Christian Maciocco

Energy-efficient interconnect via Router Parking

The increase in on-chip core counts in Chip Multi Processors (CMPs) has led to the adoption of interconnects such as Mesh and Torus, which consume an increasing fraction of the chip power. Moreover, as technology and voltage continue to scale down, static power consumes a larger fraction of the total power; reducing it is increasingly important for energy proportional computing. Currently, processor designers strive to send under-utilized cores into deep sleep states in order to reduce idling power and improve overall energy efficiency. However, even in state-of-the-art CMP designs, when a core goes to sleep the router attached to it remains active in order to continue packet forwarding. In this paper, we propose Router Parking - selectively power-gating routers attached to parked cores. Router Parking ensures that network connectivity is maintained, and limits the average interconnect latency impact of packet detouring around parked routers. We present two Router Parking algorithms - an aggressive approach to park as many routers as possible, and a conservative approach that parks a limited set of routers in order to keep the impact on latency increase minimal. Further, we propose an adaptive policy to choose between the two algorithms at run-time. We evaluate our algorithms using both synthetic traffic as well as real workloads taken from SPEC CPU2006 and PARSEC 2.1 benchmark suites. Our evaluation results show that Router Parking can achieve significant savings in the total interconnect energy (average of 32%, 40% and 41% for the synthetic, SPEC CPU2006, and PARSEC 2.1 workloads, respectively).

Energy efficient network selection and seamless handovers in Mixed Networks

Network selection is the decision process for a mobile terminal to handover between homogeneous or heterogeneous networks. This handover decision can be either mobile or network initiated. Todays decision is mainly based on the received signal strength (RSS). In the future as the number of available networks increase the selection process must evaluate additional factors such as monetary cost, offered services, network conditions, required energy to operate in a network, system conditions, user and operators preferences. Upcoming IEEE or 3GPP standards provide facilities such as network maps, handover negotiation messages, network and client event reports and message exchange like handover triggers and handover negotiation. In this paper we investigate the use of a cost function to perform an optimal network selection using information provided by these standards, such as network coverage map or network properties. The cost function provides flexibility to balance different factors in the decision making, and our research is focused on improving both seamlessness and energy efficiency of the device and handovers. We evaluated our approach based on usage scenarios over WiFi, WiMax, and 3G networks using captured signal strength traces. The results of our simulations and early implementation show that our schemes select the optimal networks and handovers were triggered at appropriate times to increase overall network connectivity as compared to traditional triggering schemes, while at the same time optimizing energy consumption of multi-radio devices.

Smart Predictive Trigger for Effective Handover in Wireless Networks

Roaming across heterogeneous wireless networks poses a challenging issue in mobility management such as seamless and efficient handover to reduce end-users service interruption. Efficient techniques for seamless handover between access points (APs) when user roams from one area to another can be categorized into three stages in conventional way, i) initiation, ii) preparation, and iii) execution. However, frequent handover may overload the network with signalling traffic and causes call dropping to increase as well. This paper takes a deeper look at predictive triggers at the link layer. With an appropriate implementation of predictive triggering algorithms, early handover initiation and preparation could be performed. This paper addresses the investigation on predictive and accurate mechanisms to generate a handover trigger.

Understanding the bottlenecks in virtualizing cellular core network functions

Network function virtualization (NFV) promises significant cost savings, flexibility and ease of deployment. However, potential challenges in implementing virtualized network elements that can support real-world performance requirements are still an open question. For example, traditional telecom networks have a lot of complex interdependencies that can affect performance. In this paper, we study the potential bottlenecks in virtualizing cellular core network functions. Using a combination of analysis and experimentation, we quantify the impact of software-based EPC elements on various metrics including physical processing, memory, IO, and bandwidth resource requirements. We use production grade, software-based cellular network elements running on general purpose Linux servers, driven by a variety of realistic workloads derived from a realworld cellular network, to examine the combined effects of control and data planes on an LTE enhanced packet core (EPC). In particular, we discover that the SGW handles about 33% of the control plane transactions and is a potential source for performance bottlenecks as a result of the interdependencies between control and data plane processing. Our results indicate that simply replacing existing EPC elements with virtualized equivalents can have severe performance bottlenecks and that virtualized EPC elements need to be carefully designed.

Reducing Power Consumption for Mobile Platforms via Adaptive Traffic Coalescing

Battery life remains to be a critical competitive metric for todays mobile platforms that offer ubiquitous connectivity through their wireless communication interfaces. With most usage models being driven by always-on communication activities, e.g, Internet video streaming, web browsing, etc., it is imperative to understand the impact of network activities on the overall platform power, and optimize power consumption for such activities. As shown by our investigation, various real-world network-driven workloads exhibit bursty and random behavior, which motivates our work on regulating and coalescing incoming packets to reduce platform wake events. To understand the performance impact of packet coalescing, we conduct an extensive investigation to study how coalescing may affect the throughput and user experience. Armed with the deep understandings, we propose, implement and evaluate an Adaptive Traffic Coalescing (ATC) scheme that monitors the incoming traffic at the Network Interface Card (NIC), and adaptively coalesces the packets for a limited duration in the NIC buffer, thus requiring no network or eco-system support. The proposed ATC scheme effectively reduces platform wake events, and enables the platform to enter and stay in the low-power state longer for energy efficiency. We have implemented the scheme in commercial wireless NICs. Using various mobile platforms, we evaluate the power savings and performance impact of the proposed ATC scheme. Experiments show that ATC achieves significant power saving for major platform components, around 20% for real-world Internet workloads, without impacting performance and user experience.

A smart triggering scheme to reduce service interruption during heterogeneous handovers

Multi-radio devices provide end-users the ability to achieve ubiquitous and seamless connectivity anytime, anywhere across heterogeneous networks. Minimal service disruption while a device roams across networks is key for a successful deployment. Todaypsilas roaming decisions are reactive and traditionally based on thresholds for signal strength or other radio properties, leading to undesirable handover delays. This paper introduces an Intel/BT client architecture to support seamless mobility for multi-radio devices and proposes a novel approach to predict when a device needs to take proactive actions to perform handovers. Significant improvement in reducing service discontinuity time is demonstrated by applying our approach to WiFi and WiMax networks. We also validate the architecture and algorithm benefits using our WiFi/WiMax multi-radio prototype in heterogeneous wireless network environments.

A collaborative memory system for high-performance and cost-effective clustered architectures

With the fast development of highly integrated distributed systems (cluster systems), especially those encapsulated within a single platform [28, 9], designers have to face interesting memory hierarchy design choices that attempt to avoid disk storage swapping. Disk swapping activities slow down application execution drastically. Leveraging remote free memory through Memory Collaboration has demonstrated its cost-effectiveness compared to overprovisioning for peak load requirements. Recent studies propose several ways on accessing the under-utilized remote memory in static system configurations, without detailed exploration on the dynamic memory collaboration. Dynamic collaboration is an important aspect given the run-time memory usage fluctuations in clustered systems. In this paper, we propose an Autonomous Collaborative Memory System (ACMS) that manages memory resources dynamically at run time, to optimize performance, and provide QoS measures for nodes engaging in the system. We implement a prototype realizing the proposed ACMS, experiment with a wide range of real-world applications, and show up to 3x performance speedup compared to a non-collaborative memory system, without perceivable performance impact on nodes that provide memory. Based on our experiments, we conduct detailed analysis on the remote memory access overhead and provide insights for future optimizations.

IDC: An Energy Efficient Communication Scheme for Connected Mobile Platforms

Mobile platforms (e.g. laptops) offer ubiquitous network connectivity through its wireless communication interfaces, with most of usage models driven by always-on communication activities. However this in turn creates significant power challenges as the battery life is a critical resource for all mobile platforms. While the communication device itself consumes a relatively small portion of the total power, the impact of communication on the overall platform power is significant, due to the non-deterministic nature of the network traffic, which tends to keep the platform busy more than necessary. In this paper, we extensively investigate characteristics of various real-world network-centric workloads, e.g., VoIP, web browsing, etc., and their impact on the mobile platform in terms of power consumption and energy. Based on the understandings, we propose, implement and evaluate an Interrupt /DMA (Direct Memory Access) Coalescing (IDC) scheme at the wireless network interface card (NIC). This scheme effectively reduces platform wakeups due to incoming network traffic, Another advantage of the scheme is that it requires only NIC modification at the receiving node, and is transparent to the user and the network. Using a commercial NIC with a laptop testing platform, we evaluate the power savings and performance impact of our proposed scheme. The measurements show that our scheme achieves significant platform power saving, around 25% of platform components, without impacting user experience.

IEEE 802.21 Assisted Seamless and Energy Efficient Handovers in Mixed Networks

Network selection is the decision process for a mobile terminal to handoff between homogeneous or heterogeneous networks. With multiple available networks, the selection process must evaluate factors like network services/conditions, monetary cost, system conditions, user preferences etc. In this paper, we investigate network selection using a cost function and information provided by IEEE 802.21. The cost function provides flexibility to balance different factors in decision making and our research is focused on improving both seamlessness and energy efficiency of handovers. Our solution is evaluated using real WiFi, WiMax, and 3G signal strength traces. The results show that appropriate networks were selected based on selection policies, handovers were triggered at optimal times to increase overall network connectivity as compared to traditional triggering schemes, while at the same time the energy consumption of multi-radio devices for both on-going operations as well as during handovers is optimized.

Using predictive triggers to improve handover performance in mixed networks

End-users of multi-radio devices expect ubiquitous connectivity anytime and anywhere across heterogeneous networks. A minimal service disruption time while roaming across networks is key for successful deployments. Todays roaming decisions are reactive and traditionally based on thresholds for signal strength, missed beacons, or other properties, leading to undesirable handover delays. In this paper we propose a novel and energy efficient approach to predict when a device needs to take proactive actions to perform either a horizontal or vertical handover. The significant improvements our solution achieved in reducing service discontinuity time are demonstrated by applying our algorithms on WiFi and WiMax networks, in both enterprise and citywide wireless environments.