Prefill Concurrency in SGLang: Consistent TTFT Under Multi-Tenant Load

Multi-tenant LLM serving on shared hardware has traditionally suffered from unpredictable latency when requests with different token generation requirements queue together. SGLang's prefill concurrency feature solves this by allowing multiple requests to share the prefill phase, preventing shorter requests from being blocked behind longer ones.

This architectural improvement is particularly valuable for self-hosted deployments where users want to run a single inference server supporting multiple applications or users. By decoupling prefill scheduling from generation scheduling, SGLang provides more predictable performance characteristics and better hardware utilization across varying workload patterns.

For production local deployments, this means better SLA compliance and more efficient resource allocation without requiring separate inference instances per application or user cohort. The technique is especially relevant as more organizations move LLM inference in-house for privacy and cost reasons.

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Source: Hacker News · Relevance: 8/10