fix ep_enabled

computility-run.yaml

@@ -13,13 +13,9 @@ command:
     - '0.92'
     - --trust-remote-code
     - -tp
-    - '2'
-    - -dp
-    - '2'
+    - '4'
     - --max-num-seqs
     - '2'
-    - -dp
-    - '2'
     - --disable-log-requests
     - --disable-frontend-multiprocessing
     - --max-num-batched-tokens
@@ -39,6 +35,8 @@ command:
 env:
     - name: VLLM_ENGINE_ITERATION_TIMEOUT_S
       value: 3600
+    - name: VLLM_ENABLE_EXPERT_PARALLEL
+      value: 1
     - name: BI100_MAX_NUM_SEQS
       value: 2
     - name: BI100_MOE_COREX_DIRECT_ROUTED

qwen3_6_scripts/ep_fused_moe_patch.py

@@ -0,0 +1,347 @@
+"""EP-aware FusedMoE override for vllm 0.6.3.
+
+PR #2269 Sub-task 2: Expert Parallelism weight sharding.
+
+Problem:
+  TP=2 on 4× BI-V100 (32 GiB each) OOMs during model loading because
+  FusedMoE.create_weights allocates ALL experts on every card, splitting
+  only the intermediate_size dimension. For Qwen3.6-35B-A3B (256 experts),
+  MoE weights alone consume ~22.5 GiB/card under TP=2.
+
+Solution:
+  When enable_expert_parallel=True, each card holds only
+  num_experts/ep_size experts with FULL intermediate_size (no TP split
+  on MoE). Forward uses all-to-all to dispatch tokens to the correct
+  expert-holding rank, compute locally, and combine results back.
+
+  EP=4: each card holds 64/256 experts → MoE weights ~5.6 GiB/card
+  (savings: 16.9 GiB/card vs TP=2)
+
+Memory layout comparison (per card, 30 MoE layers, fp16):
+  TP=2:  256 experts × (2×256×2048 + 2048×256) × 2B × 30 = 22.5 GiB
+  EP=4:   64 experts × (2×512×2048 + 2048×512) × 2B × 30 =  5.6 GiB
+
+xllm equivalent: core/layers/cuda/fused_moe.cpp
+  ep_size_ = parallel_args.ep_size();
+  num_experts_per_rank_ = num_experts / ep_size;
+  start_expert_id_ = ep_rank * num_experts_per_rank_;
+  output = cutlass_fused_moe(..., ep_size_, ep_rank_, ...);
+  output = parallel_state::reduce(output, ep_pg_);
+"""
+
+import torch
+import torch.distributed as dist
+from typing import Callable, List, Optional, Tuple
+
+from vllm.config import ParallelConfig
+from vllm.logger import init_logger
+
+logger = init_logger(__name__)
+
+
+def _is_ep_requested():
+    """Check if EP is requested via environment variable.
+
+    This is safe to call at any time (no dist dependency).
+    """
+    import os
+    return bool(int(os.environ.get("VLLM_ENABLE_EXPERT_PARALLEL", "0")))
+
+
+def _get_ep_runtime_config():
+    """Get EP size and rank at runtime when dist is initialized.
+
+    Must only be called from within worker processes (during __init__,
+    weight_loader, or forward) where torch.distributed is guaranteed
+    to be initialized.
+
+    Returns (ep_size, ep_rank).
+    """
+    if dist.is_initialized():
+        return dist.get_world_size(), dist.get_rank()
+    # Fallback — should not happen during normal model loading
+    logger.warning("[PR #2269] dist not initialized when querying EP config, "
+                   "falling back to ep_size=1")
+    return 1, 0
+
+
+def patch_fused_moe_for_ep():
+    """Monkey-patch FusedMoE.__init__, weight_loader, and forward to support EP.
+
+    Call this during model loading (e.g. in qwen3_5.py module init or
+    patch_ops.sh) BEFORE any FusedMoE layers are constructed.
+
+    Only checks the env var at patch time. Actual ep_size/ep_rank are
+    queried at runtime (inside __init__, weight_loader, forward) when
+    torch.distributed is guaranteed to be initialized.
+    """
+    from vllm.model_executor.layers.fused_moe.layer import FusedMoE
+
+    if not _is_ep_requested():
+        logger.info("[PR #2269] EP not enabled (VLLM_ENABLE_EXPERT_PARALLEL!=1), "
+                    "skipping FusedMoE EP patch")
+        return
+
+    logger.info("[PR #2269] EP requested via env var, installing FusedMoE monkey-patches "
+                "(ep_size/ep_rank will be resolved at runtime)")
+
+    _orig_init = FusedMoE.__init__
+
+    def _ep_init(self, num_experts, top_k, hidden_size, intermediate_size,
+                 params_dtype=None, reduce_results=False, renormalize=True,
+                 use_grouped_topk=False, num_expert_group=None,
+                 topk_group=None, quant_config=None, tp_size=None,
+                 prefix="", custom_routing_function=None):
+        """EP-aware __init__: allocate only local experts, full intermediate."""
+
+        # Query ep_size/ep_rank NOW — dist is initialized in worker processes
+        ep_size, ep_rank = _get_ep_runtime_config()
+
+        # Store global expert info before modifying
+        self._ep_enabled = True
+        self._ep_size = ep_size
+        self._ep_rank = ep_rank
+        self._global_num_experts = num_experts
+        assert num_experts % ep_size == 0, (
+            f"num_experts ({num_experts}) must be divisible by "
+            f"ep_size ({ep_size})")
+        self._num_experts_per_rank = num_experts // ep_size
+        self._start_expert_id = ep_rank * self._num_experts_per_rank
+
+        logger.info(
+            "[PR #2269] FusedMoE EP init: global_experts=%d, ep_size=%d, "
+            "ep_rank=%d, local_experts=%d (ids %d..%d), "
+            "intermediate_size=%d (full, no TP split)",
+            num_experts, ep_size, ep_rank,
+            self._num_experts_per_rank,
+            self._start_expert_id,
+            self._start_expert_id + self._num_experts_per_rank - 1,
+            intermediate_size)
+
+        # Call original __init__ with:
+        # - num_experts = local experts only (saves memory)
+        # - tp_size = 1 (no TP split on intermediate — EP replaces TP for MoE)
+        # - reduce_results = False (we do EP reduce ourselves)
+        _orig_init(
+            self,
+            num_experts=self._num_experts_per_rank,
+            top_k=top_k,
+            hidden_size=hidden_size,
+            intermediate_size=intermediate_size,
+            params_dtype=params_dtype,
+            reduce_results=False,  # EP does its own reduce
+            renormalize=renormalize,
+            use_grouped_topk=use_grouped_topk,
+            num_expert_group=num_expert_group,
+            topk_group=topk_group,
+            quant_config=quant_config,
+            tp_size=1,  # no TP split — EP splits by expert count instead
+            prefix=prefix,
+            custom_routing_function=custom_routing_function,
+        )
+
+        # Override num_experts to global for routing (select_experts sees all)
+        self.num_experts = num_experts
+        # But weights are sized for local experts only
+        self._reduce_results_ep = reduce_results
+
+    _orig_weight_loader = FusedMoE.weight_loader
+
+    def _ep_weight_loader(self, param, loaded_weight, weight_name,
+                          shard_id, expert_id):
+        """EP-aware weight_loader: skip experts not owned by this rank.
+
+        Critical fix: the original weight_loader calls
+        get_tensor_model_parallel_rank() internally to compute tp_rank,
+        then uses it to narrow() the loaded weight for TP sharding.
+        Under EP we pass tp_size=1 (no TP split on MoE), so weights are
+        full-sized, but tp_rank still returns the real rank (0-3).
+        rank >= 1 causes narrow(dim, 512*rank, 512) to exceed dim size 512.
+
+        Solution: temporarily monkey-patch get_tensor_model_parallel_rank
+        to return 0 during EP weight loading, so narrow() always starts
+        at offset 0 and loads the full (unsplit) weight.
+        """
+        if not getattr(self, '_ep_enabled', False):
+            return _orig_weight_loader(self, param, loaded_weight,
+                                       weight_name, shard_id, expert_id)
+
+        start = self._start_expert_id
+        end = start + self._num_experts_per_rank
+
+        # Skip experts not owned by this EP rank
+        if expert_id < start or expert_id >= end:
+            return
+
+        # Remap global expert_id to local index
+        local_expert_id = expert_id - start
+
+        # Monkey-patch tp rank to 0 during load so narrow() doesn't OOB.
+        # The weight is already full-sized (tp_size=1), no split needed.
+        import vllm.model_executor.layers.fused_moe.layer as _fused_moe_mod
+        _real_get_tp_rank = _fused_moe_mod.get_tensor_model_parallel_rank
+        _fused_moe_mod.get_tensor_model_parallel_rank = lambda: 0
+        try:
+            _orig_weight_loader(self, param, loaded_weight, weight_name,
+                                shard_id, local_expert_id)
+        finally:
+            _fused_moe_mod.get_tensor_model_parallel_rank = _real_get_tp_rank
+
+    _orig_forward = FusedMoE.forward
+
+    def _ep_forward(self, hidden_states, router_logits):
+        """EP-aware forward: all-to-all dispatch, local compute, all-to-all combine.
+
+        Flow:
+        1. Route all tokens globally (all ranks see all expert logits)
+        2. All-to-all dispatch: send each token to the rank that owns its expert
+        3. Local expert computation on owned experts only
+        4. All-to-all combine: gather results back to original token positions
+        """
+        if not getattr(self, '_ep_enabled', False):
+            return _orig_forward(self, hidden_states, router_logits)
+
+        # Step 1: Global routing — every rank computes topk over ALL experts
+        topk_weights, topk_ids = FusedMoE.select_experts(
+            hidden_states=hidden_states,
+            router_logits=router_logits,
+            use_grouped_topk=self.use_grouped_topk,
+            top_k=self.top_k,
+            renormalize=self.renormalize,
+            topk_group=self.topk_group,
+            num_expert_group=self.num_expert_group,
+            custom_routing_function=self.custom_routing_function,
+        )
+
+        ep_size = self._ep_size
+        ep_rank = self._ep_rank
+        start_expert = self._start_expert_id
+        end_expert = start_expert + self._num_experts_per_rank
+        T, H = hidden_states.shape
+        K = self.top_k
+        device = hidden_states.device
+
+        # Step 2: Determine which tokens go to which EP rank.
+        # expert_to_rank: expert_id → ep_rank
+        # For each (token, top_k_slot), find the destination rank.
+        dest_ranks = topk_ids.div(self._num_experts_per_rank, rounding_mode='trunc')  # (T, K)
+
+        # Count tokens to send to each rank
+        send_counts = torch.zeros(ep_size, dtype=torch.int64, device=device)
+        for r in range(ep_size):
+            send_counts[r] = (dest_ranks == r).sum()
+
+        # Gather all ranks' send counts so we know receive counts
+        all_counts = torch.zeros(ep_size, ep_size, dtype=torch.int64, device=device)
+        dist.all_gather_into_tensor(
+            all_counts.view(-1),
+            send_counts,
+        )
+        recv_counts = all_counts[:, ep_rank]  # what each rank sends to us
+
+        total_send = send_counts.sum().item()
+        total_recv = recv_counts.sum().item()
+
+        # Build dispatch buffers: for each (token, k) pair routed to each rank,
+        # pack (hidden_state, topk_weight, local_expert_id, original_position)
+        # Sort by destination rank for contiguous all-to-all.
+
+        # Flatten topk dimension: each (token, k_slot) is a "work item"
+        flat_ids = topk_ids.view(-1)           # (T*K,)
+        flat_weights = topk_weights.view(-1)   # (T*K,)
+        flat_dest = dest_ranks.view(-1)        # (T*K,)
+        flat_token_idx = torch.arange(T, device=device).unsqueeze(1).expand(T, K).reshape(-1)  # (T*K,)
+
+        # Sort by destination rank for all-to-all
+        sort_idx = flat_dest.argsort()
+        sorted_hidden = hidden_states[flat_token_idx[sort_idx]]   # (T*K, H)
+        sorted_weights = flat_weights[sort_idx]                   # (T*K,)
+        sorted_ids = flat_ids[sort_idx]                           # (T*K,) global expert ids
+        sorted_token_idx = flat_token_idx[sort_idx]               # (T*K,) for scatter-back
+
+        # All-to-all send/recv counts (in elements, each element = one work item)
+        send_splits = send_counts.tolist()
+        recv_splits = recv_counts.tolist()
+
+        # All-to-all: exchange hidden states
+        recv_hidden = torch.empty(total_recv, H, dtype=hidden_states.dtype, device=device)
+        dist.all_to_all_single(recv_hidden, sorted_hidden,
+                               output_split_sizes=recv_splits,
+                               input_split_sizes=send_splits)
+
+        # All-to-all: exchange expert ids
+        recv_ids = torch.empty(total_recv, dtype=sorted_ids.dtype, device=device)
+        dist.all_to_all_single(recv_ids, sorted_ids,
+                               output_split_sizes=recv_splits,
+                               input_split_sizes=send_splits)
+
+        # All-to-all: exchange topk weights
+        recv_weights = torch.empty(total_recv, dtype=sorted_weights.dtype, device=device)
+        dist.all_to_all_single(recv_weights, sorted_weights,
+                               output_split_sizes=recv_splits,
+                               input_split_sizes=send_splits)
+
+        # Step 3: Local expert computation on received tokens
+        # Remap global expert ids to local
+        local_ids = recv_ids - start_expert  # now 0..num_experts_per_rank-1
+
+        if total_recv > 0:
+            # Compute using the existing fused_experts kernel (or Python fallback)
+            from vllm.model_executor.layers.fused_moe.fused_moe import fused_experts
+            # Build per-token topk format expected by fused_experts:
+            # It expects (num_tokens, top_k) but here each recv item is
+            # a single (token, expert) pair. We reshape to (total_recv, 1).
+            local_topk_ids = local_ids.unsqueeze(1)        # (total_recv, 1)
+            local_topk_weights = recv_weights.unsqueeze(1)  # (total_recv, 1)
+
+            local_output = fused_experts(
+                hidden_states=recv_hidden,
+                w1=self.w13_weight,
+                w2=self.w2_weight,
+                topk_weights=local_topk_weights,
+                topk_ids=local_topk_ids.to(torch.int32),
+                inplace=False,
+            )
+        else:
+            local_output = torch.empty(0, H, dtype=hidden_states.dtype, device=device)
+
+        # Step 4: All-to-all combine — send results back
+        # Reverse the all-to-all: recv_splits becomes send, send_splits becomes recv
+        combine_output = torch.empty(total_send, H, dtype=hidden_states.dtype, device=device)
+        dist.all_to_all_single(combine_output, local_output,
+                               output_split_sizes=send_splits,
+                               input_split_sizes=recv_splits)
+
+        # Unsort and scatter-add back to original token positions
+        # combine_output is in the same order as sorted_* (sorted by dest rank)
+        # We need to unsort and accumulate weighted results per token.
+        final_output = torch.zeros(T, H, dtype=hidden_states.dtype, device=device)
+        # Unsort: combine_output[i] corresponds to sorted_token_idx[i]
+        unsorted_output = torch.zeros_like(combine_output)
+        unsorted_output[sort_idx] = combine_output
+
+        # Reshape back to (T, K, H) and sum over K dimension
+        # Each (token, k_slot) pair has already been weighted by topk_weight
+        # inside fused_experts. We just need to sum over k.
+        # Actually fused_experts with top_k=1 per item already applies the weight.
+        # scatter_add by token index:
+        token_indices = flat_token_idx.unsqueeze(1).expand(-1, H)  # (T*K, H)
+        final_output.scatter_add_(0, token_indices, unsorted_output)
+
+        # EP reduce (if the caller requested reduce_results, e.g. for shared experts)
+        if self._reduce_results_ep:
+            # No TP reduce needed (tp_size=1 for EP), but if the model
+            # expects an all-reduce for the MoE output (e.g. to combine
+            # with shared experts), we do it here over the EP group.
+            pass  # EP output is already complete — each token got results from its experts
+
+        return final_output
+
+    # Apply patches
+    FusedMoE.__init__ = _ep_init
+    FusedMoE.weight_loader = _ep_weight_loader
+    FusedMoE.forward = _ep_forward
+
+    logger.info(
+        "[PR #2269] FusedMoE patched for EP. "
+        "ep_size/ep_rank will be resolved per-layer at runtime.")

qwen3_6_scripts/patch_ops.sh

@@ -3,6 +3,8 @@ echo "[build] trigger 202609011237"
 echo "[build] trigger 202609011636"
 echo "[build] trigger 202609011655"
 echo "[build] trigger 202609011710"
+echo "[build] trigger 202609031035"
+echo "[build] trigger 202609031049"
 #!/usr/bin/env bash
 # BI-V100 patch script for Qwen3.6-35B-A3B (Qwen3_5 MoE architecture)
 #
@@ -170,6 +172,7 @@ cp ./bi100_env.py "${VLLM_ROOT}/bi100_env.py"
 cp ./bi100_profile.py "${VLLM_ROOT}/bi100_profile.py"
 cp ./block_major_kv_cache.py "${VLLM_ROOT}/block_major_kv_cache.py"
 cp ./gdn_prefix.py "${VLLM_ROOT}/gdn_prefix.py"
+cp ./ep_fused_moe_patch.py "${VLLM_ROOT}/ep_fused_moe_patch.py"
 
 build_stage "installing CoreX paged-KV swap compatibility"
 python3 ./patch_corex_swap_blocks.py

qwen3_6_scripts/qwen3_5.py

@@ -66,6 +66,15 @@ from vllm.model_executor.layers.linear import (ColumnParallelLinear,
                                                ReplicatedLinear,
                                                RowParallelLinear)
 from vllm.model_executor.layers.fused_moe import FusedMoE
+# [PR #2269] Apply EP patch to FusedMoE before any layers are constructed.
+# When VLLM_ENABLE_EXPERT_PARALLEL=1, this replaces TP-sharded MoE weights
+# with EP-sharded MoE weights (each card holds num_experts/ep_size experts
+# with full intermediate_size), solving the OOM under TP=2.
+try:
+    from vllm.ep_fused_moe_patch import patch_fused_moe_for_ep as _patch_ep
+    _patch_ep()
+except ImportError:
+    pass  # EP patch not installed — TP mode unchanged
 from vllm.model_executor.layers.logits_processor import LogitsProcessor
 from vllm.model_executor.layers.quantization import QuantizationConfig
 from vllm.model_executor.layers.rotary_embedding import (

qwen3_6_scripts/serving_chat.py

@@ -243,6 +243,7 @@ class OpenAIServingChat(OpenAIServing):
 
         # set up reasoning parser
         self.reasoning_parser_cls = None
+        self._template_patched = False  # [BI100] one-shot chat template patch
         if reasoning_parser:
             try:
                 from vllm.reasoning import ReasoningParserManager
@@ -309,6 +310,19 @@ class OpenAIServingChat(OpenAIServing):
             model_config = self.model_config
             tokenizer = await self.engine_client.get_tokenizer(lora_request)
 
+            # [BI100] Runtime equivalent of patch_chat_template.py.
+            # Qwen3.5/3.6-MoE templates inject '<think>\n\n</think>\n\n'
+            # when enable_thinking=false, which causes the model to
+            # degenerate (outputs '!!!!!'). Patch it out once.
+            if not self._template_patched and hasattr(tokenizer, 'chat_template'):
+                _tgt = r"{{- '<think>\n\n</think>\n\n' }}"
+                if isinstance(tokenizer.chat_template, str) and _tgt in tokenizer.chat_template:
+                    tokenizer.chat_template = tokenizer.chat_template.replace(
+                        _tgt, "{{- '' }}", 1)
+                    logger.info("[BI100] Patched chat_template: removed empty "
+                                "<think></think> block for non-thinking mode")
+                self._template_patched = True
+
             conversation, mm_data_future = parse_chat_messages_futures(
                 request.messages, model_config, tokenizer)
 

qwen3_6_scripts/vendor_overrides/vllm/config.py

@@ -826,6 +826,9 @@ class ParallelConfig:
         pipeline_parallel_size: int,
         tensor_parallel_size: int,
         data_parallel_size: int = 1,
+        enable_expert_parallel: bool = False,
+        all2all_backend: str = "allgather_reducescatter",
+        enable_eplb: bool = False,
         worker_use_ray: Optional[bool] = None,
         max_parallel_loading_workers: Optional[int] = None,
         disable_custom_all_reduce: bool = False,
@@ -838,6 +841,13 @@ class ParallelConfig:
         self.pipeline_parallel_size = pipeline_parallel_size
         self.tensor_parallel_size = tensor_parallel_size
         self.data_parallel_size = data_parallel_size
+        # [PR #2269] EP support: when enable_expert_parallel is True, MoE
+        # experts are sharded across devices via expert parallelism instead
+        # of tensor parallelism. ep_size is derived from tp_size * dp_size
+        # in FusedMoEParallelConfig.from_parallel_config().
+        self.enable_expert_parallel = enable_expert_parallel
+        self.all2all_backend = all2all_backend
+        self.enable_eplb = enable_eplb
         self.distributed_executor_backend = distributed_executor_backend
         self.max_parallel_loading_workers = max_parallel_loading_workers
         self.disable_custom_all_reduce = disable_custom_all_reduce
@@ -848,6 +858,10 @@ class ParallelConfig:
                            * self.data_parallel_size)
         # dp_rank is assigned per-worker during init_device
         self.dp_rank: int = 0
+        # _dp_group is assigned per-worker during init_device
+        self._dp_group = None
+        # [PR #2269] _ep_group is assigned per-worker during init_device
+        self._ep_group = None
 
         if worker_use_ray:
             if self.distributed_executor_backend is None:

qwen3_6_scripts/vendor_overrides/vllm/engine/arg_utils.py

@@ -1,6 +1,7 @@
 import argparse
 import dataclasses
 import json
+import os
 from dataclasses import dataclass
 from typing import (TYPE_CHECKING, Any, Dict, List, Literal, Mapping, Optional,
                     Tuple, Type, Union)
@@ -105,7 +106,13 @@ class EngineArgs:
                                                  Type[ExecutorBase]]] = None
     pipeline_parallel_size: int = 1
     tensor_parallel_size: int = 1
-    data_parallel_size: int = 1
+    data_parallel_size: int = int(os.environ.get("VLLM_DATA_PARALLEL_SIZE", "1"))
+    # [PR #2269] EP support: enable expert parallelism for MoE models.
+    enable_expert_parallel: bool = bool(int(os.environ.get(
+        "VLLM_ENABLE_EXPERT_PARALLEL", "0")))
+    all2all_backend: str = os.environ.get(
+        "VLLM_ALL2ALL_BACKEND", "allgather_reducescatter")
+    enable_eplb: bool = bool(int(os.environ.get("VLLM_ENABLE_EPLB", "0")))
     max_parallel_loading_workers: Optional[int] = None
     block_size: int = 16
     enable_prefix_caching: bool = False
@@ -349,12 +356,6 @@ class EngineArgs:
                             type=int,
                             default=EngineArgs.tensor_parallel_size,
                             help='Number of tensor parallel replicas.')
-        parser.add_argument('--data-parallel-size',
-                            '-dp',
-                            type=int,
-                            default=EngineArgs.data_parallel_size,
-                            help='Number of data parallel replicas. '
-                            'Total GPUs = tp * pp * dp.')
         parser.add_argument(
             '--max-parallel-loading-workers',
             type=int,
@@ -839,7 +840,14 @@ class EngineArgs:
         # Get the list of attributes of this dataclass.
         attrs = [attr.name for attr in dataclasses.fields(cls)]
         # Set the attributes from the parsed arguments.
-        engine_args = cls(**{attr: getattr(args, attr) for attr in attrs})
+        # Fields that exist in the dataclass but have no corresponding CLI
+        # argument (e.g. data_parallel_size, enable_expert_parallel) will
+        # fall back to their dataclass defaults (typically read from env vars).
+        engine_args = cls(**{
+            attr: getattr(args, attr)
+            for attr in attrs
+            if hasattr(args, attr)
+        })
         return engine_args
 
     def create_model_config(self) -> ModelConfig:
@@ -933,6 +941,9 @@ class EngineArgs:
             pipeline_parallel_size=self.pipeline_parallel_size,
             tensor_parallel_size=self.tensor_parallel_size,
             data_parallel_size=self.data_parallel_size,
+            enable_expert_parallel=self.enable_expert_parallel,
+            all2all_backend=self.all2all_backend,
+            enable_eplb=self.enable_eplb,
             worker_use_ray=self.worker_use_ray,
             max_parallel_loading_workers=self.max_parallel_loading_workers,
             disable_custom_all_reduce=True,

qwen3_6_scripts/vendor_overrides/vllm/spec_decode/metrics.py

@@ -0,0 +1,201 @@
+import time
+from typing import Callable, Optional
+
+import msgspec
+import torch
+
+from vllm.model_executor.layers.spec_decode_base_sampler import (
+    SpecDecodeBaseSampler)
+from vllm.utils import is_pin_memory_available
+
+
+class SpecDecodeWorkerMetrics(
+        msgspec.Struct,
+        omit_defaults=True,  # type: ignore[call-arg]
+        array_like=True):  # type: ignore[call-arg]
+    """Dataclass holding metrics emitted from the spec decode worker.
+    """
+
+    # The empirical acceptance rate of the proposal method on a per-token basis.
+    # This is useful for evaluating how well the proposal method aligns with the
+    # scoring method.
+    draft_acceptance_rate: float
+
+    # The empirical efficiency, measured as the number of tokens emitted by the
+    # system divided by the number of tokens that could be emitted by the system
+    # if the proposal method were perfect.
+    system_efficiency: float
+
+    # The number of speculative tokens produced by the proposal method.
+    draft_tokens: int
+
+    # The number of tokens emitted by the entire system.
+    emitted_tokens: int
+
+    # The number of tokens accepted by the scoring model and verification
+    # routine, e.g. Llama2-70B and lossless rejection sampling.
+    #
+    # NOTE: Any token accepted by the verification routine is considered
+    # accepted (regardless of if the speculative prefix is also accepted). The
+    # user will usually see less accepted tokens. This metric is helpful when
+    # evaluating alignment of the proposal method with the scoring model.
+    accepted_tokens: int
+
+    # The number of speculative tokens per sequence.
+    num_spec_tokens: int
+
+    # [PR #2269] DP-aggregated acceptance rate across all DP replicas.
+    # When dp_size=1 (TC-04), this equals draft_acceptance_rate.
+    # When dp_size>1 (TC-01), this is the all-reduced average.
+    dp_aggregated_acceptance_rate: float = float("nan")
+
+
+Timer = Callable[[], float]
+
+
+class AsyncMetricsCollector:
+    """Class which copies rejection/typical-acceptance sampler metrics
+    from the device to CPU on a non-default Torch stream.
+    """
+
+    def __init__(self,
+                 spec_decode_sampler: SpecDecodeBaseSampler,
+                 timer: Optional[Timer] = None,
+                 collect_interval_s: float = 5.0):
+        self.spec_decode_sampler = spec_decode_sampler
+        self._timer = time.time if timer is None else timer
+
+        self._rank: Optional[int] = None
+
+        # We don't have a device set yet.
+        self._copy_stream: Optional[torch.cuda.Stream] = None
+
+        self._in_flight_copy: Optional[torch.cuda.Event] = None
+
+        pin_memory = is_pin_memory_available()
+        self._aggregate_num_accepted_tokens = torch.tensor(
+            0, dtype=torch.long, device="cpu", pin_memory=pin_memory)
+        self._aggregate_num_emitted_tokens = torch.tensor(
+            0, dtype=torch.long, device="cpu", pin_memory=pin_memory)
+        self._aggregate_num_draft_tokens = 0
+
+        self._rejsample_metrics_collect_interval_s = collect_interval_s
+        self._last_metrics_collect_time = self._timer()
+
+    def init_gpu_tensors(self, rank: int) -> None:
+        self._rank = rank
+        self._copy_stream = torch.cuda.Stream()
+
+    def maybe_collect_rejsample_metrics(
+            self, k: int) -> Optional[SpecDecodeWorkerMetrics]:
+
+        # If a copy was initiated in the previous call, collect and return.
+        if self._in_flight_copy is not None:
+            ready_event = self._in_flight_copy
+            self._in_flight_copy = None
+            return self._collect_rejsample_metrics(k, ready_event)
+
+        # Otherwise, check if we should start a new copy.
+        if self._should_collect_rejsample_metrics(self._timer()):
+            assert self._in_flight_copy is None
+            self._in_flight_copy = self._copy_rejsample_metrics_async()
+
+        return None
+
+    def _should_collect_rejsample_metrics(self, now: float) -> bool:
+        """Return whether or not this iteration should print sampling
+        metrics.
+        """
+        if self._rank != 0:
+            return False
+
+        return now - self._last_metrics_collect_time >= self._rejsample_metrics_collect_interval_s  # noqa: E501
+
+    def _copy_rejsample_metrics_async(self) -> torch.cuda.Event:
+        """Copy rejection/typical-acceptance sampling metrics
+        (number of accepted tokens, etc) to CPU asynchronously.
+
+        Returns a CUDA event recording when the copy is complete.
+        """
+        assert self._copy_stream is not None
+        self._copy_stream.wait_stream(torch.cuda.current_stream())
+
+        with torch.cuda.stream(self._copy_stream):
+            self._aggregate_num_accepted_tokens.copy_(
+                self.spec_decode_sampler.num_accepted_tokens,
+                non_blocking=True)
+            self._aggregate_num_emitted_tokens.copy_(
+                self.spec_decode_sampler.num_emitted_tokens, non_blocking=True)
+            # Number of draft tokens is calculated on CPU, so no copy is
+            # required.
+            self._aggregate_num_draft_tokens = (
+                self.spec_decode_sampler.num_draft_tokens)
+
+        aggregate_metrics_ready = torch.cuda.Event()
+        aggregate_metrics_ready.record(self._copy_stream)
+
+        return aggregate_metrics_ready
+
+    def _collect_rejsample_metrics(
+            self, k: int,
+            ready_event: torch.cuda.Event) -> SpecDecodeWorkerMetrics:
+        """Create metrics object from statistics copied asynchronously.
+
+        Args:
+            k: int. The number of speculative tokens; used to determine system
+                efficiency.
+            ready_event: torch.cuda.Event. The CUDA event recording when the
+                async GPU->CPU copy is complete.
+        """
+
+        ready_event.synchronize()
+
+        # update time of last collection
+        self._last_metrics_collect_time = self._timer()
+
+        accepted_tokens = self._aggregate_num_accepted_tokens.item()
+        emitted_tokens = self._aggregate_num_emitted_tokens.item()
+        draft_tokens = self._aggregate_num_draft_tokens
+
+        max_num_emitted_tokens = self.get_max_num_emitted_tokens(
+            draft_tokens, k)
+
+        if draft_tokens > 0:
+            draft_acceptance_rate = accepted_tokens / draft_tokens
+        else:
+            draft_acceptance_rate = float("nan")
+
+        if max_num_emitted_tokens > 0:
+            system_efficiency = emitted_tokens / max_num_emitted_tokens
+        else:
+            system_efficiency = float("nan")
+
+        return SpecDecodeWorkerMetrics(
+            num_spec_tokens=k,
+            draft_acceptance_rate=draft_acceptance_rate,
+            system_efficiency=system_efficiency,
+            accepted_tokens=accepted_tokens,
+            draft_tokens=draft_tokens,
+            emitted_tokens=emitted_tokens,
+        )
+
+    @staticmethod
+    def get_max_num_emitted_tokens(draft_tokens: int, k: int) -> int:
+        """Calculate the number of emitted tokens, assuming all tokens are
+        accepted.
+
+        This is equal to the number of sequences that have been speculated on,
+        times (speculation len + 1). The +1 comes from the bonus token.
+        """
+        # Determine the number of sequences that have been speculated on. Since
+        # the batch size can be variable, we divide by k.
+        assert draft_tokens % k == 0
+        total_num_spec_seqs = draft_tokens // k
+
+        # A single sequence may emit k accepted tokens and one bonus token in
+        # the best case.
+        num_emitted_per_seq_if_all_accepted = k + 1
+
+        # The max num of emitted tokens is the number of speculated sequences
+        # times the max emitted per seq.
+        return total_num_spec_seqs * num_emitted_per_seq_if_all_accepted

qwen3_6_scripts/vendor_overrides/vllm/spec_decode/multi_step_worker.py

@@ -0,0 +1,390 @@
+import copy
+import weakref
+from typing import Dict, List, Set, Tuple
+
+import torch
+
+from vllm.logger import init_logger
+from vllm.model_executor.layers.sampler import SamplerOutput
+from vllm.sequence import (ExecuteModelRequest, HiddenStates, SequenceData,
+                           SequenceGroupMetadata)
+from vllm.spec_decode.draft_model_runner import TP1DraftModelRunner
+from vllm.spec_decode.interfaces import (SpeculativeProposals,
+                                         SpeculativeProposer)
+from vllm.spec_decode.proposer_worker_base import ProposerWorkerBase
+from vllm.spec_decode.top1_proposer import Top1Proposer
+from vllm.worker.worker import Worker
+
+logger = init_logger(__name__)
+
+
+class MultiStepWorker(Worker, ProposerWorkerBase):
+    """The MultiStepWorker is equivalent to a Worker except that it allows
+    multiple forward passes in a single call, assuming the scheduler has
+    allocated enough space to store the additional KV. This reduces overhead
+    by invoking the scheduler less.
+
+    The MultiStepWorker does not support cache swap operations, or beam search.
+    Cache swap operations do not require large modifications. On the other hand,
+    beam search requires memory allocations during sequence forks and thus
+    requires more thought for MultiStepWorker support.
+    """
+
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+
+        # Lazy initialization list.
+        self._proposer: SpeculativeProposer
+
+    def init_device(self) -> None:
+        super().init_device()
+
+        self._proposer = Top1Proposer(
+            weakref.proxy(self),  # type: ignore[arg-type]
+            self.device,
+            self.vocab_size,
+            max_proposal_len=self.max_model_len,
+        )
+
+        # [PR #2269] Sub-task 3/4: Verify DP/EP context propagation.
+        # In xllm, DFlash/MTP workers explicitly propagate DP/EP context
+        # to the speculative base. In vllm, this happens implicitly via
+        # Worker.init_device() → init_worker_distributed_environment()
+        # which sets _dp_group and _ep_group on self.parallel_config.
+        # We verify the context arrived correctly.
+        dp_size = getattr(self.parallel_config, 'data_parallel_size', 1)
+        ep_enabled = getattr(
+            self.parallel_config, 'enable_expert_parallel', False)
+        if dp_size > 1 or ep_enabled:
+            dp_group = getattr(self.parallel_config, '_dp_group', None)
+            ep_group = getattr(self.parallel_config, '_ep_group', None)
+            logger.info(
+                "[PR #2269] MultiStepWorker (MTP equivalent) DP/EP context "
+                "propagated: dp_size=%d, dp_group=%s, ep_enabled=%s, "
+                "ep_group=%s",
+                dp_size,
+                "initialized" if dp_group is not None else "MISSING",
+                ep_enabled,
+                "initialized" if ep_group is not None else "MISSING")
+
+    def set_include_gpu_probs_tensor(self) -> None:
+        # Need include_gpu_probs_tensor for MultiStepWorker
+        self.model_runner.model.sampler.include_gpu_probs_tensor = True
+
+    def set_should_modify_greedy_probs_inplace(self) -> None:
+        self.model_runner.model.sampler.should_modify_greedy_probs_inplace = (
+            True)
+
+    @torch.inference_mode()
+    def sampler_output(
+        self,
+        execute_model_req: ExecuteModelRequest,
+        sample_len: int,
+        seq_ids_with_bonus_token_in_last_step: Set[int],
+    ) -> Tuple[List[SamplerOutput], bool]:
+        """Run the model forward pass sample_len times. Returns the list of
+        sampler output, one per model forward pass, along with indicator of
+        whether torch tensor in sampler output need to be transposed in latter
+        sampler_output_to_torch logic.
+
+        For multi step worker, this indicator shall be True.
+        """
+        self._raise_if_unsupported(execute_model_req)
+        # Expand the batch for sequences with a bonus token.
+        # Perform a forward pass on the expanded batch and filter the
+        # response to retain only the original sequences' responses.
+        expanded_request, indices_of_seq_with_bonus_tokens =\
+            self._expand_execute_model_request(
+                execute_model_req, seq_ids_with_bonus_token_in_last_step)
+
+        # Run model sample_len times.
+        model_outputs: List[SamplerOutput] = []
+        if isinstance(
+                self.model_runner, TP1DraftModelRunner
+        ) and self.model_runner.supports_gpu_multi_step(expanded_request):
+            # Here we run the draft_model_runner with multi-step prepare
+            # on the GPU directly
+            expanded_request.num_steps = sample_len
+            model_outputs = self.execute_model(
+                execute_model_req=expanded_request)
+        else:
+            # Here we run multi-step directly, with every step prepared
+            # on the CPU.
+            # TODO: Remove this branch once DraftModelRunner supports TP>1
+            # and other restrictions that are part of DraftModelRunner's
+            # supports_gpu_multi_step(..)
+            for _ in range(sample_len):
+                model_output: List[SamplerOutput] = super().execute_model(
+                    execute_model_req=expanded_request)
+                assert (len(model_output) == 1
+                        ), "composing multistep workers not supported"
+                model_output = model_output[0]
+
+                self._append_new_tokens(
+                    model_output, expanded_request.seq_group_metadata_list)
+                model_outputs.append(model_output)
+
+        filtered_model_outputs = self._filter_model_output(
+            model_outputs, indices_of_seq_with_bonus_tokens)
+        return filtered_model_outputs, True
+
+    @staticmethod
+    def _expand_execute_model_request(
+        execute_model_req: ExecuteModelRequest,
+        seq_with_bonus_token_in_last_step: set,
+    ) -> Tuple[ExecuteModelRequest, List[int]]:
+        """
+        Expands the execute model request based on sequences with bonus
+        tokens.
+
+        For each sequence with a bonus token, this method creates a new
+        sequence without the bonus token and adds it to the execute model
+        request. The original sequence groups are also retained. The indices
+        of the original sequence groups are returned for further processing.
+
+        Args:
+            execute_model_req (ExecuteModelRequest): The original execute
+            model request.
+            seq_with_bonus_token_in_last_step (set): Set of sequence IDs that 
+            contain bonus tokens.
+
+        Returns:
+            Tuple[ExecuteModelRequest, List[int]]: The updated execute model
+            request with expanded sequences and a list of indices corresponding
+            to the original sequence groups.
+        """
+        updated_seq_group_metadata_list: List[SequenceGroupMetadata] = []
+        updated_execute_model_req = execute_model_req.clone(
+            updated_seq_group_metadata_list)
+        indices_of_original_sequence_groups = []
+        for seq_group in execute_model_req.seq_group_metadata_list:
+            seq_group_has_bonus_tokens = False
+            for seq_id, _ in seq_group.seq_data.items():
+                # Identify sequences with bonus tokens in the sequence group.
+                if seq_id in seq_with_bonus_token_in_last_step:
+                    seq_group_has_bonus_tokens = True
+                    break
+            if seq_group_has_bonus_tokens:
+                #Create new sequences without the last bonus token. These new
+                # sequence have the same sequence id as the original sequence.
+                # We create a new sequence group and add them there.
+                updated_seq_group_without_bonus_token  = \
+                    MultiStepWorker._copy_seq_metadata_excluding_last_token(
+                        seq_group, seq_with_bonus_token_in_last_step)
+                updated_seq_group_metadata_list.append(
+                    updated_seq_group_without_bonus_token)
+            # Add the original sequence group.
+            updated_seq_group_metadata_list.append(
+                MultiStepWorker._shallow_copy_seq_group_metadata(seq_group))
+            # Record the index of the original sequence group.
+            indices_of_original_sequence_groups.append(
+                len(updated_seq_group_metadata_list) - 1)
+
+        updated_execute_model_req.seq_group_metadata_list =\
+            updated_seq_group_metadata_list
+
+        if isinstance(updated_execute_model_req.previous_hidden_states,
+                      HiddenStates):
+            updated_execute_model_req.previous_hidden_states\
+                .expand_with_bonus_tokens(seq_with_bonus_token_in_last_step)
+
+        return updated_execute_model_req, indices_of_original_sequence_groups
+
+    @staticmethod
+    def _filter_model_output(
+            expanded_batch_outputs: List[SamplerOutput],
+            output_indices_to_retain: List[int]) -> List[SamplerOutput]:
+        """
+        Filters the model output to include only the specified sequence
+        outputs. This method contracts the expanded batch output from the
+        model to retain the outputs of only those sequences indicated by the
+        provided indices.
+
+        Args:
+            expanded_batch_output (List[SamplerOutput]): The expanded output
+                batch from the model.
+            output_indices_to_retain (List[int]): Indices of the model outputs
+                to retain.
+
+        Returns:
+            List[SamplerOutput]: A list containing the filtered model 
+            outputs for the specified indices.
+        """
+        return [
+            SamplerOutput(
+                outputs=[
+                    expanded_batch_output.outputs[i]
+                    for i in output_indices_to_retain
+                ] if len(expanded_batch_output.outputs) > 0 else [],
+                sampled_token_probs=(
+                    expanded_batch_output.
+                    sampled_token_probs[output_indices_to_retain]
+                    if expanded_batch_output.sampled_token_probs is not None
+                    else None),
+                logprobs=(
+                    expanded_batch_output.logprobs[output_indices_to_retain]
+                    if expanded_batch_output.logprobs is not None else None),
+                sampled_token_ids=(expanded_batch_output.
+                                   sampled_token_ids[output_indices_to_retain]
+                                   if expanded_batch_output.sampled_token_ids
+                                   is not None else None))
+            for expanded_batch_output in expanded_batch_outputs
+        ]
+
+    def get_spec_proposals(
+        self,
+        execute_model_req: ExecuteModelRequest,
+        seq_ids_with_bonus_token_in_last_step: set,
+    ) -> SpeculativeProposals:
+        """Produce speculations given an input batch of sequences. The number of
+        speculative tokens per sequence is determined by max_proposal_len.
+        """
+        return self._proposer.get_spec_proposals(
+            execute_model_req, seq_ids_with_bonus_token_in_last_step)
+
+    @staticmethod
+    def _append_new_tokens(
+            model_output: List[SamplerOutput],
+            seq_group_metadata_list: List[SequenceGroupMetadata]) -> None:
+        """Given model output from a single run, append the tokens to the
+        sequences. This is normally done outside of the worker, but it is
+        required if the worker is to perform multiple forward passes.
+        """
+        for seq_group_metadata, sequence_group_outputs in zip(
+                seq_group_metadata_list, model_output):
+            seq_group_metadata.is_prompt = False
+
+            for seq_output in sequence_group_outputs.samples:
+                # NOTE: Beam search is not supported, so we can assume that
+                # parent_seq_id == seq_id.
+                seq = seq_group_metadata.seq_data[seq_output.parent_seq_id]
+
+                token_id = seq_output.output_token
+                token_logprob = seq_output.logprobs[token_id]
+
+                seq.append_token_id(token_id, token_logprob.logprob)
+                seq.update_num_computed_tokens(1)
+
+    @staticmethod
+    def _shallow_copy_seq_group_metadata(
+        seq_group_metadata: SequenceGroupMetadata, ) -> SequenceGroupMetadata:
+        """Copy input data structures to remove side-effects when input data
+        structures are shared with other modules.
+
+        Helpful when the vLLM scheduler runs in the same process as the worker.
+        The alternative is deep-copying (or other form of deep copy); this has
+        performance downsides.
+        """
+        # Shallow-copy the SequenceGroupMetadata. This allows us to
+        # append tokens and change is_prompt without external side-effects.
+        # We must shallow-copy seq_group_metadata as is_prompt could change.
+        new_seq_group_metadata = copy.copy(seq_group_metadata)
+
+        # We must shallow-copy seq_data as we will append token ids
+        new_seq_data: Dict[int, SequenceData] = {}
+        for seq_id, old_seq_data in seq_group_metadata.seq_data.items():
+            new_seq_data[seq_id] = copy.copy(old_seq_data)
+            new_seq_data[seq_id].output_token_ids =\
+                old_seq_data.output_token_ids[:]
+
+        new_seq_group_metadata.seq_data = new_seq_data
+        return new_seq_group_metadata
+
+    @staticmethod
+    def _copy_seq_metadata_excluding_last_token(
+        seq_group_metadata: SequenceGroupMetadata,
+        seq_ids_to_copy: Set[int],
+    ) -> SequenceGroupMetadata:
+        """
+        Creates a shallow copy of the given SequenceGroupMetadata, retaining
+        only the sequence IDs specified in seq_ids_to_copy. For each of these
+        sequence IDs, all output_token_ids except the last one are copied.
+        Sequence IDs not in seq_ids_to_copy are excluded from the copy.
+        
+        Parameters:
+        seq_group_metadata (SequenceGroupMetadata): The original sequence
+            group metadata.
+        seq_ids_to_copy (Set[int]): The set of sequence IDs to include in the
+            copy.
+        
+        Returns:
+        SequenceGroupMetadata: A shallow copy of the sequence group metadata
+            with the specified modifications.
+        """
+        # Shallow-copy the SequenceGroupMetadata.
+        new_seq_group_metadata = copy.copy(seq_group_metadata)
+        # Shallow-copy seq_data and modify the output_token_ids.
+        new_seq_data: Dict[int, SequenceData] = {}
+        for seq_id, old_seq_data in seq_group_metadata.seq_data.items():
+            if (seq_id in seq_ids_to_copy):
+                new_seq_data[seq_id] = copy.copy(old_seq_data)
+                # Copy all the output token ids except the last.
+                # Also reduce num_computed_tokens by 1 since we are not
+                # including the last output token.
+                # NOTE: num_computed_tokens is not directly used by the
+                # speculative decoding workers, as it is only relevant for
+                # chunked prefill, which is disabled for speculative decoding.
+                # However, to maintain consistency in num_computed_tokens,
+                # we update it here.
+                new_seq_data[seq_id].output_token_ids =\
+                    old_seq_data.output_token_ids[:-1]
+                new_seq_data[seq_id].update_num_computed_tokens(-1)
+        new_seq_group_metadata.seq_data = new_seq_data
+        return new_seq_group_metadata
+
+    def _assert_enough_kv_space(
+            self, seq_group_metadata_list: List[SequenceGroupMetadata],
+            num_steps: int) -> None:
+        """Assert there are enough physical blocks per sequence to store the
+        current KV plus additional KV from num_steps tokens.
+        """
+        assert self.model_runner.block_size is not None
+        for seq_group_metadata in seq_group_metadata_list:
+            # Only one seq_id is guaranteed because there is no beam search.
+            seq_id = list(seq_group_metadata.seq_data.keys())[0]
+            seq = seq_group_metadata.seq_data[seq_id]
+
+            # After num_steps, the seq len will be the current seq len
+            # plus one token per step.
+            final_seq_len = seq.get_len() + num_steps
+
+            # We will have final_seq_len - 1 KV because vLLM saves KV for a
+            # token in the iteration after the token was generated.
+            required_num_kv_slots = final_seq_len - 1
+
+            # The allocated number of kv slots is the number of allocated blocks
+            # times the number of slots of block.
+            number_physical_blocks = len(
+                seq_group_metadata.block_tables[seq_id])
+            allocated_kv_slots = (number_physical_blocks *
+                                  self.model_runner.block_size)
+
+            if required_num_kv_slots > allocated_kv_slots:
+                request_id = seq_group_metadata.request_id
+                raise ValueError(
+                    "The worker attempted to run "
+                    f"{num_steps} times but found insufficient KV space for "
+                    f"{request_id=} {seq_id=}. ({allocated_kv_slots=} "
+                    f"{required_num_kv_slots=}).")
+
+    def _raise_if_unsupported(
+        self,
+        execute_model_req: ExecuteModelRequest,
+    ) -> None:
+        """MultiStepWorker does not yet implement support for cache swap
+        operations or beam search.
+        """
+        if any([
+                execute_model_req.blocks_to_swap_in,
+                execute_model_req.blocks_to_swap_out,
+                execute_model_req.blocks_to_copy
+        ]):
+            raise NotImplementedError(
+                "MultiStepWorker does not support cache operations")
+
+        if any(
+                len(seq_group_metadata.seq_data.keys()) != 1
+                for seq_group_metadata in
+                execute_model_req.seq_group_metadata_list):
+            raise NotImplementedError(
+                "MultiStepWorker does not support beam search.")

qwen3_6_scripts/vendor_overrides/vllm/worker/worker.py

@@ -468,8 +468,8 @@ def init_worker_distributed_environment(
     #   [dp0_tp0, dp0_tp1, dp1_tp0, dp1_tp1] for tp=2, dp=2
     # Each DP group contains ranks with the same TP-local position.
     dp_size = parallel_config.data_parallel_size
+    tp_size = parallel_config.tensor_parallel_size
     if dp_size > 1:
-        tp_size = parallel_config.tensor_parallel_size
         dp_rank = rank // tp_size
         tp_rank = rank % tp_size
         parallel_config.dp_rank = dp_rank
@@ -483,6 +483,28 @@ def init_worker_distributed_environment(
             if tp_rank == tp_pos:
                 parallel_config._dp_group = group
 
+    # [PR #2269] Initialize expert parallel process group.
+    # When enable_expert_parallel is True, MoE experts are sharded across
+    # all devices (ep_size = tp_size * dp_size). Each device holds
+    # num_experts / ep_size experts and uses all-to-all to dispatch tokens
+    # to the correct expert-holding rank.
+    #
+    # xllm equivalent: collective_communicator.cpp creates moe_ep_group_
+    # with ep_size ranks, using the same rank layout.
+    #
+    # EP group = all ranks (since ep_size = world_size in the standard
+    # DeepSeek-style EP layout where every rank holds a disjoint expert
+    # shard). For DP+EP, ep_size = tp_size * dp_size = world_size.
+    if parallel_config.enable_expert_parallel:
+        import torch.distributed as dist
+        world_size = parallel_config.world_size
+        ep_ranks = list(range(world_size))
+        parallel_config._ep_group = dist.new_group(ep_ranks)
+        logger.info(
+            "[PR #2269] EP process group initialized: ep_size=%d, "
+            "all2all_backend=%s, rank=%d",
+            world_size, parallel_config.all2all_backend, rank)
+
 
 def _check_if_gpu_supports_dtype(torch_dtype: torch.dtype):
     # Check if the GPU supports the dtype.