[Q-e-developers] MPI problems with ELPA

[Carlo Cavazzoni]

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
>
>
>
>
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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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