Work-stealing is a promising approach for effectively exploiting software parallelism on parallel hardware. A programmer who uses work-stealing explicitly identifies potential parallelism and the runtime then schedules work, keeping otherwise idle hardware busy while relieving overloaded hardware of its burden. Prior work has demonstrated that work-stealing is very effective in practice. However, workstealing comes with a substantial overhead: as much as 2× to 12× slowdown over orthodox sequential code.In this paper we identify the key sources of overhead in work-stealing schedulers and present two significant refinements to their implementation. We evaluate our workstealing designs using a range of benchmarks, four different work-stealing implementations, including the popular fork-join framework, and a range of architectures. On these benchmarks, compared to orthodox sequential Java, our fastest design has an overhead of just 15%. By contrast, fork-join has a 2.3× overhead and the previous implementation of the system we use has an overhead of 4.1×. These results and our insight into the sources of overhead for workstealing implementations give further hope to an already promising technique for exploiting increasingly available hardware parallelism.

No abstract

This work presents the production and extraction of the short-lived radionuclide 6 He in yet unmatched yields from the ISOLDE facility at CERN. It is the first report of 6 He production using spallation neutrons via the 9 Be(n, α) 6 He reaction. These neutrons are produced from the 1.4 GeV proton beam of the Proton Synchrotron Booster (PSB) striking a tungsten converter, and are impinging on a porous BeO material. The central position of 6 He in future experiments is due to its role as a necessary radioactive nucleus to realize the β-beam at CERN, a next-generation facility to study neutrino oscillation parameters, and hence neutrino masses. In the β-beam scenario, an intense beam of radioactive 6 He nuclei will be produced, accelerated to multi-GeV energies and stored in a dedicated storage ring. The resulting virtually mono-directional anti-neutrino beam from the decay of the stored 6 He nuclei will be directed towards a remote underground neutrino detector. A similar beam of, e.g., 18 Ne will provide neutrinos, an ideal concept to test CP violation in the neutrino sector. The results of the present experiment demonstrate for the first time that the necessary conditions for the realization of the proposed β-beam scheme with anti-neutrinos can be fulfilled.

No abstract

No abstract