基于OpenMP的磁壳参数L值并行计算研究  

Research on parallel computing of magnetic L-shell based on OpenMP

作　　者：盛红佼 张贤国 朱昌波[1,3,4] SHENG HongJiao;ZHANG XianGuo;ZHU ChangBo(National Space Science Center,Chinese Academy of Sciences,Beijing 100190,China;University of Chinese Academy of Sciences,Beijing 100049,China;Beijing Key Laboratory of Space Environment Exploration,Beijing 100190,China;Key Laboratory of Science and Technology on Environmental Space Situation Awareness,Chinese Academy of Sciences,Beijing 100190,China)

机构地区：[1]中国科学院国家空间科学中心,北京100190 [2]中国科学院大学,北京100049 [3]天基空间环境探测北京市重点实验室,北京100190 [4]中国科学院空间环境态势感知技术重点实验室,北京100190

出　　处：《中国科学：技术科学》2021年第3期356-370,共15页Scientia Sinica(Technologica)

基　　金：空间科学先导专项(编号:XDA15017100);空间科学国家实验室培育项目“太阳风暴探测关键技术研究”(编号:Z191100004319003)资助。

摘　　要：辐射带研究中(L,B)坐标系把三维问题降为二维问题,大大提升了辐射带三维空间有限观测数据的利用率.L值是其中重要的参量之一,在粒子特性分析、航天器轨道辐射环境描述以及辐射带建模等研究领域应用十分广泛.L值由磁力线追踪积分计算而得,但地球磁场位型的复杂性导致磁力线追踪步长严格受限,造成单次追踪计算步数多.此外,不同空间位置处磁力线追踪路径和追踪距离随时空变化差异显著,造成多次L值计算之间相互独立、复杂度不一且无法简并,计算速度慢、效率低.为了提高L值的计算效率,本文采用OpenMP对目前广泛应用的L值计算程序实现单机多线程并行化,并分析了并行程序的加速比和效率.结果表明,并行后L值计算效率明显提高,当线程数量设置与系统最大线程数相等时(本文所用计算机系统线程数最大为8),并行效果最优,加速比范围为1.57~2.81,并行效率范围为19.63%~35.13%.计算过程中发现,线程间负载不平衡是影响并行效果的主要因素.为了提高并行加速比和效率,本文提出了一种表征L值计算复杂度的排序因子,并基于此提出了排序和重分配(“sort”和“S”分配)的优化负载算法,对dynamic,sort+“S”,sort+dynamic,sort+“S”+dynamic四种方式优化负载不平衡的效果进行了比对分析,结果表明sort+dynamic的效果最优,加速比范围为2.33~3.30,效率为29.13%~41.25%,优化效率提升了6.12%~9.50%.本文研究表明,OpenMP可以成功实现L值计算程序的并行计算,并提高L值的计算效率,针对负载不平衡的问题,采用sort+dynamic方式调节可获得最好的并行加速比和效率,为空间物理或其他领域类似大数据分析研究中效率提升提供了有益探索.In the study of radiation belts,the(L,B)coordinate system reduces the three-dimensional problem to a two-dimensional problem,greatly improving the utilization of the limited three-dimensional observational data on radiation belts.The L-shell is one of the most important parameters in the(L,B)coordinate system.It is widely used in particle characteristics analysis,in the description of spacecrafts’orbital radiation environments,and in radiation band modeling.The L-shell is calculated as the integral of the magnetic line tracing,but the complexity of geomagnetic field configurations results in the strict limitation of the tracking step length,resulting in more steps consisting of a single tracking calculation.In addition,the tracking path and distance of different spatial position lines vary significantly with time and space.This variation results in the independence of many L-shell calculations from one another,with different levels of complexity.In such cases the summation of steps may not be able to be simplified,causing the calculation speed to be slow and the efficiency low.In order to improve the efficiency of the L-shell calculation,this paper uses OpenMP to realize singlemachine multithreading parallelization of L-shell calculation programs widely used at present.This paper then analyzes the acceleration ratio and efficiency boost of parallelization.The results show that the efficiency of L-shell calculation is much improved by parallel processing.When the number of threads is set equal to the maximum number of threads in the system(here,8),parallel performance is optimal.The acceleration ratio ranges from 1.57 to 2.81,and the parallelization efficiency boost ranges from 19.63%to 35.13%.Load imbalance among threads is the main factor affecting parallel performance.In order to improve the parallel acceleration ratio and efficiency boost,this paper proposes a sort factor,representing the complexity of L-value calculation.Based on this,an algorithm of sorting and redistribution(sort,S)is proposed for load op

关 键 词：磁壳参数L值 并行计算 OPENMP 并行加速比 并行效率 并行优化 

分 类 号：P353.4[天文地球—空间物理学]