Revert #26113 "[Frontend] CompilationConfig overhaul (#20283): deprecate use_inductor in favor of backend, simplify custom_ops" (#26472)

Signed-off-by: zjy0516 <riverclouds.zhu@qq.com>

vllm/config/compilation.py

@@ -180,11 +180,10 @@ class CompilationConfig:
     """The directory to store the compiled graph, to accelerate Inductor
     compilation. By default, it will use model-related information to generate
     a cache directory."""
-    backend: str = "inductor"
+    backend: str = ""
     """The backend for compilation. It needs to be a string:
 
-    - "" (empty string): use the default backend ("inductor" on CUDA-alike
-    platforms).
+    - "" (empty string): use the default backend.
     - "eager"/"openxla"/...: use the specified backend registered in PyTorch.
     - "full.module.name": a qualified name which can be used to import the
 
@@ -193,11 +192,7 @@ class CompilationConfig:
     distributed setting. When the compilation level is 1 or 2, the backend is
     used for the compilation directly (it sees the whole graph). When the
     compilation level is 3, the backend is used for the piecewise compilation
-    (it sees a part of the graph). The backend can not be custom for compilation
-    level 3. Furthermore, compilation is only piecewise if splitting ops is set
-    accordingly and use_inductor_cudagraphs_partition is off. Note that the
-    default options for splitting ops are sufficient for piecewise compilation.
-    """
+    (it sees a part of the graph)."""
     custom_ops: list[str] = field(default_factory=list)
     """Fine-grained control over which custom ops to enable/disable. Use 'all'
     to enable all, 'none' to disable all. Also specify a list of custom op
@@ -215,12 +210,8 @@ class CompilationConfig:
     compilation."""
 
     # Inductor capture
-    use_inductor: Optional[bool] = None
-    """
-    Whether to use inductor compilation.
-
-    This flag is deprecated and will be removed.
-    Please use the 'backend' option instead.
+    use_inductor: bool = True
+    """Whether to use inductor compilation:
 
     - False: inductor compilation is not used. graph runs in eager
         (custom_ops enabled by default).
@@ -228,11 +219,7 @@ class CompilationConfig:
         One graph for symbolic shape and one graph per size in compile_sizes
         are compiled using configurations in inductor_compile_config.
 
-    This setting is ignored if level<PIECEWISE.
-
-    For future compatibility:
-    If use_inductor is True, backend="inductor" otherwise backend="eager".
-    """
+    This setting is ignored if level<PIECEWISE."""
     compile_sizes: Optional[list[Union[int, str]]] = None
     """Sizes to compile for inductor. In addition
     to integers, it also supports "cudagraph_capture_sizes" to
@@ -538,43 +525,7 @@ class CompilationConfig:
                     "(where 'op' is the registered op name)"
                 )
 
-        # Currently only eager and inductor backend are supported.
-        # for piecewise compilation. Custom backends are not suppported for
-        # piecewise compilation. Update when more backends are supported.
-        if self.level == CompilationLevel.PIECEWISE and self.backend not in [
-            "",
-            "eager",
-            "inductor",
-        ]:
-            raise ValueError(
-                f"Invalid backend for piecewise compilation: {self.backend}"
-            )
-
-        if self.use_inductor is not None:
-            logger.warning_once(
-                "The 'use_inductor' flag is deprecated and will be\
-                    removed in a future release."
-                "Please use the 'backend' option instead.",
-            )
-            self.backend = "inductor" if self.use_inductor else "eager"
-
-        if self.backend == "":
-            self.backend = "inductor"
-
     def init_backend(self, vllm_config: "VllmConfig") -> Union[str, Callable]:
-        """
-        Initialize the backend for the compilation config from a vllm config.
-        Arguments:
-            vllm_config: The vllm config to initialize the backend from.
-        Returns:
-            The backend for the compilation config.
-        """
-        if self.level is None:
-            raise ValueError(
-                "No compilation level is set. This method should only be \
-                called via vllm config where the level is set if none is \
-                provided."
-            )
         if self.level == CompilationLevel.NO_COMPILATION:
             raise ValueError("No compilation level is set.")
 
@@ -582,15 +533,15 @@ class CompilationConfig:
 
         torch_backends = list_backends(exclude_tags=tuple())
         if self.level in [CompilationLevel.DYNAMO_AS_IS, CompilationLevel.DYNAMO_ONCE]:
+            if self.backend == "":
+                return "eager"
             if self.backend in torch_backends:
                 return self.backend
             return resolve_obj_by_qualname(self.backend)
 
+        # TODO: pass user-specified backend to piecewise compilation
+        # merge with the config use_inductor
         assert self.level == CompilationLevel.PIECEWISE
-        if self.backend not in ["eager", "inductor"]:
-            raise ValueError(
-                f"Invalid backend for piecewise compilation: {self.backend}"
-            )
 
         from vllm.compilation.backends import VllmBackend
 
@@ -743,7 +694,7 @@ class CompilationConfig:
         )
 
         inductor_used = (
-            self.level == CompilationLevel.PIECEWISE and self.backend == "inductor"
+            self.level == CompilationLevel.PIECEWISE and self.use_inductor
         ) or (
             self.level >= CompilationLevel.DYNAMO_AS_IS and self.backend == "inductor"
         )