Design and optimization of a portable LQCD Monte Carlo code using OpenACC

TL;DR

This paper presents the design and optimization of a portable LQCD Monte Carlo code using OpenACC, enabling efficient execution across diverse HPC architectures with good performance portability.

Contribution

The work demonstrates a fully OpenACC-based LQCD Monte Carlo application that achieves performance portability across CPUs and GPUs, simplifying maintenance and development.

Findings

Achieved comparable performance on CPUs and GPUs using OpenACC

Demonstrated code portability across multiple architectures

Provided performance benchmarks comparing OpenACC with architecture-specific implementations

Abstract

The present panorama of HPC architectures is extremely heterogeneous, ranging from traditional multi-core CPU processors, supporting a wide class of applications but delivering moderate computing performance, to many-core GPUs, exploiting aggressive data-parallelism and delivering higher performances for streaming computing applications. In this scenario, code portability (and performance portability) become necessary for easy maintainability of applications; this is very relevant in scientific computing where code changes are very frequent, making it tedious and prone to error to keep different code versions aligned. In this work we present the design and optimization of a state-of-the-art production-level LQCD Monte Carlo application, using the directive-based OpenACC programming model. OpenACC abstracts parallel programming to a descriptive level, relieving programmers from specifying how codes should be mapped onto the target architecture. We describe the implementation of a code fully written in OpenACC, and show that we are able to target several different architectures, including state-of-the-art traditional CPUs and GPUs, with the same code. We also measure performance, evaluating the computing efficiency of our OpenACC code on several architectures, comparing with GPU-specific implementations and showing that a good level of performance-portability can be reached.