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NAS parallel benchmarks (NPB) are a set of applications commonly used to evaluate parallel systems. We use the NPB-OpenMP version to examine the performance of the Intel's new Xeon Phi co-processor and focus specially on the many-core aspect of the Xeon Phi architecture. A first analysis studies the scalability up to 244 threads on 61 cores, the impact of affinity settings on scaling and compare performance characteristics of Xeon Phi and traditional Xeon CPUs. The application of several well-established optimization techniques allows us to identify common bottlenecks that can specifically impede performance on the Xeon Phi but are not as severe on multi-core CPUs. We also find that many of the OpenMP-parallel loops are too short (in terms of the number of loop iterations) for a balanced execution by 244 threads. New, or redesigned benchmarks will be needed to accommodate the greatly increased number of cores and threads. At the end, we summarize our findings in a set recommendations for performance optimization for Xeon Phi.

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