CSR: Small: Cross-Layer Design of Power Delivery and Load Balancing for Green Data Centers

随着越来越多的计算迁移到云端，数据中心的能源消耗从环境和成本的角度来看变得越来越重要。 因此，减少数据中心的能源和碳足迹的趋势越来越明显。虽然已经做出了相当大的努力来降低能耗，但对数据中心中的电力输送的关注相对较少。这项工作的目标是通过专门为多服务器环境设计一个联合软件和硬件功率传输架构，将高压转换损耗（目前占功率损耗的10-15%）降低到几乎为零。 该研究将大大降低数据中心的功率转换损耗，对可持续和绿色数据中心的设计具有深远的影响。鼓励代表性不足的群体参与，并将部分研究纳入云计算课程，作为实验室电力电子课程的硬件项目，并作为高级研究生水平电力电子课程中数据中心电力输送的案例研究。一个交互式在线电力使用门户网站，实时可视化测试集群中每个服务器的电力使用情况，为公众与研究互动提供了机会。这些开源软件和硬件演示使来自世界各地的从业者能够更多地了解可持续计算。本研究探索了数据中心的跨层设计方法，其中电力输送架构和软件负载平衡算法共同工作，以实现最高的电力输送效率。该研究探讨了串联连接的服务器机架，以最大限度地减少整体电源转换和随之而来的损失。串联电压堆叠中的一个关键挑战是由于串联堆叠中的计算负载的不平衡而导致的每个服务器的输入电压的变化。在这项研究中，挑战是解决在硬件和软件。在软件方面，开发了可扩展的负载平衡算法，以确保机架中每个服务器的功耗均匀。负载平衡算法同时优化响应时间和功耗。此外，硬件功率转换器和分布式能量存储（例如，电容器、电池）在单独的软件不能满足需要的情况下提供滤波和功率平衡。正在解决的一个关键问题是能量存储的合适大小，以及功率转换器所需的控制带宽，以确保实际工作负载的正确操作。此外，结合服务器在非对称输入电压下的操作来采用电压和电流的电测量的高速感测和通信，以减轻静态功耗失配。 负载平衡算法测试了两种类型的工作负载：（1）交互式Web工作负载与短周转时间和同构服务器;（2）映射减少类型的工作负载与长周转时间和服务器的数据局部性约束。

As ever more computing is moved to the cloud, the energy consumption of data centers becomes increasingly important, both from an environmental and cost viewpoint. As a result, there is an increasing trend towards reducing the energy and carbon foot- print of data centers. While there has been considerable efforts to reduce the energy consumption, relatively little attention has been paid towards the power delivery in data centers. The objective of this work is to reduce the high voltage conversion losses (currently contributing 10-15% power loss) to almost zero by designing a joint software and hardware power delivery architecture specifically for a multi-server environment. This research, which could lead to drastic reduction of power conversion losses in data centers, has far-reaching impact on the design of sustainable and green data centers. Participation of underrepresented groups is encouraged, and portions of the research is incorporated into cloud computing courses, as hardware projects into a laboratory power electronics course, and as a case study of data center power delivery in an advanced graduate level power electronics course. An interactive online power usage portal, that visualizes in real-time the power usage of each individual server in the test-cluster provides opportunities for public interaction with the research. These open-source software and hardware demonstrations enable practitioners from around the world to learn more about sustainable computing. This research explores a cross-layer design approach to data centers, where the power delivery architecture and software load balancing algorithms work together to achieve the highest possible power delivery efficiency. The research explores electrically series-connected racks of servers, to minimize overall power conversion and attendant losses. A key challenge in series voltage stacking is the variation in input voltage of each server due to imbalance of computational load in a series-stack. In this research, the challenge is addressed both in hardware and software. In software, scalable load balancing algorithms that ensure uniform power consumption in each server in the rack are developed. The load balancing algorithms simultaneously optimize for response time and power loss. Moreover, hardware power converters and distributed energy storage (e.g., capacitors, batteries) provide filtering and power balance in cases when software alone does not suffice. A key question being addressed is the suitable size of energy storage, and the required control bandwidth of the power converters to ensure proper operation for realistic workloads. In addition, high speed sensing and communication of electrical measurements of voltage and currents are employed in combination with operation of servers at asymmetric input voltages for static power consumption mismatch mitigation. The load balancing algorithms is tested with two types of workloads: (1) Interactive web workloads with short turnaround time and homogeneous servers; and (2) Map-reduce type workloads with long turnaround time and servers with data locality constraint.