Justitia: Software Multi-Tenancy in Hardware Kernel-Bypass Networks

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 latencysensitive applications at the cost of slightly decreased utilization and ensure that throughput and bandwidth of the rest are not unfairly penalized.