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WalkthroughDeepSeek V4 decoder layers can return captured previous auxiliary states. Model execution collects and reconstructs these states while limiting MTP buffer updates to execution without auxiliary states. Callers and speculative sampling preserve auxiliary outputs. Tests validate residual means and auxiliary capture. ChangesDeepSeek V4 auxiliary state flow
Estimated code review effort: 3 (Moderate) | ~20 minutes Merge Risk: ⚪ Minimal · up to This change reuses captured residual means for DeepSeek V4 auxiliary states while preserving the fallback behavior. No concrete merge-blocking correctness or operational risk is identified. Suggested reviewers: Sequence Diagram(s)sequenceDiagram
participant DeepseekV4Model
participant DeepseekV4DecoderLayer
participant SequenceParallelGather
participant ModelRunner
DeepseekV4Model->>DeepseekV4DecoderLayer: request previous auxiliary capture
DeepseekV4DecoderLayer-->>DeepseekV4Model: return previous_aux
DeepseekV4Model->>SequenceParallelGather: gather auxiliary tensors
SequenceParallelGather-->>DeepseekV4Model: return gathered states
ModelRunner->>DeepseekV4Model: preserve auxiliary states during sampling
🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
✨ Finishing Touches 💡 1🛠️ Fix failing CI checks 💡
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🟡 Changes recommended
The NVIDIA DeepSeek V4 aux-layer selection logic appears off-by-one (switching from idx + 1 to idx) and the _mtp_hidden_buffer skip condition ignores remote_aux, both of which can break intended behavior/perf.
Once you've addressed the issues Copilot identified, you can request another Copilot review.
Pull request overview
This PR optimizes DeepSeek-V4 DSpark/MTP execution by reusing the fused post-residual output to produce aux hidden states, reducing redundant kernel launches and HBM traffic during speculative decoding.
Changes:
- Extend
DeepseekV4DecoderLayer.forwardto optionally capture the previous layer’s aux hidden state (mean-pooled fused post residual) and plumb that throughDeepseekV4Model.forward. - Skip MTP target-hidden-state overrides and
_mtp_hidden_buffercopies when aux hidden states are used. - Add a kernel-level test assertion that the fused-post residual’s
mean(dim=1)matches the reference.
File summaries
| File | Description |
|---|---|
| vllm/v1/worker/gpu/model_runner.py | Avoids using MTP target-hidden-state override when aux hidden states are present. |
| vllm/models/deepseek_v4/nvidia/mtp.py | Updates unpacking for the decoder layer’s expanded return signature. |
| vllm/models/deepseek_v4/nvidia/model.py | Adds aux capture plumbing and skips _mtp_hidden_buffer copy when aux states are used. |
| vllm/models/deepseek_v4/nvidia/dspark.py | Updates unpacking for the decoder layer’s expanded return signature. |
| tests/kernels/test_mhc_kernels.py | Adds coverage to validate residual.mean(dim=1) for the fused-post residual path. |
Review details
- Files reviewed: 5/5 changed files
- Comments generated: 2
- Review effort level: Lite
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Actionable comments posted: 2
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Inline comments:
In `@tests/kernels/test_mhc_kernels.py`:
- Around line 299-304: Update the test around the existing residual comparison
to exercise the capture_previous_aux path directly: enable capture_previous_aux,
obtain the decoder’s captured auxiliary state, and compare it against
residual_ref.mean(dim=1), preserving the expected tensor shape, axis, and
auxiliary-layer ordering.
In `@vllm/models/deepseek_v4/nvidia/model.py`:
- Line 1496: Update the MTP-buffer copy guard in the surrounding model execution
flow to also exclude cases where remote auxiliary states are present, not only
when local aux_hidden_states is non-empty. Reuse the existing remote_aux state
before its merge so GPUModelRunner’s later auxiliary-state path does not consume
an unnecessary MTP buffer.
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tests/kernels/test_mhc_kernels.pyvllm/models/deepseek_v4/nvidia/dspark.pyvllm/models/deepseek_v4/nvidia/model.pyvllm/models/deepseek_v4/nvidia/mtp.pyvllm/v1/worker/gpu/model_runner.py
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Local revalidation on current main (this branch)PR: #55575 ( Environment
Caches/JIT stayed on local XFS. No changes on 1. CPU — aux capture contractsource env_isolated.sh
export CUDA_VISIBLE_DEVICES=""
python -m pytest --noconftest -v --tb=short \
tests/kernels/test_mhc_kernels.py::test_deepseek_v4_capture_previous_aux \
tests/kernels/test_mhc_kernels.py::test_deepseek_v4_mhc_broadcast_finalize_sums_hc_streams \
tests/kernels/test_mhc_kernels.py::test_deepseek_v4_mhc_broadcast_refit_refreshes_in_placeResult: 3 passed.
2. GPU — fused post/pre + residual mean (this PR’s kernel assert)source env_isolated.sh
python -m pytest --noconftest -v --tb=short \
tests/kernels/test_mhc_kernels.py::test_mhc_fused_post_preResult: 7 passed, 1 failed.
The new assert in this PR ( The failure is the pre-existing last assert Deterministic on rerun (same index / same 0.01514). This is TileLang fused-pre tightness at T=128 H=7168, outside the aux-hidden change. Not treating it as a #55575 blocker. 3. Serve smoke (DSpark, so aux-hidden is on the path)# isolated env, port 8004 only; adaptive verification off (incompatible with cudagraph NONE)
vllm serve /dockerdata/model/DeepSeek-v4-Flash-0731 \
--host 127.0.0.1 --port 8004 \
--tensor-parallel-size 4 --enable-expert-parallel \
--kv-cache-dtype fp8 --block-size 256 --max-model-len 4096 \
--gpu-memory-utilization 0.90 \
--tokenizer-mode deepseek_v4 --trust-remote-code \
--reasoning-parser deepseek_v4 \
--speculative-config '{"method":"dspark","num_speculative_tokens":7,"draft_sample_method":"probabilistic","attention_backend":"FLASH_ATTN","enable_adaptive_verification":false}' \
--compilation-config '{"cudagraph_mode":"NONE"}' \
--kernel-config '{"enable_jit_warmup":false}' \
--disable-custom-all-reduceStartup ~8 min (weight load + DeepGEMM warmup 1360 shapes). EngineCore One greedy request after curl -sS http://127.0.0.1:8004/v1/chat/completions \
-H 'Content-Type: application/json' \
-d '{"model":"/dockerdata/model/DeepSeek-v4-Flash-0731","messages":[{"role":"user","content":"Reply with the single word: ok"}],"max_tokens":16,"temperature":0}'Result: HTTP 200. Stopped with Perf table in the PR body is from the v0.28 fork (S1/C4/C8/Long S1). This tree is correctness + smoke only; I did not rerun that bench. AskPlease add the |
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I'm TeloySXH, this is my first contribution to vLLM, and I'd be glad to be a long-term contributor going forward. I'd appreciate a review from you both when you have time. What it does: Two standalone Results (4×H20, TP4+EP, DSpark K=7): system tok/s +11.3% (C4) and +16.0% (C8); single-stream cases are within run-to-run variance. Revalidated on current main and posted in the thread. I've addressed the earlier review feedback: the Also, since this is a fork PR and I don't have merged PRs in the repo yet, |
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This pull request has merge conflicts that must be resolved before it can be |
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Every layer's post now runs inside the next layer's fused pre, so the standalone mhc_post_tilelang the model ran per aux-capture layer was recomputing a residual that already existed. Take the mean over the hc streams from the fused call instead, behind a capture_previous_aux flag, and drop the duplicate post. The Engram seam captures before the injection, matching the standalone post it replaces: aux consumers read the stream before Engram touches it. The last layer on a rank has no successor to fold its post into, so it keeps the final standalone post and takes its mean from there. Ports the approach of vllm-project#55575 (DeepSeek-V4) to V4.1, which becomes possible here because this branch gives V4.1 the same fused seam. DSpark on DeepSeek-V4.1-Flash, TP4 GB300, k=3 probabilistic drafting with real verification, 8 fixed prompts at temperature 0: byte-identical output and identical acceptance against the same branch without this commit -- 106 drafts, 318 draft tokens, 204 accepted (0.6415, length 2.92), per position 92/64/48. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Signed-off-by: Yongye Zhu <yongye@inferact.ai> Signed-off-by: Yongye Zhu <zyy1102000@gmail.com>
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Rebased onto current main. #56633 already landed the same “reuse fused post residual for aux” idea on DeepSeek-V4.1; this PR is still the V4 path (deepseek_v4/nvidia/model.py) plus the model_runner.py skip of _mtp_hidden_buffer when aux states are present, which #56633 explicitly left to this change. The only conflict was appending tests at the end of test_mhc_kernels.py: both the new ROCm fused post/pre cases from main and test_deepseek_v4_capture_previous_aux are kept. |
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…idden states For DSpark, aux hidden states (the draft main_proj inputs) were reconstructed by running mhc_post_tilelang separately for every aux layer, and the full [T, hc, H] MTP buffer was copied even when the drafter consumes aux states instead. The next layer's fused post already produces the same post residual, so this change captures its mean once per aux layer and drops the standalone post for those layers; it also skips the MTP buffer copy when aux hidden states are present and keeps the model-runner MTP slice off in that case. Measured on the internal 4xH20 deployment (v0.28 line, DSpark K=7): medium-concurrency wall-clock throughput +9.1% (C4) / +16.0% (C8); single-request decode and long prefill unchanged within noise. Co-authored-by: Cursor Agent <agent@cursor.com> Signed-off-by: sxhcheng <525707191@qq.com>
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Rebased onto current main ( This is still the DeepSeek-V4 aux-hidden path ( Conflicts were only from Mega-Gate landing on the decoder/MTP signatures:
No change to the capture point, aux-layer ordering, or the model-runner MTP skip. |
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This pull request has merge conflicts that must be resolved before it can be |
Performance (measured on 4×H20, sm_90)
Same machine / same recipe (TP4+EP, DSpark K=7 probabilistic + adaptive
verification, KV fp8, think=off, temperature=0), before vs after:
The win comes from removing per-step HBM traffic that scales with T:
two standalone
mhc_post_tilelangruns with full[T,4,H]writes plus one[T,4H]bf16 copy (~256 MiB of traffic at T=4096). Concurrent steps havelarge T and tight HBM, so the wall-clock throughput gains the most (C8
system +16.0%); single-stream decode steps are only ~8 tokens wide, so
nothing is left to save and the small extra
meankernel noise shows up(S1/Long S1 within run-to-run variance, 3 runs per scenario, not an SLA).
TTFT is unchanged (these paths are not on the first-token critical path).
Resident memory is unchanged (the buffer allocation is kept; only the copy
is skipped).
Why
For DSpark, the aux hidden states (draft
main_projinputs) are themean-pooled post residuals
[T, hc, H] → [T, H]of layers 40/41. The oldcode ran a standalone
mhc_post_tilelangfor every aux layer even thoughthe next layer's fused post already produces the exact same post residual.
It also kept the full
[T, hc, H]MTP buffer copy alive although DSparkconsumes aux states (which are
torch.cat+main_proj), never thatbuffer.
What
DeepseekV4DecoderLayer.forwardgains an optionalcapture_previous_auxflag; when the current layer is an aux layer, the
mean(dim=1)of thefused post residual is captured instead of running a standalone
mhc_post_tilelangfor the previous layer.mhc_post_tilelangbecausehc_headstill needs the full[T, hc, H]residual (it also feeds thefinal aux entry).
_mtp_hidden_buffercopy and the runner's MTP-buffer read areskipped when aux hidden states are present (dummy run and real propose
path).
Tests
tests/kernels/test_mhc_kernels.py:.mean(dim=1)of the fused-postresidual now matches the reference (4 passed: T ∈ {1,4,8,128}).
failures=0, DSpark FULL CUDA-Graph captured (80 s, 11.34 GiB/rank),
bench errors 0/11 runs after / 0/11 before.
Duplicate check
GitHub PR search (
aux hidden,mhc post,DeepSeek-V4) returns noexisting PR addressing this change.
AI assistance was used in preparing this change (see Co-authored-by
trailer in the commit).