July 2019 - mpi-forum - mailman3.cels.anl.gov

Re: [Mpi-forum] "BigCount" rendering in PDF
by Jed Brown 31 Jul '19

31 Jul '19

"Jeff Squyres \(jsquyres\) via mpi-forum" <mpi-forum(a)lists.mpi-forum.org> writes: > On Jul 31, 2019, at 12:59 PM, Jeff Hammond <jeff.science(a)gmail.com> wrote: >> >> “C++ compilers shall produce the same result as C11 generic.” Why does this need to say anything different for profiling and tools? Is this impossible? > > Is there a way to have C++ overloading call the same symbols that we'll dispatch to from C11 _Generic? (i.e., not-symbol-munged MPI_Send and MPI_Send_x) You have MPI_Send and MPI_Send_x declared extern "C", so why not: #ifdef __cplusplus static inline int MPI_Send(const void *buf, MPI_Count count, MPI_Datatype datatype, int dest, int tag, MPI_Comm comm) { return MPI_Send_x(buf, count, datatype, dest, tag, comm); } #endif When compiled with any optimization, this yields a direct call to MPI_Send_x. In any case, it doesn't add any mangled symbols to libmpi. Note that you can't have an overload of the extern "C" symbol MPI_Send taking "int count", but the extern "C" version works just fine for that. C++14 §7.5.5: If two declarations declare functions with the same name and parameter-type-list (8.3.5) to be members of the same namespace or declare objects with the same name to be members of the same namespace and the declarations give the names different language linkages, the program is ill-formed

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Re: [Mpi-forum] "BigCount" rendering in PDF
by Jeff Squyres (jsquyres) 31 Jul '19

31 Jul '19

On Jul 31, 2019, at 12:59 PM, Jeff Hammond <jeff.science(a)gmail.com> wrote: > > “C++ compilers shall produce the same result as C11 generic.” Why does this need to say anything different for profiling and tools? Is this impossible? Is there a way to have C++ overloading call the same symbols that we'll dispatch to from C11 _Generic? (i.e., not-symbol-munged MPI_Send and MPI_Send_x) If there's a way to do this, my objection will be greatly reduced (but still not zero). -- Jeff Squyres jsquyres(a)cisco.com

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Re: [Mpi-forum] "BigCount" rendering in PDF
by Joseph Schuchart 31 Jul '19

31 Jul '19

I agree with Jeff H that excluding C++ from the BigCount polymorphism seems unfortunate (and unintuitive for C++ developers). The _Generic selectors in C11 map a call to MPI_YYY() to either MPI_YYY(int) or MPI_YYY_x(MPI_Count). A C++ interface could do the same, with some macro work in the background, just using function overloading to select the right C99 call to make. There wouldn't be additional PMIPI calls to cover for tools and the amount of words required for C++ in the standard would be minimal. Joseph On 7/31/19 6:59 PM, Jeff Hammond via mpi-forum wrote: > > > >> On Jul 31, 2019, at 9:50 AM, Jeff Squyres (jsquyres) <jsquyres(a)cisco.com> wrote: >> >>> On Jul 31, 2019, at 12:14 PM, Jeff Hammond <jeff.science(a)gmail.com> wrote: >>> >>>> You're ignoring the long tail of consequences here -- what about PMPI/tools? What about other C++ features that we should be using, too? ...? >>> >>> No scope creep. No slippery slope. Do the one thing we need to go and stop. Leave the rest for MPI-5. >> >> So PMPI/tools are out of scope? >> > > “C++ compilers shall produce the same result as C11 generic.” Why does this need to say anything different for profiling and tools? Is this impossible? > >> Looking forward to your pull request. > > I won’t lose any sleep if we don’t get both C11 and C++ overloads. I’m just saying it shouldn’t be hard to get C++ if we do C11. > > Jeff > _______________________________________________ > mpi-forum mailing list > mpi-forum(a)lists.mpi-forum.org > https://lists.mpi-forum.org/mailman/listinfo/mpi-forum >

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Re: [Mpi-forum] "BigCount" rendering in PDF
by Jeff Hammond 31 Jul '19

31 Jul '19

> On Jul 31, 2019, at 9:50 AM, Jeff Squyres (jsquyres) <jsquyres(a)cisco.com> wrote: > >> On Jul 31, 2019, at 12:14 PM, Jeff Hammond <jeff.science(a)gmail.com> wrote: >> >>> You're ignoring the long tail of consequences here -- what about PMPI/tools? What about other C++ features that we should be using, too? ...? >> >> No scope creep. No slippery slope. Do the one thing we need to go and stop. Leave the rest for MPI-5. > > So PMPI/tools are out of scope? > “C++ compilers shall produce the same result as C11 generic.” Why does this need to say anything different for profiling and tools? Is this impossible? > Looking forward to your pull request. I won’t lose any sleep if we don’t get both C11 and C++ overloads. I’m just saying it shouldn’t be hard to get C++ if we do C11. Jeff

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Re: [Mpi-forum] "BigCount" rendering in PDF
by Jeff Squyres (jsquyres) 31 Jul '19

31 Jul '19

On Jul 31, 2019, at 12:14 PM, Jeff Hammond <jeff.science(a)gmail.com> wrote: > >> You're ignoring the long tail of consequences here -- what about PMPI/tools? What about other C++ features that we should be using, too? ...? > > No scope creep. No slippery slope. Do the one thing we need to go and stop. Leave the rest for MPI-5. So PMPI/tools are out of scope? Looking forward to your pull request. -- Jeff Squyres jsquyres(a)cisco.com

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Re: [Mpi-forum] "BigCount" rendering in PDF
by Jeff Hammond 31 Jul '19

31 Jul '19

> >> If you don’t say C++, there’s no reason OMPI and MPICH can’t do the obvious, trivial and intelligent thing. > > I guess I disagree with all three of those hyperbolic assertions. :-) > > You're ignoring the long tail of consequences here -- what about PMPI/tools? What about other C++ features that we should be using, too? ...? No scope creep. No slippery slope. Do the one thing we need to go and stop. Leave the rest for MPI-5. Jeff

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Re: [Mpi-forum] "BigCount" rendering in PDF
by Jeff Squyres (jsquyres) 31 Jul '19

31 Jul '19

On Jul 31, 2019, at 11:59 AM, Jeff Hammond <jeff.science(a)gmail.com> wrote: > > It’s a long email to read on my phone while on vacation. Then stop reading on your phone while on vacation and defer this until next week! ;-) > If you don’t say C++, there’s no reason OMPI and MPICH can’t do the obvious, trivial and intelligent thing. I guess I disagree with all three of those hyperbolic assertions. :-) You're ignoring the long tail of consequences here -- what about PMPI/tools? What about other C++ features that we should be using, too? ...? -- Jeff Squyres jsquyres(a)cisco.com

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Re: [Mpi-forum] "BigCount" rendering in PDF
by Jeff Hammond 31 Jul '19

31 Jul '19

It’s a long email to read on my phone while on vacation. You just need a sentence that says C++ compilers support C bindings, including the C11 generic stuff, just using a very different mechanism. Is that going to delay MPI-4? In any case, all the issues with polymorphism is exactly why it’s so important to have explicit symbols for C89/C99 usage so that implementations can add extensions that do the polymorphism stuff if it doesn’t get voted in. If you don’t say C++, there’s no reason OMPI and MPICH can’t do the obvious, trivial and intelligent thing. Jeff Sent from my iPhone > On Jul 31, 2019, at 8:03 AM, Jeff Squyres (jsquyres) <jsquyres(a)cisco.com> wrote: > >> On Jul 31, 2019, at 10:52 AM, Jeff Hammond <jeff.science(a)gmail.com> wrote: >> >> You’re going to have to mention C++. You can’t just pretend that C++ supports C11 generic, because it explicitly doesn’t. > > We are mentioning C++. Please re-read my prior email. > >> And you really should do this because it’s ridiculous not to use C++ polymorphism if we use C11’s. > > There are three options: > > 1. Re-introduce C++ bindings, delay MPI-4. > 2. Re-introduce C++ bindings, BigCount misses the MPI-4 train. > 4. Do not re-introduce C++ bindings, BigCount catches the MPI-4 train. > > The feedback from the Forum was that BigCount was a blocker/gating issue for MPI-4. Hence, this is why the BigCount WG is not planning at this time to re-introduce C++ bindings via BigCount. > > There is a longer term plan (think: MPI-5) to introduce a full-featured set of C++ bindings to MPI -- one that does not necessarily have a 1:1 correspondence to the C bindings. That is a different, much longer effort, and will definitely not make it into MPI-4. > > -- > Jeff Squyres > jsquyres(a)cisco.com >

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Re: [Mpi-forum] "BigCount" rendering in PDF
by HOLMES Daniel 31 Jul '19

31 Jul '19

Hi Jeff, To be clear, C++ currently calls/uses the C99 interface for MPI (unless it uses the no-long-standard but possibly-still-present-in-libraries C++ bindings). That will still be true after these BigCount changes: C++ will see only the C99 symbols, just like any other non-C11-compliant compiler. Polymorphism will not be supported in C++ because it cannot use C11 _Generic (because that is part of the C11 standard and is *not* part of the C++ standard). It also cannot use C++ overloading because are choosing not to define any new C++ bindings in the MPI-4.0 standard. If libraries choose to supply C++ overloads, they may do so but they are not going to be part of the MPI-4.0 standard (they will have the same status as the Java bindings offered by Open MPI). Cheers, Dan. — Dr Daniel Holmes PhD Architect (HPC Research) d.holmes(a)epcc.ed.ac.uk<mailto:[email protected]> Phone: +44 (0) 131 651 3465 Mobile: +44 (0) 7940 524 088 Address: Room 2.09, Bayes Centre, 47 Potterrow, Central Area, Edinburgh, EH8 9BT — The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336. — On 31 Jul 2019, at 16:03, Jeff Squyres (jsquyres) via mpi-forum <mpi-forum(a)lists.mpi-forum.org<mailto:[email protected]>> wrote: On Jul 31, 2019, at 10:52 AM, Jeff Hammond <jeff.science(a)gmail.com<mailto:[email protected]>> wrote: You’re going to have to mention C++. You can’t just pretend that C++ supports C11 generic, because it explicitly doesn’t. We are mentioning C++. Please re-read my prior email. And you really should do this because it’s ridiculous not to use C++ polymorphism if we use C11’s. There are three options: 1. Re-introduce C++ bindings, delay MPI-4. 2. Re-introduce C++ bindings, BigCount misses the MPI-4 train. 4. Do not re-introduce C++ bindings, BigCount catches the MPI-4 train. The feedback from the Forum was that BigCount was a blocker/gating issue for MPI-4. Hence, this is why the BigCount WG is not planning at this time to re-introduce C++ bindings via BigCount. There is a longer term plan (think: MPI-5) to introduce a full-featured set of C++ bindings to MPI -- one that does not necessarily have a 1:1 correspondence to the C bindings. That is a different, much longer effort, and will definitely not make it into MPI-4. -- Jeff Squyres jsquyres(a)cisco.com<mailto:[email protected]> _______________________________________________ mpi-forum mailing list mpi-forum(a)lists.mpi-forum.org https://lists.mpi-forum.org/mailman/listinfo/mpi-forum

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Re: [Mpi-forum] "BigCount" rendering in PDF
by Jeff Squyres (jsquyres) 31 Jul '19

31 Jul '19

On Jul 31, 2019, at 10:52 AM, Jeff Hammond <jeff.science(a)gmail.com> wrote: > > You’re going to have to mention C++. You can’t just pretend that C++ supports C11 generic, because it explicitly doesn’t. We are mentioning C++. Please re-read my prior email. > And you really should do this because it’s ridiculous not to use C++ polymorphism if we use C11’s. There are three options: 1. Re-introduce C++ bindings, delay MPI-4. 2. Re-introduce C++ bindings, BigCount misses the MPI-4 train. 4. Do not re-introduce C++ bindings, BigCount catches the MPI-4 train. The feedback from the Forum was that BigCount was a blocker/gating issue for MPI-4. Hence, this is why the BigCount WG is not planning at this time to re-introduce C++ bindings via BigCount. There is a longer term plan (think: MPI-5) to introduce a full-featured set of C++ bindings to MPI -- one that does not necessarily have a 1:1 correspondence to the C bindings. That is a different, much longer effort, and will definitely not make it into MPI-4. -- Jeff Squyres jsquyres(a)cisco.com

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