The need for higher throughput and lower latency is driving kernel-bypass networking (KBN) in datacenters. Of the two related trends in KBN, hardware-based KBN is especially challenging because, unlike software KBN such as DPDK, it does not provide any control once a request is posted to the hardware. RDMA, which is the most prevalent form of hardware KBN in practice, is completely opaque. RDMA NICs (RNICs), whether they are using InfiniBand, RoCE, or iWARP, have fixed-function scheduling algorithms programmed in them. Like any other networking component, they also suffer from performance isolation issues when multiple applications compete for RNIC resources. Justitia is our attempt at introducing software control in hardware KBN.

Kernel-bypass networking (KBN) is becoming the new norm in modern datacenters. While hardware-based KBN offloads all dataplane tasks to specialized NICs to achieve better latency and CPU efficiency than software-based KBN, it also takes away the operator’s control over network sharing policies. Providing policy support in multi-tenant hardware KBN brings unique challenges — namely, preserving ultra-low latency and low CPU cost, finding a well-defined point of mediation, and rethinking traffic shapers. We present Justitia to address these challenges with three key design aspects: (i) Split Connection with message-level shaping, (ii) sender-based resource mediation together with receiver-side updates, and (iii) passive latency monitoring. Using a latency target as its knob, Justitia enables multi-tenancy policies such as predictable latencies and fair/weighted resource sharing. Our evaluation shows Justitia can effectively isolate latency-sensitive applications at the cost of slightly decreased utilization and ensure that throughput and bandwidth of the rest are not unfairly penalized.

Yiwen started working on this problem when we first observed RDMA isolation issues in Infiniswap. He even wrote a short paper in KBNets 2017 based on his early findings. Yue worked on it for quite a few months before she went to Princeton for Ph.D. Brent has been helping us getting this work into shape since the beginning. It’s been a long and arduous road; every time we fixed something, new reviewers didn’t like something else. Finally, an NSDI revision allowed us to directly address the most pressing concerns. Without commenting on how much the paper has improved after all these iterations, I can say that adding revisions to NSDI has saved us, especially Yiwen, a lot more frustrations. For what it’s worth, Justitia now has the notorious distinction of my current record for accepted-after-N-submissions; it’s been so long that I’ve lost track of the exact value of N!