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Block fusion on dynamically adaptive spacetree grids for shallow water waves.

Weinzierl, Tobias and Bader, Michael and Unterweger, Kristof and Wittmann, Roland (2014) 'Block fusion on dynamically adaptive spacetree grids for shallow water waves.', Parallel processing letters., 24 (3). p. 1441006.


Spacetrees are a popular formalism to describe dynamically adaptive Cartesian grids. Even though they directly yield a mesh, it is often computationally reasonable to embed regular Cartesian blocks into their leaves. This promotes stencils working on homogeneous data chunks. The choice of a proper block size is sensitive. While large block sizes foster loop parallelism and vectorisation, they restrict the adaptivity's granularity and hence increase the memory footprint and lower the numerical accuracy per byte. In the present paper, we therefore use a multiscale spacetree-block coupling admitting blocks on all spacetree nodes. We propose to find sets of blocks on the finest scale throughout the simulation and to replace them by fused big blocks. Such a replacement strategy can pick up hardware characteristics, i.e. which block size yields the highest throughput, while the dynamic adaptivity of the fine grid mesh is not constrained—applications can work with fine granular blocks. We study the fusion with a state-of-the-art shallow water solver at hands of an Intel Sandy Bridge and a Xeon Phi processor where we anticipate their reaction to selected block optimisation and vectorisation.

Item Type:Article
Keywords:Spacetrees, Shallow water, Adaptive Cartesian meshes, Vectorisation, Block fusion, Shared memory parallelisation.
Full text:(SMUR) Submitted Manuscript Under Review
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Status:Not peer-reviewed
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Publisher statement:Preprint of an article published in Parallel Processing Letters, 24, 3, 2014, 1441006, 10.1142/S0129626414410060 © World Scientific Publishing Company
Date accepted:30 July 2014
Date deposited:No date available
Date of first online publication:30 September 2014
Date first made open access:No date available

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