[Q-e-developers] MPI problems with ELPA

[Carlo Cavazzoni]

Ciao Gabriele,

ok, these is a memory leakage bug,
ELPA communicators must be destroyed after the diagonalization has been 
performed.
I'm wondering if there is an ELPA driver to do this (similar to 
GET_ELPA_ROW_COL_COMMS)
instead of calling directly MPI subroutines,

carlo

Il 23/10/2013 10:39, Gabriele Sclauzero ha scritto:
>
> Ciao Carlo,
>
>     thanks for the hint. As far as I can see, the only point where 
> this kind of problem could arise is here
>
> >>> grep -A6  __ELPA  ./Modules/dspev_drv.f90
>
> --
> #ifdef __ELPA
>      INTEGER     :: nprow,npcol,my_prow, my_pcol,mpi_comm_rows, 
> mpi_comm_cols
> #endif
>
>      IF( SIZE( s, 1 ) /= lds ) &
>         CALL errore( ' pdsyevd_drv ', ' wrong matrix leading dimension 
> ', 1 )
>      !
> --
> #ifdef __ELPA
>      CALL BLACS_Gridinfo(ortho_cntx,nprow, npcol, my_prow,my_pcol)
>      CALL GET_ELPA_ROW_COL_COMMS(ortho_comm, my_prow, 
> my_pcol,mpi_comm_rows, mpi_comm_cols)
>      CALL SOLVE_EVP_REAL(n,  n,   s, lds,    w,  vv, lds ,nb  
> ,mpi_comm_rows, mpi_comm_cols)
>      IF( tv )  s = vv
>      IF( ALLOCATED( vv ) ) DEALLOCATE( vv )
> #else
> --
>
>
> because the subroutine GET_ELPA_ROW_COL_COMMS internally calls 
> MPI_Comm_split, which seems to be the MPI subroutine which crashed 
> (according to the error message here below).
> Since the communicators mpi_comm_rows and mpi_comm_cols are just used 
> by ELPA in this subroutine, would it be safe to call
> MPI_Comm_free ( mpi_comm_rows, ierr )
> MPI_Comm_free ( mpi_comm_cols, ierr )
> just before #else ?
>
> If you don't see any potential problem, I would try this solution.
>
>
> Best,
>
> Gabriele
>
>
>
> On 10/23/2013 10:06 AM, Carlo Cavazzoni wrote:
>>> Ciao Gabriele,
>>>
>>> as far I understand with ELPA (which is build on a much deeper 
>>> communicator hierarchy wrt SCALAPACK)
>>> you hit a MPI environment limit (number of communicators).
>>> Even if the limit could be somehow increased, it sound like
>>> somewhere a communicator is created and not destroyed in the relax 
>>> work-flow.
>>> I guess it could be something related to temporary communicator 
>>> created to distribute atoms to processors.
>>> I don't remember exactly, but it can be checked easily searching for 
>>> communicator initialization calls
>>>
>>> carlo
>>>
>>> Il 22/10/2013 17:35, Gabriele Sclauzero ha scritto:
>>>> Dear all,
>>>>
>>>>      I've recently started using ELPA in place of Scalapack for large scale calculations and I indeed see a very good improvement of the performance.
>>>>   
>>>>      Unfortunately, I've found a recurrent problem when running relax calculations (not due to the relaxation itself, though, I believe). The program crashes because of some MPI-related issues. The error message from the system looks as follows:
>>>>
>>>> Abort(1) on node 1732 (rank 1732 in comm 1140850688): Fatal error in PMPI_Comm_split: Other MPI error, error stack:
>>>> PMPI_Comm_split(474).................: MPI_Comm_split(comm=0xc4000004, color=2, key=27, new_comm=0x1fffff7478) failed
>>>> PMPI_Comm_split(456).................:
>>>> MPIR_Comm_split_impl(228)............:
>>>> MPIR_Get_contextid_sparse_group(1071): Too many communicators
>>>>
>>>>
>>>> The crash happens during the Davidson diagonalization after a few ionic cycles of the relaxation (after roughly ~200 Davidson diagonalizations). It happens both with v.5.0.3 and with the latest SVN revision. If I compile with Scalapack in place of ELPA, both versions work fine (but are slower...).
>>>>
>>>> Compilation details (see also attached make.sys):
>>>> BG/Q machine, XLF 14.1, XLC 12.1, ESSL 5.1, Scalapack 2.0.2
>>>> ./configure --enable-openmp --with-elpa
>>>>
>>>> The calculation was run on 256 nodes with the following command line:
>>>> runjob -n 2048 -p 8 --envs OMP_NUM_THREADS=4 --cwd [...] : /home/sclauzer/Codes/espresso/5.0.3_ELPA/bin/pw.x -nband 1 -npool 1 -ndiag 1024 -ntg 4 -in [...]
>>>>
>>>> The system is quite large, a slab with ~1400 atoms and ~3000 bands. I don't know if the problem would show up for a smaller system or on fewer nodes, but I can try to provide a smaller example in order to investigate the problem more easily. Hopefully, this is something simple that the ELPA/Scalapack and BGQ experts among you can spot at a glance.
>>>>
>>>>
>>>> Best,
>>>>
>>>> Gabriele
>>
>
>
> § Gabriele Sclauzero, EPFL SB ITP CSEA
> /   PH H2 462,Station 3, CH-1015 Lausanne/
>
>
>
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-- 
Ph.D. Carlo Cavazzoni
SuperComputing Applications and Innovation Department
CINECA - Via Magnanelli 6/3, 40033 Casalecchio di Reno (Bologna)
Tel: +39 051 6171411  Fax: +39 051 6132198
www.cineca.it

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