空间加速器的受约束数据流建模与评估框架

将张量计算任务部署在空间加速器上已被证明能有效提高其执行速度和效率。为了在空间加速器上高效地进行张量计算,学术界提出了一系列数据流建模与评估框架。这些框架能够快速评估数据流,以便进行高效的设计空间探索。然而,这些框架缺乏对硬件结构的细粒度描述,因此无法有效地建模硬件结构对数据流的约束,从而无法有效地探索受到真实加速器硬件结构限制的数据流设计空间。为了解决这一问题,对硬件结构进行了细粒度建模,采用多层次的空间加速器硬件结构作为模板。每一层都包括阵列结构、存储结构和互连网络结构三部分,以分别描述硬件结构对数据流在空间展开、存储容量和数据传输方式方面的限制。提出了一种计算任务和数据流建模方法,该方法能够有效地求解数据流对硬件资源的需求。基于此,提出了一个数据流评估框架,包括需求分析、约束分析和性能分析三部分。需求分析用于求解计算任务和数据流对硬件资源的需求;约束分析旨在检查数据流是否违反硬件结构约束;性能分析用于评估数据流的延迟、数据重用和资源利用率等性能指标。实验结果表明,与之前最先进的评估框架相比,提出的框架在延迟评估方面的误差有所降低,并且能够有效地支持对受限数据流设计空间的探索。

A Model for Periodic Nonlinear Electric Field Structures in Space Plasmas

In this study,we present a physical model to explain the generation mechanism of nonlinear periodic waveswith a large amplitude electric field structures propagating obliquely and exactly parallel to the magnetic field.The'Sagdeev potential' from the MHD equations is derived and the nonlinear electric field waveforms are obtained when theMach number,direction of propagation,and the initial electric field satisfy certain plasma conditions.For the parallelpropagation,the amplitude of the electric field waves with ion-acoustic mode increases with the increase of initial electricfield and Mach number but its frequency decreases with the increase of Mach number.The amplitude and frequency ofthe electric field waves with ion-cyclotron mode decrease with the increase of Mach number and become less spiky,andits amplitude increases with the increase of initial electric field.For the oblique propagation,only periodic electric fieldwave with an ion-cyclotron mode obtained,its amplitude and frequency increase with the increase of Mach number andbecome spiky.From our model the electric field structures show periodic,spiky,and saw-tooth behaviours correspondingto different plasma conditions.