Problems / LLM serving, medium

A minute to load the weights

A self-hosted 70B model runs on 4 GPU replicas that autoscale to 16. At 20 s traffic triples, from 40 to 120 requests a second. Each new replica must load 140 GB of weights before it serves: 60 s here (2–5 minutes in practice).

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Your goals

Success ≥ 99%.

Test cases

Like a coding problem, a solution has to pass every case, not just the one it was built for. Submit in the lab runs all 3; 1 of them are hidden until then.

  1. As given. The problem’s own traffic, scheduled failures and seed.
  2. A server dies. One replica of the service with the most replicas is killed for part of the run.

The traffic

40 requests a second for 90 seconds: 100% request (reads).

The system

What each component does in this design, and what calls it. The simulator mimics each one from these settings.

ComponentIts job hereSettings
Load balancerLoad balancerTraffic enters here.Calls AI app.Layer 4 balancers route by IP and port; layer 7 balancers read HTTP and can route by path or header.–
AI appApp serviceLoad balancer forwards to it.Calls GPU serving pool (70B).Little's law: throughput ≈ concurrency ÷ latency. 200 slots at 50 ms serve about 4,000 req/s.3 replicas × 500 slots · timeout 30 s
GPU serving pool (70B)Self-hosted serving poolAI app calls it.GPU servers batch requests together; throughput rises with batch size until memory runs out.12 slots · 4–16 instances

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