2 posts tagged with "serving"

Your dashboard says the GPU is healthy. Utilization hovers around 80%, throughput in tokens-per-second looks fine, cold starts are rare, and the model is the one you asked for. Yet your pager is going off because p99 latency has tripled, a handful of users are timing out, and support tickets all describe the same thing: "the app froze for twenty seconds, then came back." You pull a trace and find an unrelated customer's 28,000-token reasoning request sitting in the same batch as every stalled call. One tenant's deep-think prompt just ate everyone else's turn.

This is head-of-line blocking, and it is the failure mode that ruins shared LLM inference the moment reasoning models enter the traffic mix. The pattern is not new — storage systems and network stacks have fought it for decades — but it takes a specific shape on GPUs because of how continuous batching and KV-cache pinning work. Most teams design for average load and discover too late that "shared inference is cheaper" stops being true the instant request sizes stop being similar.

Most LLM serving infrastructure failures in production aren't model failures—they're scheduling failures. Teams stand up a capable model, load test it, and discover they're burning expensive GPU time at 35% utilization while users wait. The culprit is almost always static batching: a default inherited from conventional deep learning that fundamentally doesn't fit how language models generate text.

Continuous batching—also called iteration-level scheduling or in-flight batching—is the mechanism that fixes this. It's not a tuning knob; it's an architectural change to how the serving loop runs. The difference between a system using it and one that isn't can be 4–8x in throughput for the same hardware.