[MPIWG Fortran] Data type of F08 subarray

Tue May 13 14:56:47 CDT 2014

On Tue, May 13, 2014 at 2:48 PM, Junchao Zhang <jczhang at mcs.anl.gov> wrote:

>
> On Tue, May 13, 2014 at 2:37 PM, Bill Long <longb at cray.com> wrote:
>
>>
>> On May 13, 2014, at 2:19 PM, Junchao Zhang <jczhang at mcs.anl.gov> wrote:
>>
>> >
>> > On Tue, May 13, 2014 at 2:00 PM, Bill Long <longb at cray.com> wrote:
>> >
>> > On May 13, 2014, at 12:44 PM, Junchao Zhang <jczhang at mcs.anl.gov>
>> wrote:
>> >
>> > >
>> > > On Tue, May 13, 2014 at 11:56 AM, Rolf Rabenseifner <
>> rabenseifner at hlrs.de> wrote:
>> > > > REAL s(100)
>> > > > MPI_SEND(s (1:100:5) , 3, dtype, ...)
>> > > > dtype can only be MPI_REAL. In other words, dtype is kind of
>> > > > redundant here since the type map is actually specified by the
>> > > > subarray.
>> >
>> > Right.  The descriptor for the first argument has a member whose value
>> is a type code.  In principal the library could verify this is compatible
>> with the data type handle supplied as the third argument, and issue an
>> error if not.  Perhaps in a “debug” mode.
>> >
>> > >
>> > > No, if dtype is a vector then it is applied to a virtual
>> > > contiguous array that consists of s(1), s(6), s(11) …
>> >
>> > dtype is not  a vector, is it?  That argument is a scalar of type
>> TYPE(MPI_DATATYPE).  At least that is what the interface says.
>> >
>> > Rolf meant dtype is an MPI datatype created by MPI_Type_vector.  For
>> this case, I will have two datatypes, one from the MPI_Datatype argument,
>> the other from the choice buffer itself. It is hard to implement that.
>> Perhaps it is useless since it obscures the program.
>>
>> OK. But one of the virtues of the new interface for users is that you do
>> not have to create such data types anymore for array sections.   Even if
>> someone did do this, you can detect that the incoming data type is
>> user-created, and in that case ignore the type code in the descriptor.  If
>> the program is valid at all, the element length, strides, and extents in
>> the descriptor should be correct.
>
>
I hope the MPI_Datatype argument is meant to specify the type of elements
in the subarray. But from Rolf's interpretation, it is not true. So, how
can I "ignore the type code in the descriptor".

>
>
>> Cheers,
>> Bill
>>
>>
>>
>> >
>> >
>> >
>> > Cheers,
>> > Bill
>> >
>> >
>> > >
>> > > That is nasty. Then I will have two data types. I even can not assume
>> any relationship between the two types. I have to allocate a scratch buffer
>> for the virtual contiguous array in MPI_ISEND etc, do memory copying and
>> then free the buffer in MPI_WAIT. I'm not sure one can implement it
>> efficiently.
>> > >
>> > >
>> > >
>> > > ----- Original Message -----
>> > > > From: "Junchao Zhang" <jczhang at mcs.anl.gov>
>> > > > To: "MPI-WG Fortran working group" <
>> mpiwg-fortran at lists.mpi-forum.org>
>> > > > Sent: Tuesday, May 13, 2014 6:23:08 PM
>> > > > Subject: Re: [MPIWG Fortran] Data type of F08 subarray
>> > > >
>> > > >
>> > > >
>> > > > Thanks, Rolf. And I feel there is a jump from contiguous subarray to
>> > > > non-contiguous subarray.
>> > > >
>> > > >
>> > > >
>> > > > For contiguous subarray, such as
>> > > >
>> > > >
>> > > >
>> > > >
>> > > > REAL s(100)
>> > > >
>> > > > MPI_SEND(s(2:50), 3, dtype, ...) s only gives the start address.
>> > > > dtype can be anything, e.g., either a basic type or a derived type
>> > > > created by MPI_Type_vector() etc.
>> > > >
>> > > >
>> > > >
>> > > > For non-contiguous subarray, such as
>> > > >
>> > > >
>> > > >
>> > > > REAL s(100)
>> > > > MPI_SEND(s (1:100:5) , 3, dtype, ...)
>> > > > dtype can only be MPI_REAL. In other words, dtype is kind of
>> > > > redundant here since the type map is actually specified by the
>> > > > subarray.
>> > > >
>> > > >
>> > > >
>> > > >
>> > > >
>> > > >
>> > > > --Junchao Zhang
>> > > >
>> > > >
>> > > > On Tue, May 13, 2014 at 10:20 AM, Rolf Rabenseifner <
>> > > > rabenseifner at hlrs.de > wrote:
>> > > >
>> > > >
>> > > > Dear Junchao,
>> > > >
>> > > > MPI-3.0 p25:7-8 describes only communication with language type
>> > > > of the buffer argument matches to the MPI datatype used
>> > > > in the datatype argument.
>> > > > Same p83:36-37.
>> > > >
>> > > > Therefore, the answer is no and the compiler cannot detect
>> > > > a mismatch beteen language buffer specification and
>> > > > MPI datatype specification.
>> > > >
>> > > > I hope my answer could help.
>> > > >
>> > > > Best regards
>> > > > Rolf
>> > > >
>> > > >
>> > > >
>> > > >
>> > > > ----- Original Message -----
>> > > > > From: "Junchao Zhang" < jczhang at mcs.anl.gov >
>> > > > > To: "MPI-WG Fortran working group" <
>> > > > > mpiwg-fortran at lists.mpi-forum.org >
>> > > > > Sent: Tuesday, May 13, 2014 5:08:30 PM
>> > > > > Subject: [MPIWG Fortran] Data type of F08 subarray
>> > > > >
>> > > > >
>> > > > >
>> > > > >
>> > > > > p626 of MPI-3.0 gives such an example
>> > > > >
>> > > > >
>> > > > > REAL s(100), r(100)
>> > > > > CALL MPI_Isend(s(1:100:5), 3, MPI_REAL, ..., rq, ierror)
>> > > > >
>> > > > > All nonblocking MPI functions behave as if the user-specified
>> > > > > elements of choice buffers are copied to a contiguous scratch
>> > > > > buffer
>> > > > > in the MPI runtime environment. All datatype descriptions (in the
>> > > > > example above, “3, MPI_REAL”) read and store data from and to this
>> > > > > virtual contiguous scratch buffer ...
>> > > > >
>> > > > > Here, data type of s(100) match with MPI_REAL, so everything is
>> > > > > fine.
>> > > > > But I want to know if MPI permits mismatched types, for example,
>> > > > > can
>> > > > > s(100) be an integer array? If the answer is no, then compilers
>> can
>> > > > > not detect this error ; if yes, then it is hard to implement that.
>> > > > > To avoid memory copying to a scratch buffer, I want to use MPI
>> > > > > datatypes. But if I have two types, one is given by the choice
>> > > > > buffer itself, the other is given by the MPI_Datatype argument,
>> how
>> > > > > could I do that?
>> > > > >
>> > > > > Any thoughts?
>> > > > >
>> > > > > Thanks
>> > > > >
>> > > > > --Junchao Zhang
>> > > > > _______________________________________________
>> > > > > mpiwg-fortran mailing list
>> > > > > mpiwg-fortran at lists.mpi-forum.org
>> > > > > http://lists.mpi-forum.org/mailman/listinfo.cgi/mpiwg-fortran
>> > > >
>> > > > --
>> > > > Dr. Rolf Rabenseifner . . . . . . . . . .. email
>> rabenseifner at hlrs.de
>> > > > High Performance Computing Center (HLRS) . phone
>> ++49(0)711/685-65530
>> > > > University of Stuttgart . . . . . . . . .. fax ++49(0)711 /
>> 685-65832
>> > > > Head of Dpmt Parallel Computing . . .
>> www.hlrs.de/people/rabenseifner
>> > > > Nobelstr. 19, D-70550 Stuttgart, Germany . . . . (Office: Room
>> 1.307)
>> > > > _______________________________________________
>> > > > mpiwg-fortran mailing list
>> > > > mpiwg-fortran at lists.mpi-forum.org
>> > > > http://lists.mpi-forum.org/mailman/listinfo.cgi/mpiwg-fortran
>> > > >
>> > > > _______________________________________________
>> > > > mpiwg-fortran mailing list
>> > > > mpiwg-fortran at lists.mpi-forum.org
>> > > > http://lists.mpi-forum.org/mailman/listinfo.cgi/mpiwg-fortran
>> > >
>> > > --
>> > > Dr. Rolf Rabenseifner . . . . . . . . . .. email rabenseifner at hlrs.de
>> > > High Performance Computing Center (HLRS) . phone ++49(0)711/685-65530
>> > > University of Stuttgart . . . . . . . . .. fax ++49(0)711 / 685-65832
>> > > Head of Dpmt Parallel Computing . . . www.hlrs.de/people/rabenseifner
>> > > Nobelstr. 19, D-70550 Stuttgart, Germany . . . . (Office: Room 1.307)
>> > > _______________________________________________
>> > > mpiwg-fortran mailing list
>> > > mpiwg-fortran at lists.mpi-forum.org
>> > > http://lists.mpi-forum.org/mailman/listinfo.cgi/mpiwg-fortran
>> > >
>> > > _______________________________________________
>> > > mpiwg-fortran mailing list
>> > > mpiwg-fortran at lists.mpi-forum.org
>> > > http://lists.mpi-forum.org/mailman/listinfo.cgi/mpiwg-fortran
>> >
>> > Bill Long
>>         longb at cray.com
>> > Fortran Technical Suport  &                                  voice:
>> 651-605-9024
>> > Bioinformatics Software Development                     fax:
>> 651-605-9142
>> > Cray Inc./ Cray Plaza, Suite 210/ 380 Jackson St./ St. Paul, MN 55101
>> >
>> >
>> > _______________________________________________
>> > mpiwg-fortran mailing list
>> > mpiwg-fortran at lists.mpi-forum.org
>> > http://lists.mpi-forum.org/mailman/listinfo.cgi/mpiwg-fortran
>> >
>> > _______________________________________________
>> > mpiwg-fortran mailing list
>> > mpiwg-fortran at lists.mpi-forum.org
>> > http://lists.mpi-forum.org/mailman/listinfo.cgi/mpiwg-fortran
>>
>> Bill Long
>>       longb at cray.com
>> Fortran Technical Suport  &                                  voice:
>> 651-605-9024
>> Bioinformatics Software Development                     fax:
>> 651-605-9142
>> Cray Inc./ Cray Plaza, Suite 210/ 380 Jackson St./ St. Paul, MN 55101
>>
>>
>> _______________________________________________
>> mpiwg-fortran mailing list
>> mpiwg-fortran at lists.mpi-forum.org
>> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpiwg-fortran
>>
>
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