[Q-e-developers] MPI problems with ELPA

[Gabriele Sclauzero]

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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