[V1][CUDA] Full cudagraph support for FlashInfer (#21367)

vllm/v1/attention/backends/utils.py

@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: Apache-2.0
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
 import abc
+import enum
 import functools
 from abc import abstractmethod
 from dataclasses import dataclass, make_dataclass
@@ -65,9 +66,24 @@ class CommonAttentionMetadata:
 M = TypeVar("M")
 
 
+class AttentionCGSupport(enum.Enum):
+    """ Constants for the cudagraph support of the attention backend
+    Here we do not consider the cascade attention, as currently
+    it is never cudagraph supported."""
+
+    NEVER = 0
+    """NO cudagraph support"""
+    PURE_DECODE_ONLY = 1
+    """Cudagraph supported for pure decode, need to run without
+    cudagraph for mixed prefill-decode batches"""
+    ALWAYS = 2
+    """Cudagraph always supported"""
+
+
 class AttentionMetadataBuilder(abc.ABC, Generic[M]):
     # Does this backend/builder support CUDA Graphs for attention.
-    full_cudagraph_supported: ClassVar[bool] = False
+    attn_cudagraph_support: ClassVar[AttentionCGSupport] = \
+        AttentionCGSupport.NEVER
 
     @abstractmethod
     def __init__(self, kv_cache_spec: AttentionSpec, layer_names: list[str],