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… groups build_offloading_config built an OffloadingGroupConfig for every KV cache group and asserted tokens_per_block % tokens_per_hash == 0 across all of them, while resolve_kv_cache_block_sizes derives tokens_per_hash from prefix-cacheable groups only. Any hybrid model with a non-prefix-cacheable scratch group (CircularBufferSpec) whose block size does not divide the hash granularity therefore crashed at boot when the OffloadingConnector was enabled. Scope the offload group list to prefix-cacheable groups, mirroring the scoping applied to the fine-grained-hit gate in e126687. Original group indices are preserved via a new OffloadingGroupConfig.group_idx field: offload keys embed them, and GPULoadStoreSpec.group_sizes/block_indices stay sized by the full KV cache group count so the worker layout is unchanged. Non-cacheable groups get no offload keys, no lookups, and no store/load slots; the divisibility assert still guards prefix-cacheable groups. supports_partial_tail conservatively requires every group to be cacheable, so models without scratch groups behave exactly as before. Co-authored-by: Claude Fable 5 <noreply@anthropic.com> Signed-off-by: noodco <info@noodco.com.au>
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Second consumer, different model family: GLM-5.3-Flash (#53906) carries a We have run the same behaviour in production since 2026-08-29 (2x H200 NVL, TP2, fp8 KV, Happy to run this branch on that stack if a second platform helps. Same class next door: AI assistance was used for this work. |
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This pull request has merge conflicts that must be resolved before it can be |
Qwen moves to PP5 with --kv-cache-memory pinned at 29 GiB per rank plus a 150 GiB CPU offload tier (native connector, ported from vllm-project#54743/vllm-project#55033): KV pool 7,244,396 tokens, 4 independent 200K prefixes resident at >=95% replay hits with graceful degradation on the 5th, single-200K replay 99.97% cached, mean TTFT 6.99 s to 3.72 s in a 3x200K mix, decode unchanged. fp8 QSA KV verdict recorded: 1.82x pool but ~9x slower cold prefill, production stays bfloat16.
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@orozery Ill have this |
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A few inline suggestions after testing on 1×H200.
| # Index of this group in KVCacheConfig.kv_cache_groups. Offload keys embed | ||
| # this index, and GPULoadStoreSpec.group_sizes stays indexed by it, so it | ||
| # is preserved even when non-prefix-cacheable groups are filtered out. | ||
| group_idx: int |
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Could we derive the original indices from KVCacheConfig at the scheduler boundary and keep them in the existing GroupOffloadConfig? Only the scheduler consumes this new field. I tried that approach on 1×H200: all 102 focused and 324 connector tests pass.
| assert offloading_config.cache.tokens_per_hash == 16 | ||
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| def test_scratch_group_gets_no_offload_keys(): |
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Could we fold these assertions into test_scratch_group_gets_no_load_slots? It already creates the scheduler, generates keys and checks their group IDs. We can remove this test and the unused RequestOffloadState import, while keeping the config-translation and misalignment tests.
| config = _make_vllm_config() | ||
| config.speculative_config = None | ||
| kv_cache_config = _make_scratch_hybrid_kv_cache_config() | ||
| spec = MockOffloadingSpec(build_offloading_config(config, kv_cache_config)) | ||
| scheduler = OffloadingConnectorScheduler(spec, config, kv_cache_config) | ||
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| request = MagicMock() | ||
| request.request_id = "req" | ||
| request.kv_transfer_params = None | ||
| request.block_hashes = [b"hash-0", b"hash-1"] | ||
| scheduler.on_new_request(request) | ||
| req_status = scheduler._req_status["req"] | ||
| req_status.update_offload_keys() | ||
| req_status.num_locally_computed_tokens = 0 |
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The current partial-tail assertion passes even without the new guard because the block and hash sizes are both 16. This combines the key assertions with the load test and uses 4-token hashes to exercise the guard. Tested: 46 config tests pass; removing the guard now fails this test.
| config = _make_vllm_config() | |
| config.speculative_config = None | |
| kv_cache_config = _make_scratch_hybrid_kv_cache_config() | |
| spec = MockOffloadingSpec(build_offloading_config(config, kv_cache_config)) | |
| scheduler = OffloadingConnectorScheduler(spec, config, kv_cache_config) | |
| request = MagicMock() | |
| request.request_id = "req" | |
| request.kv_transfer_params = None | |
| request.block_hashes = [b"hash-0", b"hash-1"] | |
| scheduler.on_new_request(request) | |
| req_status = scheduler._req_status["req"] | |
| req_status.update_offload_keys() | |
| req_status.num_locally_computed_tokens = 0 | |
| config = _make_vllm_config() | |
| config.speculative_config = None | |
| config.cache_config.prefix_match_unit = 4 | |
| kv_cache_config = _make_scratch_hybrid_kv_cache_config() | |
| spec = MockOffloadingSpec(build_offloading_config(config, kv_cache_config)) | |
| scheduler = OffloadingConnectorScheduler(spec, config, kv_cache_config) | |
| request = MagicMock() | |
| request.request_id = "req" | |
| request.kv_transfer_params = None | |
| request.block_hashes = [f"hash-{i}".encode() for i in range(8)] | |
| scheduler.on_new_request(request) | |
| req_status = scheduler._req_status["req"] | |
| req_status.update_offload_keys() | |
| assert len(req_status.group_states) == 3 | |
| assert not req_status.group_states[1].offload_keys | |
| assert scheduler._lookup_groups == (0, 2) | |
| assert not scheduler.config.supports_partial_tail | |
| req_status.num_locally_computed_tokens = 0 |
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| group_sizes: list[int] = [] | ||
| block_indices: list[int] = [] | ||
| group_sizes: list[int] = [0] * self.config.num_kv_cache_groups |
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Could we extend the existing normal-store and aligned-boundary tests with a scratch group in the middle? The new regressions only exercise loads. I checked both store paths with that layout and they pass; keeping that coverage would protect the group-index changes here.
Adapt the prefix-cacheable grouping invariant from vllm-project/vllm#54743 to the 1Cat offload layout. Preserve original worker group IDs and exact Mamba boundary stores. Co-authored-by: Codex <noreply@openai.com> Signed-off-by: Leonccaa <166551845+Leonccaa@users.noreply.github.com>
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@nood-co1, |
3 participants
[KV Offload] Scope offload group configs to prefix-cacheable KV cache groups
Purpose
build_offloading_config(vllm/distributed/kv_transfer/kv_connector/v1/offloading/config.py) builds anOffloadingGroupConfigfor everykv_cache_groupand then asserts, for all of them:But
tokens_per_hashcomes fromresolve_kv_cache_block_sizes(vllm/v1/core/kv_cache_utils.py), which derives the hash granularity from prefix-cacheable groups only (hashing_sizes = [... if group.kv_cache_spec.prefix_cacheable]). The two sides disagree about which groups are in scope, so any hybrid model with a non-prefix-cacheable scratch group (CircularBufferSpec.prefix_cacheable == False) whose block size does not divide the cacheable groups' hash granularity crashes at boot the moment the OffloadingConnector is enabled:Enabling prefix caching does not help — the message's advice cannot be followed, because the scratch group is excluded from hash-size resolution by design and its ring capacity is set by compression/lookahead geometry, not by the cache block size.
Where this bites: sparse-MLA hybrids that keep a
CircularBufferSpecring of pre-compression keys. We hit it deploying GLM-5.3-Flash (support proposed in #53906) on DGX Spark: per rank the layout is MLA + 4 GDN mamba groups at block size 3584 and an SWA drafter group at 64 (all prefix-cacheable, gcd →tokens_per_hash = 64), plus a kpool-tail scratch group at block size 4 →4 % 64 != 0→ boot crash with any--kv-transfer-configoffloading setup. Any future DeepSeek-V4-style model with a scratch spec of block size not dividing the cacheable gcd hits the same wall.Fix
Scope the offload group list to prefix-cacheable groups — the same scoping commit e126687 (#53896) applied to the fine-grained prefix-cache-hit gate in
HybridKVCacheCoordinator(our test-only PR #54663 pins that gate). Non-cacheable groups have no valid hash granularity, so they can never be keyed, looked up, stored, or loaded; building offload configs for them was never meaningful.Mechanically:
OffloadingGroupConfiggains agroup_idxfield holding the original index intoKVCacheConfig.kv_cache_groups.build_offloading_confignow emits configs only for prefix-cacheable groups, preserving those indices, and keeps the divisibility assert for them.offloading/scheduler.py) iterates the (now scoped)kv_group_configsand pairs them with per-requestgroup_statesviagroup_idxinstead of positionalzip.group_states,GPULoadStoreSpec.group_sizes, andblock_indicesstay sized by the full KV cache group count (newSchedulerOffloadConfig.num_kv_cache_groups), with zero entries for scratch groups — so the worker side (CanonicalKVCaches.group_data_refs,gpu_worker'slen(group_sizes) == len(layer_refs_per_group)invariant) is completely unchanged.supports_partial_tailadditionally requires every KV cache group to be prefix-cacheable, keeping the partial-tail CoW hand-off semantics exactly as narrow as before.FileMapperis untouched.OffloadingSpec.tokens_per_blockstays aligned withconfig.groupsand now covers prefix-cacheable groups only (documented at the attribute; original indices viagroup_idx). No existing backend or persistent fs-tier store can observe an index shift or a namespace change from this: any layout where the scoped list differs from the full list crashed on this very assert at boot, so no offloaded bytes or spec state for such layouts exist anywhere.block_sizeextra config fails loudly on the reworded "at least one prefix-cacheable KV cache group" assert.Not a duplicate:
gh pr list/gh issue listsweeps for "offloading prefix_cacheable", "build_offloading_config", "tokens_per_hash divisible", "CircularBufferSpec offload", "offloading connector hybrid assert", "offloading eligible groups" surface no PR or issue addressing this boot assert. #53889 / #50883 touch the same function for DCP block-size scaling (orthogonal); #51886 adds retention to the connector (orthogonal); #54663 is our test-only pin of the e126687 coordinator gate and changes no behavior.Test Plan
New tests in
tests/v1/kv_connector/unit/offloading_connector/test_config.py, following the file's existingMagicMock-config style:test_scratch_group_does_not_crash_config_translation— hybridKVCacheConfig(full-attention 16 +CircularBufferSpecblock 4 + mamba-align 16) previously tripped the assert; now translates, withgroup_idx == [0, 2]andtokens_per_hash == 16.test_scratch_group_gets_no_offload_keys—SchedulerOffloadConfig.from_specspans only groups {0, 2} whilenum_kv_cache_groups == 3;supports_partial_tailis off;OffloadingConnectorSchedulerboots and_lookup_groups == (0, 2);RequestOffloadState.update_offload_keysemits keys whose embedded group indices are exactly {0, 2} and the scratch group's state holds none.test_scratch_group_gets_no_load_slots—update_state_after_allocemits full-lengthGPULoadStoreSpec.group_sizes/block_indices([2, 0, 2]/[0, 0, 0], matching the worker's per-group layout) with the scratch entry zero, and no load key or destination block is drawn from the scratch group.test_prefix_cacheable_misaligned_group_still_asserts— a mamba group outside "align" mode backs the hash size off to the LCM, and the assert still fires for prefix-cacheable groups.Constructor updates for the new field in
tests/v1/kv_offload/test_factory.py,tests/v1/kv_offload/test_file_mapper.py, and eligible-aware boot checks in the connector test harness (utils.py).Environment: macOS arm64, Python 3.13, torch 2.13 CPU wheel, source tree on
PYTHONPATH(no build). The repo roottests/conftest.pysegfaults on macOS while importing multimodal assets, so runs use--noconftest(plus-p tests.v1.kv_connector.unit.offloading_connector.conftestwhere therequest_runnerfixture is needed).The failures in the two directory-wide runs are pre-existing on this platform, not caused by this PR: the same commands on unmodified
origin/main(4707679) produce the byte-identical sortedFAILED/ERRORsets (82 and 33+36 respectively; verified withdiff; the passed counts differ only by this PR's 4 new tests). They are macOS/CPU environment limitations —VllmConfigrejectsdisable_hybrid_kv_cache_manager=Falseon this platform, which everyRequestRunner-based test needs, plus CUDA-dependentkv_offload/cpuworker tests.Mutation check — reverting the
vllm/changes while keeping the tests reproduces the original crash:Lint:
ruff check/ruff format --checkclean on all changed files;uvx pre-commit run --files <changed files>(repo hook config incl. mypy-3.10, typos, SPDX) exits 0.Related
attention_groupstoprefix_cacheablegroups; this PR applies the same predicate to the offloading boundary.AI assistance disclosure
This PR was drafted with AI assistance (Claude). Submitted by nood-co1 on behalf of Blockbrain Labs (https://x.com/blockbrain_labs, GitHub org blockbrain-ai); drafted with AI assistance and reviewed by the submitter, who ran the tests listed above. The duplicate-work checks in the contribution policy were run as described above; the exact pytest commands, their full results, the pre-existing-failure baseline diff against
origin/main, and the mutation check are reported verbatim in the Test Plan.