CSR: Small: On Modeling Software Dynamics for Feedback Computing

该项目开发确保大型软件系统性能稳定性的科学技术，例如数据中心中使用的资源管理机制。这里的“稳定性”一词是在控制理论意义上使用的，它适用于动力系统，大致意思是在期望的系统状态范围内不发散。性能稳定性是指时延、响应时间、业务吞吐量、利用率、缓存命中率、超时率等性能参数的稳定性。该项目开发了确保软件稳定性所需的基础和工具，并在部署系统中发生不稳定行为时诊断和撤销其根本原因。一个重要的贡献在于探索规则和指导方针，如果遵守这些规则和指导方针，就允许以组合的方式对软件稳定性进行推理，这样组合系统的稳定性就可以从组件的稳定性中推断出来。软件性能的组成稳定性分析得益于控制理论的进步，如无源性理论和正耗散系统理论。这些进步为适合软件模型的有限类别非线性系统的稳定性和组合性提供了丰富的结果。在软件设计中，性能稳定性的挑战在很大程度上被忽视了。它们通常不会出现在小型系统中，而是随着系统的规模和复杂性而增长。越来越多的软件整合和计算服务外包的趋势需要更多的复杂性、更多的分层和各种资源管理机制之间的更多交互，这使得预测副作用变得更加困难，并且更有可能出现稳定性问题。该项目改进了当前对大型系统的设计、执行和管理的理解，这些系统利用反馈机制来实现性能和健壮性目标。教育活动包括将项目元素纳入PI教授的几门课程，并让本科生参与研究。外展活动包括校园内的“反馈计算日”、与一个大型研究会议一起提供的反馈计算教程，以及PI为从代表性不足的群体中招收学生所做的努力。传播活动包括PI在一本书中记录研究结果，并努力通过工业界的合作者实现技术转型。

This project develops science and technology for ensuring performance stability of large-scale software systems, such as resource management mechanisms used in data centers. The term "stability" is used here in a control-theoretic sense that applies to dynamical systems and roughly means freedom from divergence a range of desired system states. Performance stability refers to stability of performance parameters, such as latency, response time, service throughput, utilization, cache hit ratio, or timeout rate. The project develops the foundations and tools necessary to ensure software stability, and to diagnose and undo root causes of unstable behavior when it occurs in deployed systems. A significant contribution lies in exploring rules and guidelines that, if obeyed, allow reasoning about software stability in a compositional manner, such that stability of composite systems can be inferred from stability of components. Compositional stability analysis of software performance is facilitated by advances in control theory such as Passivity Theory and the Theory of Positive and Dissipative Systems. These advances offer a wealth of results on stability and compositionality for a restricted category of non-linear systems that fits software models. Performance stability challenges have been largely overlooked in software design. They are not typically manifest in small systems, but grow with the size and complexity of systems. The trend towards more software consolidation and outsourcing of computing services entails more complexity, more layering, and more interactions among various resource management mechanisms, making it harder to anticipate side-effects, and more likely there will be stability problems. The project improves the current understanding of the design, execution, and management of large systems that exploit feedback mechanisms to achieve performance and robustness objectives. Educational activities include incorporation of project elements into several courses taught by the PI, and involvement of undergraduate students in the research. Outreach activities include an on-campus "Feedback Computing Day", a tutorial on feedback computing to be offered in conjunction with a major research conference, and efforts by the PI to recruit students from under-represented groups. Dissemination activities include documentation of results of the research in a book by the PI, and efforts to transition technology through collaborators in industry.