[Bugfix][V1] Warm up slot mapping before JIT monitor

[lesj0610]

Problem

V1 startup warmup activates before the JIT monitor, but the normal dummy/profile path does not reliably cover BlockTable.compute_slot_mapping(). As a result, _compute_slot_mapping_kernel can still compile on the first real request after the monitor is active.

There is also a specialization issue. The slot-mapping Triton kernel was specializing on runtime request size, so warming one token count did not necessarily cover the next real request shape.

Approach

This PR keeps the scope limited to the V1 slot-mapping path.

It adds do_not_specialize=["num_tokens"] to _compute_slot_mapping_kernel while keeping max_num_tokens specialized, since max_num_tokens is engine-lifetime configuration and still useful for Triton optimization.

It also adds warmup_v1_slot_mapping_kernel(), which calls compute_slot_mapping() directly before the JIT monitor is activated. The warmup uses block id 1 instead of the null block and clears temporary state in a finally block.

A follow-up commit warms request-shaped slot-mapping variants, because the first real serving request can use small prompt/decode shapes that differ from the original synthetic warmup. This is still slot-mapping only; it does not fold attention, MoE, TurboQuant, or hybrid model kernels into this PR.

I searched open PRs for this exact V1 slot-mapping JIT warmup issue and did not find another one.

Test Plan

.venv/bin/python -m pytest tests/v1/worker/test_gpu_model_runner.py -v

pre-commit run ruff-format --files \
  vllm/v1/worker/block_table.py \
  vllm/v1/worker/gpu/warmup.py \
  vllm/v1/worker/gpu_worker.py \
  tests/v1/worker/test_gpu_model_runner.py

pre-commit run ruff-check --files \
  vllm/v1/worker/block_table.py \
  vllm/v1/worker/gpu/warmup.py \
  vllm/v1/worker/gpu_worker.py \
  tests/v1/worker/test_gpu_model_runner.py

pre-commit run mypy-3.10 --files \
  vllm/v1/worker/block_table.py \
  vllm/v1/worker/gpu/warmup.py \
  vllm/v1/worker/gpu_worker.py \
  tests/v1/worker/test_gpu_model_runner.py \
  --hook-stage manual

git diff --check

Test Result

• tests/v1/worker/test_gpu_model_runner.py: 34 passed, 16 warnings
• ruff-format / ruff-check: passed
• mypy-3.10: passed
• git diff --check: passed

Local smoke on V1 runner with Qwen3-8B text-only: HTTP 200, no _compute_slot_mapping_kernel warning on first request.

Combined warmup smoke on the integration branch also showed _compute_slot_mapping_kernel: 0 warnings after the request-shaped slot-mapping warmup was included. Other warmup buckets are handled by separate PRs.

Checklist

• Purpose
• Test plan and results
• AI assistance disclosed

AI assistance: Codex, Claude.

[claude]

Claude Code Review

This pull request is from a fork — automated review is disabled. A repository maintainer can comment @claude review to run a one-time review.

[gemini-code-assist]

Code Review

This pull request introduces a warmup mechanism for the V1 slot mapping kernel to ensure it is compiled before the JIT monitor is enabled. Key changes include the implementation of warmup_v1_slot_mapping_kernel, its integration into the GPUWorker warmup sequence, and a Triton JIT optimization to prevent specialization on num_tokens. New unit tests verify the warmup process and its error handling. I have no feedback to provide.

[lesj0610]

@ZJY0516 @qiching @tdoublep @vadiklyutiy Hi, this is follow-up fix for #40137.

I found V1 path still triggers JIT warning on first real request. _dummy_run() does not call BlockTable.compute_slot_mapping(), and the kernel was specialized on num_tokens so each different request size recompiles.

Fix is small — do_not_specialize=["num_tokens"] and direct compute_slot_mapping() call during V1 warmup before monitor activates. No synthetic execute_model() warmup, that is model-specific so I keep scope to slot mapping only.

You all reviewed #40137 so your feedback would be very helpful. Thanks.

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @lesj0610.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

[lesj0610]

Closing as superseded by the newer slot-mapping warmup branch tracked in lesj0610#85.