PROSERVE: Unified Multi-Priority Request Scheduling for LLM Serving

Abstract: The widespread deployment of LLMs for interactive applications necessitates serving systems that can handle thousands of concurrent requests with diverse Service Level Objective (SLO) requirements. A critical yet often overlooked dimension in this context is the inherent priority difference among clients; for instance, business-critical functions demand higher performance guarantees, as fulfilling such requests yields significantly greater business value. However, existing LLM serving schedulers fail to jointly optimize for both SLO attainment and client-level priorities. To bridge this gap, we first \textit{formalize multi-priority request scheduling as a service gain maximization problem}, where satisfying latency requirements for requests of different priorities contributes varying levels of gain. We then propose PROSERVE, a unified two-tier scheduling framework designed to maximize overall service gain. At the engine level, SlideBatching dynamically adapts batch formation and request ordering under varying load conditions, employing a sliding boundary mechanism to balance deadline-first and density-first strategies. At the service level, GoRouting performs gain-oriented and capability-aware dispatching across distributed instances, proactively reserving capacity for future high-priority or long requests. Extensive evaluation across four open-source datasets and a real-world industrial trace demonstrates that \systemname{} consistently outperforms state-of-the-art baselines, improving system gain by up to 35% and boosting SLO attainment by up to 52%.