Abstract
Rack scale design is a promising trend towards customized hardware design, where high density clusters of SoCs are integrated in the rack. One of the biggest challenges for rack scale computing is the interconnection network. Traditional data center topologies require too many ToR switches to support hundreds of SoCs, while distributed fabrics deliver a considerably high end-to-end latency and network oversubscription. Since no one topology fits all kinds of workloads, a flexible in-rack topology requires a careful redesign to dynamically adapt to diverse data center traffic within tight cost and space constraints in the rack. SRFabric is a semi-reconfigurable rack scale network topology that exploits the high path diversity, the cost-effectiveness of distributed fabrics, and the dynamic reconfigurability of circuit switches. This is accomplished by enabling multiple static ports and dynamic ports for each SoC. Leveraging the partial link reconfigurability, SRFabric is able to optimize its topology to dynamically adapt to various workload patterns. We further propose the design of SRFabric to decide the nearly optimal number of dynamic ports and static ports for expected communication density and performance. Extensive evaluations demonstrate that SRFabric can deliver lower average path length, i.e., 2.21 hops on average, and higher bisection bandwidth, i.e., up to 77% nonblocking bandwidth, and provide comparable performance with state-of-the-art strategy XFabric at a lower cost, i.e., XFabric costs up to 3 times more than that of SRFabric.
Highlights
Motivated by this intuition, this paper presents SRFabric that takes both cost and path diversity into consideration through reconfiguring the ports
Each static port of a SoC is connected to the corresponding static port of its neighbour, while each dynamic port of a SoC is attached to the circuit switch
We first explore the performance of SRFabric regarding the latency, which is intuitively indicated by the average path length
Summary
This paper presents SRFabric (a semi-reconfigurable rack scale fabric) that takes both cost and path diversity into consideration through reconfiguring the ports. As shown in our case studies later, the Collect Pattern (i.e., 1-to-all traffic [16, 17]) performs the worst in terms of the reconfigurability and requires plenty of dynamic ports to ensure the desired level of traffic performance Based on this observation, we first analyze the distribution in terms of the shortest path length for the Collect Pattern and further generalize the design of the topology for desired communication density by studying the relationship between the density of links, the density of nodes, i.e., SoCs, and the reconfigurability. E results show that SRFabric outperforms 3D Torus with higher bisection bandwidth and lower average path length, incurring only 2.21 hops on average, and delivers almost similar performance to XFabric at a 29% reduction on the cost These evaluations demonstrate that a higher level of reconfigurability cannot translate into salient benefits when the communication density is high.
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