Simon Peter

Matheus Stolet, Liam Arzola, Simon Peter et al.

Shared software datapaths underpin modern datacentre networking. They implement mechanisms such as virtual switching, network virtualisation tunneling, or reliable transport, and enforce policies, such as tenant rate limits, virtual network isolation, or congestion control. However, because multiple applications, containers, or VMs share them, often across tenants, they pose a tail latency isolation challenge. Current isolation approaches either sacrifice efficiency via coarse-grained core partitioning or provide weak tail latency isolation when sharing cores with basic rate limits. This paper presents Virtuoso, a time protection mechanism for shared software datapaths that provides strong cross-tenant tail latency isolation while preserving low overhead and microsecond-scale latency. Our key insight is that tail latency is fundamentally a time metric, so byte or packet throughput is the wrong metric for controlling interference when packet processing costs vary. Our design instead enforces isolation through per-tenant CPU-time budgets at datapath intervention points within run-to-completion loops, without relying on preemption. In a case study, we instantiate Virtuoso in the TAS TCP stack and demonstrate a 7.8X reduction in victim tail latency under adversarial interference while keeping throughput within 5% of unmodified TAS. We also observe a 3X per-core efficiency improvement compared to siloed datapaths under bursty workloads.

Aditya K Kamath, Ramya Prabhu, Jayashree Mohan et al.

Each request in LLM inference goes through two phases: compute-bound prefill and memory-bandwidth-bound decode. To improve GPU utilization, recent systems use hybrid batching that combines the prefill and decode phases of different requests into the same batch. This approach optimizes linear operations but remains inefficient for attention computation because existing attention kernels specialize execution independently for the prefill and decode phases. In this paper, we present POD-Attention - the first GPU kernel that efficiently computes attention for hybrid batches. POD-Attention aims to maximize the utilization of both compute and memory bandwidth by carefully allocating the GPU's resources such that prefill and decode operations happen concurrently on the same multiprocessor. POD-Attention speeds up attention computation by up to $59\%$ (mean $28\%$), enabling higher throughput and lower latency LLM inference compared to the use of independently optimized prefill and decode attention kernels.