779 research outputs found

    Energy-Efficient Interconnection Networks for High-Performance Computing

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    In recent years, energy has become one of the most important factors for de- signing and operating large scale computing systems. This is particularly true in high-performance computing, where systems often consist of thousands of nodes. Especially after the end of Dennard’s scaling, the demand for energy- proportionality in components, where energy is depending linearly on utilization, increases continuously. As the main contributor to the overall power consumption, processors have received the main attention so far. The increasing energy proportionality of processors, however, shifts the focus to other components such as interconnection networks. Their share of the overall power consumption is expected to increase to 20% or more while other components further increase their efficiency in the near future. Hence, it is crucial to improve energy proportionality in interconnection networks likewise to reduce overall power and energy consumption. To facilitate these attempts, this work provides comprehensive studies about energy saving in interconnection networks at different levels. First, interconnection networks differ fundamentally from other components in their underlying technology. To gain a deeper understanding of these differences and to identify targets for energy savings, this work provides a detailed power analysis of current network hardware. Furthermore, various applications at different scales are analyzed regarding their communication patterns and locality properties. The findings show that communication makes up only a small fraction of the execution time and networks are actually idling most of the time. Another observation is that point-to-point communication often only occurs within various small subsets of all participants, which indicates that a coordinated mapping could further decrease network traffic. Based on these studies, three different energy-saving policies are designed, which all differ in their implementation and focus. Then, these policies are evaluated in an event-based, power-aware network simulator. While two policies that operate completely local at link level, enable significant energy savings of more than 90% in most analyses, the hybrid one does not provide further benefits despite significant additional design effort. Additionally, these studies include network design parameters, such as transition time between different link configurations, as well as the three most common topologies in supercomputing systems. The final part of this work addresses the interactions of congestion management and energy-saving policies. Although both network management strategies aim for different goals and use opposite approaches, they complement each other and can increase energy efficiency in all studies as well as improve the performance overhead as opposed to plain energy saving

    Generalized load sharing for packet-switching networks

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    In this paper, we propose a framework to study how to effectively perform load sharing in multipath communication networks. A generalized load sharing (GLS) model has been developed to conceptualize how traffic is split ideally on a set of active paths. A simple traffic splitting algorithm, called weighted fair routing (WFR), has been developed at two different granularity level, namely, the packet level, and the call level, to approximate GLS with the given routing weight vector. The packet-by-packet WFR (PWFR) mimics GLS by transmitting each packet as a whole, whereas the call-by-call WFR (CWFR) imitates GLS so that all packets belonging to a single flow are sent on the same path. We have developed some performance bounds for PWFR and found that PWFR is a deterministically fair traffic splitting algorithm. This attractive property is useful in the provision of service with guaranteed performance when multiple paths can be used simultaneously to transmit packets which belong to the same flow. Our simulation studies, based on a collection of Internet backbone traces, reveal that WFR outperforms two other traffic splitting algorithms, namely, generalized round robin routing (GRR), and probabilistic routing (PRR). These promising results form a basis for designing future adaptive constraint-based multipath routing protocols.published_or_final_versio

    Improving Large-Scale Network Traffic Simulation with Multi-Resolution Models

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    Simulating a large-scale network like the Internet is a challenging undertaking because of the sheer volume of its traffic. Packet-oriented representation provides high-fidelity details but is computationally expensive; fluid-oriented representation offers high simulation efficiency at the price of losing packet-level details. Multi-resolution modeling techniques exploit the advantages of both representations by integrating them in the same simulation framework. This dissertation presents solutions to the problems regarding the efficiency, accuracy, and scalability of the traffic simulation models in this framework. The ``ripple effect\u27\u27 is a well-known problem inherent in event-driven fluid-oriented traffic simulation, causing explosion of fluid rate changes. Integrating multi-resolution traffic representations requires estimating arrival rates of packet-oriented traffic, calculating the queueing delay upon a packet arrival, and computing packet loss rate under buffer overflow. Real time simulation of a large or ultra-large network demands efficient background traffic simulation. The dissertation includes a rate smoothing technique that provably mitigates the ``ripple effect\u27\u27, an accurate and efficient approach that integrates traffic models at multiple abstraction levels, a sequential algorithm that achieves real time simulation of the coarse-grained traffic in a network with 3 tier-1 ISP (Internet Service Provider) backbones using an ordinary PC, and a highly scalable parallel algorithm that simulates network traffic at coarse time scales

    High-Performance and Wavelength-Reused Optical Network on Chip (ONoC) Architectures and Communication Schemes for Manycore Processor

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    Optical Network on Chip (ONoC) is an emerging chip-scale optical interconnection technology to realize the high-performance and power-efficient inter-core communication for many-core processors. By utilizing the silicon photonic interconnects to transmit data packets with optical signals, it can achieve ultra low communication delay, high bandwidth capacity, and low power dissipation. With the benefits of Wavelength Division Multiplexing (WDM), multiple optical signals can simultaneously be transmitted in the same optical interconnect through different wavelengths. Thus, the WDM-based ONoC is becoming a hot research topic recently. However, the maximal number of available wavelengths is restricted for the reliable and power-efficient optical communication in ONoC. Hence, with a limited number of wavelengths, the design of high-performance and power-efficient ONoC architecture is an important and challenging problem. In this thesis, the design methodology of wavelength-reused ONoC architecture is explored. With the wavelength reuse scheme in optical routing paths, high-performance and power-efficient communication is realized for many-core processors only using a small number of available wavelengths. Three wavelength-reused ONoC architectures and communication schemes are proposed to fulfil different communication requirements, i.e., network scalability, multicast communication, and dark silicon. Firstly, WRH-ONoC, a wavelength-reused hierarchical Optical Network on Chip architecture, is proposed to achieve high network scalability, namely obtaining low communication delay and high throughput capacity for hundreds of thousands of cores by reusing the limited number of available wavelengths with the modest hardware cost and energy overhead. WRH-ONoC combines the advantages of non-blocking communication in each lambda-router and wavelength reuse in all lambda-routers through the hierarchical networking. Both theoretical analysis and simulation results indicate that WRH-ONoC can achieve prominent improvement on the communication performance and scalability (e.g., 46.0% of reduction on the zero-load packet delay and 72.7% of improvement on the network throughput for 400 cores with small hardware cost and energy overhead) in comparison with existing schemes. Secondly, DWRMR, a dynamical wavelength-reused multicast scheme based on the optical multicast ring, is proposed for widely existing multicast communications in many-core processors. In DWRMR, an optical multicast ring is dynamically constructed for each multicast group and the multicast packets are transmitted in a single-send-multi-receive manner requiring only one wavelength. All the cores in the same multicast group can reuse the established multicast ring through an optical token arbitration scheme for the interactive multicast communications, thereby avoiding the frequent construction of multicast routing paths dedicatedly for each core. Simulation results indicate that DWRMR can reduce more than 50% of end-to-end packet delay with slight hardware cost, or require only half number of wavelengths to achieve the same performance compared with existing schemes. Thirdly, Dark-ONoC, a dynamically configurable ONoC architecture, is proposed for the many-core processor with dark silicon. Dark silicon is an inevitable phenomenon that only a small number of cores can be activated simultaneously while the other cores must stay in dark state (power-gated) due to the restricted power budget. Dark-ONoC periodically allocates non-blocking optical routing paths only between the active cores with as less wavelengths as possible. Thus, it can obtain high-performance communication and low power consumption at the same time. Extensive simulations are conducted with the dark silicon patterns from both synthetic distribution and real data traces. The simulation results indicate that the number of wavelengths is reduced by around 15% and the overall power consumption is reduced by 23.4% compared to existing schemes. Finally, this thesis concludes several important principles on the design of wavelength-reused ONoC architecture, and summarizes some perspective issues for the future research
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