Section: New Results

Energy Efficiency in HPC and Large Scale Distributed Systems

Participants : Mathilde Boutigny, Radu Carpa, Marcos Dias de Assunção, Thierry Gautier, Olivier Glück, Laurent Lefèvre, Jean-Christophe Mignot, Issam Rais.

Combining Shutdown Policies with Multiple Constraints

Large scale distributed systems (high performance computing centers, networks, data centers) are expected to consume huge amounts of energy. In order to address this issue, shutdown policies constitute an appealing approach able to dynamically adapt the resource set to the actual workload. However, multiple constraints have to be taken into account for such policies to be applied on real infrastructures: the time and energy cost of switching on and off, the power and energy consumption bounds caused by the electricity grid or the cooling system, and the availability of renewable energy. We propose models translating these various constraints into different shutdown policies that can be combined for a multi-constraint purpose. Our models and their combinations are validated through simulations on a real workload trace [4], [13]. This work is done through the PhD of Issam Rais in the FSN ELCI Project with the collaboration of Anne Benoit (Roma team) and Anne-Cécile Orgerie (Myriads team).

Evaluating the Impact of SDN-Induced Frequent Route Changes on TCP Flows

Traffic engineering technologies such as MPLS have been proposed to adjust the paths of data flows according to network availability. Although the time interval between traffic optimisations is often on the scale of hours or minutes, modern SDN techniques enable reconfiguring the network more frequently. It is argued, however, that changing the paths of TCP flows too often could severely impact their performance by incurring packet loss and reordering. This work analyses and evaluates the impact of frequent route changes on the performance of TCP flows. Experiments carried out on a network testbed show that rerouting a flow can affect its throughput when reassigning it a path either longer or shorter than the original path. Packet reordering has a negligible impact when compared to the increase of RTT. Moreover, constant rerouting influences the performance of the congestion control algorithm. Designed to assess the limits on SDN-induced reconfiguration, a scenario where the traffic is rerouted every 0.1s demonstrates that the throughput can be as low as 35% of that achieved without rerouting.[7], [14].

Evaluating Energy Consumption of OpenMP Runtime

In a joint-work with J.V. Lima from UFSM, Santa Maria, Brazil [26], we analyse performance and energy consumption of four OpenMP runtime systems over a NUMA platform. We present an experimental study to characterize OpenMP runtime systems on the three main kernels in dense linear algebra algorithms (Cholesky, LU and QR) in terms of performance and energy consumption. Our experimental results suggest that OpenMP runtime systems can be considered as a new energy leverage. For instance, a LU factorization with concurrent write extension from libKOMP achieved up to 1.75 of performance gain and 1.56 of energy decrease.