standards forum but I can no longer find it. http://lists.mpi-forum.org/mpi-forum/2016/01/3152.php Would it be possibly to clarify this case in the next iteration of the standard? -- Jim Edwards CESM Software Engineer National Center for Atmospheric Research Boulder, CO _______________________________________________ mpi-comments mailing list mpi-comments at lists.mpi-forum.org https://lists.mpi-forum.org/mailman/listinfo/mpi-comments -------------- next part -------------- An HTML attachment was scrubbed... URL: From jedwards at ucar.edu Thu Dec 8 18:03:31 2022 From: jedwards at ucar.edu (Jim Edwards) Date: Thu, 8 Dec 2022 17:03:31 -0700 Subject: [Mpi-comments] Use of MPI_DATATYPE_NULL In-Reply-To: <20221208235642.00003162.0113@rist.or.jp> References: <20221208235642.00003162.0113@rist.or.jp> Message-ID: Right, so how do I formally request that the standard be updated to clarify this issue? On Thu, Dec 8, 2022 at 4:56 PM gilles--- via mpi-comments < mpi-comments at lists.mpi-forum.org> wrote: > I have a different recollection. > > > > The link is broken, here is one that works for me > > https://lists.mpi-forum.org/pipermail/mpi-forum/2016-January/003152.html > > TL;DR from Bill Gropp: > > "The standard says that the null handles are invalid for input unless explicitly permitted. There?s no exemption for a datatype argument where the associated count is zero." > > > > IIRC there was no objection to updating the standard in order to allow > this, but unless this has been completed, I am afraid MPI_DATATYPE_NULL is > not a valid datatype here > > > > Gilles > > ----- Original Message ----- > > You are correct. The MPI_DATATYPE_NULL is an acceptable datatype for cases > where the target processor sends or receives no data. The standard > uses MPI_DATATYPE_NULL in 2 instances (in example 5.23) to highlight no > data movement, but fails to make a clear reference to the fact that this is > an acceptable use. > > George. > > On Thu, Dec 8, 2022 at 5:31 PM Jim Edwards via mpi-comments < > mpi-comments at lists.mpi-forum.org> wrote: > >> There seems to be some ambiguity in the standard with respect to usage of >> the MPI_DATATYPE_NULL variable. >> It would seem to me that if an MPI routine such as MPI_Send or >> MPI_ALLTOALLW has a data count argument of 0 >> then MPI_DATATYPE_NULL should be an acceptable value for the datatype. >> Here is a discussion from several years >> ago with openmpi developers. It references a discussion in the standards >> forum but I can no longer find it. >> >> http://lists.mpi-forum.org/mpi-forum/2016/01/3152.php >> >> Would it be possibly to clarify this case in the next iteration of the >> standard? >> >> -- >> Jim Edwards >> >> CESM Software Engineer >> National Center for Atmospheric Research >> Boulder, CO >> _______________________________________________ >> mpi-comments mailing list >> mpi-comments at lists.mpi-forum.org >> https://lists.mpi-forum.org/mailman/listinfo/mpi-comments > > > _______________________________________________ > mpi-comments mailing list > mpi-comments at lists.mpi-forum.org > https://lists.mpi-forum.org/mailman/listinfo/mpi-comments > -- Jim Edwards CESM Software Engineer National Center for Atmospheric Research Boulder, CO -------------- next part -------------- An HTML attachment was scrubbed... URL: From bosilca at icl.utk.edu Thu Dec 8 18:52:04 2022 From: bosilca at icl.utk.edu (George Bosilca) Date: Thu, 8 Dec 2022 19:52:04 -0500 Subject: [Mpi-comments] Use of MPI_DATATYPE_NULL In-Reply-To: References: <20221208235642.00003162.0113@rist.or.jp> Message-ID: Thanks Gilles for pointing this discussion out. It appears that the use of the MPI_DATATYPE_NULL in the example 5.23 is correct, the standard clearly mentions the receiver datatype is only significant at the root. George. On Thu, Dec 8, 2022 at 7:03 PM Jim Edwards via mpi-comments < mpi-comments at lists.mpi-forum.org> wrote: > Right, so how do I formally request that the standard be updated to > clarify this issue? > > On Thu, Dec 8, 2022 at 4:56 PM gilles--- via mpi-comments < > mpi-comments at lists.mpi-forum.org> wrote: > >> I have a different recollection. >> >> >> >> The link is broken, here is one that works for me >> >> https://lists.mpi-forum.org/pipermail/mpi-forum/2016-January/003152.html >> >> TL;DR from Bill Gropp: >> >> "The standard says that the null handles are invalid for input unless explicitly permitted. There?s no exemption for a datatype argument where the associated count is zero." >> >> >> >> IIRC there was no objection to updating the standard in order to allow >> this, but unless this has been completed, I am afraid MPI_DATATYPE_NULL is >> not a valid datatype here >> >> >> >> Gilles >> >> ----- Original Message ----- >> >> You are correct. The MPI_DATATYPE_NULL is an acceptable datatype for >> cases where the target processor sends or receives no data. The standard >> uses MPI_DATATYPE_NULL in 2 instances (in example 5.23) to highlight no >> data movement, but fails to make a clear reference to the fact that this is >> an acceptable use. >> >> George. >> >> On Thu, Dec 8, 2022 at 5:31 PM Jim Edwards via mpi-comments < >> mpi-comments at lists.mpi-forum.org> wrote: >> >>> There seems to be some ambiguity in the standard with respect to usage >>> of the MPI_DATATYPE_NULL variable. >>> It would seem to me that if an MPI routine such as MPI_Send or >>> MPI_ALLTOALLW has a data count argument of 0 >>> then MPI_DATATYPE_NULL should be an acceptable value for the datatype. >>> Here is a discussion from several years >>> ago with openmpi developers. It references a discussion in the >>> standards forum but I can no longer find it. >>> >>> http://lists.mpi-forum.org/mpi-forum/2016/01/3152.php >>> >>> Would it be possibly to clarify this case in the next iteration of the >>> standard? >>> >>> -- >>> Jim Edwards >>> >>> CESM Software Engineer >>> National Center for Atmospheric Research >>> Boulder, CO >>> _______________________________________________ >>> mpi-comments mailing list >>> mpi-comments at lists.mpi-forum.org >>> https://lists.mpi-forum.org/mailman/listinfo/mpi-comments >> >> >> _______________________________________________ >> mpi-comments mailing list >> mpi-comments at lists.mpi-forum.org >> https://lists.mpi-forum.org/mailman/listinfo/mpi-comments >> > > > -- > Jim Edwards > > CESM Software Engineer > National Center for Atmospheric Research > Boulder, CO > _______________________________________________ > mpi-comments mailing list > mpi-comments at lists.mpi-forum.org > https://lists.mpi-forum.org/mailman/listinfo/mpi-comments > -------------- next part -------------- An HTML attachment was scrubbed... URL: