TY - CHAP A1 - Wende, Florian A1 - Noack, Matthias A1 - Schütt, Thorsten A1 - Sachs, Stephen A1 - Steinke, Thomas T1 - Application Performance on a Cray XC30 Evaluation System with Xeon Phi Coprocessors at HLRN-III T2 - Cray User Group Y1 - 2015 ER - TY - CHAP A1 - Noack, Matthias A1 - Wende, Florian A1 - Steinke, Thomas A1 - Cordes, Frank T1 - A Unified Programming Model for Intra- and Inter-Node Offloading on Xeon Phi Clusters T2 - SC '14: Proceedings of the International Conference on High Performance Computing, Networking, Storage and Analysis. SC14, November 16-21, 2014, New Orleans, Louisiana, USA N2 - Standard offload programming models for the Xeon Phi, e.g. Intel LEO and OpenMP 4.0, are restricted to a single compute node and hence a limited number of coprocessors. Scaling applications across a Xeon Phi cluster/supercomputer thus requires hybrid programming approaches, usually MPI+X. In this work, we present a framework based on heterogeneous active messages (HAM-Offload) that provides the means to offload work to local and remote (co)processors using a unified offload API. Since HAM-Offload provides similar primitives as current local offload frameworks, existing applications can be easily ported to overcome the single-node limitation while keeping the convenient offload programming model. We demonstrate the effectiveness of the framework by using it to enable a real-world application from the field of molecular dynamics to use multiple local and remote Xeon Phis. The evaluation shows good scaling behavior. Compared with LEO, performance is equal for large offloads and significantly better for small offloads. Y1 - 2014 UR - http://dl.acm.org/citation.cfm?id=2683616 U6 - https://doi.org/10.1109/SC.2014.22 ER - TY - GEN A1 - Noack, Matthias T1 - HAM - Heterogenous Active Messages for Efficient Offloading on the Intel Xeon Phi N2 - The applicability of accelerators is limited by the attainable speed-up for the offloaded computations and by the offloading overheads. While GPU programming models like CUDA and OpenCL only allow to optimise the application code and its speed-up, the available low-level APIs for the Intel Xeon Phi provide opportunity to address the overheads, too. This work presents an Heterogeneous Active Message (HAM) layer that minimises software overheads for offloading on Intel’s Xeon Phi. It provides the basis for an offload API with similar semantics as the Intel Language Extensions for Offload (LEO). In contrast to LEO, HAM works within the C++ language and needs no additional compiler support. We evaluated HAM on top of SCIF and MPI as communication backends. While the SCIF backend offers the best performance, the MPI backend allows for inter-node offloads which are not possible with other offload solutions. Benchmark results show that the cost for offloading a function call can be decreased by a factor up to 18 compared with LEO. T3 - ZIB-Report - 14-23 KW - Intel Xeon Phi KW - MIC KW - Active message KW - Offloading KW - SCIF KW - MPI KW - LEO KW - HAM Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:0297-zib-50610 SN - 1438-0064 ER - TY - CHAP A1 - Noack, Matthias A1 - Wende, Florian A1 - Oertel, Klaus-Dieter ED - Reinders, James ED - Jeffers, Jim T1 - OpenCL: There and Back Again T2 - High Performance Parallelism Pearls Y1 - 2015 SN - 978-0-12-803819-2 VL - 2 SP - 355 EP - 378 PB - Morgan Kaufman, Elsevier ER - TY - JOUR A1 - Kramer, Tobias A1 - Noack, Matthias T1 - Prevailing Dust-transport Directions on Comet 67P/Churyumov–Gerasimenko JF - The Astrophysical Journal Letters N2 - Dust transport and deposition behind larger boulders on the comet 67P/Churyumov–Gerasimenko (67P/C–G) have been observed by the Rosetta mission. We present a mechanism for dust-transport vectors based on a homogeneous surface activity model incorporating in detail the topography of 67P/C–G. The combination of gravitation, gas drag, and Coriolis force leads to specific dust transfer pathways, which for higher dust velocities fuel the near-nucleus coma. By distributing dust sources homogeneously across the whole cometary surface, we derive a global dust-transport map of 67P/C–G. The transport vectors are in agreement with the reported wind-tail directions in the Philae descent area. Y1 - 2015 U6 - https://doi.org/10.1088/2041-8205/813/2/L33 VL - 813 IS - 2 SP - L33 ER - TY - CHAP A1 - Fajerski, J. A1 - Noack, Matthias A1 - Reinefeld, Alexander A1 - Schintke, Florian A1 - Schütt, Thorsten A1 - Steinke, Thomas T1 - Fast In-Memory Checkpointing with POSIX API for Legacy Exascale-Applications T2 - SPPEXA Symposium 2016 Y1 - 2016 U6 - https://doi.org/10.1007/978-3-319-40528-5_19 ER - TY - CHAP A1 - Noack, Matthias T1 - OpenCL in Scientific High Performance Computing: The Good, the Bad, and the Ugly T2 - Proceedings of the 5th International Workshop on OpenCL N2 - For writing a new scientific application, portability across existing and future hardware should be the major design goal, as there is a multitude of different compute devices, and programme codes typically outlive systems by far. Unlike other programming models that address parallelism or heterogeneity, OpenCL does provide practical portability across a wide range of HPC-relevant architectures. Other than that, it has a range of further advantages like being a library-only implementation, and using runtime kernel-compilation. We present experiences with utilising OpenCL alongside C++, MPI, and CMake in two real-world scientific codes. Our targets are a Cray XC40 supercomputer with multi- and many-core (Xeon Phi) CPUs, as well as multiple smaller systems with Nvidia and AMD GPUs. We shed light on practical issues arising in such a scenario, like the interaction between OpenCL and MPI, discuss solutions, and point out current limitations of OpenCL in the domain of scientific HPC from an application developer's and user's point of view. Y1 - 2017 U6 - https://doi.org/10.1145/3078155.3078170 SP - 12:1 EP - 12:3 ER - TY - GEN A1 - Kramer, Tobias A1 - Noack, Matthias A1 - Baum, Daniel A1 - Hege, Hans-Christian A1 - Heller, Eric J. T1 - Dust and gas emission from cometary nuclei: the case of comet 67P/Churyumov-Gerasimenko N2 - Comets display with decreasing solar distance an increased emission of gas and dust particles, leading to the formation of the coma and tail. Spacecraft missions provide insight in the temporal and spatial variations of the dust and gas sources located on the cometary nucleus. For the case of comet 67P/Churyumov-Gerasimenko (67P/C-G), the long-term obser- vations from the Rosetta mission point to a homogeneous dust emission across the entire illuminated surface. Despite the homogeneous initial dis- tribution, a collimation in jet-like structures becomes visible. We propose that this observation is linked directly to the complex shape of the nucleus and projects concave topographical features into the dust coma. To test this hypothesis, we put forward a gas-dust description of 67P/C-G, where gravitational and gas forces are accurately determined from the surface mesh and the rotation of the nucleus is fully incorporated. The emerging jet-like structures persist for a wide range of gas-dust interactions and show a dust velocity dependent bending. T3 - ZIB-Report - 17-78 Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:0297-zib-66338 SN - 1438-0064 ER - TY - CHAP A1 - Baumann, Tobias A1 - Noack, Matthias A1 - Steinke, Thomas T1 - Performance Evaluation and Improvements of the PoCL Open-Source OpenCL Implementation on Intel CPUs T2 - IWOCL'21: International Workshop on OpenCL N2 - The Portable Computing Language (PoCL) is a vendor independent open-source OpenCL implementation that aims to support a variety of compute devices in a single platform. Evaluating PoCL versus the Intel OpenCL implementation reveals significant performance drawbacks of PoCL on Intel CPUs – which run 92 % of the TOP500 list. Using a selection of benchmarks, we identify and analyse performance issues in PoCL with a focus on scheduling and vectorisation. We propose a new CPU device-driver based on Intel Threading Building Blocks (TBB), and evaluate LLVM with respect to automatic compiler vectorisation across work-items in PoCL. Using the TBB driver, it is possible to narrow the gap to Intel OpenCL and even outperform it by a factor of up to 1.3× in our proxy application benchmark with a manual vectorisation strategy. Y1 - 2021 U6 - https://doi.org/10.1145/3456669.3456698 ER -