[petsc-users] Code hangs when calling PetscIntView (MPI, fortran)
Barry Smith
bsmith at petsc.dev
Thu May 20 12:00:04 CDT 2021
You can also have the processes with no values print an array of length zero. Like
if (rank3 == PROC_ROW) then ! IF mpi PROCESS OWNS THIS ROW THEN ..
..
else
NO_A_ENTRIES = 0
call PetscIntView(NO_A_ENTRIES,JALOC(1:NO_A_ENTRIES), &
& PETSC_VIEWER_STDOUT_WORLD, ierr_pets)
> On May 20, 2021, at 5:31 AM, Matthew Knepley <knepley at gmail.com> wrote:
>
> On Thu, May 20, 2021 at 5:32 AM dazza simplythebest <sayosale at hotmail.com <mailto:sayosale at hotmail.com>> wrote:
> Dear Jose,
> Many thanks for the prompt explanation - that would definitely explain what is going on,
> I will adjust my code accordingly .
>
> If you want to print different things from each process in parallel, I suggest
>
> https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Sys/PetscSynchronizedPrintf.html <https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Sys/PetscSynchronizedPrintf.html>
>
> Thanks,
>
> Matt
>
> Thanks again,
> Dan.
>
> From: Jose E. Roman <jroman at dsic.upv.es <mailto:jroman at dsic.upv.es>>
> Sent: Thursday, May 20, 2021 9:06 AM
> To: dazza simplythebest <sayosale at hotmail.com <mailto:sayosale at hotmail.com>>
> Cc: PETSc users list <petsc-users at mcs.anl.gov <mailto:petsc-users at mcs.anl.gov>>
> Subject: Re: [petsc-users] Code hangs when calling PetscIntView (MPI, fortran)
>
> If you look at the manpage https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Sys/PetscIntView.html <https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Sys/PetscIntView.html> you will see that PetscIntView() is collective. This means that all MPI processes must call this function, so it is forbidden to call it within an IF rank==...
>
> Jose
>
> > El 20 may 2021, a las 10:25, dazza simplythebest <sayosale at hotmail.com <mailto:sayosale at hotmail.com>> escribió:
> >
> > Dear All,
> > As part of preparing a code to call the SLEPC eigenvalue solving library,
> > I am constructing a matrix in sparse CSR format row-by-row. Just for debugging
> > purposes I write out the column values for a given row, which are stored in a
> > PetscInt allocatable vector, using PetscIntView.
> >
> > Everything works fine when the number of MPI processes exactly divide the
> > number of rows of the matrix, and so each process owns the same number of rows.
> > However, when the number of MPI processes does not exactly divide the
> > number of rows of the matrix, and so each process owns a different number of rows,
> > the code hangs when it reaches the line that calls PetscIntView.
> > To be precise the code hangs on the final row that a process, other than root, owns.
> > If I however comment out the call to PetscIntView the code completes without error,
> > and produces the correct eigenvalues (hence we are not missing a row / miswriting a row).
> > Note also that a simple direct writeout of this same array using a plain fortran command
> > will write out the array without problem.
> >
> > I have attached below a small code that reproduces the problem.
> > For this code we have nominally assigned 200 rows to our matrix. The code runs without
> > problem using 1,2,4,5,8 or 10 MPI processes, all of which precisely divide 200,
> > but will hang for 3 MPI processes for example.
> > For the case of 3 MPI processes the subroutine WHOSE_ROW_IS_IT allocates the rows
> > to each process as :
> > process no first row last row no. of rows
> > 0 1 66 66
> > 1 67 133 67
> > 2 134 200 67
> >
> > The code will hang when process 1 calls PetscIntView for its last row, row 133 for example.
> >
> > One piece of additional information that may be relevant is that the code does run to completion
> > without hanging if I comment out the final slepc/MPI finalisation command
> > CALL SlepcFinalize(ierr_pets)
> > (I of course I get ' bad termination' errors, but the otherwise the run is successful.)
> >
> > I would appreciate it if anyone has any ideas on what is going wrong!
> > Many thanks,
> > Dan.
> >
> >
> > code:
> >
> > MODULE ALL_STAB_ROUTINES
> > IMPLICIT NONE
> > CONTAINS
> >
> > SUBROUTINE WHOSE_ROW_IS_IT(ROW_NO, TOTAL_NO_ROWS, NO_PROCESSES, &
> > & OWNER)
> > ! THIS ROUTINE ALLOCATES ROWS EVENLY BETWEEN mpi PROCESSES
> > #include <slepc/finclude/slepceps.h>
> > use slepceps
> > IMPLICIT NONE
> > PetscInt, INTENT(IN) :: ROW_NO, TOTAL_NO_ROWS, NO_PROCESSES
> > PetscInt, INTENT(OUT) :: OWNER
> > PetscInt :: P, REM
> >
> > P = TOTAL_NO_ROWS / NO_PROCESSES ! NOTE INTEGER DIVISION
> > REM = TOTAL_NO_ROWS - P*NO_PROCESSES
> > IF (ROW_NO < (NO_PROCESSES - REM)*P + 1 ) THEN
> > OWNER = (ROW_NO - 1)/P ! NOTE INTEGER DIVISION
> > ELSE
> > OWNER = ( ROW_NO + NO_PROCESSES - REM -1 )/(P+1) ! NOTE INTEGER DIVISION
> > ENDIF
> > END SUBROUTINE WHOSE_ROW_IS_IT
> > END MODULE ALL_STAB_ROUTINES
> >
> >
> > PROGRAM trialer
> > USE MPI
> > #include <slepc/finclude/slepceps.h>
> > use slepceps
> > USE ALL_STAB_ROUTINES
> > IMPLICIT NONE
> > PetscMPIInt rank3, total_mpi_size
> > PetscInt nl3, code, PROC_ROW, ISTATUS, jm, N_rows,NO_A_ENTRIES
> > PetscInt, ALLOCATABLE, DIMENSION(:) :: JALOC
> > PetscInt, PARAMETER :: ZERO = 0 , ONE = 1, TWO = 2, THREE = 3
> > PetscErrorCode ierr_pets
> >
> > ! Initialise sleps/mpi
> > call SlepcInitialize(PETSC_NULL_CHARACTER,ierr_pets) ! note that this initialises MPI
> > call MPI_COMM_SIZE(MPI_COMM_WORLD, total_mpi_size, ierr_pets) !! find total no of MPI processes
> > nL3= total_mpi_size
> > call MPI_COMM_RANK(MPI_COMM_WORLD,rank3,ierr_pets) !! find my overall rank -> rank3
> > write(*,*)'Welcome: PROCESS NO , TOTAL NO. OF PROCESSES = ',rank3, nl3
> >
> > N_rows = 200 ! NUMBER OF ROWS OF A NOTIONAL MATRIX
> > NO_A_ENTRIES = 12 ! NUMBER OF ENTRIES FOR JALOC
> >
> > ! LOOP OVER ROWS
> > do jm = 1, N_rows
> >
> > CALL whose_row_is_it(JM, N_rows , NL3, PROC_ROW) ! FIND OUT WHICH PROCESS OWNS ROW
> > if (rank3 == PROC_ROW) then ! IF mpi PROCESS OWNS THIS ROW THEN ..
> > ! ALLOCATE jaloc ARRAY AND INITIALISE
> >
> > allocate(jaloc(NO_A_ENTRIES), STAT=ISTATUS )
> > jaloc = three
> >
> >
> > WRITE(*,*)'JALOC',JALOC ! THIS SIMPLE PLOT ALWAYS WORKS
> > write(*,*)'calling PetscIntView: PROCESS NO. ROW NO.',rank3, jm
> > ! THIS CALL TO PetscIntView CAUSES CODE TO HANG WHEN E.G. total_mpi_size=3, JM=133
> > call PetscIntView(NO_A_ENTRIES,JALOC(1:NO_A_ENTRIES), &
> > & PETSC_VIEWER_STDOUT_WORLD, ierr_pets)
> > CHKERRA(ierr_pets)
> > deallocate(jaloc)
> > endif
> > enddo
> >
> > CALL SlepcFinalize(ierr_pets)
> > end program trialer
>
>
>
> --
> What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.
> -- Norbert Wiener
>
> https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
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