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@INPROCEEDINGS{Brmmel:818244,
      author       = {Brömmel, Dirk and Frings, Wolfgang and Wylie, Brian J. N.},
      title        = {{E}xtreme-scaling applications en route to exascale},
      address      = {New York},
      publisher    = {ACM Press},
      reportid     = {FZJ-2016-04722},
      pages        = {10},
      year         = {2016},
      comment      = {Proceedings of the Exascale Applications and Software
                      Conference 2016},
      booktitle     = {Proceedings of the Exascale
                       Applications and Software Conference
                       2016},
      abstract     = {Feedback from the previous year's very successful workshop
                      motivated the organisation of a three-day workshop from 1 to
                      3 February 2016, during which the 28-rack JUQUEEN BlueGene/Q
                      system with 458 752 cores was reserved for over 50 hours.
                      Eight international code teams were selected to use this
                      opportunity to investigate and improve their application
                      scalability, assisted by staff from JSC Simulation
                      Laboratories and Cross-Sectional Teams. Ultimately seven
                      teams had codes successfully run on the full JUQUEEN system.
                      Strong scalability demonstrated by Code Saturne and
                      Seven-League Hydro, both using 4 OpenMP threads for 16 MPI
                      processes on each compute node for a total of 1 835 008
                      threads, qualify them for High-Q Club membership. Existing
                      members CIAO and iFETI were able to show that they had
                      additional solvers which also scaled acceptably.
                      Furthermore, large-scale in-situ interactive visualisation
                      was demonstrated with a CIAO simulation using 458 752 MPI
                      processes running on 28 racks coupled via JUSITU to VisIt.
                      The two adaptive mesh refinement utilities, ICI and p4est,
                      showed that they could respectively scale to run with 458
                      752 and 971 504 MPI ranks, but both encountered problems
                      loading large meshes. Parallel file I/O issues also hindered
                      large-scale executions of PFLOTRAN. Poor performance of a
                      NEST-import module which loaded and connected 1.9 TiB of
                      neuron and synapse data was tracked down to an internal
                      data-structure mismatch with the HDF5 file objects that
                      prevented use of MPI collective file reading, which when
                      rectified is expected to enable large-scale neuronal network
                      simulations.Comparative analysis is provided to the 25 codes
                      in the High-Q Club at the start of 2016, which includes five
                      codes that qualified from the previous workshop. Despite
                      more mixed results, we learnt more about application file
                      I/O limitations and inefficiencies which continue to be the
                      primary inhibitor to large-scale simulations.},
      date          = {04262016},
      organization  = {Exascale Applications and Software
                       Conference 2016, Stockholm (Sweden), 26
                       Apr 2016 - 29 Apr 2016},
      cin          = {JSC},
      cid          = {I:(DE-Juel1)JSC-20090406},
      pnm          = {511 - Computational Science and Mathematical Methods
                      (POF3-511) / ATMLPP - ATML Parallel Performance (ATMLPP) /
                      ATMLAO - ATML Application Optimization and User Service
                      Tools (ATMLAO)},
      pid          = {G:(DE-HGF)POF3-511 / G:(DE-Juel-1)ATMLPP /
                      G:(DE-Juel-1)ATMLAO},
      typ          = {PUB:(DE-HGF)8 / PUB:(DE-HGF)7},
      doi          = {10.1145/2938615.2938616},
      url          = {https://juser.fz-juelich.de/record/818244},
}