Field-Programmable Gate Arrays (FPGAs) are more energy efficient and cost effective than CPUs for a wide variety of datacenter applications. Yet, for latency-sensitive and bursty workloads, this advantage can be difficult to harness due to high FPGA spin-up costs. We propose that a hybrid FPGA and CPU computing framework can harness the energy efficiency benefits of FPGAs for such workloads at reasonable cost. Our key insight is to use FPGAs for stable-state workload and CPUs for short-term workload bursts. Using this insight, we design Spork, a lightweight hybrid scheduler that can realize these energy efficiency and cost benefits in practice. Depending on the desired objective, Spork can trade off energy efficiency for cost reduction and vice versa. It is parameterized with key differences between FPGAs and CPUs in terms of power draw, performance, cost, and spin-up latency. We vary this parameter space and analyze various application and worker configurations on production and synthetic traces. Our evaluation of cloud workloads shows that energy-optimized Spork is not only more energy efficient but it is also cheaper than homogeneous platforms--for short application requests with tight deadlines, it is 1.53x more energy efficient and 2.14x cheaper than using only FPGAs. Relative to an idealized version of an existing cost-optimized hybrid scheduler, energy-optimized Spork provides 1.2-2.4x higher energy efficiency at comparable cost, while cost-optimized Spork provides 1.1-2x higher energy efficiency at 1.06-1.2x lower cost.

翻译：现场可编程门阵列(FPGA)在多种数据中心应用中比CPU具有更高的能效和成本效益。然而，对于延迟敏感且具有突发性的工作负载，由于FPGA启动成本高昂，这一优势往往难以发挥。我们提出，一种混合FPGA与CPU计算框架能够在合理成本下，针对此类工作负载发挥FPGA的能效优势。我们的核心洞察是：将FPGA用于稳态工作负载，而将CPU用于短期工作负载突发。基于这一洞察，我们设计了Spork——一种轻量级混合调度器，可在实践中实现上述能效与成本效益。根据优化目标，Spork可在能效与成本降低之间进行权衡，其参数化涵盖了FPGA与CPU在功耗、性能、成本和启动延迟方面的关键差异。我们通过改变这一参数空间，在生产环境轨迹与合成轨迹上分析了多种应用与工作节点配置。对云工作负载的评估表明，能效优化的Spork不仅比同构平台更节能，且成本更低——对于截止时间紧迫的短应用请求，其能效比仅使用FPGA的方案高1.53倍，成本低2.14倍。相较于现有成本优化混合调度器的理想化版本，能效优化的Spork在可比成本下能效提高1.2-2.4倍，而成本优化的Spork在成本降低1.06-1.2倍的同时能效提升1.1-2倍。