Engaging applications with diverse SLO requirements has become indispensable for production-scale LLM serving systems. However, existing systems rely on iteration-level scheduling, which enforces inflexible, unified execution across multi-SLO workloads, significantly constraining the serving efficiency.

In this paper, we introduce layer-level scheduling, a novel mechanism that advances beyond conventional iteration-level granularity. This mechanism decomposes per-iteration computation into fine-grained layer operations, enabling the tailored execution of requests with differing requirements. However, this increased granularity introduces new challenges in both intra-instance request execution and cross-instance coordination, posing significant barriers to practical deployment. To address these challenges, we introduce Laser, a system designed for efficient multi-SLO LLM serving. The key aspect lies in the seamless integration of inter-instance request dispatching with layer-level scheduling within instances, delivering high serving throughput with SLO guarantees. Evaluations with real-world applications reveal that Laser effectively improves throughput by over 1.67x while maintaining the same SLO attainment rate compared to state-of-the-art systems.