Belén Bermejo - Academia.edu (original) (raw)

Papers by Belén Bermejo

The Journal of supercomputing/Journal of supercomputing, Feb 15, 2024

Virtualization technologies are extensively utilized in data centers, particularly cloud computin... more Virtualization technologies are extensively utilized in data centers, particularly cloud computing. This facilitates data center management and diminishes the number of physical machines (servers) and, subsequently, their cooling requirements, leading to cost, space, and power consumption reductions. When applications in data centers are executing independent parallel transactions, but with similar performance requirements, the appropriate level of virtual machine consolidation on a server poses a fundamental challenge for capacity planning. This article introduces a method to evaluate the performance speedup achieved through virtualization on any server and the effects of virtualization and consolidation overheads on physical or virtual machine scalability. This research formalizes the speedup and overheads, using classical computer architecture statements. but at the same time proposes a new method to analyze these overhead amounts and types, showing the scalability and efficiency of different consolidations in the same server and its comparison against no consolidation. This work also proposes a new way to determine the optimal number of physical servers and the optimal number of consolidated virtual machines for a given transaction workload. The real experimentation was performed with different workload sizes, types of virtualizations and different servers. The method presented also facilitates the representation of linear scalability against the real degree of parallelism of either physical machines or consolidated virtual machines for a given transaction workload, as well as striking the right balance between speedup and energy in virtual server consolidation. The authors Carlos Juiz and Belen Bermejo have contributed equally to this work.

Sustainable Computing: Informatics and Systems, Jul 1, 2023

IEEE Transactions on Parallel and Distributed Systems, Nov 1, 2018

Resource management is a key factor in the performance and efficient utilization of cloud systems... more Resource management is a key factor in the performance and efficient utilization of cloud systems, and many research works have proposed efficient policies to optimize such systems. However, these policies have traditionally managed the resources individually, neglecting the complexity of cloud systems and the interrelation between their elements. To illustrate this situation, we present an approach focused on virtualized Hadoop for a simultaneous and coordinated management of virtual machines and file replicas. Specifically, we propose determining the virtual machine allocation, virtual machine template selection, and file replica placement with the objective of minimizing the power consumption, physical resource waste, and file unavailability. We implemented our solution using the non-dominated sorting genetic algorithm-II, which is a multi-objective optimization algorithm. Our approach obtained important benefits in terms of file unavailability and resource waste, with overall improvements of approximately 400% and 170% compared to three other optimization strategies. The benefits for the power consumption were smaller, with an improvement of approximately 1.9%.

Journal of Parallel and Distributed Computing, Jun 1, 2023

BenchCouncil transactions on benchmarks, standards and evaluations, Apr 1, 2022

Presentamos una herramienta docente para la explicación del conjunto de técnicas de paralelismo a... more Presentamos una herramienta docente para la explicación del conjunto de técnicas de paralelismo a nivel de instrucción, conocido con el acrónimo en inglés de ILP. Hemos programado un diseño modular de la arquitectura MIPS que permite la ejecución segmentada de una instrucción, con el objetivo de ofrecer la posibilidad de comparar diferentes escenarios según los parámetros y elementos deseados. La herramienta ofrece un volcado de métricas de rendimiento para estudios comparativos y su programación orientada a objetos, relativamente sencilla, permite implementar nuevos módulos como algoritmos de especulación de salto o planificación de código. Además, adjuntamos unos recursos didácticos para mostrar su funcionalidad y potencial, junto con una valoración de experiencia docente en el uso de dicha herramienta por parte de los alumnos.

IEEE Access

Much of the research has focused on performance evaluation and, particularly, the response time o... more Much of the research has focused on performance evaluation and, particularly, the response time of clusters in cloud computing. However, one important topic has hardly been addressed: the impact of virtual machine consolidation on real business cases, on companies driven by requirements for high performance in transaction response time, specifically on intermediation trip companies. The ability to provide quality service, guaranteed within several milliseconds, is crucial to the business success of these cluster platforms. We present a case study for evaluating the performance of the seat availability service used by a flight carrier. The case study is the application of the performance evaluation methodology that ranges from monitoring to tuning options of a real-world service running on virtual machines, to understand capacity planning or possible substitution by other configurations of virtualization or containerization of the architecture of the cloud platform. This case study also proposes a workload characterisation using data clusters, allowing the architecture to be modeled as a simple network of multiclass queues of any virtual machine on the platform. Additionally, we estimate the new transaction response time by the possibility of either reducing or incrementing the number of virtual machines and their replacement by containers INDEX TERMS Virtual machines, performance evaluation, monitoring, workload characterization, discreteevent simulation, overhead, containers.

Lecture notes in networks and systems, Feb 21, 2022

This paper presents a method to determine the metrics to assess the uptake of Ambient Assisted Li... more This paper presents a method to determine the metrics to assess the uptake of Ambient Assisted Living (AAL) platforms. The different platforms are offering various resources to construct digital health products oriented to Active and Healthy Ageing (AHA) and social health care. This research work is addressed to identify and define which metrics could be Key Performance Indicators (KPIs) to be tracked for successful uptake, interoperability, synergies, and cost-benefit analysis of open platforms.

The Journal of Supercomputing, 2022

Server consolidation is one of the most commonly used techniques for reducing energy consumption ... more Server consolidation is one of the most commonly used techniques for reducing energy consumption in datacenters; however, this results in inherent performance degradation due to the coallocation of virtual servers, i.e., virtual machines (VMs) and containers, in physical ones. Given the widespread use of containers and their combination with VMs, it is necessary to quantify the performance degradation in these new consolidation scenarios, as this information will help system administrators make decisions based on server performance management. In this paper, a general method for quantifying performance degradation, that is, server overhead, is proposed for arbitrary consolidation scenarios. To demonstrate the applicability of the method, we develop a set of experiments with varying combinations of VMs, containers, and workload demands. From the results, we can obtain a suitable method for quantifying performance degradation that can be implemented as a recursive algorithm. From the ...

Cluster Computing, 2020

The increased use of cloud services has turned the virtualization in the main technology that sup... more The increased use of cloud services has turned the virtualization in the main technology that supports cloud datacentres. To reduce the increment of power consumption caused in datacenters due to the addition of physical servers, system administrators are using virtual machine consolidation (VMC) techniques which tries to allocate the adequate number of virtual machines per physical server. Therefore, VMC increases server resources utilization and as a consequence its performance degradation and the energy consumption too. Then, a trade-off between the performance and the energy consumption exists when consolidating virtual machines. This trade-off is difficult to quantify and also to determine the servers efficiency taking into account a specific number of allocated virtual machines. Because of this, it is crucial for system administrators having a simple metric that assists the VMC making-decision process. In this paper, we propose the CiS2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$CiS^2$$\end{document} index, a metric to quantify this performance-energy trade-off. Also, this index can help system administrators to decide about the servers’ efficiency through benchmarking and to select the most efficient server through a proposed algorithm. Besides, we propose a simple graphical representation of the index to distinguish graphically the efficient and non-efficient server consolidations. We validate the index in a theoretical manner and performing real experiments in different physical servers under CPU workload saturation. Obtained results show that the proposed index reflects the performance-energy trade-off behaviour and it helps systems’ administrators when consolidating virtual machines.

The Journal of Supercomputing, 2019

This survey is an up-to-date account of the research on virtual machine consolidation overhead. T... more This survey is an up-to-date account of the research on virtual machine consolidation overhead. The overhead influencing factors are analyzed throughout this work. Based on these factors, we propose a categorization that classifies the most important research works on virtualization and virtual machine consolidation overhead. We have analyzed and summarized 46 selected research works from an initial set of 428, attempting to update the state of the art with the most recent papers in this field.

Informatics

During the last few years, learning techniques have changed, both in basic education and in highe... more During the last few years, learning techniques have changed, both in basic education and in higher education. This change has been accompanied by new technologies such as Augmented Reality (AR) and Virtual Reality (AR). The combination of these technologies in education has allowed a greater immersion, positively affecting the learning and teaching processes. In addition, since the COVID-19 pandemic, this trend has been growing due to the diversity of the different fields of application of these technologies, such as heterogeneity in their combination and their different experiences. It is necessary to review the state of the art to determine the effectiveness of the application of these technologies in the field of university higher education. In the present paper, this aim is achieved by performing a systematic literature review from 2012 to 2022. A total of 129 papers were analyzed. Studies in our review concluded that the application of AR/VR improves learning immersion, especia...

Information Technology (IT) functions and departments around the world are adopting several Green... more Information Technology (IT) functions and departments around the world are adopting several Green IT practices, but sometimes not connected with the rest of the organization. Thus, a framework is needed to help organizations implement the governance and management of Green IT. In this paper, we propose a framework that allows implementing Balanced Scorecards (BSCs) for Green IT within the context of IT Governance. We illustrate our proposal through the BSC construction with a generalizable example based on the virtualization of a data center. In our example, we focus on the construction of the strategic map to the KPIs (Key Performance Indicators) monitoring needed for Green IT governance. We develop the example from the sustainability objectives that we already include in the strategic map that aims to minimize the negative impact of IT operations on the environment.

HPC-based datacenters consume significant energy, despite of a multitude of efforts in reducing i... more HPC-based datacenters consume significant energy, despite of a multitude of efforts in reducing it. Virtual Machine Consolidation is an effective technique to minimize the number of physical servers in order to reduce energy consumption, and, consequently, data center costs. However, consolidating virtual machines also reduces performance of servers. Thus, an efficient number of virtual machines consolidated in a physical server is one key issue to optimize the tradeoff between performance and energy efficiency in datacenters. In this paper, we propose a new index, namely CiS2 (Consolidation index for Server CPU in Saturation), to quantify the relation of performance degradation and energy efficiency of virtual machine consolidation under parallel workload execution, that is, the tradeoff of performance and energy in consolidation. As a result, CiS2 provides an approach to help performance engineers to decide about the suitability of a number of consolidated virtual machines. CiS2 c...

Integrated Series in Information Systems, 2017

IT governance in public organizations and enterprises has encountered challenges due to internal ... more IT governance in public organizations and enterprises has encountered challenges due to internal and external factors. Most of these challenges are related to strategic alignment issues involving governance bodies and their communication with stakeholders. Furthermore, public organizations are now more concerned about receiving the most value from IT services. This requires effective IT governance that enables IT alignment and creates business value from IT investments. The contribution presented in this chapter is to depict the evolution in the IT-business relationship over the last years and highlight the challenges in IT governance. Second, the current IT governance standardization and its consequences in public enterprises will be reviewed. Finally, dFogIT is presented as real case of involving the implementation of the IT governance framework in a public organization.

Proceedings of the 2018 International Conference on Technical Debt, 2018

Technical debt has successfully captured the interest of practitioners and researchers alike. We ... more Technical debt has successfully captured the interest of practitioners and researchers alike. We argue that the concept of technical debt holds much more currency within the strategic Information Systems literature. Hence, we have developed a research framework for expanding the concept of technical debt into a new concept we dub “technology debt”. This expanded concept aims at capturing the path-dependencies reported in literature in regard to digital investments, and to make these both researchable and manageable. Technology debt is defined as the constraining effects of previous governance decisions on future decisions, including technical debt as important factor, but not unique. According to the findings, technology debt is a feasible method for highlighting the constraining aspects of IT investments and including these in the investment evaluation by governing body. This offers support for corporate stakeholders involved in the decision-making surrounding IT related investments, particularly in IT governance and management processes.

Research Advances in Cloud Computing, 2017

The growth of power consumption in Cloud Computing systems is one of the current concerns of syst... more The growth of power consumption in Cloud Computing systems is one of the current concerns of systems designers. In previous years, several studies have been carried out in order to find new techniques to decrease the cloud power consumption. These techniques range from decisions on locations for data centres to techniques that enable efficient resource management. Resource Allocation, as a process of Resource Management, assigns available resources throughout the data centre in an efficient manner, minimizing the power consumption and maximizing the system performance. The contribution presented in this chapter is an overview of the Resource Management and Resource Allocation techniques, which contribute to the reduction of energy consumption without compromising the cloud user and provider constraints. We will present key concepts regarding energy consumption optimization in cloud data centres. Moreover, two practical cases are presented to illustrate the theoretical concepts of Resource Allocation. Finally, we discuss the open challenges that Resource Management must face in the coming years.

Advances in Computational Collective Intelligence, 2021

The Journal of Supercomputing, 2018

This survey is an up-to-date account of the research on the performance-energy tradeoff in virtua... more This survey is an up-to-date account of the research on the performance-energy tradeoff in virtualized environments, specifically in virtual machine consolidation. The factors that influence the performance and energy in consolidated data centres and the performance-energy trade-off itself are analysed. Based on these factors, we propose a categorization that classifies the most important research on performance and energy in consolidated systems. We have analysed and summarized 91 selected research works from an initial set of 1030. This article summarizes all previous surveys on the subject of virtual machine consolidation and updates them with the most recent papers in the field.