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Re: [mpiwg-abi] MPI_Fint in the ABI
by Jeff Hammond 18 Aug '23

18 Aug '23

I just realized that option 3 doesn’t work for MPI_Status f2c/c2f, so it must be rejected. We have to choose 1 or 2. We are building an ABI to allow people to write libraries that just work with all of the implementations. This includes enabling programmers to write C libraries that interoperate with arbitrary MPI Fortran code. This code needs a way to know what MPI_Fint is without interacting with the Fortran environment. That is why we need to either prescribe the value of MPI_Fint or make it queryable from C code using MPI features. As far as ABI information, the proposal includes the following: int MPI_Abi_supported(int *flag) Int MPI_Abi_version(int *major, int *minor) int MPI_Abi_sizes(int *aint_size, int *offset_size, int *count_size, int *fint_size) int MPI_Abi_details(int *buflen, char *details) My intent with MPI_Abi_details was to allow implementations to disclose their non-standard ABI info there when flag=false. I’m happy to add an MPI_Info there if people prefer that method of including data. The struct design you propose isn’t really the MPI Way (TM). I’m not personally opposed but we don’t have a nice way to expose that in Fortran. I do not understand the need for MPIABI_info_t. We have MPI_TYPE_SIZE to query what the size of the MPI types arrow, which is what one needs to know when interacting with the ABI. Can you describe the use case where non-C code needs to know the size of a C long double, for example? If Julia is going to pass long double data into MPI, what matters if MPI_LONG_DOUBLE. Jeff > On 17. Aug 2023, at 17.35, Erik Schnetter <schnetter(a)gmail.com> wrote: > > Jeff > > As per the Fortran standard, the sizes of integer and real need to be > the same. In practice this means that integers have 4 bytes. If > someone chooses to change this – either changing the size of real as > well or not – then they are breaking the Fortran standard, and > probably know what they are doing, and are aware of the various > incompatibilities and problems this will introduce. I would thus > suggest keeping things simple for the common case. I would not expect > there to be some code that interoperates with Fortran, and which is > unaware of the Fortran integer size and still expects to get things > right. People will either assume that integer = int, or will know the > Fortran ABI details. > > In the MPI ABI we assume that the caller knows sizeof(int) and > sizeof(void*), and I would also assume that they know sizeof(integer). > I would keep `MPI_Fint` a fixed type. > > To cover all bases I also suggest that we provide a global constant > struct with as much ABI information as we can think of, such as > > const struct MPIABI_info_t { > int32_t MPIABI_version_major, MPIABI_version_minor; > int32_t sizeof_bool; > int32_t sizeof_char; > int32_t sizeof_short; > int32_t sizeof_int; > int32_t sizeof_long; > int32_t sizeof_long_long; > int32_t sizeof_float; > int32_t sizeof_double; > int32_t sizeof_long_double; > int32_t sizeof_void_p; > int32_t sizeof_logical; > int32_t sizeof_integer; > int32_t sizeof_real; > int32_t sizeof_char; > } MPIABI_info; > > This information would not be necessary to use the ABI, but it will be > convenient to check assumptions. Unsupported types report a size of > -1. > > This struct can be extended in the future. > > -erik > > On Wed, Aug 16, 2023 at 4:09 AM Jeff Hammond <jeff.science(a)gmail.com> wrote: >> >> As we all know, Fortran users are permitted to change the size of INTEGER with compiler flags. This creates a problem for the MPI C ABI. >> >> I have considered three options and would like your opinions on them: >> >> 1. MPI_Fint is defined to be a C int in the standard ABI. This means MPI implementations that elect to provide an ILP64 MPI Fortran ABI on an I32LP64 system, for example, must not call this an implementation of the standard ABI. >> >> This would make a lot of things easier, but it might cause problems in the rare cases where users are using ILP64 in Fortran and using C code that actually uses MPI_Fint. >> >> 2. MPI_Fint ceases to be a compile-time fixed type in the standard ABI. The C code that uses MPI_Fint must make an MPI library call to figure out the size and do all of the necessary things to call the correct size. >> >> 3. MPI_Fint is not a fixed size but the standard ABI specifies that Fortran handle values must always fit into the range of a C int and we rely on the pass-by-value behavior of all the f2c/c2f APIs to behave properly when they are truncated. >> >> This is my preference but it breaks Example 19.11 in a serious way, because that user code makes use of a MPI_Fint pointer. However, this code isn't standard-compliant and relies on universal but non-standard argument passing conventions in Fortran. Writing a standard-compliant interface from Fortran to C - by doing the cast to INTEGER(kind=c_int) in Fortran - would resolve this. >> >> Example 19.11 is awful (https://github.com/mpi-forum/mpi-issues/issues/739) but it is nonetheless important to instruct users that if Option 3 is implemented, they need to do the casting to INTEGER(kind=c_int) and know that this is safe with the standard ABI. >> >> >> None of these options is perfect. I'm not sure how much code is even impacted by MPI_Fint so it's hard to know which option breaks the most stuff, although Option 2 seems the least desirable in any case. >> >> Thanks, >> >> Jeff >> >> -- >> Jeff Hammond >> jeff.science(a)gmail.com >> http://jeffhammond.github.io/ >> -- >> mpiwg-abi mailing list >> mpiwg-abi(a)lists.mpi-forum.org >> https://lists.mpi-forum.org/mailman/listinfo/mpiwg-abi > > > > -- > Erik Schnetter <schnetter(a)gmail.com> > http://www.perimeterinstitute.ca/personal/eschnetter/

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Re: [mpiwg-abi] MPI_Fint in the ABI
by William Robert Williams 18 Aug '23

18 Aug '23

Is there a reason not to mix 1 and 3: MPI_Fint is a fixed C type, decouple it from INTEGER, and require Fortran handles to stay within the smaller of INTEGER and MPI_Fint in order to be valid? (Yes, backwards compatibility, but that’s probably gone regardless in order to ABI-specify MPI_Fint.) This way an implementation can have larger or smaller INTEGERs vs. C ints as it desires, as long as it guarantees that they are valid MPI_Fints as well, and Fint stays fixed. 19.3.4 will need revision no matter what we decide. —Bill > On 18. Aug 2023, at 11:35, Jeff Hammond <jeff.science(a)gmail.com> wrote: > > MPI_Fint is part of the C ABI. It is strictly used in MPI C code to allow conversion of Fortran handles to C handles and vice versa. It must be part of the C ABI for the f2c/c2f functions to be part of the C ABI. > > For example, from 19.3.4: > > C binding > MPI_Comm MPI_Comm_f2c(MPI_Fint comm) > MPI_Fint MPI_Comm_c2f(MPI_Comm comm) > > MPI_Fint is not part of the Fortran API or ABI, because Fortran handles are defined to be INTEGER (or an INTEGER inside of a type(MPI_Handle) object). > > Jeff > >> On 17. Aug 2023, at 17.52, Zhou, Hui <zhouh(a)anl.gov> wrote: >> >> I haven't gone through all the use cases, but my current opinion is, it is really a Fortran binding issue and should be left out of C ABI. >> >> Hui >> >> From: mpiwg-abi <mpiwg-abi-bounces(a)lists.mpi-forum.org <mailto:[email protected]>> on behalf of Erik Schnetter <schnetter(a)gmail.com <mailto:[email protected]>> >> Sent: Thursday, August 17, 2023 9:35 AM >> To: Jeff Hammond <jeff.science(a)gmail.com <mailto:[email protected]>> >> Cc: mpiwg-abi <mpiwg-abi(a)lists.mpi-forum.org <mailto:[email protected]>>; MPI Forum <mpiwg-fortran(a)lists.mpi-forum.org <mailto:[email protected]>> >> Subject: Re: [mpiwg-abi] MPI_Fint in the ABI >> >> Jeff >> >> As per the Fortran standard, the sizes of integer and real need to be >> the same. In practice this means that integers have 4 bytes. If >> someone chooses to change this – either changing the size of real as >> well or not – then they are breaking the Fortran standard, and >> probably know what they are doing, and are aware of the various >> incompatibilities and problems this will introduce. I would thus >> suggest keeping things simple for the common case. I would not expect >> there to be some code that interoperates with Fortran, and which is >> unaware of the Fortran integer size and still expects to get things >> right. People will either assume that integer = int, or will know the >> Fortran ABI details. >> >> In the MPI ABI we assume that the caller knows sizeof(int) and >> sizeof(void*), and I would also assume that they know sizeof(integer). >> I would keep `MPI_Fint` a fixed type. >> >> To cover all bases I also suggest that we provide a global constant >> struct with as much ABI information as we can think of, such as >> >> const struct MPIABI_info_t { >> int32_t MPIABI_version_major, MPIABI_version_minor; >> int32_t sizeof_bool; >> int32_t sizeof_char; >> int32_t sizeof_short; >> int32_t sizeof_int; >> int32_t sizeof_long; >> int32_t sizeof_long_long; >> int32_t sizeof_float; >> int32_t sizeof_double; >> int32_t sizeof_long_double; >> int32_t sizeof_void_p; >> int32_t sizeof_logical; >> int32_t sizeof_integer; >> int32_t sizeof_real; >> int32_t sizeof_char; >> } MPIABI_info; >> >> This information would not be necessary to use the ABI, but it will be >> convenient to check assumptions. Unsupported types report a size of >> -1. >> >> This struct can be extended in the future. >> >> -erik >> >> On Wed, Aug 16, 2023 at 4:09 AM Jeff Hammond <jeff.science(a)gmail.com <mailto:[email protected]>> wrote: >> > >> > As we all know, Fortran users are permitted to change the size of INTEGER with compiler flags. This creates a problem for the MPI C ABI. >> > >> > I have considered three options and would like your opinions on them: >> > >> > 1. MPI_Fint is defined to be a C int in the standard ABI. This means MPI implementations that elect to provide an ILP64 MPI Fortran ABI on an I32LP64 system, for example, must not call this an implementation of the standard ABI. >> > >> > This would make a lot of things easier, but it might cause problems in the rare cases where users are using ILP64 in Fortran and using C code that actually uses MPI_Fint. >> > >> > 2. MPI_Fint ceases to be a compile-time fixed type in the standard ABI. The C code that uses MPI_Fint must make an MPI library call to figure out the size and do all of the necessary things to call the correct size. >> > >> > 3. MPI_Fint is not a fixed size but the standard ABI specifies that Fortran handle values must always fit into the range of a C int and we rely on the pass-by-value behavior of all the f2c/c2f APIs to behave properly when they are truncated. >> > >> > This is my preference but it breaks Example 19.11 in a serious way, because that user code makes use of a MPI_Fint pointer. However, this code isn't standard-compliant and relies on universal but non-standard argument passing conventions in Fortran. Writing a standard-compliant interface from Fortran to C - by doing the cast to INTEGER(kind=c_int) in Fortran - would resolve this. >> > >> > Example 19.11 is awful (https://github.com/mpi-forum/mpi-issues/issues/739 <https://github.com/mpi-forum/mpi-issues/issues/739>) but it is nonetheless important to instruct users that if Option 3 is implemented, they need to do the casting to INTEGER(kind=c_int) and know that this is safe with the standard ABI. >> > >> > >> > None of these options is perfect. I'm not sure how much code is even impacted by MPI_Fint so it's hard to know which option breaks the most stuff, although Option 2 seems the least desirable in any case. >> > >> > Thanks, >> > >> > Jeff >> > >> > -- >> > Jeff Hammond >> > jeff.science(a)gmail.com <mailto:[email protected]> >> > http://jeffhammond.github.io/ <http://jeffhammond.github.io/> >> > -- >> > mpiwg-abi mailing list >> > mpiwg-abi(a)lists.mpi-forum.org <mailto:[email protected]> >> > https://lists.mpi-forum.org/mailman/listinfo/mpiwg-abi <https://lists.mpi-forum.org/mailman/listinfo/mpiwg-abi> >> >> >> >> -- >> Erik Schnetter <schnetter(a)gmail.com <mailto:[email protected]>> >> http://www.perimeterinstitute.ca/personal/eschnetter/ <http://www.perimeterinstitute.ca/personal/eschnetter/> >> -- >> mpiwg-abi mailing list >> mpiwg-abi(a)lists.mpi-forum.org <mailto:[email protected]> >> https://lists.mpi-forum.org/mailman/listinfo/mpiwg-abi <https://lists.mpi-forum.org/mailman/listinfo/mpiwg-abi> > -- > mpiwg-abi mailing list > mpiwg-abi(a)lists.mpi-forum.org > https://lists.mpi-forum.org/mailman/listinfo/mpiwg-abi -- Bill Williams Wiss. Mitarbeiter ZIH-IAK, TU-Dresden Falkenbrunnen, Room 009 Chemnitzer Straße 50 01187 Dresden Phone: +49 351 463-39976 e-mail: william.williams(a)tu-dresden.de He/him/his

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Re: [mpiwg-abi] MPI_Fint in the ABI
by Jeff Hammond 18 Aug '23

18 Aug '23

MPI_Fint is part of the C ABI. It is strictly used in MPI C code to allow conversion of Fortran handles to C handles and vice versa. It must be part of the C ABI for the f2c/c2f functions to be part of the C ABI. For example, from 19.3.4: C binding MPI_Comm MPI_Comm_f2c(MPI_Fint comm) MPI_Fint MPI_Comm_c2f(MPI_Comm comm) MPI_Fint is not part of the Fortran API or ABI, because Fortran handles are defined to be INTEGER (or an INTEGER inside of a type(MPI_Handle) object). Jeff > On 17. Aug 2023, at 17.52, Zhou, Hui <zhouh(a)anl.gov> wrote: > > I haven't gone through all the use cases, but my current opinion is, it is really a Fortran binding issue and should be left out of C ABI. > > Hui > > From: mpiwg-abi <mpiwg-abi-bounces(a)lists.mpi-forum.org <mailto:[email protected]>> on behalf of Erik Schnetter <schnetter(a)gmail.com <mailto:[email protected]>> > Sent: Thursday, August 17, 2023 9:35 AM > To: Jeff Hammond <jeff.science(a)gmail.com <mailto:[email protected]>> > Cc: mpiwg-abi <mpiwg-abi(a)lists.mpi-forum.org <mailto:[email protected]>>; MPI Forum <mpiwg-fortran(a)lists.mpi-forum.org <mailto:[email protected]>> > Subject: Re: [mpiwg-abi] MPI_Fint in the ABI > > Jeff > > As per the Fortran standard, the sizes of integer and real need to be > the same. In practice this means that integers have 4 bytes. If > someone chooses to change this – either changing the size of real as > well or not – then they are breaking the Fortran standard, and > probably know what they are doing, and are aware of the various > incompatibilities and problems this will introduce. I would thus > suggest keeping things simple for the common case. I would not expect > there to be some code that interoperates with Fortran, and which is > unaware of the Fortran integer size and still expects to get things > right. People will either assume that integer = int, or will know the > Fortran ABI details. > > In the MPI ABI we assume that the caller knows sizeof(int) and > sizeof(void*), and I would also assume that they know sizeof(integer). > I would keep `MPI_Fint` a fixed type. > > To cover all bases I also suggest that we provide a global constant > struct with as much ABI information as we can think of, such as > > const struct MPIABI_info_t { > int32_t MPIABI_version_major, MPIABI_version_minor; > int32_t sizeof_bool; > int32_t sizeof_char; > int32_t sizeof_short; > int32_t sizeof_int; > int32_t sizeof_long; > int32_t sizeof_long_long; > int32_t sizeof_float; > int32_t sizeof_double; > int32_t sizeof_long_double; > int32_t sizeof_void_p; > int32_t sizeof_logical; > int32_t sizeof_integer; > int32_t sizeof_real; > int32_t sizeof_char; > } MPIABI_info; > > This information would not be necessary to use the ABI, but it will be > convenient to check assumptions. Unsupported types report a size of > -1. > > This struct can be extended in the future. > > -erik > > On Wed, Aug 16, 2023 at 4:09 AM Jeff Hammond <jeff.science(a)gmail.com <mailto:[email protected]>> wrote: > > > > As we all know, Fortran users are permitted to change the size of INTEGER with compiler flags. This creates a problem for the MPI C ABI. > > > > I have considered three options and would like your opinions on them: > > > > 1. MPI_Fint is defined to be a C int in the standard ABI. This means MPI implementations that elect to provide an ILP64 MPI Fortran ABI on an I32LP64 system, for example, must not call this an implementation of the standard ABI. > > > > This would make a lot of things easier, but it might cause problems in the rare cases where users are using ILP64 in Fortran and using C code that actually uses MPI_Fint. > > > > 2. MPI_Fint ceases to be a compile-time fixed type in the standard ABI. The C code that uses MPI_Fint must make an MPI library call to figure out the size and do all of the necessary things to call the correct size. > > > > 3. MPI_Fint is not a fixed size but the standard ABI specifies that Fortran handle values must always fit into the range of a C int and we rely on the pass-by-value behavior of all the f2c/c2f APIs to behave properly when they are truncated. > > > > This is my preference but it breaks Example 19.11 in a serious way, because that user code makes use of a MPI_Fint pointer. However, this code isn't standard-compliant and relies on universal but non-standard argument passing conventions in Fortran. Writing a standard-compliant interface from Fortran to C - by doing the cast to INTEGER(kind=c_int) in Fortran - would resolve this. > > > > Example 19.11 is awful (https://github.com/mpi-forum/mpi-issues/issues/739) but it is nonetheless important to instruct users that if Option 3 is implemented, they need to do the casting to INTEGER(kind=c_int) and know that this is safe with the standard ABI. > > > > > > None of these options is perfect. I'm not sure how much code is even impacted by MPI_Fint so it's hard to know which option breaks the most stuff, although Option 2 seems the least desirable in any case. > > > > Thanks, > > > > Jeff > > > > -- > > Jeff Hammond > > jeff.science(a)gmail.com <mailto:[email protected]> > > http://jeffhammond.github.io/ > > -- > > mpiwg-abi mailing list > > mpiwg-abi(a)lists.mpi-forum.org <mailto:[email protected]> > > https://lists.mpi-forum.org/mailman/listinfo/mpiwg-abi > > > > -- > Erik Schnetter <schnetter(a)gmail.com <mailto:[email protected]>> > http://www.perimeterinstitute.ca/personal/eschnetter/ > -- > mpiwg-abi mailing list > mpiwg-abi(a)lists.mpi-forum.org <mailto:[email protected]> > https://lists.mpi-forum.org/mailman/listinfo/mpiwg-abi

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Re: [mpiwg-abi] MPI_Fint in the ABI
by Zhou, Hui 17 Aug '23

17 Aug '23

I haven't gone through all the use cases, but my current opinion is, it is really a Fortran binding issue and should be left out of C ABI. Hui ________________________________ From: mpiwg-abi <mpiwg-abi-bounces(a)lists.mpi-forum.org> on behalf of Erik Schnetter <schnetter(a)gmail.com> Sent: Thursday, August 17, 2023 9:35 AM To: Jeff Hammond <jeff.science(a)gmail.com> Cc: mpiwg-abi <mpiwg-abi(a)lists.mpi-forum.org>; MPI Forum <mpiwg-fortran(a)lists.mpi-forum.org> Subject: Re: [mpiwg-abi] MPI_Fint in the ABI Jeff As per the Fortran standard, the sizes of integer and real need to be the same. In practice this means that integers have 4 bytes. If someone chooses to change this – either changing the size of real as well or not – then they are breaking the Fortran standard, and probably know what they are doing, and are aware of the various incompatibilities and problems this will introduce. I would thus suggest keeping things simple for the common case. I would not expect there to be some code that interoperates with Fortran, and which is unaware of the Fortran integer size and still expects to get things right. People will either assume that integer = int, or will know the Fortran ABI details. In the MPI ABI we assume that the caller knows sizeof(int) and sizeof(void*), and I would also assume that they know sizeof(integer). I would keep `MPI_Fint` a fixed type. To cover all bases I also suggest that we provide a global constant struct with as much ABI information as we can think of, such as const struct MPIABI_info_t { int32_t MPIABI_version_major, MPIABI_version_minor; int32_t sizeof_bool; int32_t sizeof_char; int32_t sizeof_short; int32_t sizeof_int; int32_t sizeof_long; int32_t sizeof_long_long; int32_t sizeof_float; int32_t sizeof_double; int32_t sizeof_long_double; int32_t sizeof_void_p; int32_t sizeof_logical; int32_t sizeof_integer; int32_t sizeof_real; int32_t sizeof_char; } MPIABI_info; This information would not be necessary to use the ABI, but it will be convenient to check assumptions. Unsupported types report a size of -1. This struct can be extended in the future. -erik On Wed, Aug 16, 2023 at 4:09 AM Jeff Hammond <jeff.science(a)gmail.com> wrote: > > As we all know, Fortran users are permitted to change the size of INTEGER with compiler flags. This creates a problem for the MPI C ABI. > > I have considered three options and would like your opinions on them: > > 1. MPI_Fint is defined to be a C int in the standard ABI. This means MPI implementations that elect to provide an ILP64 MPI Fortran ABI on an I32LP64 system, for example, must not call this an implementation of the standard ABI. > > This would make a lot of things easier, but it might cause problems in the rare cases where users are using ILP64 in Fortran and using C code that actually uses MPI_Fint. > > 2. MPI_Fint ceases to be a compile-time fixed type in the standard ABI. The C code that uses MPI_Fint must make an MPI library call to figure out the size and do all of the necessary things to call the correct size. > > 3. MPI_Fint is not a fixed size but the standard ABI specifies that Fortran handle values must always fit into the range of a C int and we rely on the pass-by-value behavior of all the f2c/c2f APIs to behave properly when they are truncated. > > This is my preference but it breaks Example 19.11 in a serious way, because that user code makes use of a MPI_Fint pointer. However, this code isn't standard-compliant and relies on universal but non-standard argument passing conventions in Fortran. Writing a standard-compliant interface from Fortran to C - by doing the cast to INTEGER(kind=c_int) in Fortran - would resolve this. > > Example 19.11 is awful (https://github.com/mpi-forum/mpi-issues/issues/739) but it is nonetheless important to instruct users that if Option 3 is implemented, they need to do the casting to INTEGER(kind=c_int) and know that this is safe with the standard ABI. > > > None of these options is perfect. I'm not sure how much code is even impacted by MPI_Fint so it's hard to know which option breaks the most stuff, although Option 2 seems the least desirable in any case. > > Thanks, > > Jeff > > -- > Jeff Hammond > jeff.science(a)gmail.com > http://jeffhammond.github.io/ > -- > mpiwg-abi mailing list > mpiwg-abi(a)lists.mpi-forum.org > https://lists.mpi-forum.org/mailman/listinfo/mpiwg-abi -- Erik Schnetter <schnetter(a)gmail.com> http://www.perimeterinstitute.ca/personal/eschnetter/ -- mpiwg-abi mailing list mpiwg-abi(a)lists.mpi-forum.org https://lists.mpi-forum.org/mailman/listinfo/mpiwg-abi

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Re: [mpiwg-abi] MPI_Fint in the ABI
by Erik Schnetter 17 Aug '23

17 Aug '23

Jeff As per the Fortran standard, the sizes of integer and real need to be the same. In practice this means that integers have 4 bytes. If someone chooses to change this – either changing the size of real as well or not – then they are breaking the Fortran standard, and probably know what they are doing, and are aware of the various incompatibilities and problems this will introduce. I would thus suggest keeping things simple for the common case. I would not expect there to be some code that interoperates with Fortran, and which is unaware of the Fortran integer size and still expects to get things right. People will either assume that integer = int, or will know the Fortran ABI details. In the MPI ABI we assume that the caller knows sizeof(int) and sizeof(void*), and I would also assume that they know sizeof(integer). I would keep `MPI_Fint` a fixed type. To cover all bases I also suggest that we provide a global constant struct with as much ABI information as we can think of, such as const struct MPIABI_info_t { int32_t MPIABI_version_major, MPIABI_version_minor; int32_t sizeof_bool; int32_t sizeof_char; int32_t sizeof_short; int32_t sizeof_int; int32_t sizeof_long; int32_t sizeof_long_long; int32_t sizeof_float; int32_t sizeof_double; int32_t sizeof_long_double; int32_t sizeof_void_p; int32_t sizeof_logical; int32_t sizeof_integer; int32_t sizeof_real; int32_t sizeof_char; } MPIABI_info; This information would not be necessary to use the ABI, but it will be convenient to check assumptions. Unsupported types report a size of -1. This struct can be extended in the future. -erik On Wed, Aug 16, 2023 at 4:09 AM Jeff Hammond <jeff.science(a)gmail.com> wrote: > > As we all know, Fortran users are permitted to change the size of INTEGER with compiler flags. This creates a problem for the MPI C ABI. > > I have considered three options and would like your opinions on them: > > 1. MPI_Fint is defined to be a C int in the standard ABI. This means MPI implementations that elect to provide an ILP64 MPI Fortran ABI on an I32LP64 system, for example, must not call this an implementation of the standard ABI. > > This would make a lot of things easier, but it might cause problems in the rare cases where users are using ILP64 in Fortran and using C code that actually uses MPI_Fint. > > 2. MPI_Fint ceases to be a compile-time fixed type in the standard ABI. The C code that uses MPI_Fint must make an MPI library call to figure out the size and do all of the necessary things to call the correct size. > > 3. MPI_Fint is not a fixed size but the standard ABI specifies that Fortran handle values must always fit into the range of a C int and we rely on the pass-by-value behavior of all the f2c/c2f APIs to behave properly when they are truncated. > > This is my preference but it breaks Example 19.11 in a serious way, because that user code makes use of a MPI_Fint pointer. However, this code isn't standard-compliant and relies on universal but non-standard argument passing conventions in Fortran. Writing a standard-compliant interface from Fortran to C - by doing the cast to INTEGER(kind=c_int) in Fortran - would resolve this. > > Example 19.11 is awful (https://github.com/mpi-forum/mpi-issues/issues/739) but it is nonetheless important to instruct users that if Option 3 is implemented, they need to do the casting to INTEGER(kind=c_int) and know that this is safe with the standard ABI. > > > None of these options is perfect. I'm not sure how much code is even impacted by MPI_Fint so it's hard to know which option breaks the most stuff, although Option 2 seems the least desirable in any case. > > Thanks, > > Jeff > > -- > Jeff Hammond > jeff.science(a)gmail.com > http://jeffhammond.github.io/ > -- > mpiwg-abi mailing list > mpiwg-abi(a)lists.mpi-forum.org > https://lists.mpi-forum.org/mailman/listinfo/mpiwg-abi -- Erik Schnetter <schnetter(a)gmail.com> http://www.perimeterinstitute.ca/personal/eschnetter/

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MPI_Fint in the ABI
by Jeff Hammond 16 Aug '23

16 Aug '23

As we all know, Fortran users are permitted to change the size of INTEGER with compiler flags. This creates a problem for the MPI C ABI. I have considered three options and would like your opinions on them: 1. MPI_Fint is defined to be a C int in the standard ABI. This means MPI implementations that elect to provide an ILP64 MPI Fortran ABI on an I32LP64 system, for example, must not call this an implementation of the standard ABI. This would make a lot of things easier, but it might cause problems in the rare cases where users are using ILP64 in Fortran and using C code that actually uses MPI_Fint. 2. MPI_Fint ceases to be a compile-time fixed type in the standard ABI. The C code that uses MPI_Fint must make an MPI library call to figure out the size and do all of the necessary things to call the correct size. 3. MPI_Fint is not a fixed size but the standard ABI specifies that Fortran handle values must always fit into the range of a C int and we rely on the pass-by-value behavior of all the f2c/c2f APIs to behave properly when they are truncated. This is my preference but it breaks Example 19.11 in a serious way, because that user code makes use of a MPI_Fint pointer. However, this code isn't standard-compliant and relies on universal but non-standard argument passing conventions in Fortran. Writing a standard-compliant interface from Fortran to C - by doing the cast to INTEGER(kind=c_int) in Fortran - would resolve this. Example 19.11 is awful (https://github.com/mpi-forum/mpi-issues/issues/739) but it is nonetheless important to instruct users that if Option 3 is implemented, they need to do the casting to INTEGER(kind=c_int) and know that this is safe with the standard ABI. None of these options is perfect. I'm not sure how much code is even impacted by MPI_Fint so it's hard to know which option breaks the most stuff, although Option 2 seems the least desirable in any case. Thanks, Jeff -- Jeff Hammond jeff.science(a)gmail.com http://jeffhammond.github.io/

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Re: [mpiwg-abi] asynchronous voting to determine what requires more discussion (ie a meeting)
by Raffenetti, Ken 24 Apr '23

24 Apr '23

We have an item on our ABI wishlist to extend MPI_MAX_INFO_VAL once we have the chance. I believe the motivator was some RMA info extensions Min was working on years ago. So something > 1024 sounds good to me. Nothing else on our wishlist has any impact at this stage, I don't think. For reference: https://github.com/pmodels/mpich/wiki/ABI-Change-Wishlist Ken -----Original Message----- From: mpiwg-abi <mpiwg-abi-bounces(a)lists.mpi-forum.org <mailto:[email protected]>> on behalf of "Holmes, Daniel John" <daniel.john.holmes(a)intel.com <mailto:[email protected]>> Date: Monday, April 24, 2023 at 9:47 AM To: Christoph Niethammer <niethammer(a)hlrs.de <mailto:[email protected]>>, Jeff Hammond <jeff.science(a)gmail.com <mailto:[email protected]>> Cc: mpiwg-abi <mpiwg-abi(a)lists.mpi-forum.org <mailto:[email protected]>> Subject: Re: [mpiwg-abi] asynchronous voting to determine what requires more discussion (ie a meeting) Or a new set of INFO keys of the form "io_node_list_part_N" where N is 1,2,3,... for as many parts as are needed to express the whole value -- the user is invited to concatenate the INFO string values together to obtain the whole node list. PRO: arbitrarily extendable; CON: faff. Best wishes, Dan. -----Original Message----- From: mpiwg-abi <mpiwg-abi-bounces(a)lists.mpi-forum.org <mailto:[email protected]>> On Behalf Of Christoph Niethammer Sent: 24 April 2023 15:42 To: Jeff Hammond <jeff.science(a)gmail.com <mailto:[email protected]>> Cc: mpiwg-abi <mpiwg-abi(a)lists.mpi-forum.org <mailto:[email protected]>> Subject: Re: [mpiwg-abi] asynchronous voting to determine what requires more discussion (ie a meeting) For the io_node_list I could think of a solution by providing a new info key to give a path to a file containing a node list like the PBS/SLURM node list. However this might be tricky again if we have no shared file system on hand. Looking forward to Quincy's expertise in the field. Best Christoph ----- Original Message ----- From: "Jeff Hammond" <jeff.science(a)gmail.com <mailto:[email protected]>> To: "Christoph Niethammer" <niethammer(a)hlrs.de <mailto:[email protected]>> Cc: "mpiwg-abi" <mpiwg-abi(a)lists.mpi-forum.org <mailto:[email protected]>> Sent: Monday, 24 April, 2023 16:28:03 Subject: Re: [mpiwg-abi] asynchronous voting to determine what requires more discussion (ie a meeting) > > 4. Looking at the string constants I am a bit concerned about the > limit of MPI_MAX_INFO_VAL choice of only 1024. > We have, e.g., the Info keys "io_node_list" or "filename" where I could imagine that we could run into problems. > The "io_node_list" key could be a problem on lager systems that come with more than 100 cabinets - assuming for hostnames typically around 9 characters/15 byte string IP + 1 comma for separation. > The "filename" key could be a problem if we interpret the description in the standard - "This hint specifies the file name used when the file was opened." - to include the path. > This is unlimited in length for nearly all common filesystems (thinking ext4, lustre, ...). However, Linux will limit the combined filenames/path length to 4096 characters for us. Interesting. I have merely worked on the assumption that MPICH and OMPI already thought about this enough and that the larger of their choices was sufficient. It is possible that is not the case. For filename, it seems that the problem appears only in MPI_FILE_GET_INFO, because I don't see a limit for the input to MPI_FILE_OPEN. I'm not sure that making the max info val larger is the right solution. I'd be more inclined to ask the IO WG to add MPI_FILE_GET_NAME that is designed for accessing this, and design it to not have a hard-coded limit. I wonder what Quincy thinks about io_node_list, since he may work for the company with the largest ensemble of distributed storage on the planet. Jeff -- mpiwg-abi mailing list mpiwg-abi(a)lists.mpi-forum.org <mailto:[email protected]> https://lists.mpi-forum.org/mailman/listinfo/mpiwg-abi <https://lists.mpi-forum.org/mailman/listinfo/mpiwg-abi> -- mpiwg-abi mailing list mpiwg-abi(a)lists.mpi-forum.org <mailto:[email protected]> https://lists.mpi-forum.org/mailman/listinfo/mpiwg-abi <https://lists.mpi-forum.org/mailman/listinfo/mpiwg-abi>

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Re: [mpiwg-abi] asynchronous voting to determine what requires more discussion (ie a meeting)
by Jeff Hammond 24 Apr '23

24 Apr '23

Yeah, I’m definitely in favor of letting implementations innovate here when the time comes, and to live within the current understanding of what and how to implement the thing we have now. Jeff > On 24. Apr 2023, at 17.47, Holmes, Daniel John <daniel.john.holmes(a)intel.com> wrote: > > Or a new set of INFO keys of the form "io_node_list_part_N" where N is 1,2,3,... for as many parts as are needed to express the whole value -- the user is invited to concatenate the INFO string values together to obtain the whole node list. PRO: arbitrarily extendable; CON: faff. > > Best wishes, > Dan. > > -----Original Message----- > From: mpiwg-abi <mpiwg-abi-bounces(a)lists.mpi-forum.org> On Behalf Of Christoph Niethammer > Sent: 24 April 2023 15:42 > To: Jeff Hammond <jeff.science(a)gmail.com> > Cc: mpiwg-abi <mpiwg-abi(a)lists.mpi-forum.org> > Subject: Re: [mpiwg-abi] asynchronous voting to determine what requires more discussion (ie a meeting) > > For the io_node_list I could think of a solution by providing a new info key to give a path to a file containing a node list like the PBS/SLURM node list. However this might be tricky again if we have no shared file system on hand. > > Looking forward to Quincy's expertise in the field. > > Best > Christoph > > > > ----- Original Message ----- > From: "Jeff Hammond" <jeff.science(a)gmail.com> > To: "Christoph Niethammer" <niethammer(a)hlrs.de> > Cc: "mpiwg-abi" <mpiwg-abi(a)lists.mpi-forum.org> > Sent: Monday, 24 April, 2023 16:28:03 > Subject: Re: [mpiwg-abi] asynchronous voting to determine what requires more discussion (ie a meeting) > >> >> 4. Looking at the string constants I am a bit concerned about the >> limit of MPI_MAX_INFO_VAL choice of only 1024. >> We have, e.g., the Info keys "io_node_list" or "filename" where I could imagine that we could run into problems. >> The "io_node_list" key could be a problem on lager systems that come with more than 100 cabinets - assuming for hostnames typically around 9 characters/15 byte string IP + 1 comma for separation. >> The "filename" key could be a problem if we interpret the description in the standard - "This hint specifies the file name used when the file was opened." - to include the path. >> This is unlimited in length for nearly all common filesystems (thinking ext4, lustre, ...). However, Linux will limit the combined filenames/path length to 4096 characters for us. > > Interesting. I have merely worked on the assumption that MPICH and OMPI already thought about this enough and that the larger of their choices was sufficient. It is possible that is not the case. > > For filename, it seems that the problem appears only in MPI_FILE_GET_INFO, because I don't see a limit for the input to MPI_FILE_OPEN. I'm not sure that making the max info val larger is the right solution. I'd be more inclined to ask the IO WG to add MPI_FILE_GET_NAME that is designed for accessing this, and design it to not have a hard-coded limit. > > I wonder what Quincy thinks about io_node_list, since he may work for the company with the largest ensemble of distributed storage on the planet. > > Jeff > -- > mpiwg-abi mailing list > mpiwg-abi(a)lists.mpi-forum.org > https://lists.mpi-forum.org/mailman/listinfo/mpiwg-abi

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Re: [mpiwg-abi] asynchronous voting to determine what requires more discussion (ie a meeting)
by Holmes, Daniel John 24 Apr '23

24 Apr '23

Or a new set of INFO keys of the form "io_node_list_part_N" where N is 1,2,3,... for as many parts as are needed to express the whole value -- the user is invited to concatenate the INFO string values together to obtain the whole node list. PRO: arbitrarily extendable; CON: faff. Best wishes, Dan. -----Original Message----- From: mpiwg-abi <mpiwg-abi-bounces(a)lists.mpi-forum.org> On Behalf Of Christoph Niethammer Sent: 24 April 2023 15:42 To: Jeff Hammond <jeff.science(a)gmail.com> Cc: mpiwg-abi <mpiwg-abi(a)lists.mpi-forum.org> Subject: Re: [mpiwg-abi] asynchronous voting to determine what requires more discussion (ie a meeting) For the io_node_list I could think of a solution by providing a new info key to give a path to a file containing a node list like the PBS/SLURM node list. However this might be tricky again if we have no shared file system on hand. Looking forward to Quincy's expertise in the field. Best Christoph ----- Original Message ----- From: "Jeff Hammond" <jeff.science(a)gmail.com> To: "Christoph Niethammer" <niethammer(a)hlrs.de> Cc: "mpiwg-abi" <mpiwg-abi(a)lists.mpi-forum.org> Sent: Monday, 24 April, 2023 16:28:03 Subject: Re: [mpiwg-abi] asynchronous voting to determine what requires more discussion (ie a meeting) > > 4. Looking at the string constants I am a bit concerned about the > limit of MPI_MAX_INFO_VAL choice of only 1024. > We have, e.g., the Info keys "io_node_list" or "filename" where I could imagine that we could run into problems. > The "io_node_list" key could be a problem on lager systems that come with more than 100 cabinets - assuming for hostnames typically around 9 characters/15 byte string IP + 1 comma for separation. > The "filename" key could be a problem if we interpret the description in the standard - "This hint specifies the file name used when the file was opened." - to include the path. > This is unlimited in length for nearly all common filesystems (thinking ext4, lustre, ...). However, Linux will limit the combined filenames/path length to 4096 characters for us. Interesting. I have merely worked on the assumption that MPICH and OMPI already thought about this enough and that the larger of their choices was sufficient. It is possible that is not the case. For filename, it seems that the problem appears only in MPI_FILE_GET_INFO, because I don't see a limit for the input to MPI_FILE_OPEN. I'm not sure that making the max info val larger is the right solution. I'd be more inclined to ask the IO WG to add MPI_FILE_GET_NAME that is designed for accessing this, and design it to not have a hard-coded limit. I wonder what Quincy thinks about io_node_list, since he may work for the company with the largest ensemble of distributed storage on the planet. Jeff -- mpiwg-abi mailing list mpiwg-abi(a)lists.mpi-forum.org https://lists.mpi-forum.org/mailman/listinfo/mpiwg-abi

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Re: [mpiwg-abi] asynchronous voting to determine what requires more discussion (ie a meeting)
by Christoph Niethammer 24 Apr '23

24 Apr '23

For the io_node_list I could think of a solution by providing a new info key to give a path to a file containing a node list like the PBS/SLURM node list. However this might be tricky again if we have no shared file system on hand. Looking forward to Quincy's expertise in the field. Best Christoph ----- Original Message ----- From: "Jeff Hammond" <jeff.science(a)gmail.com> To: "Christoph Niethammer" <niethammer(a)hlrs.de> Cc: "mpiwg-abi" <mpiwg-abi(a)lists.mpi-forum.org> Sent: Monday, 24 April, 2023 16:28:03 Subject: Re: [mpiwg-abi] asynchronous voting to determine what requires more discussion (ie a meeting) > > 4. Looking at the string constants I am a bit concerned about the limit of > MPI_MAX_INFO_VAL choice of only 1024. > We have, e.g., the Info keys "io_node_list" or "filename" where I could imagine that we could run into problems. > The "io_node_list" key could be a problem on lager systems that come with more than 100 cabinets - assuming for hostnames typically around 9 characters/15 byte string IP + 1 comma for separation. > The "filename" key could be a problem if we interpret the description in the standard - "This hint specifies the file name used when the file was opened." - to include the path. > This is unlimited in length for nearly all common filesystems (thinking ext4, lustre, ...). However, Linux will limit the combined filenames/path length to 4096 characters for us. Interesting. I have merely worked on the assumption that MPICH and OMPI already thought about this enough and that the larger of their choices was sufficient. It is possible that is not the case. For filename, it seems that the problem appears only in MPI_FILE_GET_INFO, because I don’t see a limit for the input to MPI_FILE_OPEN. I’m not sure that making the max info val larger is the right solution. I’d be more inclined to ask the IO WG to add MPI_FILE_GET_NAME that is designed for accessing this, and design it to not have a hard-coded limit. I wonder what Quincy thinks about io_node_list, since he may work for the company with the largest ensemble of distributed storage on the planet. Jeff

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