[Q-e-developers] MPI problems with ELPA

[Gabriele Sclauzero]

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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