[AMD] move shared expert check function to quark

python/sglang/srt/layers/quantization/quark/quark.py

@@ -37,6 +37,18 @@
 
 logger = logging.getLogger(__name__)
 
+_MOE_SHARED_EXPERT_QUANT_LAYER0_BASES: tuple[str, ...] = (
+    "model.layers.0",
+    "model.language_model.layers.0",
+)
+
+_SHARED_EXPERT_BODY_PROJ_SUFFIXES: tuple[str, ...] = (
+    "gate_proj",
+    "up_proj",
+    "gate_up_proj",
+    "down_proj",
+)
+
 
 class QuarkConfig(QuantizationConfig):
 
@@ -492,6 +504,38 @@ def get_moe_scheme(
     def get_scaled_act_names(self) -> List[str]:
         return []
 
+    def can_fuse_shared_expert(self) -> bool:
+        # Shared-expert body excluded from quant; the gate must not veto fusion.
+        if any(
+            "shared_expert" in layer
+            and "shared_expert_gate" not in layer
+            and not layer.startswith("mtp.")
+            for layer in self.exclude_layers
+        ):
+            return False
+
+        # No per-layer config -> uniform spec, nothing to compare.
+        layer_quant_config = self.quant_config.get("layer_quant_config") or {}
+        if not layer_quant_config:
+            return True
+
+        # Compare routed vs shared specs at layer 0 (stub module needed by
+        # _find_matched_config; an unmatched name -> ValueError -> cannot fuse).
+        lookup_stub = torch.nn.Module()
+        try:
+            for base in _MOE_SHARED_EXPERT_QUANT_LAYER0_BASES:
+                moe_name = f"{base}.mlp.experts"
+                moe_cfg = self._find_matched_config(moe_name, lookup_stub)
+                for suffix in _SHARED_EXPERT_BODY_PROJ_SUFFIXES:
+                    shared_name = f"{base}.mlp.shared_expert.{suffix}"
+                    shared_cfg = self._find_matched_config(shared_name, lookup_stub)
+                    if not deep_compare(moe_cfg, shared_cfg):
+                        return False
+        except ValueError:
+            return False
+
+        return True
+
 
 class QuarkLinearMethod(LinearMethodBase):
 

python/sglang/srt/models/qwen2_moe.py

@@ -156,20 +156,17 @@ def can_fuse_shared_expert(
     ):
         return False
 
-    # If the shared expert is excluded from quantization (stored as FP32 in the
-    # checkpoint), fusing it into the quantized MoE weight tensor requires online
-    # quantization which is not supported. Disable fusion in this case.
     if quant_config is not None:
         exclude_layers = getattr(quant_config, "exclude_layers", None)
         if exclude_layers is None:
             exclude_layers = getattr(quant_config, "ignored_layers", [])
-        if any(
-            "shared_expert" in layer
-            and "shared_expert_gate" not in layer
-            and not layer.startswith("mtp.")
-            for layer in exclude_layers
-        ):
-            return False
+
+        # Other backends than quark do not exclude the shared expert here, so they
+        # intentionally fall through and remain fusable
+        can_fuse_fn = getattr(quant_config, "can_fuse_shared_expert", None)
+        if can_fuse_fn is not None:
+            if not can_fuse_fn():
+                return False
 
     return True
 

python/sglang/srt/models/qwen3_5.py

@@ -80,7 +80,11 @@
     default_weight_loader,
     sharded_weight_loader,
 )
-from sglang.srt.models.qwen2_moe import Qwen2MoeMLP, Qwen2MoeSparseMoeBlock
+from sglang.srt.models.qwen2_moe import (
+    Qwen2MoeMLP,
+    Qwen2MoeSparseMoeBlock,
+    can_fuse_shared_expert,
+)
 
 # Models
 from sglang.srt.models.qwen3_vl import Qwen3VLForConditionalGeneration
@@ -1117,6 +1121,21 @@ def get_hidden_dim(self, module_name: str, layer_idx: int):
                 f"get_hidden_dim not implemented for {module_name}"
             )
 
+    def _maybe_autodisable_shared_experts_fusion(self, config, quant_config):
+        # Auto-disable fusion when the checkpoint can't fuse (e.g. MXFP4 Qwen3.5)
+        # so the model still gets the #25885 multi-streaming path. ROCm-only.
+        server_args = get_global_server_args()
+        if (
+            config.model_type == "qwen3_5_moe_text"
+            and not server_args.disable_shared_experts_fusion
+            and not can_fuse_shared_expert(config, quant_config)
+        ):
+            server_args.disable_shared_experts_fusion = True
+            logger.info(
+                "Qwen3.5: shared-expert fusion not supported for this checkpoint; "
+                "auto-disabling (multi-streaming #25885 still applies)."
+            )
+
     def __init__(
         self,
         config: Qwen3_5TextConfig,
@@ -1129,6 +1148,9 @@ def __init__(
         self.hidden_size = config.hidden_size
         self.pp_group = get_pp_group()
 
+        if _is_hip:
+            self._maybe_autodisable_shared_experts_fusion(config, quant_config)
+
         alt_stream = torch.cuda.Stream() if _is_cuda or _hip_use_alt_stream else None
 
         # Embedding layer