[mpich-discuss] MPI_PUT Implementation Bug or Pilot Error?

[Timothy Stitt]

Thanks Rajeev. That makes sense now...and a modified version using separate storage per iteration works perfectly.

Tim.

On Mar 29, 2013, at 1:55 PM, Rajeev Thakur <thakur at mcs.anl.gov<mailto:thakur at mcs.anl.gov>> wrote:

MPI_Put is nonblocking. You are changing the contents of the source buffer before the put is complete.

Rajeev

On Mar 29, 2013, at 12:01 PM, Timothy Stitt wrote:

Hi all,

I've come across some strange behavior with a code that uses MPI_PUT(). I can confirm that this problem appears in older MPICH2 v1.4.x releases as well as the latest MPICH v3.0.3 release. I can also confirm that I receive the correct results when using Open MPI.

I am attaching a reproducer code below that simulates the problem I am having (following the code will hopefully explain its purpose better than what I can describe here in a few lines). This case is hardcoded for a 4-process run. For some reason MPICH implementations are losing some data elements and duplicating others after the communication is complete. I would be grateful if someone can confirm whether this is indeed an implementation bug or a subtle problem with how I've implemented the one-sided communication.

Thanks in advance,

Tim.

program reproducer

use mpi

implicit none

integer :: error,dum_com(2),my_rank,i
integer :: win_values_points, type_integer,NProc=4
INTEGER(KIND=MPI_ADDRESS_KIND) :: win_values_size, target_disp
integer,allocatable :: neighbor_values(:), ncount_in(:)

call MPI_INIT(error)
call MPI_COMM_RANK(MPI_COMM_WORLD,my_rank,error)

CALL MPI_Type_size(MPI_INTEGER,type_integer,error)

! Calculate Size Of Window (in bytes)
win_values_size=2*type_integer*NProc

! Allocate Window Storage
allocate(neighbor_values(0:2*Nproc-1))
neighbor_values=0

! Define Input Values
allocate(ncount_in(NProc))
if (my_rank .eq. 0) ncount_in = (/1,2,3,4/)
if (my_rank .eq. 1) ncount_in = (/5,6,7,8/)
if (my_rank .eq. 2) ncount_in = (/9,10,11,12/)
if (my_rank .eq. 3) ncount_in = (/13,14,15,16/)

! Create Window
CALL MPI_WIN_CREATE(neighbor_values, win_values_size, type_integer, MPI_INFO_NULL, MPI_COMM_WORLD, win_values_points, error)   ! Create Neighbor Storage Win
dow
call MPI_Win_Fence(0,win_values_points,error)

! Print pre-communication data
print*,my_rank,ncount_in
call flush(5)
call MPI_BARRIER(MPI_COMM_WORLD,error)

! Communicate Data Values to all proceses
do i = 1,4
   target_disp=2*my_rank
   dum_com(1)=ncount_in(i)
   dum_com(2)=99
   CALL MPI_PUT(dum_com,2,MPI_INTEGER,Nproc-i,target_disp,2,MPI_INTEGER,win_values_points,error)
end do

call MPI_Win_Fence(0,win_values_points,error)

! Print post-communication values
print *
print *,my_rank,neighbor_values
call flush(5)
call MPI_BARRIER(MPI_COMM_WORLD,error)

! Free Window Storage
call mpi_win_free(win_values_points,error)

call MPI_FINALIZE(error)

end program reproducer


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Tim Stitt PhD
User Support Manager (CRC)
Research Assistant Professor (Computer Science & Engineering)
Room 108, Center for Research Computing | University of Notre Dame |
P.O. Box 539, Notre Dame, IN 46556 | Phone:  574-631-5287 | Email: tstitt at nd.edu<mailto:tstitt at nd.edu>

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