Speck, RobertRobertSpeckRuprecht, DanielDanielRuprechtKrause, RolfRolfKrauseEmmett, MatthewMatthewEmmettMinion, MichaelMichaelMinionWinkel, MathiasMathiasWinkelGibbon, PaulPaulGibbon2021-10-192021-10-192012International Conference for High Performance Computing, Networking, Storage and Analysis (SC), 2012 : 10 - 16 Nov. 2012, Salt Lake City, Utah. - Piscataway, NJ, 2012. - (): 6468522 1-11 (2012)http://hdl.handle.net/11420/10557We present a novel space-time parallel version of the Barnes-Hut tree code PEPC using PFASST, the Parallel Full Approximation Scheme in Space and Time. The naive use of increasingly more processors for a fixed-size N-body problem is prone to saturate as soon as the number of unknowns per core becomes too small. To overcome this intrinsic strong-scaling limit, we introduce temporal parallelism on top of PEPC's existing hybrid MPI/PThreads spatial decomposition. Here, we use PFASST which is based on a combination of the iterations of the parallel-in-time algorithm parareal with the sweeps of spectral deferred correction (SDC) schemes. By combining these sweeps with multiple space-time discretization levels, PFASST relaxes the theoretical bound on parallel efficiency in parareal. We present results from runs on up to 262,144 cores on the IBM Blue Gene/P installation JUGENE, demonstrating that the spacetime parallel code provides speedup beyond the saturation of the purely space-parallel approach. © 2012 IEEE.enInformatikConference Paper10.1109/SC.2012.6Other