[LLM] First commit the llm deployment code

fastdeploy/model_executor/layers/attention/attention_selecter.py

@@ -0,0 +1,55 @@
+"""
+# Copyright (c) 2025 PaddlePaddle Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""
+
+"""
+attention backend selecter
+"""
+from fastdeploy.model_executor.layers.attention.base_attention_backend import AttentionBackend
+from fastdeploy.platforms import current_platform
+from fastdeploy.utils import resolve_obj_from_strname
+from functools import cache
+from fastdeploy.platforms import _Backend
+
+
+def backend_name_to_enum(backend_name: str):
+    """backend_name_to_enum """
+    assert backend_name is not None
+    return _Backend.__members__.get(backend_name)
+
+
+@cache
+def _get_attn_backend(
+    selected_backend
+):
+    """_get_attn_backend """
+    if isinstance(selected_backend, str):
+        selected_backend = backend_name_to_enum(selected_backend)
+    attention_cls = current_platform.get_attention_backend_cls(
+        selected_backend)
+
+    if not attention_cls:
+        raise ValueError(
+            f"Invalid attention backend for {current_platform.device_name}")
+    return resolve_obj_from_strname(attention_cls)
+
+
+def get_attention_backend(
+    selected_backend
+):
+    """Selects which attention backend ."""
+    return _get_attn_backend(
+        selected_backend
+    )