105 lines
2.4 KiB
Markdown
105 lines
2.4 KiB
Markdown
# vLLM Mock Engine
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`vllm-mock-engine` is a small engine-side process for frontend stress testing. It
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joins a frontend-owned startup handshake, reports a large ready response, treats
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prefill as instant, and emits random decode tokens until each request reaches
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its `max_tokens`.
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The frontend must own the handshake socket. Start the frontend first, then start
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the mock engine with the same handshake address.
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## Start the mock engine
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```bash
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cargo run -p vllm-mock-engine -- \
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--handshake-address tcp://127.0.0.1:29550 \
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--engine-count 1 \
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--output-token-chunk-size 1 \
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--vocab-size 32000 \
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--seed 0 \
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--log-requests
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```
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Useful knobs:
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- `--engine-count` must match the frontend's expected data-parallel engine
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count.
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- `--output-token-chunk-size` controls how many token IDs appear in one
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`EngineCoreOutput`; values greater than 1 are useful for MTP/spec-decode
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shaped frontend tests.
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- `--vocab-size` should stay within the tokenizer vocabulary of the model used
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by the frontend.
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Stop it with Ctrl-C.
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## Rust Frontend
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Terminal 1:
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```bash
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cargo run --bin vllm-rs -- serve Qwen/Qwen3-0.6B \
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--data-parallel-size 1 \
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--data-parallel-size-local 0 \
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--handshake-port 29550
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```
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Terminal 2:
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```bash
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cargo run -p vllm-mock-engine -- \
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--handshake-address tcp://127.0.0.1:29550
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```
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For multiple mock engines, set both sides to the same count:
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```bash
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cargo run --bin vllm-rs -- serve Qwen/Qwen3-0.6B \
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--data-parallel-size 4 \
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--data-parallel-size-local 0 \
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--handshake-port 29550
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cargo run -p vllm-mock-engine -- \
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--handshake-address tcp://127.0.0.1:29550 \
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--engine-count 4
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```
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## Python Frontend
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Use `vllm serve` with `--data-parallel-size-local 0` so the Python process runs
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as a frontend/API server and waits for external engines on
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`--data-parallel-rpc-port`.
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Terminal 1:
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```bash
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vllm serve Qwen/Qwen3-0.6B \
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--data-parallel-address 127.0.0.1 \
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--data-parallel-rpc-port 29550 \
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--data-parallel-size 1 \
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--data-parallel-size-local 0
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```
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Terminal 2:
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```bash
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cargo run -p vllm-mock-engine -- \
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--handshake-address tcp://127.0.0.1:29550
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```
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## Smoke Request
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After either frontend is ready:
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```bash
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curl http://127.0.0.1:8000/v1/chat/completions \
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-H "Content-Type: application/json" \
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-d '{
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"model": "Qwen/Qwen3-0.6B",
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"messages": [{"role": "user", "content": "hello"}],
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"max_tokens": 16,
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"stream": true
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}'
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```
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Always pass `max_tokens`; the mock engine stops by length.
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