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DCP supports hybrid attention - #40996

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ywang96 merged 16 commits into
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Yancey0623:qwen35_hybrid_attn_dcp
Jul 10, 2026
Merged

DCP supports hybrid attention#40996
ywang96 merged 16 commits into
vllm-project:mainfrom
Yancey0623:qwen35_hybrid_attn_dcp

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@Yancey0623

@Yancey0623 Yancey0623 commented Apr 27, 2026

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Purpose

Add DCP support for hybrid-attention models. Hybrid-attention models such as Qwen/Qwen3.5-0.8B contain both DCP-capable full-attention layers and non-DCP layers. This PR enables DCP for supported
attention groups without globally blocking hybrid-attention DCP, while keeping
non-DCP groups on local cache/state handling.

Test Plan

Run focused hybrid-attention DCP validation with
tests/distributed/test_context_parallel.py using model Qwen/Qwen3.5-0.8B.

Tested two configurations:

Config TP DCP Model
TP4 4 1 Qwen/Qwen3.5-0.8B
TP4DCP2 4 2 Qwen/Qwen3.5-0.8B
TP4DCP1 4 1 Qwen/Qwen3.5-397B-A17B-FP8
TP4DCP2 4 2 Qwen/Qwen3.5-397B-A17B-FP8

Test Result

GSM8K smoke accuracy, 256 questions, 5-shot, temperature 0.0:

Config Accuracy Correct / Total
TP4DCP1 0.277344 71 / 256
TP4DCP2 0.273438 70 / 256

GSM8K smoke accuracy for Qwen/Qwen3.5-397B-A17B-FP8, 256 questions, 5-shot:

Config Accuracy Correct / Total
TP4DCP1 0.9140625 234 / 256
TP4DCP2 0.91015625 233 / 256

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Code Review

This pull request introduces support for Decode Context Parallelism (DCP) in hybrid models within the v1 engine, updating the KV cache coordinator, speculative decoding, and CUDA graph capture logic. Key modifications include a supports_dcp flag for layers, batch splitting for DCP execution in FlashAttention, and DCP-aware slot mapping kernels. Review feedback identifies critical bugs in the FlashAttention backend, specifically incorrect slicing of quantization descales by request count rather than token count and a lack of null checks for these descales in non-FP8 models. Furthermore, a typo in vllm/v1/worker/block_table.py using PAD_SLOT_ID instead of PADDING_SLOT_ID must be fixed to avoid runtime failures.

Comment thread vllm/v1/attention/backends/flash_attn.py Outdated
Comment thread vllm/v1/attention/backends/flash_attn.py Outdated
Comment thread vllm/v1/attention/backends/flash_attn.py Outdated
Comment thread vllm/v1/worker/block_table.py Outdated
@cjackal

cjackal commented Apr 27, 2026

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cf. #36480 for the previous work.

I remembered that it had accuracy issue on 397b MoE, wonder if it has been resolved.

@Yancey0623

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cf. #36480 for the previous work.
I remembered that it had accuracy issue on 397b MoE, wonder if it has been resolved.

@cjackal yes, there is no accuracy issue on Qwen3.5-397B-A17B-FP8, and I also updated this test result in the description box.

Config Accuracy Correct / Total
TP4DCP1 0.9140625 234 / 256
TP4DCP2 0.91015625 233 / 256

@ehfd

ehfd commented May 8, 2026

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@pisceskkk @LucasWilkinson

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ehfd commented May 8, 2026

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@njhill

num_decode_tokens,
num_prefill_tokens,
) = self._get_dcp_split_boundaries(attn_metadata)
if num_prefills > 0 and num_decodes > 0:

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Why do we need to handle the prefill and decode stages separately? Did I miss something?

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it's used to split prefill-decode requests in a batch, and after code polish, this pr removed this split, please review the latest codebase, thanks!

@mergify

mergify Bot commented May 23, 2026

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This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @Yancey0623.

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

@mergify mergify Bot added the needs-rebase label May 23, 2026
@Yancey0623
Yancey0623 force-pushed the qwen35_hybrid_attn_dcp branch from 4f5ba69 to 9da2b8b Compare May 27, 2026 10:54
Yancey0623 and others added 4 commits July 8, 2026 21:16
Signed-off-by: YanXu <yancey.yx@alibaba-inc.com>
- Move max_num_blocks_per_req sizing into KVCacheSpec subclasses:
  AttentionSpec applies DCP/PCP token sharding, MambaSpec keeps
  replicated-state sizing (align mode documents the row-length vs
  resident-blocks distinction and uses the encoder-aware max_len).
  Drops the Any-typed helper from cp_utils.
- Reinitialize InputBatch when per-group max_num_blocks or slot-mapping
  modes change, not only block sizes; otherwise the unsharded
  placeholder sizing silently survives for single-group DCP models.
- Reject hybrid KV cache layouts with dcp > 1 unless every group is
  full-attention or Mamba, restoring fail-closed behavior for e.g.
  sliding-window hybrid models.
- Scope the DCP + speculative-decoding ban to hybrid models; non-hybrid
  DCP + MTP remains supported.
- Keep prefix caching opt-in rather than default-on for hybrid models;
  the capability is still reported as supported.
- Remove the dead CUDA-tensor branch in split_dcp_context_queries.

Co-authored-by: Claude <noreply@anthropic.com>
Signed-off-by: Jingyi Yang <girasoley@inferact.ai>

Signed-off-by: Jingyi Yang <girasoleyang@gmail.com>
The skip-context-attention fast path was gated on this rank's local
context length (get_dcp_local_seq_lens with dcp_rank). Contexts shorter
than a full interleave round land entirely on a subset of DCP ranks, so
ranks with zero local context took the early return in _forward_with_dcp
and skipped the query all-gather + LSE-combine collectives while other
ranks entered them, deadlocking the DCP group (e.g. first decode after a
short prompt, or a short chunked-prefill step).

Gate on the global context lengths instead, which are identical on all
ranks. Cold pure-prefill batches (global context == 0) still skip; a
rank whose local share is empty now runs the context pass with zero
seqused_k and contributes -inf LSE, as before this optimization.

Co-authored-by: Claude <noreply@anthropic.com>
Signed-off-by: Jingyi Yang <girasoley@inferact.ai>

Signed-off-by: Jingyi Yang <girasoleyang@gmail.com>
Signed-off-by: YanXu <yancey.yx@alibaba-inc.com>
@Yancey0623
Yancey0623 force-pushed the qwen35_hybrid_attn_dcp branch from 23faf73 to a663710 Compare July 8, 2026 13:18
wangyichao1999 pushed a commit to wangyichao1999/vllm-ascend that referenced this pull request Jul 9, 2026
### What this PR does / why we need it?
#### vllm_ascend/distributed/weight_transfer/npu_ipc_engine.py
#### vllm_ascend/distributed/weight_transfer/hccl_engine.py
- Conditionally implement start_weight_update() and
finish_weight_update() as no-op methods for non-0.23.0 releases.
- Keep the NPU IPC weight transfer engine compatible with the updated
WeightTransferEngine interface.
- Upstream source: vllm#44353
(vllm-project/vllm#44353).

---

#### vllm_ascend/patch/platform/patch_torch_accelerator.py
- Redirect torch.accelerator.get_memory_info() to
torch.npu.mem_get_info() on non-0.23.0.
- Avoid crashes caused by the unsupported C10 DeviceAllocator path when
constructing MemorySnapshot.
- Align with the existing NPU-specific memory API patches.
- Upstream source: commit 747b068 (v0.24.0+
MemorySnapshot(device=device) path).

--- 

#### vllm_ascend/patch/worker/patch_qwen3_dflash.py
- Wrap DFlashQwen3ForCausalLM._read_mask_embedding() to ignore optional
mask embedding download failures.
- Preserve the expected "mask embedding not present" behavior when the
file is unavailable.
- Upstream source: vllm#46104
(vllm-project/vllm#46104).

--- 

#### vllm_ascend/worker/v2/model_runner.py
#### vllm_ascend/patch/worker/patch_v2/patch_input_batch.py
- Forward is_padding and prompt_lens when constructing AscendInputBatch.
- Match the updated upstream InputBatch interface and avoid
initialization failures on newer releases.
- Upstream source: vllm#40654
(vllm-project/vllm#40654).

--- 

#### vllm_ascend/patch/worker/patch_deepseek_v2.py
- Add the reduce_results argument to DeepseekV2MLAAttention.
- Forward the parameter to RowParallelLinear to stay compatible with the
updated upstream attention initialization.
- Keep the implementation compatible across all supported vLLM versions.
- Upstream source: vllm#45895
(vllm-project/vllm#45895).

--- 

#### vllm_ascend/distributed/device_communicators/npu_communicator.py
- Register a no-op all2all_manager for NPUCommunicator.
- Bypass the upstream MoE fault-tolerance check (which queries
all2all_manager when data_parallel_size > 1 and is_moe) while preserving
the existing MC2 communication path.
- Keep compatibility with the updated distributed initialization.
- Related upstream changes:
- vllm#46892 (vllm-project/vllm#46892)

--- 

#### vllm_ascend/ops/fused_moe/fused_moe.py
- Share routed expert parameters through direct nn.Parameter aliasing
instead of creating wrapper parameters.
- Ensure both legacy and routed_experts parameter paths reference the
same underlying weights.
- Apply the aliasing strategy to all routed-expert MoE models on newer
vLLM releases.
- Related upstream changes:
- vllm#40996 (vllm-project/vllm#40996)
- vllm#46892 (vllm-project/vllm#46892)

--- 

#### vllm_ascend/worker/worker.py
#### vllm_ascend/distributed/weight_transfer/npu_ipc_engine.py
#### vllm_ascend/distributed/weight_transfer/hccl_engine.py
#### vllm_ascend/patch/platform/patch_weight_transfer_engine.py
- Adapt WeightTransferEngineFactory.create_engine() and
WeightTransferEngine.__init__() to support both legacy and current
upstream signatures.
- Keep weight transfer compatible across v0.23.0, v0.24.0, and newer
upstream releases.
- Upstream source: vllm#44353
(vllm-project/vllm#44353).

--- 

#### vllm_ascend/patch/worker/patch_deepseek_v2.py
- Remove the upstream model-level all-gather path for DeepSeek-V2 on
non-0.23.0.
- Keep the implementation compatible with the Ascend MC2 dispatch flow.
- Avoid tensor shape mismatches and residual concatenation failures
introduced by the upstream refactor.
- Related upstream changes:
- vllm#41184 (vllm-project/vllm#41184)
--- 
#### vllm_ascend/ops/fused_moe/fused_moe.py
- Remove the unnecessary .contiguous() call after weight transposition
on non-0.23.0.
- Reduce transient NPU peak memory during MoE weight loading.
- Prevent OOM caused by duplicate temporary tensor allocations.
- Related upstream changes:
- vllm#44589 (vllm-project/vllm#44589)

- vLLM version: v0.23.0
- vLLM main:
vllm-project/vllm@ee0da84
---------
Signed-off-by: hfadzxy <starmoon_zhang@163.com>
@ywang96
ywang96 merged commit 95ed0fe into vllm-project:main Jul 10, 2026
139 of 142 checks passed
@github-project-automation github-project-automation Bot moved this to Done in NVIDIA Jul 10, 2026
ZJY0516 added a commit to ZJY0516/vllm that referenced this pull request Jul 10, 2026
Resolve semantic conflicts with vllm-project#40996 (DCP supports hybrid attention):
- keep fine-grained partial-hit machinery; finders still return
  (blocks, hit_length) and resolve block hashes internally
- FullAttentionManager resolves hashes at the DCP/PCP-scaled block size
- coordinator eagle margin / FA truncation use the manager's effective
  (scaled) block size
- gate enable_partial_hash_hits on dcp_world_size == 1

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

Signed-off-by: zjy0516 <riverclouds.zhu@qq.com>
@Yancey0623
Yancey0623 deleted the qwen35_hybrid_attn_dcp branch July 10, 2026 06:20
Spicy-Stick pushed a commit to Spicy-Stick/vllm-ascend that referenced this pull request Jul 10, 2026
### What this PR does / why we need it?
#### vllm_ascend/distributed/weight_transfer/npu_ipc_engine.py
#### vllm_ascend/distributed/weight_transfer/hccl_engine.py
- Conditionally implement start_weight_update() and
finish_weight_update() as no-op methods for non-0.23.0 releases.
- Keep the NPU IPC weight transfer engine compatible with the updated
WeightTransferEngine interface.
- Upstream source: vllm#44353
(vllm-project/vllm#44353).

---

#### vllm_ascend/patch/platform/patch_torch_accelerator.py
- Redirect torch.accelerator.get_memory_info() to
torch.npu.mem_get_info() on non-0.23.0.
- Avoid crashes caused by the unsupported C10 DeviceAllocator path when
constructing MemorySnapshot.
- Align with the existing NPU-specific memory API patches.
- Upstream source: commit 747b068 (v0.24.0+
MemorySnapshot(device=device) path).

---

#### vllm_ascend/patch/worker/patch_qwen3_dflash.py
- Wrap DFlashQwen3ForCausalLM._read_mask_embedding() to ignore optional
mask embedding download failures.
- Preserve the expected "mask embedding not present" behavior when the
file is unavailable.
- Upstream source: vllm#46104
(vllm-project/vllm#46104).

---

#### vllm_ascend/worker/v2/model_runner.py
#### vllm_ascend/patch/worker/patch_v2/patch_input_batch.py
- Forward is_padding and prompt_lens when constructing AscendInputBatch.
- Match the updated upstream InputBatch interface and avoid
initialization failures on newer releases.
- Upstream source: vllm#40654
(vllm-project/vllm#40654).

---

#### vllm_ascend/patch/worker/patch_deepseek_v2.py
- Add the reduce_results argument to DeepseekV2MLAAttention.
- Forward the parameter to RowParallelLinear to stay compatible with the
updated upstream attention initialization.
- Keep the implementation compatible across all supported vLLM versions.
- Upstream source: vllm#45895
(vllm-project/vllm#45895).

---

#### vllm_ascend/distributed/device_communicators/npu_communicator.py
- Register a no-op all2all_manager for NPUCommunicator.
- Bypass the upstream MoE fault-tolerance check (which queries
all2all_manager when data_parallel_size > 1 and is_moe) while preserving
the existing MC2 communication path.
- Keep compatibility with the updated distributed initialization.
- Related upstream changes:
- vllm#46892 (vllm-project/vllm#46892)

---

#### vllm_ascend/ops/fused_moe/fused_moe.py
- Share routed expert parameters through direct nn.Parameter aliasing
instead of creating wrapper parameters.
- Ensure both legacy and routed_experts parameter paths reference the
same underlying weights.
- Apply the aliasing strategy to all routed-expert MoE models on newer
vLLM releases.
- Related upstream changes:
- vllm#40996 (vllm-project/vllm#40996)
- vllm#46892 (vllm-project/vllm#46892)

---

#### vllm_ascend/worker/worker.py
#### vllm_ascend/distributed/weight_transfer/npu_ipc_engine.py
#### vllm_ascend/distributed/weight_transfer/hccl_engine.py
#### vllm_ascend/patch/platform/patch_weight_transfer_engine.py
- Adapt WeightTransferEngineFactory.create_engine() and
WeightTransferEngine.__init__() to support both legacy and current
upstream signatures.
- Keep weight transfer compatible across v0.23.0, v0.24.0, and newer
upstream releases.
- Upstream source: vllm#44353
(vllm-project/vllm#44353).

---

#### vllm_ascend/patch/worker/patch_deepseek_v2.py
- Remove the upstream model-level all-gather path for DeepSeek-V2 on
non-0.23.0.
- Keep the implementation compatible with the Ascend MC2 dispatch flow.
- Avoid tensor shape mismatches and residual concatenation failures
introduced by the upstream refactor.
- Related upstream changes:
- vllm#41184 (vllm-project/vllm#41184)
---
#### vllm_ascend/ops/fused_moe/fused_moe.py
- Remove the unnecessary .contiguous() call after weight transposition
on non-0.23.0.
- Reduce transient NPU peak memory during MoE weight loading.
- Prevent OOM caused by duplicate temporary tensor allocations.
- Related upstream changes:
- vllm#44589 (vllm-project/vllm#44589)

- vLLM version: v0.23.0
- vLLM main:
vllm-project/vllm@ee0da84
---------
Signed-off-by: hfadzxy <starmoon_zhang@163.com>
Signed-off-by: Spicy-Stick <873805887@qq.com>
xqchen7 pushed a commit to nv-action/vllm-benchmarks that referenced this pull request Jul 15, 2026
### What this PR does / why we need it?
#### vllm_ascend/distributed/weight_transfer/npu_ipc_engine.py
#### vllm_ascend/distributed/weight_transfer/hccl_engine.py
- Conditionally implement start_weight_update() and
finish_weight_update() as no-op methods for non-0.23.0 releases.
- Keep the NPU IPC weight transfer engine compatible with the updated
WeightTransferEngine interface.
- Upstream source: vllm#44353
(vllm-project/vllm#44353).

---

#### vllm_ascend/patch/platform/patch_torch_accelerator.py
- Redirect torch.accelerator.get_memory_info() to
torch.npu.mem_get_info() on non-0.23.0.
- Avoid crashes caused by the unsupported C10 DeviceAllocator path when
constructing MemorySnapshot.
- Align with the existing NPU-specific memory API patches.
- Upstream source: commit 747b068 (v0.24.0+
MemorySnapshot(device=device) path).

---

#### vllm_ascend/patch/worker/patch_qwen3_dflash.py
- Wrap DFlashQwen3ForCausalLM._read_mask_embedding() to ignore optional
mask embedding download failures.
- Preserve the expected "mask embedding not present" behavior when the
file is unavailable.
- Upstream source: vllm#46104
(vllm-project/vllm#46104).

---

#### vllm_ascend/worker/v2/model_runner.py
#### vllm_ascend/patch/worker/patch_v2/patch_input_batch.py
- Forward is_padding and prompt_lens when constructing AscendInputBatch.
- Match the updated upstream InputBatch interface and avoid
initialization failures on newer releases.
- Upstream source: vllm#40654
(vllm-project/vllm#40654).

---

#### vllm_ascend/patch/worker/patch_deepseek_v2.py
- Add the reduce_results argument to DeepseekV2MLAAttention.
- Forward the parameter to RowParallelLinear to stay compatible with the
updated upstream attention initialization.
- Keep the implementation compatible across all supported vLLM versions.
- Upstream source: vllm#45895
(vllm-project/vllm#45895).

---

#### vllm_ascend/distributed/device_communicators/npu_communicator.py
- Register a no-op all2all_manager for NPUCommunicator.
- Bypass the upstream MoE fault-tolerance check (which queries
all2all_manager when data_parallel_size > 1 and is_moe) while preserving
the existing MC2 communication path.
- Keep compatibility with the updated distributed initialization.
- Related upstream changes:
- vllm#46892 (vllm-project/vllm#46892)

---

#### vllm_ascend/ops/fused_moe/fused_moe.py
- Share routed expert parameters through direct nn.Parameter aliasing
instead of creating wrapper parameters.
- Ensure both legacy and routed_experts parameter paths reference the
same underlying weights.
- Apply the aliasing strategy to all routed-expert MoE models on newer
vLLM releases.
- Related upstream changes:
- vllm#40996 (vllm-project/vllm#40996)
- vllm#46892 (vllm-project/vllm#46892)

---

#### vllm_ascend/worker/worker.py
#### vllm_ascend/distributed/weight_transfer/npu_ipc_engine.py
#### vllm_ascend/distributed/weight_transfer/hccl_engine.py
#### vllm_ascend/patch/platform/patch_weight_transfer_engine.py
- Adapt WeightTransferEngineFactory.create_engine() and
WeightTransferEngine.__init__() to support both legacy and current
upstream signatures.
- Keep weight transfer compatible across v0.23.0, v0.24.0, and newer
upstream releases.
- Upstream source: vllm#44353
(vllm-project/vllm#44353).

---

#### vllm_ascend/patch/worker/patch_deepseek_v2.py
- Remove the upstream model-level all-gather path for DeepSeek-V2 on
non-0.23.0.
- Keep the implementation compatible with the Ascend MC2 dispatch flow.
- Avoid tensor shape mismatches and residual concatenation failures
introduced by the upstream refactor.
- Related upstream changes:
- vllm#41184 (vllm-project/vllm#41184)
---
#### vllm_ascend/ops/fused_moe/fused_moe.py
- Remove the unnecessary .contiguous() call after weight transposition
on non-0.23.0.
- Reduce transient NPU peak memory during MoE weight loading.
- Prevent OOM caused by duplicate temporary tensor allocations.
- Related upstream changes:
- vllm#44589 (vllm-project/vllm#44589)

- vLLM version: v0.23.0
- vLLM main:
vllm-project/vllm@ee0da84
---------
Signed-off-by: hfadzxy <starmoon_zhang@163.com>
Signed-off-by: xqchen7 <chenxueqing7@huawei.com>
NickLucche pushed a commit to NickLucche/vllm that referenced this pull request Jul 15, 2026
Signed-off-by: YanXu <yancey.yx@alibaba-inc.com>
Signed-off-by: Jingyi Yang <girasoleyang@gmail.com>
Co-authored-by: Jingyi Yang <girasoleyang@gmail.com>
Comment thread vllm/config/model.py
Comment on lines -1888 to 1886
return False
logger.debug("Generative hybrid models support prefix caching.")
return True
elif attn_type == "attention_free":

@noooop noooop Aug 4, 2026

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May I ask what is the particular reason for this?

Comment thread vllm/engine/arg_utils.py
Comment on lines -2496 to 2502
default_prefix_caching = model_config.is_prefix_caching_supported
# Hybrid models support prefix caching but keep it opt-in for now
# while the feature matures.
default_prefix_caching = (
model_config.is_prefix_caching_supported and not model_config.is_hybrid
)

if self.enable_chunked_prefill is None:

@noooop noooop Aug 4, 2026

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May I ask what is the particular reason for this?

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Labels

cpu Related to CPU backends multi-modality Related to multi-modality (#4194) nvidia ready ONLY add when PR is ready to merge/full CI is needed speculative-decoding tpu Related to Google TPUs v1 verified Run pre-commit for new contributors without triggering other tests

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