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

随着越来越多的计算转移到云上，从环境和成本的角度来看，数据中心的能源消耗变得越来越重要。因此，减少数据中心的能源和碳足迹的趋势越来越大。虽然已经做出了相当大的努力来降低能源消耗，但相对较少的关注数据中心的电力输送。这项工作的目标是通过设计专门用于多服务器环境的联合软件和硬件供电架构，将高压转换损耗(目前占10%-15%的功率损耗)降低到几乎为零。这项研究可能会大幅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，以及作为高级研究生级别电力电子课程中数据中心电力交付的案例研究。交互式在线电源使用门户，实时显示测试集群中每台服务器的电源使用情况，为公众与研究互动提供机会。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。本研究探索了一种数据中心的跨层设计方法，在这种方法中，电源交付架构和软件负载平衡算法协同工作，以实现尽可能高的电源交付效率。这项研究探索了电气串联的服务器机架，以最大限度地减少总体功率转换和随之而来的损失。串联电压堆叠的一个关键挑战是由于串联堆栈中计算负载的不平衡而导致每个服务器的输入电压的变化。在这项研究中，从硬件和软件两个方面解决了这一挑战。在软件方面，开发了可扩展的负载平衡算法，以确保机架中每台服务器的统一功耗。负载均衡算法同时优化响应时间和功率损耗。此外，硬件功率转换器和分布式能量存储(例如，电容器、电池)在仅有软件不能满足要求的情况下提供过滤和功率平衡。正在解决的一个关键问题是能量存储的合适大小，以及确保实际工作负载正确运行所需的功率转换器的控制带宽。此外，采用了电压和电流电气测量的高速传感和通信，并结合服务器在非对称输入电压下的操作来降低静态功耗失配。通过两种类型的负载对负载均衡算法进行了测试：(1)具有短周转时间的交互式Web负载和同构服务器；(2)具有较长周转时间的Map-Reduce型负载和具有数据局部性约束的服务器。

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.