Suchergebnisse

Minimizing latency and power are key goals in the design of NoC routers. Different proposals combine lookahead routing and router bypass to skip the arbitration and buffering, reducing router delay. However, the conditions to use them requires completely empty buffers in the intermediate routers. This restricts the amount of flits that use the bypass pipeline especially at medium and high loads, increasing latency and power. This paper presents NEBB, Non-Empty Buffer Bypass, a mechanism that allows to bypass flits even if the buffers to bypass are not empty. The mechanism applies to wormhole and virtual-cut-through, each of them with different advantages. NEBB-Hybrid is proposed to employ the best flow control in each situation. The mechanism is extended to torus topologies, using FBFC and shared buffers. The proposals have been evaluated using Booksim, showing up to 75% reduction of the buffered flits for single-flit packets, which translates into latency and dynamic power reductions of up to 30% and 23% respectively. For bimodal traffic, these improvements are 20 and 21% respectively. Additionally, the bypass utilization is largely independent of the number of VCs when using shared buffers and very competitive with few private ones, allowing to simplify the allocation mechanisms. ; This work was supported by the Spanish Ministry of Science, Innovation and Universities, FPI grant BES-2017-079971, the Spanish Ministry of Science, Innovation and Universities under contract TIN2016-76635-C2-2-R (AEI/FEDER, UE) and the European HiPEAC Network of Excellence. The Mont-Blanc project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 671697 ; Peer Reviewed ; Postprint (author's final draft)

High-radix hierarchical networks are cost-effective topologies for large scale computers. In such networks, routers are organized in super nodes, with local and global interconnections. These networks, known as Dragonflies, outperform traditional topologies such as multi-trees or tori, in cost and scalability. However, depending on the traffic pattern, network congestion can lead to degraded performance. Misrouting (non-minimal routing) can be employed to avoid saturated global or local links. Nevertheless, with the current deadlock avoidance mechanisms used for these networks, supporting misrouting implies routers with a larger number of virtual channels. This exacerbates the buffer memory requirements that constitute one of the main constraints in high-radix switches. In this paper we introduce two novel deadlock-free routing mechanisms for Dragonfly networks that support on-the-fly adaptive routing. Using these schemes both global and local misrouting are allowed employing the same number of virtual channels as in previous proposals. Opportunistic Local Misrouting obtains the best performance by providing the highest routing freedom, and relying on a deadlock-free escape path to the destination for every packet. However, it requires Virtual Cut-Through flow-control. By contrast, Restricted Local Misrouting prevents the appearance of cycles thanks to a restriction of the possible routes within super nodes. This makes this mechanism suitable for both Virtual Cut-Through and Wormhole networks. Evaluations show that the proposed deadlock-free routing mechanisms prevent the most frequent pathological issues of Dragonfly networks. As a result, they provide higher performance than previous schemes, while requiring the same area devoted to router buffers. ; This work has been supported by the Spanish Ministry of Science under contracts TIN2010-21291-C02-02, TIN2012-34557, and by the European HiPEAC Network of Excellence. The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP/2007-2013) / ERC Grant Agreement n. ERC-2012-Adg-321253-RoMoL. M. Garc´ıa and M. Odriozola participated in this research work while they were affiliated with the University of Cantabria. ; Peer Reviewed ; Postprint (author's final draft)

High-radix hierarchical networks are cost-effective topologies for large scale computers. In such networks, routers are organized in super nodes, with local and global interconnections. These networks, known as Dragonflies, outperform traditional topologies such as multi-trees or tori, in cost and scalability. However, depending on the traffic pattern, network congestion can lead to degraded performance. Misrouting (non-minimal routing) can be employed to avoid saturated global or local links. Nevertheless, with the current deadlock avoidance mechanisms used for these networks, supporting misrouting implies routers with a larger number of virtual channels. This exacerbates the buffer memory requirements that constitute one of the main constraints in high-radix switches. In this paper we introduce two novel deadlock-free routing mechanisms for Dragonfly networks that support on-the-fly adaptive routing. Using these schemes both global and local misrouting are allowed employing the same number of virtual channels as in previous proposals. Opportunistic Local Misrouting obtains the best performance by providing the highest routing freedom, and relying on a deadlock-free escape path to the destination for every packet. However, it requires Virtual Cut-Through flow-control. By contrast, Restricted Local Misrouting prevents the appearance of cycles thanks to a restriction of the possible routes within super nodes. This makes this mechanism suitable for both Virtual Cut-Through and Wormhole networks. Evaluations show that the proposed deadlock-free routing mechanisms prevent the most frequent pathological issues of Dragonfly networks. As a result, they provide higher performance than previous schemes, while requiring the same area devoted to router buffers. ; This work has been supported by the Spanish Ministry of Science under contracts TIN2010-21291-C02-02, TIN2012-34557, and by the European HiPEAC Network of Excellence. The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP/2007-2013) / ERC Grant Agreement n. ERC-2012-Adg-321253-RoMoL. M. Garc´ıa and M. Odriozola participated in this research work while they were affiliated with the University of Cantabria. ; Peer Reviewed ; Postprint (author's final draft)

Adaptive deadlock-free routing mechanisms are required to handle variable traffic patterns in dragonfly networks. However, distance-based deadlock avoidance mechanisms typically employed in Dragonflies increase the router cost and complexity as a function of the maximum allowed path length. This paper presents on-the-fly adaptive routing (OFAR), a routing/flow-control scheme that decouples the routing and the deadlock avoidance mechanisms. OFAR allows for in-transit adaptive routing with local and global misrouting, without imposing dependencies between virtual channels, and relying on a deadlock-free escape subnetwork to avoid deadlock. This model lowers latency, increases throughput, and adapts faster to transient traffic than previously proposed mechanisms. The low capacity of the escape subnetwork makes it prone to congestion. A simple congestion management mechanism based on injection restriction is considered to avoid such issues. Finally, reliability is considered by introducing mechanisms to find multiple edge-disjoint Hamiltonian rings embedded on the dragonfly, allowing to use multiple escape subnetworks. ; This work has been supported by the Spanish Ministry of Education, FPU grant AP2010-4900; the Spanish Science and Technology Commission (CICYT) under contracts TIN2010-21291-C02-02, TIN2012-34557 and TIN2013- 46957-C2-2-P; the European Union FP7 under Agreements ICT-288777 (Mont-Blanc) and ERC-321253 (RoMoL); the European HiPEAC Network of Excellence and the JSA no. 2013-119 as part of the IBM/BSC Technology Center for Supercomputing agreement. ; Peer Reviewed ; Postprint (published version)

Adaptive deadlock-free routing mechanisms are required to handle variable traffic patterns in dragonfly networks. However, distance-based deadlock avoidance mechanisms typically employed in Dragonflies increase the router cost and complexity as a function of the maximum allowed path length. This paper presents on-the-fly adaptive routing (OFAR), a routing/flow-control scheme that decouples the routing and the deadlock avoidance mechanisms. OFAR allows for in-transit adaptive routing with local and global misrouting, without imposing dependencies between virtual channels, and relying on a deadlock-free escape subnetwork to avoid deadlock. This model lowers latency, increases throughput, and adapts faster to transient traffic than previously proposed mechanisms. The low capacity of the escape subnetwork makes it prone to congestion. A simple congestion management mechanism based on injection restriction is considered to avoid such issues. Finally, reliability is considered by introducing mechanisms to find multiple edge-disjoint Hamiltonian rings embedded on the dragonfly, allowing to use multiple escape subnetworks. ; This work has been supported by the Spanish Ministry of Education, FPU grant AP2010-4900; the Spanish Science and Technology Commission (CICYT) under contracts TIN2010-21291-C02-02, TIN2012-34557 and TIN2013- 46957-C2-2-P; the European Union FP7 under Agreements ICT-288777 (Mont-Blanc) and ERC-321253 (RoMoL); the European HiPEAC Network of Excellence and the JSA no. 2013-119 as part of the IBM/BSC Technology Center for Supercomputing agreement. ; Peer Reviewed ; Postprint (published version)

The Graph500 benchmark attempts to steer the design of High-Performance Computing systems to maximize the performance under memory-constricted application workloads. A realistic simulation of such benchmarks for architectural research is challenging due to size and detail limitations. By contrast, synthetic traffic workloads constitute one of the least resource-consuming methods to evaluate the performance. In this work, we provide a simulation tool for network architects that need to evaluate the suitability of their interconnect for BigData applications. Our development is a low computation- and memory-demanding synthetic traffic model that emulates the behavior of the Graph500 communications and is publicly available in an open-source network simulator. The characterization of network traffic is inferred from a profile of several executions of the benchmark with different input parameters. We verify the validity of the equations in our model against an execution of the benchmark with a different set of parameters. Furthermore, we identify the impact of the node computation capabilities and network characteristics in the execution time of the model in a Dragonfly network ; The authors would like to thank the European HiPEAC Network of Excellence for partially funding this work through a Collaboration Grant. They would like to thank as well Crist´obal Camarero for his help. This work has been supported by the Spanish Ministry of Education, FPU grants FPU13/00337 and FPU14/02253, the Spanish Ministry of Economy, Industry and Competitiveness under contract TIN2016-76635-C2-2-R (AEI/FEDER, UE), and by the Mont-Blanc project. The Mont-Blanc project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 671697. Santander Supercomputacion support group from the University of Cantabria provided access to the Altamira Supercomputer at the Institute of Physics of Cantabria (IFCA-CSIC). ; Peer Reviewed ; Postprint (author's final draft)

The Graph500 benchmark attempts to steer the design of High-Performance Computing systems to maximize the performance under memory-constricted application workloads. A realistic simulation of such benchmarks for architectural research is challenging due to size and detail limitations. By contrast, synthetic traffic workloads constitute one of the least resource-consuming methods to evaluate the performance. In this work, we provide a simulation tool for network architects that need to evaluate the suitability of their interconnect for BigData applications. Our development is a low computation- and memory-demanding synthetic traffic model that emulates the behavior of the Graph500 communications and is publicly available in an open-source network simulator. The characterization of network traffic is inferred from a profile of several executions of the benchmark with different input parameters. We verify the validity of the equations in our model against an execution of the benchmark with a different set of parameters. Furthermore, we identify the impact of the node computation capabilities and network characteristics in the execution time of the model in a Dragonfly network ; The authors would like to thank the European HiPEAC Network of Excellence for partially funding this work through a Collaboration Grant. They would like to thank as well Crist´obal Camarero for his help. This work has been supported by the Spanish Ministry of Education, FPU grants FPU13/00337 and FPU14/02253, the Spanish Ministry of Economy, Industry and Competitiveness under contract TIN2016-76635-C2-2-R (AEI/FEDER, UE), and by the Mont-Blanc project. The Mont-Blanc project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 671697. Santander Supercomputacion support group from the University of Cantabria provided access to the Altamira Supercomputer at the Institute of Physics of Cantabria (IFCA-CSIC). ; Peer Reviewed ; Postprint (author's final draft)