D. Richins, et al., “Missing the Forest for the Trees: End-to-End AI Application Performance in Edge Data Centers,” in International Symposium on High Performance Computer Architecture (HPCA), 2020.Abstract

Artificial intelligence and machine learning are experiencing widespread adoption in the industry, academia, and even public consciousness. This has been driven by the rapid advances in the applications and accuracy of AI through increasingly complex algorithms and models; this, in turn, has spurred research into developing specialized hardware AI accelerators. The rapid pace of the advances makes it easy to miss the forest for the trees: they are often developed and evaluated in a vacuum without considering the full application environment in which they must eventually operate. In this paper, we deploy and characterize Face Recognition, an AI-centric edge video analytics application built using open source and widely adopted infrastructure and ML tools. We evaluate its holistic, end-to-end behavior in a production-size edge data center and reveal the “AI tax” for all the processing that is involved. Even though the application is built around state-of-the-art AI and ML algorithms, it relies heavily on pre- and post-processing code which must be executed on a general-purpose CPU. As AI-centric applications start to reap the acceleration promised by so many accelerators, we find they impose stresses on the underlying software infrastructure and the data center’s capabilities: storage and network bandwidth become major bottlenecks with increasing AI acceleration. By not having to serve a wide variety of applications, we show that a purpose-built edge data center can be designed to accommodate the stresses of accelerated AI at 15% lower TCO than one de-rived from homogeneous servers and infrastructure. We also discuss how our conclusions generalize beyond Face Recognition as many AI-centric applications at the edge rely upon the same underlying software and hardware infrastructure.

M. Halpern, B. Boroujerdian, T. Mummert, E. Duesterwald, and V. J. Reddi, “One Size Does Not Fit All: Quantifying and Exposing the Accuracy-Latency Trade-off in Machine Learning Cloud Service APIs via Tolerance Tiers,” in Proceedings of the 19th International Symposium on Performance Analysis of Systems and Software (ISPASS), 2019.Abstract

Today's cloud service architectures follow a “one size fits all” deployment strategy where the same service version instantiation is provided to the end users. However, consumers are broad and different applications have different accuracy and responsiveness requirements, which as we demonstrate renders the “one size fits all” approach inefficient in practice. We use a production grade speech recognition engine, which serves several thousands of users, and an open source computer vision based system, to explain our point. To overcome the limitations of the “one size fits all” approach, we recommend Tolerance Tiers where each MLaaS tier exposes an accuracy/responsiveness characteristic, and consumers can programmatically select a tier. We evaluate our proposal on the CPU-based automatic speech recognition (ASR) engine and cutting-edge neural networks for image classification deployed on both CPUs and GPUs. The results show that our proposed approach provides a MLaaS cloud service architecture that can be tuned by the end API user or consumer to outperform the conventional “one size fits all” approach.

W. Cui, D. Richins, Y. Zhu, and V. J. Reddi, “Tail Latency in Node.js: Energy Efficient Turbo Boosting for Long Latency Requests in Event-Driven Web Services,” in Proceedings of the 15th ACM SIGPLAN/SIGOPS International Conference on Virtual Execution Environments (VEE), 2019.Abstract

Cloud-based Web services are shifting to the event-driven, scripting language-based programming model to achieve productivity, flexibility, and scalability. Implementations of this model, however, generally suffer from long tail latencies, which we measure using Node.js as a case study. Unlike in traditional thread-based systems, reducing long tails is difficult in event-driven systems due to their inherent asynchronous programming model. We propose a framework to identify and optimize tail latency sources in scripted eventdriven Web services. We introduce profiling that allows us to gain deep insights into not only how asynchronous eventdriven execution impacts application tail latency but also how the managed runtime system overhead exacerbates the tail latency issue further. Using the profiling framework, we propose an event-driven execution runtime design that orchestrates the hardware’s boosting capabilities to reduce tail latency. We achieve higher tail latency reductions with lower energy overhead than prior techniques that are unaware of the underlying event-driven program execution model. The lessons we derive from Node.js apply to other event-driven services based on scripting language frameworks.

Paper Presentation
D. Richins, T. Ahmed, R. Clapp, and V. J. Reddi, “Amdahl's Law in Big Data Analytics: Alive and Kicking in TPCx-BB (BigBench),” in IEEE International Symposium on High Performance Computer Architecture (HPCA), 2018, pp. 630–642. Publisher's VersionAbstract

Big data, specifically data analytics, is responsible for driving many of consumers’ most common online activities, including shopping, web searches, and interactions on social media. In this paper, we present the first (micro)architectural investigation of a new industry-standard, open source benchmark suite directed at big data analytics applications—TPCx-BB (BigBench). Where previous work has usually studied benchmarks which oversimplify big data analytics, our study of BigBench reveals that there is immense diversity among applications, owing to their varied data types, computational paradigms, and analyses. In our analysis, we also make an important discovery generally restricting processor performance in big data. Contrary to conventional wisdom that big data applications lend themselves naturally to parallelism, we discover that they lack sufficient thread-level parallelism (TLP) to fully utilize all cores. In other words, they are constrained by Amdahl’s law. While TLP may be limited by various factors, ultimately we find that single-thread performance is as relevant in scale-out workloads as it is in more classical applications. To this end we present core packing: a software and hardware solution that could provide as much as 20% execution speedup for some big data analytics applications.

Paper Presentation
M. Halpern, T. Mummert, M. Novak, E. Duesterwald, and V. J. Reddi, “The Case for Node Multi-Versioning in Cognitive Cloud Services: Achieving Responsiveness and Accuracy at Datacenter Scale,” Workshop on Cognitive Architectures (CogArch). 2016.Abstract

Cognitive cloud services seek to provide end-users with functionalities that have historically required human intellect to complete. End-users expect these services to be both responsive and accurate, which pose conflicting requirements for service providers. Today’s cloud services deployment schemes follow a “one size fits all” scale-out strategy, where multiple instantiations of the same version of the service are used to scale-out and handle all end-users. Meanwhile, many cognitive services are of a statistical nature where deeper exploration yields more accurate results but also requires more processing time. Finding a single service configuration setting that satisfies the latency and accuracy requirements for the largest number of expected end-user requests can be a challenging task. As a result, cognitive cloud service providers are conservatively configured to maximize the number of enduser requests for which a satisfactory latency-accuracy tradeoff can be achieved. Using a production-grade Automatic Speech Recognition cloud service as a representative example to study, we demonstrate the inefficiencies of this single version approach and propose a new service node multi-versioning deployment scheme for cognitive services instead. We present an oracle-based limit study where we show that service node multi-versioning can provide a 2.5X reduction in execution time together with a 24% improvement in accuracy over a traditional single version deployment scheme. We also discuss several design considerations to address when implementing service node multi-versioning.

V. J. Reddi, B. Lee, T. Chilimbi, and K. Vaid, “Mobile Processors for Energy-Efficient Web Search,” in Transactions on Computer Systems, 2011, 4th ed. vol. 29.Abstract

As cloud and utility computing spreads, computer architects must ensure continued capability growth for the data centers that comprise the cloud. Given megawatt scale power budgets, increasing data center capability requires increasing computing hardware energy efficiency. To increase the data center’s capability for work, the work done per Joule must increase. We pursue this efficiency even as the nature of data center applications evolves. Unlike traditional enterprise workloads, which are typically memory or I/O bound, big data computation and analytics exhibit greater compute intensity. This article examines the efficiency of mobile processors as a means for data center capability. In particular, we compare and contrast the performance and efficiency of the Microsoft Bing search engine executing on the mobile-class Atom processor and the server-class Xeon processor. Bing implements statistical machine learning to dynamically rank pages, producing sophisticated search results but also increasing computational intensity. While mobile processors are energy-efficient, they exact a price for that efficiency. The Atom is 5× more energy-efficient than the Xeon when comparing queries per Joule. However, search queries on Atom encounter higher latencies, different page results, and diminished robustness for complex queries. Despite these challenges, quality-of-service is maintained for most, common queries. Moreover, as different computational phases of the search engine encounter different bottlenecks, we describe implications for future architectural enhancements, application tuning, and system architectures. After optimizing the Atom server platform, a large share of power and cost go toward processor capability. With optimized Atoms, more servers can fit in a given data center power budget. For a data center with 15MW critical load, Atom-based servers increase capability by 3.2× for Bing.

V. J. Reddi, B. Lee, T. Chilimbi, and K. Vaid, “Web Search Using Mobile Cores: Quantifying and Mitigating the Price of Efficiency,” in International Symposium on Computer Architecture, 2010. Publisher's VersionAbstract

The commoditization of hardware, data center economies of scale, and Internet-scale workload growth all demand greater power efficiency to sustain scalability. Traditional enterprise workloads, which are typically memory and I/O bound, have been well served by chip multiprocessors comprising of small, power-efficient cores. Recent advances in mobile computing have led to modern small cores capable of delivering even better power efficiency. While these cores can deliver performance-per-Watt efficiency for data center workloads, small cores impact application quality-of-service robustness, and flexibility, as these workloads increasingly invoke computationally intensive kernels. These challenges constitute the price of efficiency. We quantify efficiency for an industry-strength online web search engine in production at both the microarchitecture- and system-level, evaluating search on server and mobile-class architectures using Xeon and Atom processors.

Categories and Subject Descriptors

C.0 [Computer Systems Organization]: General—System architectures; C.4 [Computer Systems Organization]: Performance of Systems—Design studies, Reliability, availability, and serviceability

General Terms

Measurement, Experimentation, Performance

S. M. Figueira and V. J. Reddi, “Topology-Based Hypercube Structures for Global Communication in Heterogeneous Networks,” in European Conference on Parallel Processing, 2005, pp. 994–1004.Abstract

Hypercube structures are heavily used by parallel algorithms that require all-to-all communication. When communicating over a heterogeneous and irregular network, the performance obtained by the hypercube structure will depend on the matching of the hypercube structure to the topology of the underlying network. In this paper, we present strategies to build topology-based hypercubes structures. These strategies do not assume any kind of topology. They take into account the communication cost between pair of nodes to provide a performance-efficient hypercube structure. These enhanced hypercube structures help improve the performance of parallel applications that require all-to-all communication in heterogeneous networks by up to ~30%.