Evangelos Tasoulas successfully defended his PhD
Evangelos Tasoulas has successfully defended his PhD. (Photo: Simula/Elin Backe Christophersen)

Evangelos Tasoulas successfully defended his PhD


On Thursday December 14th, Evangelos Tasoulas defended his PhD thesis "Towards High Performance Dynamic Cloud Environments". The defense took place at 11:15 at Storstua, Simula.

The advent of the Internet of Things, sensor and social networks, to mention just a few examples, all contribute towards the solid establishment of the Big Data era. High Performance Computing (HPC) becomes necessary for the efficient processing of the massive amounts of data our society generates, and cloud computing is a critical component to deliver this processing power to a broader audience that cannot afford to acquire and maintain such complex computing systems themselves. However, HPC specific technology and performance is not yet apt to be delivered efficiently over highly flexible and dynamic environments, as typically are the virtualized cloud infrastructures.

In this thesis, we address challenges that arise in high performance dynamic cloud environments that are equipped with HPC specific technology, in the context of networking and virtualization. We use InfiniBand, a high performance lossless interconnection network as the basis of our research, and first show that lossless networks pose prime challenges when the nature of the infrastructure is very dynamic, i.e. exhibits continuous changes. Then we propose a network I/O virtualization architecture, the InfiniBand vSwitch architecture, that can make lossless network technologies more favorable in the cloud. Moreover, we propose different network reconfiguration methods to enable performance-driven reconfigurations in very large network topologies that are commonly found in data centers. Performance-driven reconfigurations are frequently needed to adapt to unpredictable workload changes resulting from the shared and on-demand nature of a cloud platform, or when cloud providers employ live migration of virtual machines to optimize the resource usage of their infrastructure. Last but not least, we propose a new Quality-of-Service metric, called 'delay', to capture the directly observable service degradation in consolidated cloud environments. We suggest that the 'delay' can be used as a direct service level agreement metric between cloud providers and cloud tenants.

The thesis is written within the field of Comunication Systems. The work has been conducted at Simula Research Laboratory.

Prior to the defense, at 09:15, Evangelos Tasoulaspresented histrial lecture "Networking for Next Generation HPC Clusters and Clouds: prospects with and without SDN".

The adjudication committee

  • Professor Dhabaleswar K. Panda, Department of Computer Science and Engineering, The Ohio State University
  • Professor Odej Kao, Department of Telecommunication Systems, Technische Universität Berlin
  • Professor Carsten Griwodz, Department of Informatics, University of Oslo

Chair of the disputation

  • Professor Fritz Albregtsen, Institute of Informatics,University of Oslo


  • Associate Professor Ernst Gunnar Gran, Department of InformationSecurity and Technology, Norwegian University of Science and Technology
  • Professor Tor Skeie, Department of Informatics, University of Oslo
  • Associate Professor Kyrre Begnum, Faculty of Technology, Art and Design,Department of Computer Science, Oslo and Akershus University College of Applied Sciences

Read more:

Announcement of the PhD defense at the University of Oslo's web pages.