Allow LMCacheConnectorV1 to support hybrid KV loads#42620
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avifenesh
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NickLucche,
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njhill,
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xuechendi and
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Code Review
This pull request introduces support for Hybrid Model Architecture (HMA) within the LMCacheConnectorV1. Key updates include the implementation of the SupportsHMA interface, a new supports_mamba_external_kv property, and the request_finished_all_groups method to manage multiple KV cache groups. Additionally, the scheduler now validates external KV support for Mamba blocks, and comprehensive unit tests have been added to cover these changes. I have no feedback to provide as no review comments were present.
| if num_external_computed_tokens != 0: | ||
| supports_external_mamba = bool( | ||
| self.connector is not None | ||
| and getattr(self.connector, "supports_mamba_external_kv", False) |
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If something like this is needed, then it should be added to the base KV connector interface and well documented
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Thanks, addressed in 421b29d by moving this from an ad hoc scheduler getattr into the KV connector interface.
Changes made:
- added KVConnectorBase_V1.supports_mamba_external_kv with a documented default of False
- changed the scheduler to call the typed connector property directly
- delegated the capability through MultiConnector, requiring all child connectors to support it
- added a focused MultiConnector unit test for the aggregation behavior
Fresh validation after the change:
- uvx ruff check vllm/distributed/kv_transfer/kv_connector/v1/base.py vllm/distributed/kv_transfer/kv_connector/v1/multi_connector.py vllm/v1/core/sched/scheduler.py tests/v1/kv_connector/unit/test_multi_connector.py
- uvx ruff format --check vllm/distributed/kv_transfer/kv_connector/v1/base.py vllm/distributed/kv_transfer/kv_connector/v1/multi_connector.py vllm/v1/core/sched/scheduler.py tests/v1/kv_connector/unit/test_multi_connector.py
- python -m py_compile vllm/distributed/kv_transfer/kv_connector/v1/base.py vllm/distributed/kv_transfer/kv_connector/v1/multi_connector.py vllm/v1/core/sched/scheduler.py tests/v1/kv_connector/unit/test_multi_connector.py
- pytest -q tests/v1/kv_connector/unit/test_lmcache_connector.py tests/v1/kv_connector/unit/test_multi_connector.py::test_multi_connector_overrides_all_base_methods tests/v1/kv_connector/unit/test_multi_connector.py::test_multi_connector_supports_mamba_external_kv -> 29 passed
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Follow-up in b824e57: I strengthened the documentation part of this change instead of relying only on the initial short docstring.
What changed:
- expanded KVConnectorBase_V1.supports_mamba_external_kv docs to describe the scheduler consumer, why attention KV alone is unsafe for hybrid/Mamba requests, the exact opt-in guarantee, and the safe default of False
- documented LMCacheConnectorV1 as adapter-gated so older LMCache adapters remain false by default
- documented MultiConnector as requiring every child connector to opt in
- added a public docs section in docs/features/disagg_prefill.md under Development: Hybrid/Mamba external cache hits
Fresh validation:
- uvx ruff check on the touched Python files and focused test file: passed
- uvx ruff format --check on the same files: passed
- python -m py_compile on the touched Python files and focused test file: passed
- pytest -q tests/v1/kv_connector/unit/test_lmcache_connector.py tests/v1/kv_connector/unit/test_multi_connector.py::test_multi_connector_overrides_all_base_methods tests/v1/kv_connector/unit/test_multi_connector.py::test_multi_connector_supports_mamba_external_kv -> 29 passed
- VLLM_TARGET_DEVICE=empty API_AUTONAV_EXCLUDE=vllm uv run --with-requirements requirements/docs.txt mkdocs build --site-dir /tmp/vllm-docs-site-noapi -> built successfully; the new section renders in docs/features/disagg_prefill.md
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Documentation preview: https://vllm--42620.org.readthedocs.build/en/42620/ |
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Thanks for the work @avifenesh , I am not really convinced about the necessity of introducing supports_mamba_external_kv here.
Looking at it more broadly, If a connector (NOT an offloading connector) does not support mamba prefix caching, it can easily validate that within its class.
This flag is just maintaining the validation scheduler side, which is frankly not of much value: the assert was there simply because prefix caching+connector was postponed to a separate PR.
I am actually proposing to get rid of that entirely here #42554.
If your connector does not yet support prefix caching, just force/advertise --no-enable-prefix-caching as we've been doing for nixl until #42554.
Signed-off-by: Avi Fenesh <aviarchi1994@gmail.com> Assisted-by: OpenAI Codex
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Thanks @NickLucche, agreed with the direction. I dropped the
I also removed the public docs/tests around the dropped capability flag and updated the PR description to call out the dependency graph explicitly: #42554 owns scheduler admission for Mamba external hits, this PR exposes the HMA plumbing to LMCache, and LMCache/LMCache#3284 performs connector-local validation by only reporting hits when the matching hybrid state is available. Fresh validation on the final two-file diff:
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| def get_lmcache_kv_cache_config(self) -> "KVCacheConfig | None": | ||
| """ | ||
| Return the vLLM KV cache config for LMCache's integration adapter. | ||
| """ | ||
| return self._kv_cache_config |
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this method might get picked up as dead code.
We should either comment that it's being used externally or use the property kv_cache_config directly.
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Done in 8b58c3ed5d: I removed the LMCache-specific getter and exposed the config through the connector attribute instead.
vLLM side:
LMCacheConnectorV1.__init__now setsself.kv_cache_config = kv_cache_configget_lmcache_kv_cache_config()was removed
Companion LMCache side is updated in LMCache/LMCache#3284 commit 6ae3e7f7 to read parent.kv_cache_config directly.
Fresh validation:
timeout 60 uvx ruff check vllm/distributed/kv_transfer/kv_connector/v1/lmcache_connector.py tests/v1/kv_connector/unit/test_lmcache_connector.pytimeout 60 uvx ruff format --check vllm/distributed/kv_transfer/kv_connector/v1/lmcache_connector.py tests/v1/kv_connector/unit/test_lmcache_connector.py.venv/bin/python -m py_compile vllm/distributed/kv_transfer/kv_connector/v1/lmcache_connector.py tests/v1/kv_connector/unit/test_lmcache_connector.py.venv/bin/python -m pytest -q tests/v1/kv_connector/unit/test_lmcache_connector.py->26 passed, 16 warnings
Signed-off-by: Avi Fenesh <aviarchi1994@gmail.com> Assisted-by: OpenAI Codex
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this is blocked on the pre-run-check gate - i dont have 4 merged prs in this repo yet, so it needs the ready or verified label from a maintainer for tests to run. could someone take a look and add it? |
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Summary
This keeps the vLLM-side change scoped to
LMCacheConnectorV1HMA plumbing. It intentionally does not add a scheduler/basesupports_mamba_external_kvcapability flag; connector-local safety is handled in the companion LMCache PR, and scheduler-side Mamba external-hit admission is owned by #42554 or an equivalent scheduler change.What changes here:
LMCacheConnectorV1implementsSupportsHMALMCacheConnectorV1exposes the vLLMKVCacheConfigto the LMCache adapterrequest_finished_all_groups()forwards the block IDs for the LMCache-selected attention KV group instead of assuming group 0Companion LMCache PR: LMCache/LMCache#3284
The full hybrid/Mamba external-hit path requires three pieces:
LMCacheConnectorV1receive the HMA KV cache config and all group block IDsWhy This Is Not Duplicating Existing PRs
I re-checked open PRs with:
gh pr list --repo vllm-project/vllm --state open --search "LMCacheConnectorV1 HMA"-> only this PRgh pr list --repo vllm-project/vllm --state open --search "mamba prefix caching connector"-> related Mamba/PD work, but not this non-MP LMCache connector adapter handoffgh pr list --repo vllm-project/vllm --state open --search "request_finished_all_groups LMCache"-> [KV connector] LMCacheMPConnector: SupportsHMA for hybrid models #42437 and this PRRelationship to the closest PRs:
LMCacheConnectorV1to HMA and LMCache's adapter contract.LMCacheMPConnector; this PR targets the existing non-MPLMCacheConnectorV1path and pairs with LMCache v0.3.3 - Module not found when deploying modes to Inferentia2/NeuronSDK #3284, not LMCache 8bit quantization #3261.Validation
Current final diff:
git diff --check upstream/main...HEAD-> passeduv run --with ruff ruff check vllm/distributed/kv_transfer/kv_connector/v1/lmcache_connector.py tests/v1/kv_connector/unit/test_lmcache_connector.py-> passeduv run --with ruff ruff format --check vllm/distributed/kv_transfer/kv_connector/v1/lmcache_connector.py tests/v1/kv_connector/unit/test_lmcache_connector.py->2 files already formatted.venv/bin/python -m py_compile vllm/distributed/kv_transfer/kv_connector/v1/lmcache_connector.py tests/v1/kv_connector/unit/test_lmcache_connector.py-> passed.venv/bin/python -m pytest -q tests/v1/kv_connector/unit/test_lmcache_connector.py->26 passed, 16 warningsFull-stack runtime smoke from the validated feature stack, using this LMCache HMA plumbing plus the companion LMCache patch and scheduler admission enabled (#42554 now owns the scheduler side), Qwen 3.6 27B AutoRound int4, 14 fill prompts then repeat first prompt:
0.845s, repeat latency1.192s8.216s, repeat latency8.548s-7.371s(9.73xfaster,89.7%lower), latency-7.356s(7.17xfaster,86.0%lower)Relevant runtime log lines from that full-stack smoke:
LMCache selected vLLM KV cache group 3 (FullAttentionSpec) with 16 layer(s), block_size=1568LMCache detected 3 hybrid state KV cache group(s): [(0, 16, 1568), (1, 16, 1568), (2, 16, 1568)]Loaded hybrid state ... at 10976 token(s)Retrieved 10976 out of 10976 required tokens ... cost 13.9687 msAI Assistance Disclosure
This PR was prepared with AI coding-agent assistance. I reviewed the changes, ran the validations listed above, and take responsibility for the contribution.