[Bugfix] Handle `process_weights_after_loading` for `QKVCrossParallelLinear` (#15328)

Signed-off-by: Isotr0py <2037008807@qq.com>

vllm/model_executor/layers/linear.py

@@ -1353,6 +1353,7 @@ class QKVCrossParallelLinear(LinearBase):
             prefix=f"{prefix}.kv_proj_encoder")
 
         # `kv_proj_encoder.num_kv_heads` accounts for sharding with tp>1.
+        self.q_size = self.q_proj_decoder.output_size_per_partition
         self.kv_size = self.kv_proj_encoder.num_kv_heads * head_size
 
         if bias:
@@ -1364,20 +1365,31 @@ class QKVCrossParallelLinear(LinearBase):
         else:
             self.bias = None
 
+    def process_weights_after_loading(self):
+        for layer in self.proj.values():
+            if self.quant_method is not None:
+                self.quant_method.process_weights_after_loading(layer)
+
     @property
     def q_proj_decoder(self) -> ColumnParallelLinear:
         layer = self.proj["q_proj_decoder"]
         for name, param in self.named_parameters():
-            target_param = getattr(layer, name)
-            self.sync_weight_attrs(param, target_param, mode="q_proj_decoder")
+            target_param = getattr(layer, name, None)
+            if target_param is not None:
+                self.sync_weight_attrs(param,
+                                       target_param,
+                                       mode="q_proj_decoder")
         return layer
 
     @property
     def kv_proj_encoder(self) -> QKVParallelLinear:
         layer = self.proj["kv_proj_encoder"]
         for name, param in self.named_parameters():
-            target_param = getattr(layer, name)
-            self.sync_weight_attrs(param, target_param, mode="kv_proj_encoder")
+            target_param = getattr(layer, name, None)
+            if target_param is not None:
+                self.sync_weight_attrs(param,
+                                       target_param,
+                                       mode="kv_proj_encoder")
         return layer
 
     def sync_weight_attrs(
@@ -1466,11 +1478,14 @@ class QKVCrossParallelLinear(LinearBase):
                  if loaded_shard_id == "q" else self.kv_proj_encoder)
         target_param = self.select_proj_params(layer, param)
         shard_id_args = (loaded_shard_id, ) if loaded_shard_id != "q" else ()
-        layer.weight_loader(target_param, loaded_weight, *shard_id_args)
+        if self.quant_method.__class__.__name__ in WEIGHT_LOADER_V2_SUPPORTED:
+            layer.weight_loader_v2(target_param, loaded_weight, *shard_id_args)
+        else:
+            layer.weight_loader(target_param, loaded_weight, *shard_id_args)
 
     def extra_repr(self) -> str:
         s = f"in_features={self.input_size}"
-        s += f", q_size={self.q_proj_decoder.output_size_per_partition}"
+        s += f", q_size={self.q_size}"
         s += f", kv_size={self.kv_size}"
         s += f", bias={self.bias is not None}"
         s += f", tp_size={get_tensor_model_parallel_world_size()}"

vllm/model_executor/layers/quantization/fp8.py

@@ -254,6 +254,7 @@ class Fp8LinearMethod(LinearMethodBase):
                     weight_loader=weight_loader,
                 )
                 scale[:] = torch.finfo(torch.float32).min
+                set_weight_attrs(scale, {"scale_type": "weight_scale"})
                 layer.register_parameter("weight_scale", scale)
             else:
                 assert self.quant_config.activation_scheme == "dynamic"
@@ -268,6 +269,7 @@ class Fp8LinearMethod(LinearMethodBase):
                     weight_loader=weight_loader,
                 )
                 scale[:] = torch.finfo(torch.float32).min
+                set_weight_attrs(scale, {"scale_type": "weight_scale"})
                 # The weight_scale_inv name is intentional for deepseekv3
                 layer.register_parameter("weight_scale_inv", scale)
 
@@ -278,6 +280,7 @@ class Fp8LinearMethod(LinearMethodBase):
                                                 weight_loader=weight_loader)
 
                 scale[:] = torch.finfo(torch.float32).min
+                set_weight_attrs(scale, {"scale_type": "input_scale"})
                 layer.register_parameter("input_scale", scale)
             else:
                 layer.register_parameter("input_scale", None)

vllm/model_executor/model_loader/loader.py

@@ -33,11 +33,15 @@ from vllm.distributed import (get_tensor_model_parallel_rank,
                               get_tensor_model_parallel_world_size)
 from vllm.envs import VLLM_USE_MODELSCOPE
 from vllm.logger import init_logger
+# yapf conflicts with isort for this block
+# yapf: disable
 from vllm.model_executor.layers.linear import (LinearBase,
                                                MergedColumnParallelLinear,
+                                               QKVCrossParallelLinear,
                                                QKVParallelLinear,
                                                ReplicatedLinear,
                                                RowParallelLinear)
+# yapf: enable
 from vllm.model_executor.layers.quantization.base_config import (
     QuantizeMethodBase)
 from vllm.model_executor.model_loader.tensorizer import (
@@ -160,6 +164,11 @@ def _initialize_model(
 def _process_weights_after_loading(model: nn.Module, model_config: ModelConfig,
                                    target_device: torch.device) -> None:
     for _, module in model.named_modules():
+        if isinstance(module, QKVCrossParallelLinear):
+            # NOTE(Isotr0py): special case for cross QKV layer because
+            # q and kv proj aren't registered as submodules intentionally
+            module.process_weights_after_loading()
+            continue
         quant_method = getattr(module, "quant_method", None)
         if isinstance(quant_method, QuantizeMethodBase):
             # When quant methods need to process weights after loading