The past decade witnessed the inclusion of power measurements to evaluate the energy efficiency of software systems, thus making energy a prime indicator along with performance. Nevertheless, measuring the energy consumption of a software system remains a tedious task for practitioners. In particular, the energy measurement process may be subject to a lot of variations that hinder the relevance of potential comparisons. While the state of the art mostly acknowledged the impact of hardware factors (chip printing process, CPU temperature), this paper investigates the impact of controllable factors on these variations. More specifically, we conduct an empirical study of multiple controllable parameters that one can easily tune to tame the energy consumption variations when benchmarking software systems. To better understand the causes of such variations, we ran more than a 1, 000 experiments on more than 100 nodes with different workloads and configurations. The main factors we studied encompass: experimental protocol, CPU features (C-states, Turbo Boost, core pinning) and generations, as well as the operating system. Our experiments showed that, for some workloads, it is possible to tighten the energy variation by up to 30×. Finally, we summarize our results as guidelines to tame energy consumption variations. We argue that the guidelines we deliver are the minimal requirements to be considered prior to any energy efficiency evaluation. CCS CONCEPTS • Hardware → Power and energy; Power estimation and optimization; Platform power issue; Enterprise level and data centers power issues.

Background. As software took control over hardware in many domains, the question of the energy footprint induced by the software is becoming critical for our society, as the resources powering the underlying infrastructure are finite. Yet, beyond this growing interest, energy consumption remains a difficult concept to master for a developer. Aims. The purpose of this study is to better understand the root causes that prevent the issue of software energy consumption to be more widely considered by developers and companies. Method. To investigate this issue, this paper reports on a qualitative study we conducted in an industrial context. We applied an in-depth analysis of the interviews of 10 experienced developers and summarized a set of implications. Results. We argue that our study delivers i) insightful feedback on how green software design is considered among the interviewed developers and ii) a set of findings to build helpful tools, motivate further research, and establish better development strategies to promote green software design. Conclusion. This paper covers an industrial case study of developers' awareness of green software design and how to promote it within the company. While it might not be generalizable for any company, we believe our results deliver a common body of knowledge with implications to be considered for similar cases and further researches.

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