Implementing packet trimming support in hardware

Abstract: Packet trimming is a primitive that has been proposed for datacenter networks: to minimize latency, switches run small queues; when the queue overflows, rather than dropping packets the switch trims off the packet payload and either forwards the header to the destination or back to the source. In this way a low latency network that is largely lossless for metadata can be built. Ideally, trimming would be implemented as a primitive in switch ASICs, but hardware development cycles are slow, costly, and require demonstrated customer demand. In this paper we investigate how trimming can be implemented in existing programmable switches which were not designed with trimming in mind, with a particular focus on a P4 implementation on the Tofino switch ASIC. We show that it is indeed possible to closely approximate idealized trimming and demonstrate that trimming can be integrated into a production-grade datacenter switch software stack.