We 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.

In the past several years, many scientific applications from various domains have taken advantage of e-science infrastructures that share storage or computational resources such as supercomputers, clusters or PC server farms across multiple organizations. Especially within e-science infrastructures driven by high-performance computing (HPC) such as DEISA, online visualization and computational steering (COVS) has become an important technique to save compute time on shared resources by dynamically steering the parameters of a parallel simulation. This paper argues that future supercomputers in the Petaflop/s performance range with up to 1 million CPUs will create an even stronger demand for seamless computational steering technologies. We discuss upcoming challenges for the development of scalable HPC applications and limits of future storage/IO technologies in the context of next generation e- science infrastructures and outline potential solutions.

Many production Grid infrastructures such as DEISA, EGEE, or TeraGrid have begun to offer services to endusers that include access to computational resources. The major goal of these infrastructures is to facilitate the routine interaction of scientists and their workflows with advanced tools and seamless access to computational resources via Grid middleware systems such as UNICORE, gLite or Globus Toolkits. While UNICORE 5 is used in production Grids since several years, recently an early prototype of the new Web services-based UNICORE 6 became available that will be continuously improved in the next months for its use in production. In absence of a widely accepted framework for visualization and steering, the new UNICORE 6 Grid middleware provides not such a higher level service by default. This motivates this contribution to support e-Scientists in upcoming WS-based UNICORE Grids with visualization and steering techniques. In this paper we present the augmentation of the early standards-based UNICORE 6 prototype with a higher-level service for collaborative online visualization and steering. It describes the seamless integration of this service within UNICORE Grids by retaining the convenient single sign-on feature.