[DCP][Mooncake] Harden hybrid prefix-cache external hits by YukioZzz · Pull Request #53730 · vllm-project/vllm

YukioZzz · 2026-08-25T13:35:22Z

Summary

Harden MooncakeStoreConnector for Kimi-K3 hybrid DCP prefix-cache reuse.

This PR is the Mooncake external-cache layer of the Kimi-K3 DCP split. It assumes the runtime DCP support from #51705 and the core hybrid cache geometry from #53598.

Problem

Kimi-K3 under DCP has multiple cache groups with different physical layouts: attention / MLA KV is DCP-sharded, replicated Mamba state is not DCP-sharded, local cache hits can be finer than externally transferable block regions, and external loads can fail partially and must not leave a request with mismatched group state.

Mooncake previously treated the external tier too much like a single-layout KV cache. Under hybrid DCP, that can either keep the external tier cold or load blocks that are valid for one group but invalid for another.

Implementation Details

Grouped external-cache metadata: Mooncake requests carry group-aware block metadata so sharded attention groups and replicated Mamba groups are handled independently.
External hit geometry: The connector uses the same group geometry as the core cache manager, preserving the distinction between scheduler hash blocks and physical transfer blocks.
Safe partial coverage: Split external loads invalidate every unattempted or failed block beyond the safe prefix boundary, so a partial external hit falls back to recompute instead of returning mixed-prefix KV.
Recovery semantics: Failed loads truncate the request to a boundary every group agrees on and evict downstream group blocks.
Bounded PUT waves: External PUT work is bounded so concurrent TP ranks fit inside the registered-memory owner. A batch is published only after the corresponding KV regions are actually stored.
Rank-local transfer compatibility: The connector supports rank-local binding and preferred segments, matching the expected single-node external-cache ownership model.
No draft requirement: The standalone validation target for this PR is no-draft DCP + core + Mooncake. Drafted Mooncake validation depends on additional PRs and is intentionally not claimed here.

Non-Goals

DSpark/DCP runtime attention changes are in [ROCm][MLA][DCP] Support causal multi-token verification #51705.
Core hybrid prefix-cache geometry is in [ROCm][DSpark][DCP] Serve prefix cache hits under DCP for Kimi-K3 #53598.
The full drafted Mooncake stack is integration-only until the dependent PRs land.

Split

Runtime DSpark/DCP support: [ROCm][MLA][DCP] Support causal multi-token verification #51705.
Core hybrid DCP prefix-cache geometry: [ROCm][DSpark][DCP] Serve prefix cache hits under DCP for Kimi-K3 #53598.
Mooncake external-cache hardening: this PR.

Validation

Validated the no-draft DCP + core + Mooncake stack with DCP=8, prefix caching enabled, and MooncakeStoreConnector enabled.

Smoke: passed with an end-to-end /v1/completions request.
GSM8K full: 1270/1319, 96.29%, errors=0.
Prefix cache cold/hot/reuse: cold path started at 0 hits; shared-prefix reuse reached prefix_cache_hits_total=96768 and prefix_cache_queries_total=189492.
Mooncake external-cache cold/hot/reuse: after forcing local-prefix eviction with unique long prompts, target reuse increased external_prefix_cache_hits_total from 0 to 3072 and recorded successful Mooncake load_get operations: 8 calls, 32 keys, 679477248 bytes, failed_keys=0.
Mooncake store write path: successful save_put traffic was observed with failed_keys=0 during the shared-prefix and eviction probes.

Derive each cache manager's DCP size from its spec so sharded full-attention groups and replicated Mamba groups use their real block geometry. Reuse that per-group geometry for local prefix lookup and CPU offload, while keeping external transfers physically aligned and allowing hash-granular local DCP hits. Co-authored-by: andyluo7 <andy.luo@amd.com> Signed-off-by: Yichao Zhu <Yichao.Zhu@amd.com>

Align hybrid cache retention with fine-grained local hash hits, retain the EAGLE-adjusted replay boundaries needed by replicated Mamba state, and split prefill at those materialization points. Cover Kimi-K3-scale prefix geometries. Assisted-by: OpenAI Codex Signed-off-by: andyluo7 <andy.luo@amd.com>

`_update_requests_with_invalid_blocks` unpacked a single group's block ids, so a hybrid KV cache layout could not recover from a failed external load at all. Locate failed blocks with each group's own block size, truncate the request at the earliest failed boundary every group can agree on, and evict each group's downstream blocks. Hand a full-attention group's boundary block to the connector under DCP, where KV below the prompt boundary is append-only and the request's own block is a durable source. Take the CoW source from the request's current block table so a stale partial-hit record cannot leave a shared block writable in place, and drop a dying request's queued hand-offs in the base manager now that more than Mamba enqueues them. Signed-off-by: Yichao Zhu <Yichao.Zhu@amd.com>

Scale attention cache blocks for DCP while keeping recurrent state replicated. Preserve the actual stored hash boundary through hybrid prefix-hit reconciliation so loads do not derive missing Mooncake keys. Align coordinator behavior for multiple attention groups and add regression coverage for DCP, Mamba, EAGLE, and partial-prefix loads. Assisted-by: OpenAI Codex Signed-off-by: wzhao18 <wzhao18.sz@gmail.com> (cherry picked from commit 47e85a3deb44f6ee0d0d34dda2f31dea28001fc6)

Signed-off-by: wzhao18 <wzhao18.sz@gmail.com> (cherry picked from commit 322a0a53d798b13a4b91345f230e30e5bfb1da2b)

Signed-off-by: wzhao18 <wzhao18.sz@gmail.com> (cherry picked from commit 379a87a80241e0d796bb7535f7cdb7c6f0f9b7ca)

Signed-off-by: wzhao18 <wzhao18.sz@gmail.com> (cherry picked from commit 574d2e4092d96bf2bac99e9dfa1ffecf39de334e)

Builds on the hybrid-DCP store support cherry-picked from vllm-project#53324, which already lifts the outright DCP rejection and derives each group's external block span from `resolve_dcp_kv_block_size`. This covers what a K3 run still needs on top of it. Reject the layouts DCP does not define per group instead of per process: only sharded full attention and replicated Mamba have DCP-aware external block geometry, so any other spec in a hybrid config is refused by name. Mirror core's partial-hit predicate for full-attention groups, not only Mamba. Under DCP a full-attention group's effective block spans several hash blocks, so `HybridKVCacheCoordinator` enables fine-grained hits for it; the connector must agree or the scheduler and the coordinator disagree about where a hit lands. Both read the same shared helper. Keep Eagle's boundary marker on the incomplete block alone: emitting it for earlier complete blocks aliases their real block-end keys and can poison later loads. Bound each rank's PUT wave so concurrent TP ranks fit in a standalone owner's registered memory while finished waves drain to disk, and publish KV events per batch so a failed wave never advertises blocks it did not store. Log the resolved cache geometry once at startup, since a scheduler/worker geometry disagreement is otherwise only visible as a permanently cold cache. Signed-off-by: Yichao Zhu <Yichao.Zhu@amd.com>

Preserve effective DCP geometry through uniform cache wrappers, defer partial-tail persistence until replicated Mamba has a durable CoW source, and invalidate every unattempted split-load block after an early failure. Add focused unit and mock-HMA regressions for the unsafe handoff, DCP8 lookup geometry, rotated split loads, exception recovery, and cross-group eviction. Assisted-by: OpenAI Codex Signed-off-by: andyluo7 <andy.luo@amd.com>

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github-actions · 2026-08-25T13:35:31Z

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YukioZzz · 2026-08-25T13:39:37Z

Validation plan update for the split Kimi-K3 DCP stack.

This PR is the MooncakeStoreConnector hardening layer for Kimi-K3 hybrid DCP prefix-cache reuse.

Scope of this PR:

Group-aware Mooncake external-cache behavior for hybrid DCP layouts.
External cache load/recompute recovery behavior.
Mooncake handling needed after the core cache geometry work in [ROCm][DSpark][DCP] Serve prefix cache hits under DCP for Kimi-K3 #53598.

Important split note:

This PR intentionally does not include the ROCm DSpark/DCP runtime changes from [ROCm][MLA][DCP] Support causal multi-token verification #51705.
It also does not include the full integration-only stack used for local end-to-end validation.
Runtime validation is being run in two layers:
- no-draft DCP + core + Mooncake for external-cache cold/hot/reuse;
- full integration only after the independent DCP/core path is established.

I will post runtime test results after the no-draft Mooncake validation completes; not recording test results on this PR yet.

mergify · 2026-08-27T16:14:17Z

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

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

andyluo7 and others added 10 commits August 25, 2026 14:14

simplify PartialHitBoundary to TailKeyBoundary for all groups

915a444

Signed-off-by: wzhao18 <wzhao18.sz@gmail.com> (cherry picked from commit 322a0a53d798b13a4b91345f230e30e5bfb1da2b)

Minor polish

b686689

Signed-off-by: wzhao18 <wzhao18.sz@gmail.com> (cherry picked from commit 379a87a80241e0d796bb7535f7cdb7c6f0f9b7ca)

Minor polish

10ad0f0

Signed-off-by: wzhao18 <wzhao18.sz@gmail.com> (cherry picked from commit 574d2e4092d96bf2bac99e9dfa1ffecf39de334e)

YukioZzz requested review from ApostaC, NickLucche, WoosukKwon, alexm-redhat, heheda12345, ivanium, njhill, orozery, robertgshaw2-redhat, xuechendi and ywang96 as code owners August 25, 2026 13:35

claude Bot reviewed Aug 25, 2026

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mergify Bot added kv-connector scheduler kv-cache-manager labels Aug 25, 2026

This was referenced Aug 25, 2026

[ROCm][MLA][DCP] Support causal multi-token verification #51705

Merged

[ROCm][DSpark][DCP] Serve prefix cache hits under DCP for Kimi-K3 #53598

Merged

[Bugfix][DCP] Handle hybrid cache geometry in offload recovery #53917

Closed

YukioZzz marked this pull request as draft August 26, 2026 18:55

mergify Bot added the needs-rebase label Aug 27, 2026

mergify Bot added the mooncake Mooncake KV-transfer / EC-transfer label Oct 1, 2026

nwpu-zxr mentioned this pull request Oct 19, 2026

[Mooncake][PD] Support DCP transfer for MLA/GQA models #53205

Draft

3 of 10 tasks

whx-sjtu mentioned this pull request Oct 27, 2026

[Bugfix][Mooncake] Let decodes reuse divergent local hybrid prefix hits #63971

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[DCP][Mooncake] Harden hybrid prefix-cache external hits - #53730

[DCP][Mooncake] Harden hybrid prefix-cache external hits#53730
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Summary

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