CRAFT: A library for easier application-level Checkpoint/Restart and Automatic Fault Tolerance

In order to efficiently use the future generations of supercomputers, fault tolerance and power consumption are two of the prime challenges anticipated by the High Performance Computing (HPC) community. Checkpoint/Restart (CR) has been and still is the most widely used technique to deal with hard failures. Application-level CR is the most effective CR technique in terms of overhead efficiency but it takes a lot of implementation effort. This work presents the implementation of our C++ based library CRAFT (Checkpoint-Restart and Automatic Fault Tolerance), which serves two purposes. First, it provides an extendable library that significantly eases the implementation of application-level checkpointing. The most basic and frequently used checkpoint data types are already part of CRAFT and can be directly used out of the box. The library can be easily extended to add more data types. As means of overhead reduction, the library offers a build-in asynchronous checkpointing mechanism and also supports the Scalable Checkpoint/Restart (SCR) library for node level checkpointing. Second, CRAFT provides an easier interface for User-Level Failure Mitigation (ULFM) based dynamic process recovery, which significantly reduces the complexity and effort of failure detection and communication recovery mechanism. By utilizing both functionalities together, applications can write application-level checkpoints and recover dynamically from process failures with very limited programming effort. This work presents the design and use of our library in detail. The associated overheads are thoroughly analyzed using several benchmarks

Efficient multicore-aware parallelization strategies for iterative stencil computations

Stencil computations consume a major part of runtime in many scientific simulation codes. As prototypes for this class of algorithms we consider the iterative Jacobi and Gauss-Seidel smoothers and aim at highly efficient parallel implementations for cache-based multicore architectures. Temporal cache blocking is a known advanced optimization technique, which can reduce the pressure on the memory bus significantly. We apply and refine this optimization for a recently presented temporal blocking strategy designed to explicitly utilize multicore characteristics. Especially for the case of Gauss-Seidel smoothers we show that simultaneous multi-threading (SMT) can yield substantial performance improvements for our optimized algorithm.Comment: 15 pages, 10 figure

Lattice Boltzmann Benchmark Kernels as a Testbed for Performance Analysis

Lattice Boltzmann methods (LBM) are an important part of current computational fluid dynamics (CFD). They allow easy implementations and boundary handling. However, competitive time to solution not only depends on the choice of a reasonable method, but also on an efficient implementation on modern hardware. Hence, performance optimization has a long history in the lattice Boltzmann community. A variety of options exists regarding the implementation with direct impact on the solver performance. Experimenting and evaluating each option often is hard as the kernel itself is typically embedded in a larger code base. With our suite of lattice Boltzmann kernels we provide the infrastructure for such endeavors. Already included are several kernels ranging from simple to fully optimized implementations. Although these kernels are not fully functional CFD solvers, they are equipped with a solid verification method. The kernels may act as an reference for performance comparisons and as a blue print for optimization strategies. In this paper we give an overview of already available kernels, establish a performance model for each kernel, and show a comparison of implementations and recent architectures.Comment: preprint, submitted to Computer & Fluids Special Issue DSFD201

Looking Under the Hood of Competency-Based Education: The Relationship Between Competency-Based Education Practices and Students' Learning Skills, Behaviors, and Dispositions

The Nellie Mae Education Foundation (Nellie Mae), in partnership with the American Institutes for Research (AIR), has recently released a comprehensive analysis of competency-based education (CBE), an instructional approach that emphasizes what students learn and master rather than time spent in a classroom. The study, titled "Looking Under the Hood of Competency-Based Education," examines the relationship between various competency-based practices and increased student learning capacity. Additionally, the study highlights the varying degrees of CBE practices in schools that have an existing reputation for implementation."Schools across the country are increasingly seeking ways to provide a competency-based education for students, yet many educators are not sure of where to begin or how they can implement this approach to learning," said Eve Goldberg, Director of Research at the Nellie Mae Education Foundation. "The framework developed by AIR of learning skills, behaviors, and dispositions and the findings on specific practices can help educators strengthen their practices and gives them the tools to continuously improve their practice. We hope educators interested in making this shift will benefit from this analysis.""Looking Under the Hood" analyzes a variety of competency-based practices to examine how schools implement CBE and determine how it relates to students' learning capacities. Some notable findings include:Learning in contexts outside the classroom (for example, internships) positively relates to increasing students' learning capacitiesThe option for students to learn at a comfortable pace (for example, extra time to finish a topic or unit and the opportunity to retake an exam or re-do a final project) has a positive association with self-efficacy and increasing students' motivation to learnThe option for students to receive both instruction and assessment in a variety of formats, including collaborative group projects, helped students' intrinsic motivationEstablishing clear learning targets was positively related to increasing students' learning capacitiesOverall, the study finds that many students' experiences with CBE-aligned practices were positively associated with changes in learning capacities in several areas, most notably in students' intrinsic motivation for classroom work."Competency-based education varies tremendously from school to school and even across classrooms, so it can be hard to determine if it is working," said Erin Haynes, Senior Researcher at the American Institutes for Research. "This study examined specific CBE-aligned practices, giving us a more finely-honed view of how such practices are related to students' capacity to learn. We hope this research will help inform future efforts to implement competency-based methods across districts, schools and classrooms.

Gamma-widths, lifetimes and fluctuations in the nuclear quasi-continuum

Statistical $\gamma$-decay from highly excited states is determined by the nuclear level density (NLD) and the $\gamma$-ray strength function ($\gamma$SF). These average quantities have been measured for several nuclei using the Oslo method. For the first time, we exploit the NLD and $\gamma$SF to evaluate the $\gamma$-width in the energy region below the neutron binding energy, often called the quasi-continuum region. The lifetimes of states in the quasi-continuum are important benchmarks for a theoretical description of nuclear structure and dynamics at high temperature. The lifetimes may also have impact on reaction rates for the rapid neutron-capture process, now demonstrated to take place in neutron star mergers.Comment: CGS16, Shanghai 2017, Proceedings, 5 pages, 3 figure