Chip-level and multi-node analysis of energy-optimized lattice-Boltzmann CFD simulations

TL;DR

This paper analyzes energy-efficient lattice-Boltzmann CFD simulations at chip and multi-node levels, identifying key optimization strategies for reducing energy consumption while maintaining performance.

Contribution

It provides a detailed performance and energy analysis of LBM on multicore processors, offering guidelines for optimizing energy efficiency in parallel CFD simulations.

Findings

High single-core performance is crucial for energy efficiency.

Optimal number of active cores minimizes energy to solution.

Energy savings of up to 35% achieved through targeted optimizations.

Abstract

Memory-bound algorithms show complex performance and energy consumption behavior on multicore processors. We choose the lattice-Boltzmann method (LBM) on an Intel Sandy Bridge cluster as a prototype scenario to investigate if and how single-chip performance and power characteristics can be generalized to the highly parallel case. First we perform an analysis of a sparse-lattice LBM implementation for complex geometries. Using a single-core performance model, we predict the intra-chip saturation characteristics and the optimal operating point in terms of energy to solution as a function of implementation details, clock frequency, vectorization, and number of active cores per chip. We show that high single-core performance and a correct choice of the number of active cores per chip are the essential optimizations for lowest energy to solution at minimal performance degradation. Then we extrapolate to the MPI-parallel level and quantify the energy-saving potential of various optimizations and execution modes, where we find these guidelines to be even more important, especially when communication overhead is non-negligible. In our setup we could achieve energy savings of 35% in this case, compared to a naive approach. We also demonstrate that a simple non-reflective reduction of the clock speed leaves most of the energy saving potential unused.