P4KP: QoS-Aware Top-K Best Path Using Programmable Switch

Data center networks offer multiple parallel paths between a source-destination pair. But, due to the use of TCAM based single logical step `path-search and selection' mechanism in the switches, most of the existing packet forwarding systems can utilize only a single-best path. It prevents them from utilizing the benefit of multiple paths for achieving application-specific QoS objectives. In this work, we propose P4KP, a programmable switch-based novel scheme for utilizing the top-k best paths toward a destination in a QoS-aware manner. P4KP complements TCAM's path-selection capability using SRAM; decouples path-searching from path-selection and facilitates the path-selection using an SRAM-based data structure. Its SRAM-based data structure reduces costly TCAM usage and enables the efficient update of the top-k best paths in the data plane. P4KP also provides a bitmask-based API to express the QoS-based policy for selecting one-of-the-top-k best paths. We implemented P4KP using P4 language to demonstrate that it is realizable in currently available programmable switches while maintaining line-rate throughput. Our preliminary evaluation shows that P4KP significantly reduces the stateful memory consumption in programmable switches and achieves improved performance.