Guilherme C. Januario

GreenSDN: Bringing energy efficiency to an SDN emulation environment

A significant number of green, energy-saving network protocols have been invented in recent years in response to demand for reducing the amount of energy consumed by network infrastructure. In this paper, we report on the difficulties we encountered when building an SDN environment that could emulate energy saving protocols operating at different layers of the network. We propose solutions, based on the Mininet environment and the POX Openflow controller, that emulate the effects of three different energy saving protocols. Our approach is validated by comparing energy savings obtained by activating these protocols in an emulated network topology inspired by the Brazilian Research Network.

Orchestration of energy efficiency capabilities in networks

The energy demand for operating Information and Communication Technology (ICT) systems has been growing, implying in high operational costs and consequent increase of carbon emissions. Both in datacenters and telecom infrastructures, the networks represent a significant amount of energy spending. Given that, there is an increased demand for energy efficiency solutions, and several capabilities to save energy have been proposed. However, it is very difficult to orchestrate such energy efficiency capabilities, that is, coordinate or combine them in the same network, ensuring a conflict-free operation and choosing the best one for a given scenario, ensuring that a capability not suited to the current bandwidth utilization will not be applied and lead to congestion or packet loss. There is neither a way to do this taking business directives into account. In this regard, a method able to orchestrate different energy efficiency capabilities is proposed considering the possible combinations and conflicts among them, as well as the best option for a given workload and network characteristics. The business policies are refined down to the network level in order to bring high-level directives into the operation, and a Utility Function is used to combine energy efficiency and performance requirements. A Decision Tree able to determine what to do in each scenario is deployed in a Software Defined Network environment. The proposed method was validated with different experiments, testing the Utility Function, checking the extra savings when combining several capabilities, the decision tree interpolation and dynamicity aspects. The orchestration proved valid to solve the problem of finding the best combination for a given scenario, achieving additional savings due to the combination, besides ensuring a conflict-free operation. HighlightsA method able to orchestrate different energy efficiency capabilities is proposed.It considers the possible combinations and conflicts among the capabilities.It refines business policies to bring high-level directives into the operation.The method solves the problem of finding the best combination for a given scenario.And achieved additional savings, besides ensuring a conflict-free operation.

A Survey of Policy Refinement Methods as a Support for Sustainable Networks

Green sustainability-oriented features have become common in network nodes and protocols. Running a network in an energy-efficient way is an important concern of network operators and datacenter networks. The implementation and coordination of the myriad of existing network features poses a challenging task. The energy efficiency capabilities must be selected according to the network conditions and can be combined to increase energy savings. However, they can conflict if not orchestrated in a proper manner. Policy-Based Network Management is a well-known approach to addressing the complexity of network management tasks. In conjunction with a refinement process to translate high-level policies down to low-level policies, it can bring business directives to the network, including sustainability goals. In this survey, we identify the major characteristics of sustainability-oriented policies, as well as the requirements a policy refinement method for such type of policies has to fulfill, including energy efficiency capabilities orchestration. We then analyze existing policy refinement techniques and discuss the challenges on how they address or need to be modified in order to be applicable to sustainability-oriented policies.

Orchestration of Energy Efficiency Functionalities for a Sustainable Network Management

The energy demand for operating Information and Communication Technologies is growing, implying in high operational costs and consequent carbon emissions. Both in datacenters and in telecom infrastructures, the networks represent a significant amount of energy spending. This implies in an increased demand for energy efficiency, and several functionalities to save energy are being proposed. However, there is no proposal on how to coordinate or combine such energy efficiency functionalities in the same network, or choosing the best one for a given scenario. There is neither a way to do this using business directives, telling, for instance, the period of the day to apply such functionalities or the operational conditions (e.g. If the network usage is low). In this regard, we propose a method able to orchestrate different energy efficiency functionalities considering the possible combinations and conflicts among them, as well as the best option for a given workload and network characteristics, such as topology and power profiles of devices. The business policies are refined down to the network level in order to bring high-level directives into the operation. Our method operation is validated with an example which achieves near 50% of savings for the given scenario by combining two different energy efficiency functionalities.

Dynamic method to evaluate code optimization effectiveness

The identification of redundant computation is in general undecidable and prevents the obtainment of an ideal case as reference to the measurement of the remaining unexploited potential for redundancy removal and to the evaluation of code optimization effectiveness. This paper presents a methodology for optimization effectiveness analysis by observing the complete dynamic stream of executed instructions and memory references in the whole program execution, and by applying an extended value numbering algorithm to the execution trace. This method reduces the interprocedural analysis to the analysis of a large basic block and detects redundant memory and arithmetic operations that are visible only at the run-time. This way, the work extends the load-reuse analysis and provides both a more accurate approximation of the upper bound of exploitable optimization in the program and a reference point to evaluate optimization effectiveness. The results of applying this method to representative benchmark (SPECInt 2006) executables created with each compiler optimization level in GNU C/C++ Compiler are reported. The programs are run with a full-system simulator based on Power ISA 64-bit (version 2.06), and the whole application execution trace is collected. The proposed analysis reveals a significant amount of remaining unexploited redundancies even with the highest optimization level available. Sources of inefficiency and implications on exploring dynamic optimizations are discussed.

Speeding Up Stencil Computations with Kernel Convolution

A technique to speed up stencil computation is introduced. Computation and data reuse schemes are developed for its application to 1- and 3-dimensional stencils. The approach traverses the data domain fewer times than a state-of-the-art, straightforward iterative stencil implementation would. Performance results are shown for a variety of platforms, exemplifying how it can be straightforwardly applied with existing techniques and frameworks. The technique, named Aggregate Stencil-Loop Iteration (ASLI), works by applying a stencil obtained by the original stencil operator convolved with itself one or more times. This more complex operator creates new opportunities for in-register data reuse and increases the FLOPs-to-load ratio. The total number of FLOPs decreases for 1D but increases for 2D and 3D star-shaped stencils. In both scenarios, speed-up relative to the state-of-the-art is achieved. ASLI is relatively easy to implement and works synergistically with existing methods to optimize stencil computations.

A demonstration of energy efficiency capabilities orchestration in networks

Various energy efficiency network capabilities have been proposed in recent years in response to the demand of reducing the amount of energy consumed by the network infrastructure. In this regard, we demonstrate SOS, a method able to orchestrate different energy efficiency capabilities considering the possible combinations and conflicts among them, as well as the best option for a given bandwidth utilization and network characteristics, such as topology and power profiles of devices. The method was tested on GreenSDN, a testbed based on the Mininet environment and the POX controller, which emulates the effects of different energy efficiency capabilities. During the demonstration, we will show the energy efficiency achieved by the orchestration method, highlighting the additional savings due to capabilities orchestration, and, at the same time, considering performance constraints and different policies.