Modeling the Temperature Bias of Power Consumption for Nanometer-Scale CPUs in Application Processors

We introduce and experimentally validate a new macro-level model of the CPU temperature/power relationship within nanometer-scale application processors or system-on-chips. By adopting a holistic view, this model is able to take into account many of the physical effects that occur within such systems. Together with two algorithms described in the paper, our results can be used, for instance by engineers designing power or thermal management units, to cancel the temperature-induced bias on power measurements. This will help them gather temperature-neutral power data while running multiple instance of their benchmarks. Also power requirements and system failure rates can be decreased by controlling the CPU's thermal behavior. Even though it is usually assumed that the temperature/power relationship is exponentially related, there is however a lack of publicly available physical temperature/power measurements to back up this assumption, something our paper corrects. Via measurements on two pertinent platforms sporting nanometer-scale application processors, we show that the power/temperature relationship is indeed very likely exponential over a 20{\deg}C to 85{\deg}C temperature range. Our data suggest that, for application processors operating between 20{\deg}C and 50{\deg}C, a quadratic model is still accurate and a linear approximation is acceptable.Comment: Submitted to SAMOS 2014; International Conference on Embedded Computer Systems: Architectures, Modeling, and Simulation (SAMOS XIV

La loi de convexité énergie-fréquence de la consommation des programmes : modélisation, thermosensibilité et applications

Cette thèse s’intéresse à la consommation énergétique d’un système embarqué durant l’execution d’un programme. Une preuve théorique est présentée dans cette thèse et expérimentale de l’existence d’une loi de convexité énergie-fréquence de la consommation des programmes, qui concerne la consommation d’énergie et la fréquence des microprocesseurs à l’échelle nanométrique. Des noyaux de calcul intensif spécifiques ont été exécutés sur des processeurs d’applications typiques, à l’échelle nanométrique, et leurs caractéristiques mesurées en utilisant des capteurs de puissance à haute résolution. Lesdonnées recueillies lors de nombreuses campagnes d’acquisition de données longues de plusieurs semaines chacune suggèrent que la consommation est fortement corrélée avec la fréquence du microprocesseur et, ce qui est extrêmement intéressant, que la courbe présente un minimum clair sur la gamme de fréquences utilisables sur les processeurs.Un modèle analytique de ce comportement est fourni et motivé; il cadre particulièrement bien avec les données. Les circonstances dans lesquelles cette règle de convexité peut être exploitée sont discutées, en particulier dans le but d’améliorer l’efficacité énergétique du microprocesseur. La loi de convexité énergie-fréquence de la consommation des programmesest potentiellement plus exploitable par les systèmes de faible puissance, tels que les systèmes embarqués et alimentés par piles ou batteries, et moins susceptible de l’être par les systèmes informatiques de haute performance. La loi de convexité énergiefréequence de la consommation des programmes est également appliquée aux systèmes multi-coeurs, à la loi d’Amdahl et aux systèmes informatiques hétérogènes.Etant donné que la consommation d’énergie du microprocesseur dépend de sa température, une relation température/puissance au niveau macro pour les processeurs d’application est également introduite et validée expérimentalement dans cette thèse. En adoptant une vision holistique, ce modèle est capable de prendre en compte de nombreux effets physiques qui se produisent dans de tels systèmes. Via des mesures sur deux platesformes pertinentes comportant des processeurs d’applications à l’échelle nanométrique, il est montré que la relation puissance/température se comporte de manière exponentielle entre 20C et 85C.Les données suggèrent de plus que, pour une plage de températures comprise entre 20C et 55C, un modèle quadratique est toujours suffisamment précis et qu’une approximation linéaire est même acceptable. Des modèles de transformationd’énergie visant à annuler les biais liés à la température dans les mesures de puissance sont également présentés.Ces modèles de transformation ont été mis au point afin d’augmenter la précision et la pertinence des traces de mesure de puissance.Outre les mesures statiques de puissance, les comportements transitoires en puissance et température sont également analysés à l’aide des lois de refroidissement et des modèles température/puissance. Il s’avère que des modèles de refroidissement exponentiels sont justifiés pour des microprocesseurs refroidis de manière active. Cependant, pour les processeursrefroidis passivement que l’on trouve fréquemment dans les systèmes embarqués, une loi exponentielle ne peut pas être justifiée théoriquement. En conséquence, la loi ex-acte de refroidissement pour un corps à refroidissement passif est analysée, sous condition de refroidissement radiatif et d’un niveau modeste de perte de chaleur par convection.Si l’on se concentre sur les microprocesseurs embarqués, il y a une différence de performance entre la nouvelle loi de refroidissement passif et celle, exponentielle, classiquement utilisée. On montre que, pour les grandes surfaces, le refroidissement par rayonnement peut être comparable à celui lié à la convection. Toutefois, pour les grandes surfaces derefroidissement de l’ordre de 1dm2 ou plus, les différences entre la loi de refroidissement passif et la loi exponentielle de refroidissement sont importantes. Ces résultats suggèrent donc que, en l’absence de mesures précises de la température, une loi exponentielle de refroidissement n’est suffisamment précise que pour les petits systèmes SoC ne nécessitant qu’une faible charge de traitement.Both theoretical and experimental evidence is presented in this work for the existence of an Energy/Frequency Convexity Rule, which relates energy consumption and microprocessor frequency for nanometer-scale microprocessors. Typical nanometer-scale application processorswere monitored running specific compute-intensive kernels using high-resolution power gauges. Data gathered during several week-long acquisition campaigns suggest that energy consumed is strongly correlated with the microprocessor’s frequency, and, more interestingly, the curve exhibits a clear minimum over the processor’s frequency range. An analytical model for this behavior is provide and motivated, which fits well with the data.The circumstances are discussed under which this convexity rule can be exploited, and when other methods are more effective, with the aim of improving the microprocessor’s energy efficiency. The Energy/Frequency Convexity Rule is potentially more exploitable by low-power systems, such as battery-powered and embedded systems, and less likely by high-performance computer systems. The Energy/Frequency Convexity Rule is also applied to multi-buddy systems, Amdahl’s law and heterogeneous computing. Given that the microprocessor’s energy consumption is temperature-dependent, a macro-level temperature/power relationship for application processors is introduced and experimentally validated. By adopting a holistic view, this model is able to take into account many of the physical effects that occur within such systems. Via measurements on two pertinent platforms sporting nanometer-scale application processors, it is shown that the power/temperature relationship is indeed very likely exponential over a 20C to 85C temperature range. The data suggest that, for a temperature range between 20C and 55C, a quadratic model is still accurate and a linear approximation is acceptable. Power transformation models are also presented that aim at canceling the temperature biases in power traces. These transformation models are developed to increase the accuracy andmeaningfulness of power measurement traces.Besides static power measurements, the transient power and thermal behavior are also analyzed by means of the cooling laws and the temperature/power relationship models. Exponential cooling models are justified for actively-cooled microprocessors. For passively cooled processors however, as frequently found in embedded systems, an exponential law may not be theoretically justified. Here, the tractability of the exact cooling law fora passively-cooled body is analyzed, subject to radiative cooling and a modest level of heat loss via convection. Focusing then on embedded microprocessors, the performance difference between the new passive cooling law and the conventionally-used exponential one is compared. It is shown that, for large surface sizes, the radiative cooling component can be comparable to the convective cooling one. However, for large cooling surfaceareas of the order of 10 cm2 or more, it is shown that the differences between the passive cooling law and the exponential cooling law are significant. The results thus suggest that, in the absence of accurate temperature measurements, an exponential cooling law is only accurate enough for small-sized SoC systems that require low processing overhead

Parameter Sensitivity Analysis of the Energy/Frequency Convexity Rule for Nanometer-scale Application Processors

International audienceBoth theoretical and experimental evidence are presented in this work in order to validate the existence of an Energy/Frequency Convexity Rule, which relates energy consumption and microprocessor frequency for nanometer-scale microprocessors. Data gathered during several month-long experimental acquisition campaigns, supported by several independent publications, suggest that energy consumed is indeed depending on the microprocessor's clock frequency, and, more interestingly, the curve exhibits a clear minimum over the processor's frequency range. An analytical model for this behavior is presented and motivated, which fits well with the experimental data. A parameter sensitivity analysis shows how parameters affect the energy minimum in the clock frequency space. The conditions are discussed under which this convexity rule can be exploited, and when other methods are more effective, with the aim of improving the computer system's energy management efficiency. We show that the power requirements of the computer system, besides the microprocessor, and the overhead affect the location of the energy minimum the most. The sensitivity analysis of the Energy/Frequency Convexity Rule puts forward a number of simple guidelines especially for by low-power systems, such as battery-powered and embedded systems, and less likely by high-performance computer systems

Modélisation de la consommation énergétique des programmes : aspects thermiques et loi de convexité énergie-fréquence

National audienc

Thermal behavior and Energy/Frequency Convexity Rule of Energy Consumption for Programs

International audienceNo abstrac

Constrained-Path Discovery by Selective Diffusion

The demand for live and interactive multimedia services over the Internet raises questions on how well the Internet Protocol (IP)\u92s best-effort effort service can be adapted to provide adequate end-to-end quality of service (QoS) for the users. Although the Internet community has developed two different IP-based QoS architectures, neither has been widely deployed. Overlay networks are seen as a step to address the demand for end-to-end QoS until a better solution can be obtained. As part of the telecommunication research at Blekinge Institute of Technology (BTH) in Karlskrona, Sweden we are investigating new theories and algorithms concerning QoS routing. We are in the process of developing Overlay Routing Protocol (ORP), a framework for overlay QoS routing consisting of two protocols: Route Discovery Protocol (RDP) and Route Management Protocol (RMP). In this paper we describe RDP and provide preliminary simulation results for it

Constrained-Path Discovery by Selective Diffusion

The demand for live and interactive multimedia services over the Internet raises questions on how well the Internet Protocol (IP)\u92s best-effort effort service can be adapted to provide adequate end-to-end quality of service (QoS) for the users. Although the Internet community has developed two different IP-based QoS architectures, neither has been widely deployed. Overlay networks are seen as a step to address the demand for end-to-end QoS until a better solution can be obtained. As part of the telecommunication research at Blekinge Institute of Technology (BTH) in Karlskrona, Sweden we are investigating new theories and algorithms concerning QoS routing. We are in the process of developing Overlay Routing Protocol (ORP), a framework for overlay QoS routing consisting of two protocols: Route Discovery Protocol (RDP) and Route Management Protocol (RMP). In this paper we describe RDP and provide preliminary simulation results for it

PERIMETER : A User-Centric Mobility Framework

This demo shows a prototype of a user-centric mobility framework that provides handover for macro-mobility on handheld devices. The framework is designed for mobile- controlled handover and does not require modification of the Internet infrastructure. The end-users are so able to control the roaming process governed by user considerations in addition to business objectives. To achieve seamless mobility UDP tunneling is used as a basis for the handover process. Additionally, measurements are performed on the tunnels to acquire Quality of Service (QoS) metrics and hence serve for roaming decision making processes