[Kernel] Centralize platform kernel import in `current_platform.import_kernels` (#26286)

Signed-off-by: NickLucche <nlucches@redhat.com>

vllm/_custom_ops.py

@@ -12,8 +12,7 @@ from vllm.scalar_type import ScalarType
 
 logger = init_logger(__name__)
 
-current_platform.import_core_kernels()
-supports_moe_ops = current_platform.try_import_moe_kernels()
+current_platform.import_kernels()
 
 if TYPE_CHECKING:
 
@@ -1921,7 +1920,7 @@ def moe_wna16_marlin_gemm(
     )
 
 
-if supports_moe_ops and hasattr(torch.ops._moe_C, "marlin_gemm_moe"):
+if hasattr(torch.ops, "_moe_C") and hasattr(torch.ops._moe_C, "marlin_gemm_moe"):
 
     @register_fake("_moe_C::marlin_gemm_moe")
     def marlin_gemm_moe_fake(

vllm/platforms/interface.py

@@ -170,22 +170,15 @@ class Platform:
             return device_id
 
     @classmethod
-    def import_core_kernels(cls) -> None:
+    def import_kernels(cls) -> None:
         """Import any platform-specific C kernels."""
         try:
             import vllm._C  # noqa: F401
         except ImportError as e:
             logger.warning("Failed to import from vllm._C: %r", e)
-
-    @classmethod
-    def try_import_moe_kernels(cls) -> bool:
-        """Import any platform-specific MoE kernels."""
         with contextlib.suppress(ImportError):
             import vllm._moe_C  # noqa: F401
 
-            return True
-        return False
-
     @classmethod
     def get_vit_attn_backend(cls, head_size: int, dtype: torch.dtype) -> "_Backend":
         from vllm.attention.backends.registry import _Backend

vllm/platforms/tpu.py

 # SPDX-License-Identifier: Apache-2.0
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
 
+import contextlib
 from typing import TYPE_CHECKING, Optional, Union, cast
 
 import torch
@@ -45,8 +46,10 @@ class TpuPlatform(Platform):
     additional_env_vars: list[str] = ["TPU_CHIPS_PER_HOST_BOUNDS", "TPU_HOST_BOUNDS"]
 
     @classmethod
-    def import_core_kernels(cls) -> None:
-        pass
+    def import_kernels(cls) -> None:
+        # Do not import vllm._C
+        with contextlib.suppress(ImportError):
+            import vllm._moe_C  # noqa: F401
 
     @classmethod
     def get_attn_backend_cls(

vllm/platforms/xpu.py

 # SPDX-License-Identifier: Apache-2.0
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
 
+import contextlib
 import os
 from typing import TYPE_CHECKING, Optional
 
@@ -35,8 +36,10 @@ class XPUPlatform(Platform):
     device_control_env_var: str = "ZE_AFFINITY_MASK"
 
     @classmethod
-    def import_core_kernels(cls) -> None:
-        pass
+    def import_kernels(cls) -> None:
+        # Do not import vllm._C
+        with contextlib.suppress(ImportError):
+            import vllm._moe_C  # noqa: F401
 
     @classmethod
     def get_attn_backend_cls(