The ESCAPE project : Energy-efficient Scalable Algorithms for Weather Prediction at Exascale

In the simulation of complex multi-scale flows arising in weather and climate modelling, one of the biggest challenges is to satisfy strict service requirements in terms of time to solution and to satisfy budgetary constraints in terms of energy to solution, without compromising the accuracy and stability of the application. These simulations require algorithms that minimise the energy footprint along with the time required to produce a solution, maintain the physically required level of accuracy, are numerically stable, and are resilient in case of hardware failure. The European Centre for Medium-Range Weather Forecasts (ECMWF) led the ESCAPE (Energy-efficient Scalable Algorithms for Weather Prediction at Exascale) project, funded by Horizon 2020 (H2020) under the FET-HPC (Future and Emerging Technologies in High Performance Computing) initiative. The goal of ESCAPE was to develop a sustainable strategy to evolve weather and climate prediction models to next-generation computing technologies. The project partners incorporate the expertise of leading European regional forecasting consortia, university research, experienced high-performance computing centres, and hardware vendors. This paper presents an overview of the ESCAPE strategy: (i) identify domain-specific key algorithmic motifs in weather prediction and climate models (which we term Weather & Climate Dwarfs), (ii) categorise them in terms of computational and communication patterns while (iii) adapting them to different hardware architectures with alternative programming models, (iv) analyse the challenges in optimising, and (v) find alternative algorithms for the same scheme. The participating weather prediction models are the following: IFS (Integrated Forecasting System); ALARO, a combination of AROME (Application de la Recherche a l'Operationnel a Meso-Echelle) and ALADIN (Aire Limitee Adaptation Dynamique Developpement International); and COSMO-EULAG, a combination of COSMO (Consortium for Small-scale Modeling) and EULAG (Eulerian and semi-Lagrangian fluid solver). For many of the weather and climate dwarfs ESCAPE provides prototype implementations on different hardware architectures (mainly Intel Skylake CPUs, NVIDIA GPUs, Intel Xeon Phi, Optalysys optical processor) with different programming models. The spectral transform dwarf represents a detailed example of the co-design cycle of an ESCAPE dwarf. The dwarf concept has proven to be extremely useful for the rapid prototyping of alternative algorithms and their interaction with hardware; e.g. the use of a domain-specific language (DSL). Manual adaptations have led to substantial accelerations of key algorithms in numerical weather prediction (NWP) but are not a general recipe for the performance portability of complex NWP models. Existing DSLs are found to require further evolution but are promising tools for achieving the latter. Measurements of energy and time to solution suggest that a future focus needs to be on exploiting the simultaneous use of all available resources in hybrid CPU-GPU arrangements

The ESCAPE project: Energy-efficient Scalable Algorithms for Weather Prediction at Exascale

Abstract. In the simulation of complex multi-scale flows arising in weather and climate modelling, one of the biggest challenges is to satisfy strict service requirements in terms of time to solution and to satisfy budgetary constraints in terms of energy to solution, without compromising the accuracy and stability of the application. These simulations require algorithms that minimise the energy footprint along with the time required to produce a solution, maintain the physically required level of accuracy, are numerically stable, and are resilient in case of hardware failure. The European Centre for Medium-Range Weather Forecasts (ECMWF) led the ESCAPE (Energy-efficient Scalable Algorithms for Weather Prediction at Exascale) project, funded by Horizon 2020 (H2020) under the FET-HPC (Future and Emerging Technologies in High Performance Computing) initiative. The goal of ESCAPE was to develop a sustainable strategy to evolve weather and climate prediction models to next-generation computing technologies. The project partners incorporate the expertise of leading European regional forecasting consortia, university research, experienced high-performance computing centres, and hardware vendors. This paper presents an overview of the ESCAPE strategy: (i) identify domain-specific key algorithmic motifs in weather prediction and climate models (which we term Weather & Climate Dwarfs), (ii) categorise them in terms of computational and communication patterns while (iii) adapting them to different hardware architectures with alternative programming models, (iv) analyse the challenges in optimising, and (v) find alternative algorithms for the same scheme. The participating weather prediction models are the following: IFS (Integrated Forecasting System); ALARO, a combination of AROME (Application de la Recherche à l'Opérationnel à Meso-Echelle) and ALADIN (Aire Limitée Adaptation Dynamique Développement International); and COSMO–EULAG, a combination of COSMO (Consortium for Small-scale Modeling) and EULAG (Eulerian and semi-Lagrangian fluid solver). For many of the weather and climate dwarfs ESCAPE provides prototype implementations on different hardware architectures (mainly Intel Skylake CPUs, NVIDIA GPUs, Intel Xeon Phi, Optalysys optical processor) with different programming models. The spectral transform dwarf represents a detailed example of the co-design cycle of an ESCAPE dwarf. The dwarf concept has proven to be extremely useful for the rapid prototyping of alternative algorithms and their interaction with hardware; e.g. the use of a domain-specific language (DSL). Manual adaptations have led to substantial accelerations of key algorithms in numerical weather prediction (NWP) but are not a general recipe for the performance portability of complex NWP models. Existing DSLs are found to require further evolution but are promising tools for achieving the latter. Measurements of energy and time to solution suggest that a future focus needs to be on exploiting the simultaneous use of all available resources in hybrid CPU–GPU arrangements

Contributions to the efficient use of general purpose coprocessors: kernel density estimation as case study

142 p.The high performance computing landscape is shifting from assemblies of homogeneous nodes towards heterogeneous systems, in which nodes consist of a combination of traditional out-of-order execution cores and accelerator devices. Accelerators provide greater theoretical performance compared to traditional multi-core CPUs, but exploiting their computing power remains as a challenging task.This dissertation discusses the issues that arise when trying to efficiently use general purpose accelerators. As a contribution to aid in this task, we present a thorough survey of performance modeling techniques and tools for general purpose coprocessors. Then we use as case study the statistical technique Kernel Density Estimation (KDE). KDE is a memory bound application that poses several challenges for its adaptation to the accelerator-based model. We present a novel algorithm for the computation of KDE that reduces considerably its computational complexity, called S-KDE. Furthermore, we have carried out two parallel implementations of S-KDE, one for multi and many-core processors, and another one for accelerators. The latter has been implemented in OpenCL in order to make it portable across a wide range of devices. We have evaluated the performance of each implementation of S-KDE in a variety of architectures, trying to highlight the bottlenecks and the limits that the code reaches in each device. Finally, we present an application of our S-KDE algorithm in the field of climatology: a novel methodology for the evaluation of environmental models

Performance and results of the high-resolution biogeochemical model PELAGOS025 v1.0 within NEMO v3.4

Abstract. The present work aims at evaluating the scalability performance of a high-resolution global ocean biogeochemistry model (PELAGOS025) on massive parallel architectures and the benefits in terms of the time-to-solution reduction. PELAGOS025 is an on-line coupling between the Nucleus for the European Modelling of the Ocean (NEMO) physical ocean model and the Biogeochemical Flux Model (BFM) biogeochemical model. Both the models use a parallel domain decomposition along the horizontal dimension. The parallelisation is based on the message passing paradigm. The performance analysis has been done on two parallel architectures, an IBM BlueGene/Q at ALCF (Argonne Leadership Computing Facilities) and an IBM iDataPlex with Sandy Bridge processors at the CMCC (Euro Mediterranean Center on Climate Change). The outcome of the analysis demonstrated that the lack of scalability is due to several factors such as the I/O operations, the memory contention, the load unbalancing due to the memory structure of the BFM component and, for the BlueGene/Q, the absence of a hybrid parallelisation approach

Metodi e strumenti per la valutazione delle prestazioni del software parallelo attraverso un caso di studio: il software ROMS

L’obiettivo di questa tesi è quello individurare e studiare metodi e strumenti per la valutazione di software, a partire dalla valutazione di architetture che sfruttano il parallelismo, alle tecniche per il profiling e valutazione di software eseguiti su architetture ad alte prestazioni (HPC); ciò viene fatto analizzando le prestazioni del codice sorgente evidenziando i colli di bottiglia che ne limitano l'efficienza e individuando i kernel computazionalmente più onerosi. Un aspetto necessario per la valutazione è il confronto tra la prestazione ’standard’ della macchina (di picco e sostenuta), confrontandola con quella ottenuta dall'applicazione di interesse. Queste analisi possono suggerire come il software può essere eseguito in maniera efficiente e ’prestante’ su le architetture analizzate. Ci si pone le seguenti domande: Il sistema di calcolo a disposizione è adeguato all'esecuzione di questo software? Tale software raggiunge le prestazioni attese? Si pone l'attenzione su due macro-aree: una relativa al calcolo delle prestazioni di una architettura, l'altra allo studio delle prestazioni di un software. Occorre dare una risposta da un lato sui limiti del sistema di calcolo dall'altro sulle cause che portano un software a non utilizzare efficacemente l'architettura utilizzata, e quindi alle azioni da intraprendere per migliorarle. Si analizzeranno gli strumenti per valutare un sistema di calcolo chiamati benchmark, e gli strumenti ed i modelli che rivolgono l'attenzione alla valutazione delle prestazioni ottenute dall'applicazione di interesse. Ogni sistema di calcolo è costituito da elementi che vanno analizzati singolarmente. Sarà necessario porre l'attenzione su diversi aspetti: Calcolo, Comunicazione, I/O, Memoria

Harmony in marriage: integrating sustainable solutions into historic house museums without interfering with the historic fabric

textHistoric buildings live a double life between climate-adapted largely-passive structures and draughty, poorly-maintained ones. Preservation professionals argue that preserving these structures is more resource effective than constructing new buildings, and that pre-electricity structures were built to take advantage of climate and geography, using passive technologies to perform efficiently. Modern technologies have also been adopted- electrical lights, air conditioning, fire alarms - as a natural progression of inhabitation. Yet in historic house museums, there is still the promise of historic representation, one unmarred by ‘inauthentic’ additions. If modern and past technological changes have been accepted and integrated, how is the historic house museum not a ‘living building culture’? And if house museums are indeed a living building culture, why not allow a more flexible representation of our historic properties if they are interpreted with integrity and honesty? The EPA estimates that buildings represent 65% of the U.S. electricity use, and predictions estimate 80% of the 2030 building stock exists today. If we truly plan to reduce our energy consumption, we must confront the reality that existing buildings are a significant contributor to our output. If, as curators, it is our hope for historic buildings to represent preservation, then we must admit that in preserving the past for the future, we must begin by preserving our future. This thesis analyses the opportunities and risks for historic house museums to respect their historic interpretation but adapt to changing conditions. Examples of energy efficiency strategies both historic and current, will be examined in historic structures, illustrating that caretakers of historic buildings are making value judgments about the future of their property, in terms of environmental, fiscal and historical sustainability. This thesis includes the analysis of a case study historic house museum in Austin, Texas, the French Legation Museum, which is used as a base model for estimating energy efficiency gains from the adoption of some low-energy technologies. Calculations based on this information indicate which integrations and additions could offer the greatest return on investment for this historic building to operate as or more efficiently than a modern code construction without visible or egregious alteration to the historic fabric.Architectur

Effectiveness of roof overhang on mid-rise buildings: field measurements and improved assessment based on ISO standard

Wind-driven rain (WDR), as one of the most important boundary conditions, not only influences hydrothermal performance and material durability of the building enclosures but also its penetration through building’s assemblies may lead to different types of moisture related failures. In recently completed studies, a unique set of high resolution data through field measurements under real life conditions is provided by monitoring three mid-rise buildings in three Canadian cities (Vancouver, Montreal and Fredericton). All test buildings are instrumented with weather stations and driving rain gauges for wind driven-rain measurements on building’s façade. In addition, Vancouver building is equipped with a retractable overhang extendable to 1.2 m, partially covering east and north facades. The previous studies have shown that estimation of wind driven-rain by applying semi-empirical methods, is generally subjected to overestimation in comparison with measured wind driven-rain. The accuracy of ISO method can be improved significantly by using more accurate wall factors calculated based on onsite measurements. Moreover, the effectiveness of roof overhang in reduction of wind driven-rain deposition on a mid-rise building have been studied and quantified for 0.6 m and 1.2 m overhang. As a follow-up, this thesis conducted further analysis and tests with the purpose of improving wind-driven rain assessment based on ISO standard by achieving three main objectives: first, to develop a correlation between overhang width and amount of wind driven-rain load reduction on the facade under it, with respect to wind characteristics; second, to develop a methodology to generalize the proposed reduction coefficient for similar mid-rise building geometry being protected by roof overhang; and finally, to carry out further investigation of error sources for the discrepancy between measurements and calculated wall indices, therefore, improving the accuracy of ISO semi-empirical model. To fulfill these objectives, established methodology in previous studies such as the similarity and symmetry approach is followed by analyzing additional available data. Proposed wind driven-rain reduction coefficient is calculated based on the weighted-effectiveness methodology. Validation of generalizing proposed reduction coefficients for similar mid-rise building geometry is conducted by comparison of wind velocity near the upstream façade of study buildings model, with and without overhang, in Concordia’s atmospheric boundary layer wind tunnel. In addition, more detailed analysis regarding the effect of time resolution and data conversion on the accuracy of ISO model is provided. The detailed study of meteorological wind data, registered onsite and reported by the weather station, confirms that wind characteristic changes from point to point could be stated as other sources of discrepancies