Collaborative Research: SHF: Medium: Neural-Network-based Stochastic Computing Architectures with applications to Machine Learning

现代计算硬件受到极小尺寸、低功耗和高可靠性等苛刻要求的限制。因此，直接解决这些问题的非传统计算方法，如随机计算(SC)，越来越引起人们的兴趣，特别是在人工智能(AI)中的机器学习(ML)应用。SC是一种新颖的计算框架，其中输入数据以比特流的形式连续提供；因此，可以通过对流进行简单的逐位运算来计算复杂的计算。SC的主要吸引力在于它实现了非常低成本和低功耗的体系结构实现，特别是对于使用简单逻辑元件的算术运算。此功能与神经网络(NNS)非常相关，因为NNS需要大量的硬件资源，因此在处理ML的大数据集时会消耗大量的功率。此外，当前的神经网络体系结构很难配置以适应不同的应用，因为硬件相当复杂，并且不是很灵活。因此，随着ML系统使用NNS达到计算的基本极限，SC已成为一种合理而实用的解决方案，以满足大规模并行和快速部署硬件的性能、能量和弹性要求，以支持直接影响技术和国民经济增长的人工智能。该项目的目标是开发依赖于横切方案(跨越硬件单元、算法和应用)的不同计算特征的神经网络体系结构，旨在设计这样高效的基于SC的神经网络。该项目所追求的技术工作利用了SC的主要特征，并提出了一个具有几个新概念的完善的研究计划。这项研究的第一个新奇之处在于，它通过关注体系结构级硬件目标以及SC的重要指标(如减少延迟和提高准确性，主要是在推理和训练方面)，使SC网络的设计成为可能。这项工作的第二个创新之处在于，它解决了基本问题，其中简单的SC硬件自适应地利用数据来支持NNS中的高级并行计算；解决方案围绕可配置的自下而上方案，其中最初的低级硬件(如神经元和处理功能单元)被模块化地应用于NN中，以支持较高级别的计算。还提出了在使用SC时纠正错误的新的存储器组织；这也增强了与应用相关的需求。第三个创新是在一个组合硬件实现上同时具有SC和传统(二进制)计算；这是在SC不满足手头应用程序的精度要求的情况下优化计算性能的额外好处。因此，这一及时的研究针对的是与计算和ML社区相关的新兴计算系统和体系结构的持续技术创新，以及对社会和整个美国计算行业的进步的强烈影响；此外，该项目坚定地致力于扩大对计算(BPC)的参与及其成功。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Modern computing hardware is constrained by stringent requirements such as extremely small size, low power consumption, and high reliability. Consequently, unconventional computing methods, such as Stochastic Computing (SC), that directly address these issues are of increasing interest, especially for Machine Learning (ML) applications in Artificial Intelligence (AI). SC is a novel computation framework in which input data is continuously provided as a streams of bits; therefore, complex computations can then be computed by simple bit-wise operations on the streams. The main attraction of SC is that it enables very low-cost and low-power architectural implementations, especially for arithmetic operations using simple logic elements. This feature is very relevant to Neural Networks (NNs), because NNs require significant hardware resources, therefore consuming substantial power when processing big datasets for ML. Moreover, current NN architectures are difficult to configure to suit different applications, because the hardware is rather complex and not very flexible. Thus, as ML systems are reaching the fundamental limits of computation using NNs, SC has emerged as a plausible and practical solution to meet performance, energy and resilience requirements for massive parallelism and fast deployment of hardware to support AI with direct impact on technology and national economic growth. The goal of this project is to develop NN architectures that rely on different computational features for cross-cutting schemes (spanning hardware units, algorithms, and applications) aimed at designing such efficient SC-based NNs.The technical work pursued under this project exploits the main features of SC and proposes a sound research program with several novel concepts. The first novelty of this investigation is that it makes possible the design of SC NNs by focusing on architectural-level hardware targeting also important metrics for SC (such as reducing latency and improving accuracy, mostly in inference and training). The second novelty of this work is that it addresses fundamental issues in which simple SC hardware is utilized adaptively to data to sustain a high level of parallel computation in NNs; solutions revolve around a configurable bottom-up scheme in which initially low-level hardware (such as neurons and processing function units) are modularly employed in the NNs to support computation at higher levels. Novel memory organizations to remedy errors when SC is employed are also proposed; this also enhances application-dependent requirements. The third novelty is the provision of having both SC as well as conventional (binary) computation on one combined hardware implementation; this is an added benefit for optimizing computing performance just in case the SC does not meet the accuracy requirements of the application at hand. Therefore, this timely research is directed to the continued technical innovation for emerging computing systems and architectures with relevance to both the computing and ML communities and strong implications on advancements in society and the US computing industry-at-large; moreover, this project is strongly committed to Broadening Participation in Computing (BPC) and its success.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.