Contributions to fault-tolerant NoC-based many-core processors and flexible Off-Chip supercomputer interconnects
Speaker: Dr. Fabien Chaix, National Institute of Informatics, Japan
Date: 03 October 2014 Time: 14:30 - 15:30
Location: "Alkiviades C. Payatakes" Seminar Room, FORTH, Heraklion, Crete
Host: Prof. Manolis Katevenis


Manufacturing processors with aggressive CMOS topologies paves the way  to more efficient and powerful computers, but also introduces new  challenges to the computer industry. As the architecture of processors  evolves towards massively multi-core paradigm, the efficient design  and use of Network On Chips (NoCs) is paramount, but the exploitation  of such devices is hampered by increasing variability and defect  rates. In the field of supercomputers, the energy consumption and cost  of processor chips decreased so much that the Off-Chip network now  takes a very significant  share of the supercomputer cost, energy and application latencies.

Inside chips, we then propose the adoption of more complex routing  algorithms to better exploit the processor resources in the presence  of defects. This approach increases the interconnect throughput by up  to a factor 10 in the presence of 20 % of defects. We also propose a  method for applications to deploy dynamically their task across cores  while avoiding faulty  cores, avoiding less efficient cores, and  minimizing the expected energy consumption. Finally, a few elements of  the NoC simulation model that was developed for this thesis are  explained, with a focus on its graphical visualization features.

Outside chips, our focus is on the proposition of topologies allowing  better performances, while reducing the interconnect cost. Hence, the  team at NII contributed several randomly-generated topologies that  take advantage of the small world effect and the physical clustering  of nodes to both reduce the network diameter and cabling cost. While  this approach is very effective for latency-bound applications,  throughput-bound applications are generally best run on a meshed or  hierarchical topology. Another issue is that supercomputers are often  built in more than one stage, and hence the cabling should be  incremental too, which is far from trivial  for high-radix topologies.

Hence, we propose a method for cabling  multiple topologies in a more efficient and incremental way, thus enabling a more agile deployment of the Off-Chip  interconnect in supercomputers.


Fabien Chaix received an engineer degree in Electronics and Computer systems as well as a master degree in Micro-electronics from the Grenoble University, France in 2008. In 2013, he defended his PhD. thesis entitled "Contributions for late CMOS many-core processors: NoC fault-tolerant routing and auto-adaptive applications" at the TIMA laboratory, Grenoble, France. He is currently a Post-doctorate researcher in the Computer Architecture division  of the National Institute of Informatics in Tokyo, Japan. His research interests include fault-tolerant designs and systems as well as On- and Off- chip networks for embedded and high-performance computing.

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