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@TECHREPORT{Brmmel:283461,
      author       = {Brömmel, Dirk and Frings, Wolfgang and Wylie, Brian J. N.},
      title        = {{JUQUEEN} {E}xtreme {S}caling {W}orkshop 2016},
      number       = {FZJ-JSC-IB-2016-01},
      reportid     = {FZJ-2016-01816, FZJ-JSC-IB-2016-01},
      series       = {JSC Internal Report},
      pages        = {67 p.},
      year         = {2016},
      abstract     = {Feedback from last year's very successful workshop
                      motivated the organisation of a three-day workshop 1-3
                      February 2016, during which the entire 28-rack JUQUEEN
                      BlueGene/Q system with 458,752 cores was reserved for over
                      50 hours. Eight 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. $Code_Saturne$ from
                      Daresbury Lab and Seven-League Hydro from HITS (Heidelberg)
                      were both able to display good strong scalability and
                      thereby become candidates for High-Q Club membership. Both
                      used 4 OpenMP threads per MPI process, over 1.8 million
                      threads in total. Existing members, CIAO from RWTH-ITV and
                      iFETI from University of Cologne and TU Freiberg, were able
                      to show that they had additional solvers which also scaled
                      acceptably. In-situ interactive visualisation was
                      demonstrated with a CIAO simulation using 458,752 MPI
                      processes running on 28 racks coupled via JUSITU to VisIt.
                      Two adaptive mesh refinement libraries, p4est from
                      University of Bonn and IciMesh from Ecole Central de Nantes,
                      showed that they could respectively scale to run with
                      917,504 and 458,752 MPI ranks, but both encountered problems
                      loading large meshes. Parallel file I/O limitations also
                      prevented large-scale executions of the FZJ IEK-6/Amphos21
                      PFLOTRAN subsurface flow and reactive transport code,
                      however, a NEST-import HDF5 module developed by the EPFL
                      Blue Brain Project could be optimised to use collective MPI
                      file reading calls to load and connect 1.9TB of neuron and
                      synapse data and enable large-scale data-driven neuronal
                      network simulations with 458,752 threads. Detailed reports
                      are provided by each code-team, and additional comparative
                      analysis to the 25 High-Q Club member codes. Despite more
                      mixed results than the previous workshop, we learnt more
                      about application file I/O limitations and inefficiencies
                      which continue to be the primary inhibitor to large-scale
                      simulations, and all of the participants found the workshop
                      to have been very valuable.},
      cin          = {JSC},
      cid          = {I:(DE-Juel1)JSC-20090406},
      pnm          = {511 - Computational Science and Mathematical Methods
                      (POF3-511) / 513 - Supercomputer Facility (POF3-513) /
                      ATMLPP - ATML Parallel Performance (ATMLPP) / ATMLAO - ATML
                      Application Optimization and User Service Tools (ATMLAO)},
      pid          = {G:(DE-HGF)POF3-511 / G:(DE-HGF)POF3-513 /
                      G:(DE-Juel-1)ATMLPP / G:(DE-Juel-1)ATMLAO},
      typ          = {PUB:(DE-HGF)3 / PUB:(DE-HGF)15},
      url          = {https://juser.fz-juelich.de/record/283461},
}