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Virtual switches, used for end-host networking, drop packets when the receiving application is not fast enough to consume them. This is called the slow receiver problem, and it is important because packet loss hurts tail communication latency and wastes CPU cycles, resulting in application-level performance degradation. Further, solving this problem is challenging because application throughput is highly variable over short timescales as it depends on workload, memory contention, and OS thread scheduling. This paper presents Backdraft, a new lossless virtual switch that addresses the slow receiver problem by combining three new components: (1) Dynamic Per-Flow Queuing (DPFQ) to prevent HOL blocking and provide on-demand memory usage; (2) Doorbell queues to reduce CPU overheads; (3) A new overlay network to avoid congestion spreading. We implemented Backdraft on top of BESS and conducted experiments with real applications on a 100 Gbps cluster with both DCTCP and Homa, a state-of-the-art congestion control scheme. We show that an application with Backdraft can achieve up to 20x lower tail latency at the 99th percentile. 

This paper presents the motivation and design of MTP, a new offload-friendly message transport protocol. Existing transport protocols like TCP, MPTCP, and UDP/Quic all have key limitations when used in a network that may potentially offload computation from end-servers into NICs, switches, and other network devices. To enable important new in-network computing use cases and correct congestion control in the face of ever changing network paths and application replicas, MTP introduces a new message transport protocol design and pathlet congestion control, a new approach where end-hosts explicitly communicate messaging information to network devices and network devices explicitly communicate network path and congestion information back to end-hosts.