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[None][feat] KDA verify: optional per-token states in the V2 hybrid cache manager - #19817

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Description

KDA speculative verification on the V2 hybrid cache manager keeps per-slot replay caches (conv windows, q/k/g, v,
beta of the last round's drafts). The next round replays the accepted drafts from those caches to rebuild the
recurrent state. A verify kernel can instead keep a compact record per draft (the row innovations vn, beta * k and
the decay) and replay the accepted drafts (prev_num_accepted_tokens) from those records at the start of its next
launch, S = decay * S + vn (beta k), with no q/k/g, v or beta caches.

This PR adds the cache side of that option, off by default:

  • MambaHybridCacheManagerV2(kda_token_states=False). With the KDA replay path enabled and the option on, the
    manager allocates kda_state_tok: fp32 [mamba layers, slots, 3, num_spec, H, K], zero-initialised: per draft
    of the slot's last verify round, vn, then beta * k, then the decay (V = K on this path; the SSM pool keeps the
    state after the round's first, non-draft token). The q/k/g, v and beta replay caches are then not allocated; the
    extended conv caches stay. A verify kernel replays the first n records when the round accepted n > 0 drafts
    (prev_num_accepted_tokens); a slot reset for a new request has n = 0, so a previous owner's records are never
    read and no reset copy is needed.
  • kda_state_tok is allocated per SSM pool slot, outside the V2 pools. The per-slot state budget
    (_mamba_state_bytes_per_slot, used for the quota computed from max_tokens and for the live-quota check)
    counts these records, and shutdown() releases them with the other replay buffers.
  • The V2 manager sizes the SSM pool group by the typical step's ratio, so its slot count grows with the cache
    quota, and kda_state_tok with it. Without block reuse a slot past the min-slots floor (resident
    sequences plus reserved dummy slots) never holds a request. So with the records and block reuse off,
    the SSM pool keeps only its floor: ceil(floor / max_util_for_resume) slots, the floor's min-slots constraint
    as the runtime scales it. The records of those slots are taken out of the GPU cache quota before the pools
    are sized, and the typical step's request capacity is raised until its attention pages take the rest. The quota
    computed from max_tokens and the minimum quota count every one of those slots with its states and its records,
    so the attention pages still fit max_tokens at max_util_for_resume. Without the records, or with block reuse,
    the ratio sizes the pool as before.
  • The layer's view goes into the speculative state (SpeculativeState.kda_state_tok), and slot relocation moves it
    with the other replay buffers. has_kda_replay_caches follows the conv caches, so the replay path holds with
    either the replay caches or the records; relocation, the disaggregated-generation slot seeding and the per-layer
    view handle the absent caches.
  • keeps_kda_token_states reports whether the manager has it (the base class says False).
  • _create_kv_cache_manager passes kda_token_states=True only when the KDA replay caches are on, the manager is
    the V2 one, and the model's backbone sets kda_token_states. No model sets it in this PR, so nothing changes for
    any existing model.

Memory, when enabled: layers x slots x 3 x num_spec x H x K x 4 bytes beside the V2 pools, in place of the q/k/g,
v and beta replay caches. With block reuse off the slots are the floor (the resident sequences plus the reserved
dummy slots) over max_util_for_resume, and the bytes come out of the cache quota. The runtime rounds the pools'
quota up to whole allocation grains (2-32 MiB), so the pools can take back less than one grain of it, and when the
SSM slots are smaller than a grain the pool can keep a slot more, whose records are not reserved. For example
Kimi K3 at TP16 (69 KDA layers, 6 heads of 128 per rank, 7 drafts) needs 4.45 MB of records per slot, and the
replay caches it no longer allocates took 5.95 MB per slot (arithmetic).

The records need the SSM live floor (block reuse off, no pool_ratio, attention layers on the rank), where the
slot count is known before the pools are sized. _build_cache_config raises ValueError for kda_token_states off
the floor: a ratio-sized pool would keep many more slots, and their records would sit outside the quota. The floor's
slot count rounds max_util_for_resume through float32, as the runtime does, so the minimum quota and the quota
for max_tokens count the same slots the build reserves.

The first user is the Kimi K3 decode path (#19832's k3_kda_verify / k3_kda_attn, CuTe DSL verify kernels that
write these records and replay the accepted drafts from them); it lands separately.

Test Coverage

tests/unittest/_torch/executor/kv_cache/test_mamba_cache_manager.py:

  • test_kimi_explicit_v2_manager_kda_token_states_follow_the_model[True|False] (CPU): the factory asks for the
    states only when the backbone does.
  • test_kimi_explicit_v2_manager_enables_kda_replay (CPU): no kda_token_states by default.
  • test_v2_kda_token_states_replace_the_replay_caches[2|None] (GPU): the records' shape [slots, 3, num_spec, H, K], dtype, the per-layer view and zero init; no q/k/g, v or beta caches, the conv caches kept and
    has_kda_replay_caches true; nothing allocated without the replay path.
  • test_v2_kda_replay_allocates_logical_slot_caches (GPU): the default manager has the replay caches, no records,
    and has_kda_replay_caches.
  • test_v2_kda_token_states_relocate_with_their_slot (GPU): without the replay caches, slot moves copy a slot's
    conv caches, records and draft count bit for bit, and shutdown() releases them.
  • test_v2_kda_token_states_seed_disaggregated_generation_slots (CPU): seeding a transferred request's slot without
    the replay caches sets its conv caches and clears its draft count, and leaves its records alone.
  • test_kda_replay_path_stays_on_with_the_drafts_records (CPU): has_kda_replay_caches holds with the replay
    caches and with the records, and not without the replay path.
  • test_v2_kda_token_states_count_in_the_per_slot_budget (GPU): with the option on, a slot's budget grows by
    exactly the records: three fp32 [H, K] per draft and layer.
  • test_v2_kda_token_states_keep_ssm_pool_at_live_floor[True-False-True|False-False-False|False-True-False] (GPU):
    the V2 storage for a 128 MiB quota with 2 MiB state slots. With the records and no block reuse the SSM pool keeps
    its floor (plus one for max_util_for_resume), and the pools plus the records of every SSM slot fill the quota to
    within one 2 MiB grain: the runtime rounds the reduced quota up to whole grains. Without the records, or with
    block reuse, the pool keeps its ratio share (more than 10x the floor).
  • test_v2_kda_token_states_reserve_quota_before_sizing (no GPU work): at the floor the GPU tier quota handed to
    the runtime is reduced by the records of ceil(3 / max_util_for_resume) = 4 slots, and the minimum quota and the
    quota for max_tokens exceed those of the same manager without the records by the records of all 4 and the 4th
    slot's states.
  • test_v2_kda_token_states_reserve_the_slots_the_runtime_keeps (no GPU work): at a floor of 19 slots and a ratio of
    0.95 the minimum quota and the build both count 21 slots (the runtime's float32 ratio), the minimum quota with the
    2 extra slots' states.
  • test_v2_kda_token_states_refuse_a_pool_off_the_live_floor[block_reuse|pool_ratio|no_attention]: the records
    off the live floor raise ValueError. The ratio-sizing case of ..._keep_ssm_pool_at_live_floor now runs
    without the states, since that combination is refused.

The Kimi stub model config in that file gains mapping=None and spec_config=None. Since #19273
get_kv_cache_manager_cls reads model_config.mapping, so every Kimi factory test failed on the stub; on main those
tests are waived under nvbugs/6818710. With the fields, all Kimi factory tests pass. Their waive entries are left to
that bug's owner.

Results on GB200: main ca37c9f725 with this PR on one GPU, and main alone on another GPU of the same node, at the
same time (same container image and build):

Tests This PR main
executor/kv_cache/test_mamba_cache_manager.py 167 passed, 24 failed 151 passed, 34 failed
the rest of executor/kv_cache/ 770 passed, 20 failed 770 passed, 20 failed
modules/kimi_kda/ 116 passed, 2 skipped 116 passed, 2 skipped
  • test_mamba_cache_manager.py:
    • The 24 fail on both, with the same error: the hybrid factory tests whose stubs have no mapping
      (test_hybrid_cache_manager_factory_*, test_qwen3_gdn_replay_uses_v2_preference). Main waives them under
      nvbugs/6818710; this PR does not touch their stubs.
    • The other 10 main failures are the Kimi factory tests (test_kimi_explicit_v2_manager_*, test_kimi_disagg_*,
      test_kimi_without_v2_preference_uses_mixed_manager). They pass with the stub fields above.
    • The 6 new tests pass.
  • The rest of executor/kv_cache/: the same 20 tests fail on main. 18 have stale stubs or mocks (11
    SimpleNamespace without _max_cuda_graph_batch_size, 5 Mock used in arithmetic or len, 2 KvCacheCreator
    without _cache_transceiver_config). The other 2 hit the 300 s timeout on these nodes
    (test_world_ranks_converge_on_hostless_fallback, test_multi_rank_syncs_to_fleet_min).

The follow-up commits on GB200 (same image and build):

  • The SSM pool at its live floor: test_v2_kda_token_states_keep_ssm_pool_at_live_floor[True-False-True] fails on
    the first commit (the SSM pool holds 49 slots for a floor of 3) and passes with the follow-up. The whole file has
    3 more passing tests (the new cases) and the same failing tests as the first commit, run in the same environment.
  • The token states taken out of the quota: with the new tests on the previous commit, the same case fails (128 MiB
    of pools plus 16 MiB of token states for a 128 MiB quota), and
    test_v2_kda_token_states_reserve_quota_before_sizing fails (the minimum quota counts 3 slots of token states, not
    4). Both pass with the fix. The whole file has 1 more passing test (the new one) and the same 24 failing tests as
    the previous commit, run at the same time on the same node.
  • The same fix served on the Kimi K3 stack (16 GB200 GPUs, DSpark with 7 drafts, batch 8, 10 SSM slots per rank): the
    token states' 1.77 GiB now sit inside the cache quota. The estimation quota from max_tokens is 2.57 GiB (2.38
    before), and the final quota is 15.35 GiB as before, of which the pools get 13.58 GiB. The 8 fixed prompts give
    the same outputs as the previous commit in the same session, and decode throughput is unchanged (665.0 vs 664.8
    tokens/s).
  • Capacity, with those commits' full-state sizing: the KV cache pools got the states' bytes less than when the
    states sat outside the quota, 13.58 instead of 15.35 GiB per rank on that K3 configuration. The records
    follow-ups below shrink the reservation to 0.04 GiB.

CI lists: no change needed. The file is collected through unittest/_torch/executor (for example l0_h100.yml and
l0_b300.yml); it carries no cpu_only mark, so l0_cpu does not collect it.

The two newest follow-up commits ([None][fix] KV cache manager V2: count the live-floor KDA token-state slots as the runtime does, [None][fix] KV cache manager V2: refuse per-token KDA states off the SSM live floor), on GB200:

  • the new tests on the previous commit: 4 fail ("DID NOT RAISE" for the three refused pools; the minimum quota one
    slot short at a floor of 19) and 1 passes. All 5 pass with the fixes.
  • test_mamba_cache_manager.py whole: 175 passed / 24 failed against 171 / 24 before. The failing set is the same,
    and the 4 new tests pass.
  • No Kimi K3 serving configuration changes: K3 runs at the floor (9 slots at 0.95 give 10 slots either way), with
    block reuse off.

The records follow-ups (dc903ae9d6 kda_state_tok sized for the drafts' records, c05a0c3a45 no replay caches
beside the records, de2f7e12ef every live-floor SSM slot in the KDA quotas), on GB200 (same image and build):

PR Checklist

Please review the following before submitting your PR:

  • PR description clearly explains what and why. If using CodeRabbit's summary, please make sure it makes sense.

  • PR Follows TRT-LLM CODING GUIDELINES to the best of your knowledge.

  • Test cases are provided for new code paths (see test instructions)

  • If PR introduces API changes, an appropriate PR label is added - either api-compatible or api-breaking. For api-breaking, include BREAKING in the PR title. (No LLM API change.)

  • Any new dependencies have been scanned for license and vulnerabilities (No new dependencies.)

  • CODEOWNERS updated if ownership changes (No ownership change.)

  • Documentation updated as needed (No user-facing change: the option is off by default and no model turns it on; the docstrings describe it.)

  • Update tava architecture diagram if there is a significant design change in PR. (No significant design change.)

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Dev Engineer Review

The current diff changes import formatting and line wrapping in _util.py and mamba_cache_manager.py. It does not change runtime behavior. The KDA token-state implementation is present in the files, but it is not part of this diff.

QA Engineer Review

No test changes.

Per-File QA Perspective

  • tensorrt_llm/_torch/pyexecutor/_util.py: Changes are formatting-only. They introduce no observable behavior change that requires new QA coverage.
  • tensorrt_llm/_torch/pyexecutor/kv_cache/mamba_cache_manager.py: Changes are formatting-only. They introduce no observable behavior change that requires new QA coverage.

…ache manager

MambaHybridCacheManagerV2 takes kda_token_states (default off). With the
KDA replay caches it then also keeps the fp32 state after every draft of
the last verify round per slot (kda_state_tok, [layers, slots, num_spec,
H, V, K]), passes the layer's view in the speculative state and moves it
with the slot. A verify kernel can start the next round from the state
after the accepted drafts instead of replaying them. The cache factory
enables it when the model's backbone sets kda_token_states.

Signed-off-by: Vasanth Sabavat <vsabavat@nvidia.com>
@svc-trtllm-gh-bot svc-trtllm-gh-bot added the Community want to contribute PRs initiated from Community label Oct 2, 2026
…with per-token KDA states

With per-token KDA states, kda_state_tok holds num_spec recurrent states
per SSM state slot, outside the cache quota, addressed by the request's
SSM slot (_allocate_pool_replay_buffers). V2 sizes the SSM pool group by
the typical step's ratio, so its slot count, and kda_state_tok with it,
grows with the quota. Without block reuse a slot past the min-slots
floor (resident sequences plus reserved dummies) never holds a request,
so those slots only add memory. On the Kimi K3 stack (7 DSpark drafts,
TP16, max_seq_len 4096, free_gpu_memory_fraction 0.25) the pool got 183
slots: 32.4 GiB of kda_state_tok beside a 13.2 GiB quota. It ran out of
device memory above fraction 0.28 at max_seq_len 4096, and above 0.16
at 512.

With per-token KDA states and block reuse off, the typical step's
request capacity is now raised until its attention pages alone take the
quota. The ratio then gives the SSM pool group fewer slots than its
floor, so the min-slots constraint sets its size and attention gets the
rest. Without per-token states (replay caches only), or with block
reuse, the ratio sizes the pool as before.

test_v2_kda_token_states_keep_ssm_pool_at_live_floor builds the V2
storage for a 128 MiB quota with 2 MiB state slots: with per-token
states the SSM pool keeps its floor (plus one for max_util_for_resume)
and attention takes the rest of the quota; without them, or with block
reuse, the pool keeps its ratio share.

Signed-off-by: Vasanth Sabavat <vsabavat@nvidia.com>
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Walkthrough

The V2 hybrid Mamba cache manager can retain KDA per-token states when the model backbone enables them. The manager allocates, exposes, relocates, and accounts for these states in cache sizing. Tests cover option selection, allocation, cache operations, and memory sizing.

Changes

KDA per-token state retention

Layer / File(s) Summary
Enable and allocate token states
tensorrt_llm/_torch/pyexecutor/_util.py, tensorrt_llm/_torch/pyexecutor/kv_cache/mamba_cache_manager.py, tests/unittest/_torch/executor/kv_cache/test_mamba_cache_manager.py
The factory passes kda_token_states when the model backbone enables it. The V2 manager allocates FP32 state for each draft token when KDA replay is active and supplies token records or legacy replay caches to layer caches. Tests cover option selection, allocation, and replay-cache detection.
Account for token-state memory
tensorrt_llm/_torch/pyexecutor/kv_cache/mamba_cache_manager.py, tests/unittest/_torch/executor/kv_cache/test_mamba_cache_manager.py
Per-slot sizing and quotas include token-state storage. Eligible configurations keep the SSM pool at its live floor and adjust GPU quota and typical request capacity. Tests cover configuration constraints and memory calculations.
Preserve token states across cache operations
tensorrt_llm/_torch/pyexecutor/kv_cache/mamba_cache_manager.py, tests/unittest/_torch/executor/kv_cache/test_mamba_cache_manager.py
Slot relocation copies the active draft representation. Disaggregated seeding conditionally clears legacy replay caches, and shutdown clears the token-state buffer. Tests cover relocation, seeding, and release.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~25 minutes

Change: Feature

Sequence Diagram(s)

sequenceDiagram
  participant Backbone as Model backbone
  participant Util as _util.py
  participant Manager as MambaHybridCacheManagerV2
  participant LayerCache
  Backbone->>Util: Provides kda_token_states setting
  Util->>Manager: Passes option when enabled
  Manager->>LayerCache: Supplies token records or legacy replay caches
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Suggested reviewers: bowenfu

Merge Risk: 🔵 Low · up to de2f7

Some tightly budgeted records-mode configurations may exceed their GPU cache quota during initialization. The risk is bounded, but owners should account for it before enabling the option.

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Check name Status Explanation Resolution
Docstring Coverage ⚠️ Warning Docstring coverage is 58.49% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 53 functions across 3 files. Write docstrings for the functions missing them to satisfy the coverage threshold.
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Check name Status Explanation
Linked Issues check ✅ Passed Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check ✅ Passed Check skipped because no linked issues were found for this pull request.
Title check ✅ Passed The title follows the required [None][feat] format and clearly identifies the main change: optional KDA per-token state storage in the V2 hybrid cache manager.
Description check ✅ Passed The description is complete and directly related to the changes. It explains the purpose, implementation, memory and quota behavior, constraints, test coverage, CI results, and checklist status.
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Inline comments:
Review comments at
@tensorrt_llm/_torch/pyexecutor/kv_cache/mamba_cache_manager.py:
- Around line 3532-3537: Update _build_cache_config so the GPU quota reserved
for pools excludes the full kda_state_tok tensor size in the KDA token-state
live-floor path, or allocate that tensor from quota-managed storage. Extend
test_v2_kda_token_states_keep_ssm_pool_at_live_floor to assert that pool and
token-state bytes combined stay within quota.

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… the GPU quota at the SSM live floor

With per-token KDA states and block reuse off, the SSM pool is held at
its live floor and the typical step's attention pages fill the GPU
quota. kda_state_tok, num_spec fp32 states per SSM slot, is allocated
beside the pools afterwards. So the pools took the whole quota and the
states came on top of it: initialization could run out of device
memory although _minimum_live_gpu_quota() passed.

At the floor the SSM pool keeps ceil(floor / max_util_for_resume)
slots: the floor's min-slots constraint, as the runtime scales it.
_build_cache_config now takes the token states of that many slots out
of the GPU tier quota before the pools are sized, and logs the split.
The runtime rounds each pool up to whole allocation grains, which can
add SSM slots when a slot is smaller than a grain; their states are not
reserved.

The quota for max_tokens and the minimum quota count the token states
of all those slots (_state_quota), not only the floor's. Otherwise the
attention pages could get less than max_tokens needs: on Kimi K3
(DSpark with 7 drafts, TP16, max_batch_size 8: a floor of 9 slots, 10
kept) the estimation quota for max_tokens 16896 would leave the KV pool
about 13.5K tokens. With it the quota is 2.56 GiB and the pool about
20.6K tokens (arithmetic from the logged 2.38 GiB quota at 27648 bytes
per token).

test_v2_kda_token_states_keep_ssm_pool_at_live_floor now also checks
that the pools and the token states of every SSM slot fit in the
quota, with attention taking the rest of it to within one grain.
test_v2_kda_token_states_reserve_quota_before_sizing checks the
reserved bytes, and that the minimum quota and the quota for max_tokens
exceed those of the same manager without token states by the states of
every kept slot.

Signed-off-by: Vasanth Sabavat <vsabavat@nvidia.com>
@juney-nvidia

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/bot run

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PR_Github #76169 [ run ] triggered by Bot. Commit: e30477f Link to invocation

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PR_Github #76169 [ run ] completed with state SUCCESS. Commit: e30477f
/LLM/main/L0_MergeRequest_PR pipeline #62796 completed with status: 'FAILURE'

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The L0 failure on e30477f (build 62796) looks unrelated to this change:

  • L40S-PyTorch-2: llmapi/test_llm_api_pytorch_t5.py::test_t5_pytorch_generate_encoder_decoder_end_to_end[bf16-kv-v1-cuda-graph-on-beam2-flan-t5-small] timed out in llm.generate (T5 encoder-decoder on KV cache manager V1). This PR changes the Mamba hybrid cache managers (almost all of it in MambaHybridCacheManagerV2) and, in _create_kv_cache_manager, a branch taken only for Kimi-linear / GLM5-next models with a speculative config; that test reaches none of it. The same test passed in the 28 other recent PR builds and the post-merge run we checked.
  • It was the only failing test; the multi-GPU stages were blocked after it.
    @juney-nvidia could you re-run CI when you have a moment? Thanks.

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/bot run

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PR_Github #76181 [ run ] triggered by Bot. Commit: e30477f Link to invocation

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PR_Github #76181 [ run ] completed with state FAILURE. Commit: e30477f

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… slots as the runtime does

The runtime holds max_util_for_resume as a C++ float, and
_build_cache_config passed that value to _live_floor_token_state_slots,
while _state_quota (behind _minimum_live_gpu_quota and
_get_quota_from_max_tokens) passed the Python double. When the floor
divided by the ratio is a whole number, the two ceilings differ by one
slot: at 0.95, a floor of 19 slots keeps 21 slots (19 / float32(0.95) is
just above 20), while the double gave 20. The minimum and the quota for
max_tokens then counted one slot's token states fewer than the build
reserves.

_live_floor_token_state_slots now rounds the ratio through float32, as
kv_cache_manager_v2.py does for its own floor. The new test checks that
the minimum quota and the build reserve the same 21 slots at a floor of
19 and a ratio of 0.95.

Signed-off-by: Vasanth Sabavat <vsabavat@nvidia.com>
…SSM live floor

kda_state_tok is allocated for every slot the SSM pool keeps, beside
the V2 pools. Its bytes come out of the GPU quota only at the live
floor (block reuse off, no pool_ratio, attention layers on the rank),
where the slot count is known before the pools are sized. With block
reuse, a pool_ratio, or no attention layers, the ratio-sized pool kept
many more slots and kda_state_tok took their states outside the quota.
The K3 targets only refused block reuse at their first forward, after
the manager had allocated.

_build_cache_config now raises ValueError for per-token states off the
live floor. test_v2_kda_token_states_refuse_a_pool_off_the_live_floor
covers the three cases. The ratio-sizing case of
test_v2_kda_token_states_keep_ssm_pool_at_live_floor now runs without
the states, since that combination is refused.

Signed-off-by: Vasanth Sabavat <vsabavat@nvidia.com>
@vsabavat

vsabavat commented Oct 4, 2026

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54b87a2 adds two small fixes to the KV cache manager V2 quota for the per-token KDA states, with unit tests. @juney-nvidia could you run CI on it when you have a moment? Thanks.

@vsabavat

vsabavat commented Oct 6, 2026

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@juney-nvidia could you please /bot run on the current head (54b87a2)? The last run failed on an older head. This one unblocks #19832. Thanks!

@karljang karljang removed the Community want to contribute PRs initiated from Community label Oct 6, 2026
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Correct me if I'm misunderstanding something, but doesn't caching every intermediate draft token state defeat the purpose of SSM replay? The point is to reduce memory traffic by trading compute. This PR seems to be an improvement on the legacy replay-off path; do you have numbers comparing this to replay on?

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@vsabavat

vsabavat commented Oct 7, 2026

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Thanks, fair question. The PR text invites it, because it describes the buffer as more than it is used for. In short: the buffer's one user, the K3 verify kernels, still replays drafts. They do not cache per-draft states. The buffer is sized as if they did, though, and that part should change.

What the buffer holds in practice.

  • This PR documents and sizes kda_state_tok as the full state after every draft: fp32 [layers, slots, num_spec, H, V, K] (mamba_cache_manager.py:3538-3543; per-slot budget at :3840-3846).
  • Its only user is the Kimi K3 verify kernels in [None][feat] modeling_v2 catalog: Kimi K3 KDA and MLA decode kernels as stateful entries (sm_100) #19832 (k3_kda_verify, k3_kda_attn), and they never write full states. Per draft they write a compact record: the row innovation vn [H][V], then beta·k and the decay [H][K]. That is 9 KiB per draft at TP16 (k3_kda_verify_kernel.py:356-363, k3_kda_attn_kernel.py:121-129).
  • In its prologue, the next verify replays the accepted drafts from those records: S = fma(decay, S, vn * (beta k)) per draft. It is still replay, with the same compute-for-traffic trade as replay-on. It just uses a smaller record than main's replay caches (q / k / g, v, beta: 12 KiB per draft), inside the verify launch.
  • Bytes per request per KDA layer, at TP16 with 7 drafts and 3 accepted:
    • both paths read and write the 384 KiB fp32 state and the conv caches;
    • replay-on adds 120 KiB of replay-cache traffic, and the records path 90 KiB;
    • full per-draft states would add 2.6 MiB.

Numbers vs replay-on. One GB200, TP16 per-rank shapes (6 heads x 128), 8 verify tokens per request, CUDA graphs with PDL. Each value is the µs a KDA layer adds after a PDL predecessor, over 12 layer copies, so the weights are HBM-cold. Both arms start from the same projection rows and end at the gated core:

  • replay-on is main's forward_verify_fused: f_b, kda_mtp_decode on the replay caches, and the gated norm;
  • records is k3_kda_verify, which folds f_b and the gated norm in.
requests accepted drafts replay-on (µs / layer) records (µs / layer) per step, x 69 KDA layers
1 3 38.8 4.7 2.68 vs 0.32 ms
2 3 40.6 4.8 2.80 vs 0.33 ms
4 3 39.4 6.6 2.72 vs 0.46 ms
8 3 40.2 13.1 2.78 vs 0.90 ms
1 / 2 / 4 / 8 5 41.3 / 42.9 / 41.8 / 42.8 4.7 / 4.7 / 6.6 / 13.9 2.85-2.96 vs 0.32-0.96 ms
  • Most of the gap is the kernel, not the record format. k3_kda_verify is one latency-tuned launch, while kda_mtp_decode alone takes 19.7-23.3 µs.
  • The replay itself is cheap on both paths. Two more accepted drafts (3 to 5) add 2.4-3.0 µs to kda_mtp_decode and 0-0.8 µs to k3_kda_verify.
  • From the layer input, with each path's own projection, the totals are 59-69 µs (replay-on) vs 9.5-28.5 µs (records).
  • We have no end-to-end A/B. On the K3 path the per-token states cannot be turned off by configuration. Doing it in code would also change the MoE all-reduce on verify steps, so the A/B would not isolate this.

What should change here: the footprint.

The Kimi K3 verify kernels keep, per draft of the last verify round, the
row innovations vn [H, V], beta * k and the decay [H, K] in
kda_state_tok, and replay the accepted drafts from them. They never
write a draft's full state. The buffer was sized and documented as the
full state after every draft, [layers, slots, num_spec, H, V, K] fp32,
so ~98 % of it was never used; at the SSM live floor those bytes came
out of the KV cache quota.

kda_state_tok is now [layers, slots, 3, num_spec, H, K] fp32, in the
kernels' record order (vn, then beta * k, then the decay). The per-slot
budget and the live-floor quota count those bytes. V = K holds wherever
the replay caches exist, since their [Q | K | V] sections are equal. For
Kimi K3 at TP16 with 7 drafts, a slot's records take 4.45 MB over the
69 KDA layers instead of 190 MB.

The token-state tests now expect the records' shape and bytes. The
runtime rounds the pools' quota up to whole 2 MiB grains, and the
live-floor test's records are now less than one grain, so that test
allows the pools and the records up to one grain over the quota.

Signed-off-by: Vasanth Sabavat <vsabavat@nvidia.com>
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Thanks, that makes sense. I jumped to that conclusion by looking at the buffer size, but looks like we need to shrink that buffer before landing this one anyways.

Also, with this new mechanism on, k3_kda_verify doesn't read kda_qkg_cache / kda_v_cache / kda_beta_cache, do we still need them?

…place

With kda_token_states, the verify kernels replay the accepted drafts
from the drafts' records (kda_state_tok). Nothing then reads the
per-draft replay caches kda_qkg_cache, kda_v_cache and kda_beta_cache:
their only reader is the built-in fused verify (kda_mtp_decode), which
a model that asks for the records replaces. They are no longer
allocated in that mode. The extended conv caches stay, since the
records' verify reads them too.

has_kda_replay_caches now follows the conv caches, so the replay path
stays on with either the replay caches or the records. Slot
relocation, the disaggregated-generation slot seeding and the
per-layer view handle the absent caches. Without kda_token_states
nothing changes.

For Kimi K3 at TP16 with 7 drafts this frees 86,240 B per slot and
KDA layer, 59.5 MB per rank at 10 SSM slots.

The tests check that the caches are not allocated with the records,
that the view, relocation and seeding work without them, and that the
replay path holds in both modes.

Signed-off-by: Vasanth Sabavat <vsabavat@nvidia.com>
…he KDA quotas

At the live floor the runtime keeps ceil(floor / max_util_for_resume)
SSM slots, and kda_state_tok has an entry for each. The max_tokens and
minimum quotas counted the states of the floor's slots only and the
drafts' records of all of them, so the slots past the floor were left
without their states. The full-state token buffers' share of the
1 / max_util_for_resume headroom used to cover that; the records do
not. For Kimi K3 at batch 8 (9 slots, 10 kept), the max_tokens 16,896
estimation pool could resume about 16,469 attention tokens.

The quotas now count every slot the floor keeps with its states and its
records. For that K3 configuration the estimation pool resumes about
17,485 tokens (arithmetic on the logged sizes). The pools that serving
sizes from the memory fraction, and models without the records, do not
change.

The quota tests now expect the extra slots' states.

Signed-off-by: Vasanth Sabavat <vsabavat@nvidia.com>
vsabavat added a commit to vsabavat/TensorRT-LLM that referenced this pull request Oct 7, 2026
With the Kimi K3 verify kernels' draft records (kda_state_tok, NVIDIA#19817),
the per-draft replay caches kda_qkg_cache, kda_v_cache and
kda_beta_cache are not allocated. The suspend-time commit indexed them
per layer and the slot relocation asserted them, so both would fail on
such a manager. The commit now passes None for absent caches (the
records' replay never reads them), and the relocation moves the buffers
that exist, the drafts' records included. With the replay caches
nothing changes.

The new test builds a manager with the records and without the caches.
It compares the suspend-time commit bit for bit with the records' replay
and the conv store run on their own, and checks that relocation moves
a slot's conv caches, records and draft count.

Signed-off-by: Vasanth Sabavat <vsabavat@nvidia.com>
@vsabavat

vsabavat commented Oct 7, 2026

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Follow-up to my earlier comment: kda_state_tok is now sized for the drafts' records, with one new commit on each of the three PRs.

One difference from my earlier comment, which said [.., num_spec, 3, H, 128]: the kernels already write their records component-major (vn for every draft, then beta·k, then the decay). The buffer keeps that order, so only the per-slot stride changed.

Footprint (Kimi K3, TP16, 7 drafts, 69 KDA layers): 4.45 MB per slot instead of 190 MB, so 42.5 MiB instead of 1.77 GiB per rank at batch 8 (10 SSM slots). In the K3 serving config below (free_gpu_memory_fraction 0.25), each rank's KV pools grow from 13.01 to 15.13 GiB, from about 495k to 578k tokens (+17 %). Of the 2.13 GiB, 1.73 GiB is the smaller buffer. The other 0.40 GiB comes from the memory profiler, which no longer counts the old buffer in its peak.

Checks

  • Kernels, bit for bit against the current heads: k3_kda_verify with 1 / 3 / 5 / 7 drafts at 1-8 requests (and with the external gate at 1 / 4 / 8 requests), and k3_kda_attn. Each case runs 4 verify rounds, so every round replays the previous round's records. Outputs, SSM states, conv caches and records are identical in all 36 cases.
  • Unit tests (cache manager, kernels, modeling_v2, suspend): the same results as the current heads, apart from the updated records tests, which fail on the current heads and pass with the follow-ups.
  • Kimi K3 end to end on 16 GB200, current heads vs follow-ups, interleaved:
    • fixed prompts: 8 / 8 identical outputs;
    • GSM8K: 96.21 / 96.13 (flexible / strict) on both, with all 1319 responses identical;
    • TPOT at batch 1 / 2 / 4 / 8: 1.011 / 1.698 / 1.915 / 2.550 ms before and 1.011 / 1.704 / 1.930 / 2.555 ms after (medians of 10 runs each). The differences are within run-to-run noise.

@vsabavat

vsabavat commented Oct 7, 2026

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Good catch: with the records on, nothing reads kda_qkg_cache / kda_v_cache / kda_beta_cache. Their only reader is the built-in fused verify (kda_mtp_decode), which the K3 verify replaces whenever kda_state_tok is set, and the suspend-time commit replays the records instead.

c05a0c3a45 stops allocating them when kda_token_states is on. The extended conv caches stay, because the K3 verify reads those too. has_kda_replay_caches now follows the conv caches, so the replay path stays on in both modes. Slot relocation, the disaggregated-generation slot seeding and the per-layer view handle the missing caches, and without kda_token_states nothing changes. For K3 at TP16 with 7 drafts this saves another 86 KB per slot and KDA layer: 59.5 MB per rank at batch 8. #19846's suspend-time commit and slot relocation get the matching change in 003f8d088d, since they pass the caches through.

Tests, each failing on the previous head and passing with this commit: with the records the caches are not allocated, and has_kda_replay_caches holds in both modes; relocation moves a slot's conv caches, records and draft count without them; seeding a transferred slot works without them. K3 end to end on 16 GB200, interleaved with the previous head: fixed prompts 8 / 8 identical, GSM8K 1319 / 1319 responses identical, and TPOT at batch 1 / 2 / 4 / 8 within run-to-run noise (-0.1 / +0.0 / +0.2 / -0.5 %).

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vsabavat commented Oct 7, 2026

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/bot run

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PR_Github #76600 [ run ] triggered by Bot. Commit: de2f7e1 Link to invocation

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PR_Github #76600 [ run ] completed with state SUCCESS. Commit: de2f7e1
/LLM/main/L0_MergeRequest_PR pipeline #63162 completed with status: 'FAILURE'

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@nvpohanh
nvpohanh requested a review from VALLIS-NERIA October 8, 2026 04:02
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nvpohanh commented Oct 8, 2026

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[by Claude Code] @VALLIS-NERIA Could you review this PR? Thanks!

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vsabavat commented Oct 8, 2026

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Superseded by the consolidated draft PR: #19989. Source commits and follow-ups are retained; prior reviews remain historical evidence, not approval of the replacement heads.

@vsabavat vsabavat closed this Oct 8, 2026
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