[MPI3 Fortran] Deprecate mpif.h?
Craig Rasmussen
crasmussen at newmexicoconsortium.org
Tue Mar 9 11:30:56 CST 2010
If we use DIMENSION(..) then a descriptor will be passed to the
procedure. So there will be no problems due to data copying.
If we keep the current MPI C semantics then implementors can easily
get a C pointer to the array and proceed as currently. This will
place the responsibility on the user to pass contiguous memory and so
they can't use array sections.
Jeff seems OK with MPI-3 having implementors doing a little extra work
and processing the fortran descriptor to allow users to pass array
sections. I believe that Fortran users would vote to allow array
sections. This is also less error prone. If anyone is interested I
could write the C code to process a non-contiguous array section and
copy it to contiguous memory for MPI to transfer.
-craig
On Mar 6, 2010, at 2:37 PM, Rolf Rabenseifner wrote:
> I want to point here to a technical problem with the nice section
> MPI-2.2 482:39-484:18 "Problems Due to Data Copying and Sequence
> Association"
>
> I've done a test with assumed-shape and assumed-size formal
> arguments as buffer and using a strided actual argument when calling
> the
> routine (e.g. MPI_IRECV).
>
> With assumed-size, the compiler did call-by-in-and-out-copy,
> with assumed-shape, the compiler did call-by-reference.
>
> To overcome the restrictions shown in "Problems Due to Data Copying",
> one needs call-by-reference.
>
> With assumed-shape, we have also assumed-rank (is this correct?)
> and therefore we have to 15 times overload a function with one buffer
> and 225 times with two buffers?
>
> And we cannot use our wrappers to current C routines, because now,
> the array descriptor is handed over, and the extracting of
> the data from the strided input must be done by MPI.
>
> If the user itself uses additionally a strided datatype handle,
> then both mechanisms must be applied to the unstrided array
> handed over by Fortran to C.
>
> Do I miss something? Or is it such complicated?
> Do we want this implementation effort?
>
> Attached is a small test-routine, to be compiled with mpif90,
> but started directly (there is no MPI_Init inside).
>
> Best regards
> Rolf
>
> ----- "N.M. Maclaren" <nmm1 at cam.ac.uk> wrote:
>
> ...
>>
>>> The TR features can be implemented on top of an
>>> existing Fortran 2003 compiler - it is not necessary for the vendor
>> to
>>> implement the new features of Fortran 2008 first. It is not even
>>> required that all of Fortran 2003 be implemented before the TR. You
>>
>>> really just need the support for C interoperability and allocatable
>>> dummy arguments from Fortran 2003, and most compilers already
>>> support
>>
>>> those features.
>>
>> Yes. That's not the problem.
>>
>> A bigger one is how to bind the various models together. For
>> example,
>> with the current TR's approach, you cannot have a single MPI function
>> that takes both assumed-size array arguments (which are heavily used)
>> and assumed-shape/assumed-rank ones. MPI is going to have to decide
>> how to handle that one.
>>
>> Similarly, MPI is going to have to address the fact that the TR
>> doesn't
>> help with using Fortran derived types on heterogeneous clusters. And
>> what to do about one-sided transfers (ugh) - actually, those are
>> going
>> to be a BIG semantic problem with the forthcoming C++ and C standards
>> as well.
>>
>> Regards,
>> Nick Maclaren.
>>
>> _______________________________________________
>> mpi3-fortran mailing list
>> mpi3-fortran at lists.mpi-forum.org
>> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi3-fortran
>
> _____________________________________________________________________
>
> module test_mpi
> contains
>
> subroutine TEST_RECV_ASSUMED_SIZE(buf,cnt,dt,src,tag,comm,status)
> use mpi
> implicit none
>
> REAL, dimension(*) :: buf
> integer :: cnt
> integer :: dt
> integer :: src
> integer*8 :: tag
> integer :: comm
> integer, dimension(MPI_STATUS_SIZE) :: status
>
> integer i
> integer*8 :: base
>
> base = tag
> do i=1,cnt
> write(*,'(A,I1,A,F5.1,A,I1,A,I)') ' buf(',i,')=',buf(i), ',
> loc(buf(',i,'))-base=', loc(buf(i))-base
> end do
> return
> end subroutine TEST_RECV_ASSUMED_SIZE
>
> subroutine TEST_RECV_ASSUMED_SHAPE(buf,cnt,dt,src,tag,comm,status)
> use mpi
> implicit none
>
> REAL, dimension(1:) :: buf
> integer :: cnt
> integer :: dt
> integer :: src
> integer*8 :: tag
> integer :: comm
> integer, dimension(MPI_STATUS_SIZE) :: status
>
> integer i
> integer*8 :: base
>
> base = tag
> do i=1,cnt
> write(*,'(A,I1,A,F5.1,A,I1,A,I)') ' buf(',i,')=',buf(i), ',
> loc(buf(',i,'))-base=', loc(buf(i))-base
> end do
> return
> end subroutine TEST_RECV_ASSUMED_SHAPE
>
> end module test_mpi
>
> program test
> use mpi
> use test_mpi
> implicit none
>
> REAL, dimension(6) :: buffer
> REAL, dimension(3,2) :: buffer2dim
> integer*8 :: base
> integer, dimension(MPI_STATUS_SIZE) :: sts
> integer i,j
>
> do i=1,6
> buffer(i)=100*i
> end do
>
> do i=1,3
> do j=1,2
> buffer2dim(i,j)=100*i+j
> end do
> end do
>
> base=loc(buffer(1))
>
> write (*,*) ; write (*,*) 'With 1-dim buffer'
>
> write (*,*) ; write (*,*) 'Assumed SIZE - calling with "buffer":'
> call TEST_RECV_ASSUMED_SIZE(buffer,6,MPI_REAL,
> 0,base,MPI_COMM_WORLD, sts)
>
> ! write (*,*) ; write (*,*) 'Assumed SIZE - calling with
> "buffer(1:6:1)":'
> ! call TEST_RECV_ASSUMED_SIZE(buffer(1:6:1),6,MPI_REAL,
> 0,base,MPI_COMM_WORLD, sts)
>
> ! write (*,*) ; write (*,*) 'Assumed SIZE - calling with
> "buffer(1:3:1)":'
> ! call TEST_RECV_ASSUMED_SIZE(buffer(1:3:1),3,MPI_REAL,
> 0,base,MPI_COMM_WORLD, sts)
>
> write (*,*) ; write (*,*) 'Assumed SIZE - calling with
> "buffer(1:6:2)":'
> call TEST_RECV_ASSUMED_SIZE(buffer(1:6:2),3,MPI_REAL,
> 0,base,MPI_COMM_WORLD, sts)
>
> write (*,*) ; write (*,*) 'Assumed SHAPE - calling with "buffer":'
> call TEST_RECV_ASSUMED_SHAPE(buffer,6,MPI_REAL,
> 0,base,MPI_COMM_WORLD, sts)
>
> ! write (*,*) ; write (*,*) 'Assumed SHAPE - calling with
> "buffer(1:6:1)":'
> ! call TEST_RECV_ASSUMED_SHAPE(buffer(1:6:1),6,MPI_REAL,
> 0,base,MPI_COMM_WORLD, sts)
>
> ! write (*,*) ; write (*,*) 'Assumed SHAPE - calling with
> "buffer(1:3:1)":'
> ! call TEST_RECV_ASSUMED_SHAPE(buffer(1:3:1),3,MPI_REAL,
> 0,base,MPI_COMM_WORLD, sts)
>
> write (*,*) ; write (*,*) 'Assumed SHAPE - calling with
> "buffer(1:6:2)":'
> call TEST_RECV_ASSUMED_SHAPE(buffer(1:6:2),3,MPI_REAL,
> 0,base,MPI_COMM_WORLD, sts)
>
> write (*,*) ; write (*,*) 'With 2-dim buffer2dim'
>
> write (*,*) ; write (*,*) 'Assumed SIZE - calling with "buffer2dim":'
> call TEST_RECV_ASSUMED_SIZE(buffer2dim,6,MPI_REAL,
> 0,base,MPI_COMM_WORLD, sts)
>
> ! write (*,*) ; write (*,*) 'Assumed SIZE - calling with
> "buffer2dim(1:3:1,1:2:1)":'
> ! call TEST_RECV_ASSUMED_SIZE(buffer2dim(1:3:1,1:2:1),6,MPI_REAL,
> 0,base,MPI_COMM_WORLD, sts)
>
> ! write (*,*) ; write (*,*) 'Assumed SIZE - calling with
> "buffer2dim(1:3:1,2:2:1)":'
> ! call TEST_RECV_ASSUMED_SIZE(buffer2dim(1:3:1,2:2:1),3,MPI_REAL,
> 0,base,MPI_COMM_WORLD, sts)
>
> write (*,*) ; write (*,*) 'Assumed SIZE - calling with
> "buffer2dim(1:3:2,1:2:1)":'
> call TEST_RECV_ASSUMED_SIZE(buffer2dim(1:3:2,1:2:1),4,MPI_REAL,
> 0,base,MPI_COMM_WORLD, sts)
>
> write (*,*) ; write (*,*) 'Assumed SHAPE - calling with "buffer":'
> !!!! call TEST_RECV_ASSUMED_SHAPE(buffer2dim,6,MPI_REAL,
> 0,base,MPI_COMM_WORLD, sts)
> write(*,*) ' ---- NOT ALLOWED'
>
> ! write (*,*) ; write (*,*) 'Assumed SHAPE - calling with
> "buffer2dim(1:3:1,1:2:1)":'
> ! call TEST_RECV_ASSUMED_SHAPE(buffer2dim(1:3:1,1:2:1),6,MPI_REAL,
> 0,base,MPI_COMM_WORLD, sts)
>
> ! write (*,*) ; write (*,*) 'Assumed SHAPE - calling with
> "buffer2dim(1:3:1,2:2:1)":'
> ! call TEST_RECV_ASSUMED_SHAPE(buffer2dim(1:3:1,2:2:1),3,MPI_REAL,
> 0,base,MPI_COMM_WORLD, sts)
>
> write (*,*) ; write (*,*) 'Assumed SHAPE - calling with
> "buffer2dim(1:3:2,1:2:1)":'
> !!!! call TEST_RECV_ASSUMED_SHAPE(buffer2dim(1:3:2,1:2:1),
> 4,MPI_REAL,0,base,MPI_COMM_WORLD, sts)
> write(*,*) ' ---- NOT ALLOWED'
>
> end program test
>
> _____________________________________________________________________
>
> With 1-dim buffer
>
> Assumed SIZE - calling with "buffer":
> buf(1)=100.0, loc(buf(1))-base= 0
> buf(2)=200.0, loc(buf(2))-base= 4
> buf(3)=300.0, loc(buf(3))-base= 8
> buf(4)=400.0, loc(buf(4))-base= 12
> buf(5)=500.0, loc(buf(5))-base= 16
> buf(6)=600.0, loc(buf(6))-base= 20
>
> Assumed SIZE - calling with "buffer(1:6:2)":
> buf(1)=100.0, loc(buf(1))-base= 17592185944224
> buf(2)=300.0, loc(buf(2))-base= 17592185944228
> buf(3)=500.0, loc(buf(3))-base= 17592185944232
>>>>>>> The result shows clearly call-by-in-and-out-copy !!!!!
>
> Assumed SHAPE - calling with "buffer":
> buf(1)=100.0, loc(buf(1))-base= 0
> buf(2)=200.0, loc(buf(2))-base= 4
> buf(3)=300.0, loc(buf(3))-base= 8
> buf(4)=400.0, loc(buf(4))-base= 12
> buf(5)=500.0, loc(buf(5))-base= 16
> buf(6)=600.0, loc(buf(6))-base= 20
>
> Assumed SHAPE - calling with "buffer(1:6:2)":
> buf(1)=100.0, loc(buf(1))-base= 0
> buf(2)=300.0, loc(buf(2))-base= 8
> buf(3)=500.0, loc(buf(3))-base= 16
>
> With 2-dim buffer2dim
>
> Assumed SIZE - calling with "buffer2dim":
> buf(1)=101.0, loc(buf(1))-base= 32
> buf(2)=201.0, loc(buf(2))-base= 36
> buf(3)=301.0, loc(buf(3))-base= 40
> buf(4)=102.0, loc(buf(4))-base= 44
> buf(5)=202.0, loc(buf(5))-base= 48
> buf(6)=302.0, loc(buf(6))-base= 52
>
> Assumed SIZE - calling with "buffer2dim(1:3:2,1:2:1)":
> buf(1)=101.0, loc(buf(1))-base= 17592185944208
> buf(2)=301.0, loc(buf(2))-base= 17592185944212
> buf(3)=102.0, loc(buf(3))-base= 17592185944216
> buf(4)=302.0, loc(buf(4))-base= 17592185944220
>>>>>>> The result shows clearly call-by-in-and-out-copy !!!!!
>
> Assumed SHAPE - calling with "buffer":
> ---- NOT ALLOWED
>
> Assumed SHAPE - calling with "buffer2dim(1:3:2,1:2:1)":
> ---- NOT ALLOWED
>
> _____________________________________________________________________
>
> --
> 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: Allmandring
> 30)<type-star-test.f90><type-star-
> test.out.txt>_______________________________________________
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