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fix(vllm): support legacy generate session API - #15008
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Signed-off-by: wenxin.zhang <wenxin.zhang@intel.com>
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WalkthroughThe vLLM handler now inspects ChangesvLLM session compatibility
Priority: ⬇️ Low Estimated code review effort: 2 (Simple) | ~10 minutes Merge Risk: 🔵 Low · up to The compatibility fix is low risk, but coverage should verify that legacy engines work without session_id. 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
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- 🪄 Fix CodeRabbit comments on this PR
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In `@components/src/dynamo/vllm/handlers.py`:
- Around line 3275-3281: Add a handler test for generate_tokens using a fake
engine whose generate signature omits session_id, and assert generation succeeds
without that unsupported keyword being passed. Update the relevant fake generate
implementation and test setup while preserving existing generation behavior and
coverage.
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Previously reported defects still present:
- Original discussion: The legacy
generatesignature coverage defect remains present: the PR changesgenerate_tokensto omitsession_idonly when the engine signature rejects it, but the nearest handler tests still use fakegeneratefunctions that acceptsession_id, so they would not fail if the unsupported keyword were still forwarded.
| def _engine_generate_session_kwargs( | ||
| engine_client: Any, session_id: str | None | ||
| ) -> dict[str, str | None]: | ||
| """Return session_id only when the installed vLLM engine accepts it.""" |
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This private helper's docstring restates behavior already expressed by its name and signature inspection; it records no non-obvious compatibility constraint or rationale.
🤖 AI Fix
Remove the redundant docstring.
| trace_headers=trace_headers, | ||
| priority=priority, | ||
| session_id=session_id, | ||
| **_engine_generate_session_kwargs(self.engine_client, session_id), |
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This compatibility guard only covers BaseWorkerHandler.generate_tokens. DecodeWorkerHandler.generate routes use_vllm_tokenizer=True requests through _generate_text_mode, which still calls engine_client.generate(..., session_id=session_id) directly, and PrefillWorkerHandler._generate_token_mode does the same. Both paths therefore still raise TypeError on the stated legacy vLLM engine, leaving supported text-mode decode and prefill requests broken.
🤖 AI Fix
Apply _engine_generate_session_kwargs to every remaining direct engine_client.generate call that forwards session_id, including text-mode decode and prefill generation.
| trace_headers=trace_headers, | ||
| priority=priority, | ||
| session_id=session_id, | ||
| **_engine_generate_session_kwargs(self.engine_client, session_id), |
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This compatibility helper is applied only to the BaseWorkerHandler token path. Legacy vLLM still receives session_id unconditionally from DecodeWorkerHandler's supported text-mode path and PrefillWorkerHandler's supported disaggregated prefill path, so an XPU vLLM 0.27.1 worker raises TypeError for those requests even after this fix. Apply the same conditional expansion at both direct engine_client.generate call sites.
🤖 AI Fix
Use _engine_generate_session_kwargs(self.engine_client, session_id) for every direct vLLM generate invocation that forwards session_id, including decode text mode and prefill mode.
| trace_headers=trace_headers, | ||
| priority=priority, | ||
| session_id=session_id, | ||
| **_engine_generate_session_kwargs(self.engine_client, session_id), |
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This compatibility wrapper is only used by generate_tokens. The direct AsyncLLM.generate calls in DecodeWorkerHandler._generate_text_mode and PrefillWorkerHandler._generate_token_mode still pass session_id=session_id; on the supported XPU vLLM 0.27.1 signature, both paths raise TypeError before producing output, including when no session ID was supplied.
🤖 AI Fix
Apply _engine_generate_session_kwargs to every remaining direct engine_client.generate call that forwards session_id.
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Signed-off-by: Wenxin Zhang <wenxin.zhang@intel.com>
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Overview:
Fix vLLM XPU runtime compatibility after #14428 began forwarding
session_idtoAsyncLLM.generate().Details:
#14428 added request-native session ID forwarding to vLLM to support the newer vLLM API introduced by vllm-project/vllm#48048. However, Dynamo's XPU runtime currently uses vLLM
0.27.1, whoseAsyncLLM.generate()does not accept thesession_idkeyword argument.As a result, XPU serve tests fail with:
This change inspects the installed engine's
generatesignature and forwardssession_idonly when the engine supports it. This preserves session ID propagation for newer vLLM versions while restoring compatibility with the existing XPU runtime.Where should the reviewer start?
components/src/dynamo/vllm/handlers.py_engine_generate_session_kwargsBaseWorkerHandler.generate_tokensRelated Issues
🚫 This PR is NOT linked to an issue:
Related: #14428
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