Hierarchical organization is widely used in high-radix routers to enable efficient scaling to higher switch port count. A general-purpose hierarchical router must be symmetrically designed with the same input buffer depth, resulting in a large amount of unused input buffers due to the different link lengths. Sharing input buffers between different input ports can improve buffer utilization, but the implementation overhead also increases with the number of shared ports. Previous work allowed input buffers to be shared among all router ports, which maximizes the buffer utilization but also introduces higher implementation complexity. Moreover, such design can impair performance when faced with long packets, due to the head-of-line blocking in intermediate buffers. In this work, we explain that sharing unused buffers between a subset of router ports is a more efficient design. Based on this observation, we propose Centralized Input Buffer Design in Hierarchical High-radix Routers (CIB-HIER), a novel centralized input buffer design for hierarchical high-radix routers. CIB-HIER integrates multiple input ports onto a single tile and organizes all unused input buffers in the tile as a centralized input buffer. CIB-HIER only allows the centralized input buffer to be shared between ports on the same tile, without introducing additional intermediate virtual channels or global scheduling circuits. Going beyond the basic design of CIB-HIER, the centralized input buffer can be used to relieve the head-of-line blocking caused by shallow intermediate buffers, by stashing long packets in the centralized input buffer. Experimental results show that CIB-HIER is highly effective and can significantly increase the throughput of high-radix routers.

中文翻译：

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CIB-HIER

分层组织广泛用于高基数路由器，以实现有效扩展至更高的交换机端口数。通用的分层路由器必须对称地设计相同的输入缓冲区深度，导致由于链路长度不同而导致大量未使用的输入缓冲区。在不同输入端口之间共享输入缓冲区可以提高缓冲区利用率，但实现开销也随着共享端口的数量而增加。以前的工作允许在所有路由器端口之间共享输入缓冲区，这最大限度地利用了缓冲区，但也引入了更高的实现复杂性。此外，由于中间缓冲区中的行头阻塞，这种设计在面对长数据包时会损害性能。在这项工作中，我们解释说，在路由器端口子集之间共享未使用的缓冲区是一种更有效的设计。基于这一观察，我们提出了分层高基路由器（CIB-HIER）中的集中输入缓冲区设计，这是一种用于分层高基路由器的新型集中输入缓冲区设计。CIB-HIER 将多个输入端口集成到单个块上，并将块中所有未使用的输入缓冲区组织为集中输入缓冲区。CIB-HIER 仅允许集中输入缓冲区在同一块上的端口之间共享，而无需引入额外的中间虚拟通道或全局调度电路。超越 CIB-HIER 的基本设计，集中输入缓冲区可用于通过在集中输入缓冲区中存储长数据包来缓解由浅中间缓冲区引起的行头阻塞。