Extending Geant4 Parallelism with External Libraries (MPI, TBB) and Its   Use on HPC Resources
  With Geant4 Version 10.0, released in December 2013, one of the most widely used Monte-Carlo codes has been ported to take full advantage of multi- and many-core CPUs thanks to the introduction of event-level parallelism via multithreading. In this paper we review recent developments to allow for a better integration of parallel Geant4 jobs with external libraries. We have chosen to develop examples using the popular Intel Threading Building Block (for short TBB) as an alternative parallelization approach to the native Geant4 POSIX. To simplify the scaling of a Geant4 application across nodes on a cluster we are improving the support of MPI in Geant4. In particular it is now possible to run an hybrid MPI/MT application that uses MPI to scale across nodes and MT to scale across cores. %The recent developments allow users to easily implement parallel application resources that scale on a very large number of nodes and cores typical of HPC resources. 
Andrea Dotti, Makoto Asai, Guy Barrand, Ivana Hrivnacova, Koichi   Murakami
physics.comp-ph hep-ex