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Improving Energy-Efficiency of Multicores using First-Order Modeling
Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Computer Systems.
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In the recent decades, power consumption has evolved to one of the most critical resources in a computer system. In the form of electricity bill in data centers, battery life in mobile devices, or thermal constraints in desktops and laptops, power consumption imposes several limitations in today’s processors and improving power and energy efficiency is one of the most urgent research topics of Computer Architecture.

Dynamic Voltage and Frequency Scaling (DVFS) and Cache Resizing are among the most popular energy saving techniques. Previous work, however, has focused on developing heuristics and trial-and-error methods that yield acceptable savings, but fail to provide insight and understanding of how these techniques affect power and performance of a computer system. In contrast, this Thesis proposes the use of first-order modeling to improve the energy efficiency of computer systems. A first-order model needs to be (i) accurate enough to efficiently drive DVFS and Cache Resizing decisions, and (ii) simple enough to eliminate the overhead of collecting the required inputs to the model. We show that such models can be constructed and successfully applied in modern systems.

For DVFS, we propose to scale frequency down to exploit applications’ memory slack, i.e., periods that the processor spends waiting for data to be fetched from the main memory. In such cases, the processor frequency can be scaled down to save energy without inordinate performance penalty. Our DVFS models can detect slack and predict the impact of DVFS in both power and performance with great accuracy. Cache Resizing, on the other hand, relies on the fact that many applications do not benefit from the vast amount of cache that modern processors are equipped with. In such cases, the cache can be resized to save static energy consumption at limited performance cost. Since both techniques are related with the memory behavior of applications, we propose a unified model to manage the two techniques in tandem and maximize energy efficiency through synergistic DVFS and Cache Resizing.

Finally, our experience with DVFS in real systems motivated us to contribute to the integration of DVFS into the gem5 simulator. Unlike other simulators that ignore the role of OS in DVFS, we extend the gem5 simulator by developing the hardware and software components that allow existing Linux DVFS infrastructure to be seamlessly integrated in the simulator.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. , 52 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1404
Keyword [en]
Computer Architecture, DVFS, Cache Resizing, Interval modeling, Power modeling
National Category
Computer Science
Research subject
Computer Science
Identifiers
URN: urn:nbn:se:uu:diva-300947ISBN: 978-91-554-9652-4OAI: oai:DiVA.org:uu-300947DiVA: diva2:952966
Public defence
2016-09-29, ITC/2446, Lägerhyddsvägen 2, Uppsala, 13:00 (English)
Opponent
Supervisors
Available from: 2016-09-06 Created: 2016-08-16 Last updated: 2016-09-13
List of papers
1. Interval-based models for run-time DVFS orchestration in superscalar processors
Open this publication in new window or tab >>Interval-based models for run-time DVFS orchestration in superscalar processors
2010 (English)In: Proc. 7th International Conference on Computing Frontiers, New York: ACM Press , 2010, 287-296 p.Conference paper (Refereed)
Place, publisher, year, edition, pages
New York: ACM Press, 2010
National Category
Computer Engineering Computer Science
Identifiers
urn:nbn:se:uu:diva-142687 (URN)10.1145/1787275.1787338 (DOI)978-1-4503-0044-5 (ISBN)
Projects
UPMARC
Available from: 2010-05-19 Created: 2011-01-14 Last updated: 2016-09-02Bibliographically approved
2. Green governors: A framework for continuously adaptive DVFS
Open this publication in new window or tab >>Green governors: A framework for continuously adaptive DVFS
2011 (English)In: Proc. International Green Computing Conference and Workshops: IGCC 2011, Piscataway, NJ: IEEE , 2011, 1-8 p.Conference paper (Refereed)
Place, publisher, year, edition, pages
Piscataway, NJ: IEEE, 2011
National Category
Computer Engineering
Identifiers
urn:nbn:se:uu:diva-165805 (URN)10.1109/IGCC.2011.6008552 (DOI)978-1-4577-1222-7 (ISBN)
Projects
UPMARC
Available from: 2012-01-10 Created: 2012-01-09 Last updated: 2016-09-02Bibliographically approved
3. Power-Sleuth: A Tool for Investigating your Program's Power Behavior
Open this publication in new window or tab >>Power-Sleuth: A Tool for Investigating your Program's Power Behavior
2012 (English)In: International Symposium on Modeling, Analysis and Simulation of Computer and Telecommunication Systems (MASCOTS'12), 2012, 241-250 p.Conference paper (Refereed)
Abstract [en]

Modern processors support aggressive power saving techniques to reduce energy consumption. However, traditional profiling techniques have mainly focused on performance, which does not accurately reflect the power behavior of applications. For example, the longest running function is not always the most energy-hungry function. Thus software developers cannot always take full advantage of these power-saving features.

We present \powersleuth, a power/performance estimation tool which is able to provide a full description of an application's behavior for any frequency from a single profiling run. The tool combines three techniques: a power and a performance estimation model with a program phase detection technique to deliver accurate, per-phase, per-frequency analysis.

Our evaluation (against real power measurements) shows that we can accurately predict power and performance across different frequencies with average errors of 3.5% and 3.9% respectively.

National Category
Computer Systems Computer Science Computer Engineering
Research subject
Computer Science; Computer Systems
Identifiers
urn:nbn:se:uu:diva-180147 (URN)10.1109/MASCOTS.2012.36 (DOI)978-1-4673-2453-3 (ISBN)
Conference
International Symposium on Modeling, Analysis and Simulation of Computer and Telecommunication Systems (MASCOTS), August 2012, Washington, DC, USA
Projects
CoDeR-MPUPMARCVRERA
Available from: 2012-08-30 Created: 2012-08-30 Last updated: 2016-09-02Bibliographically approved
4. Introducing DVFS-Management in a Full-System Simulator
Open this publication in new window or tab >>Introducing DVFS-Management in a Full-System Simulator
Show others...
2013 (English)In: Proc. 21st International Symposium on Modeling, Analysis and Simulation of Computer and Telecommunication Systems, IEEE Computer Society, 2013Conference paper (Refereed)
Abstract [en]

Dynamic Voltage and Frequency Scaling (DVFS) is an essential part of controlling the power consumption of any computer system, ranging from mobile phones to servers. DVFS efficiency relies on hardware-software co-optimization, thus using existing hardware cannot reveal the full optimization potential beyond the current implementation’s characteristics. To explore the vast design space for DVFS efficiency, that straddles software and hardware, a simulation infrastructure must provide features that are not readily available today, for example: software controllable clock and voltage domains, support for the OS and the frequency scaling module of it, and an online power estimation methodology. As the main contribution,this work enables DVFS studies in a full-system simulator. We extend the gem5 simulator to support full-system DVFS modeling. By doing so, we enable energy-efficiency experiments to be performed in gem5 and we showcase such studies. Finally, we show that both existing and novel frequency governors for Linux and Android can be effortlessly integrated in the framework, and we evaluate the efficiency of different DVFS schemes.

Place, publisher, year, edition, pages
IEEE Computer Society, 2013
National Category
Computer Systems
Identifiers
urn:nbn:se:uu:diva-212809 (URN)
Conference
MASCOTS 2013
Projects
UPMARC
Available from: 2013-12-15 Created: 2013-12-15 Last updated: 2016-09-02
5. A unified DVFS-cache resizing framework
Open this publication in new window or tab >>A unified DVFS-cache resizing framework
Show others...
2016 (English)Report (Other academic)
Series
Technical report / Department of Information Technology, Uppsala University, ISSN 1404-3203 ; 2016-014
National Category
Computer Science
Identifiers
urn:nbn:se:uu:diva-300840 (URN)
Available from: 2016-08-15 Created: 2016-08-15 Last updated: 2016-09-02Bibliographically approved

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