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Title Characterization of voltage noise in big, small and single-ISA heterogeneous systems
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Date Accessioned
Discipline/Department Computer Sciences
University/Publisher University of Texas – Austin
Abstract Sensitivity of the microprocessor to voltage fluctuations is becoming a major concern with growing emphasis on designing power-efficient microprocessors. Voltage fluctuations that exceed a certain threshold cause "emergencies" that can lead to timing errors in the processor, thus risking reliability. To guarantee correctness under such conditions, large voltage guardbands are employed, at the cost of reduced performance and wastage of power. Trends in microprocessor technology indicate that worst-case operating voltage margins are not sustainable. Since voltage emergencies occur only infrequently, resilient architectures with aggressive guardbands are needed. However, to enable the exploration of the design space of resilient processors, it is important to have a deep understanding of the characteristics of voltage noise in different system configurations. Prior research in this area has mostly focused on systems with very few cores. Given the increasing relevance of large multi-core systems, this thesis presents a detailed characterization of voltage noise on chip multi-processors, consisting of large number of cores. The data indicates that while the worst case voltage droop increases with increase in the number of cores, the frequency of occurrence of the droops is not greatly impacted, emphasizing the feasibility of employing resilient microarchitectures with aggressive voltage margins. The thesis also presents a comparative study of voltage noise in CMPs consisting of either high-performant out-of-order cores and power-efficient in-order cores. The study highlights that the out-of-order cores experience much larger voltage variations when compared to the in-order cores, but offer a clear advantage in terms of performance. Experiments indicate that in-order configurations that offer equivalent performance to the out-of-order cores result in large energy-delay product, indicating the trade-offs involved in designing for performance, power and reliability. The thesis also presents a study of voltage noise in single-ISA heterogeneous configurations, to highlight the benefits of such systems towards lowering the worst-case voltage margins, which improve both performance and power. The experimental results indicate that the worst-case voltage droop in such heterogeneous systems lies in between the out-of-order and in-order cores and provide reasonable power-efficiency and performance. Further, the work highlights the importance of exploring the design-space of heterogeneous systems considering reliability as an important design criteria.
Subjects/Keywords Voltage noise; Multi-cores; Single-ISA heterogeneous; Power modeling; Voltage modeling; Reliability
Contributors John, Lizy Kurian (advisor); Reddi, Vijay Janapa (committee member)
Country of Publication us
Record ID handle:2152/40992
Repository texas
Date Indexed 2018-10-22
Note [department] Computer Sciences;

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…important microprocessor design criteria. Efforts to improve the energy efficiency of high performance processors has led to another class of multi-cores, called heterogeneous multi-cores. Heterogeneous systems may consist of different-ISA cores, like CPU…

…x5D; comprising of big out-of-order cores and small in-order cores. [10][16][18] [21][32] illustrates that such heterogeneous multi-cores can provide energy efficiency when workloads are appropriately…

…scheduled on the most suitable cores. Thus, heterogeneous system architec2 ture is a promising design, especially for the power constrained mobile devices. Given the importance of reliability, it is necessary to understand how voltage noise impacts the…

…design of heterogeneous systems. In this thesis, I present a detailed characterization of voltage fluctuations in a multi-core system with large number of cores and present a comparative study of voltage fluctuations in the high performant out-of-order…

…and small, energy-efficient in-order cores. The study also characterizes voltage noise in single-ISA heterogeneous systems. The results indicate that while the big cores yield better performance, they require extremely large voltage guardbands…

…compared to the smaller, in-order cores, leading to reduced powerefficiency. The study also indicates that the heterogeneous systems not only provide energy-efficiency, they allow reduced voltage margins, thus effectively increasing performance. The main…

…consisting of big, small and a combination of big and small cores, to demonstrate that single-ISA heterogeneous systems achieve better energy-efficiency and reduced worst case voltage fluctuations. 4 Chapter 2 Background This chapter provides a brief…

…small, energyefficient in-order cores. To the best of my knowledge, this is the first comparative study of voltage noise in big and small cores. The thesis also demonstrates 13 trends in voltage noise in single-ISA heterogeneous CMP systems. 14…

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