[Perf] Increase default max splits for FA3 full cudagraphs (#25495)

Signed-off-by: Lucas Wilkinson <lwilkins@redhat.com>

vllm/envs.py

@@ -119,7 +119,7 @@ if TYPE_CHECKING:
     VLLM_SERVER_DEV_MODE: bool = False
     VLLM_V1_OUTPUT_PROC_CHUNK_SIZE: int = 128
     VLLM_MLA_DISABLE: bool = False
-    VLLM_FLASH_ATTN_MAX_NUM_SPLITS_FOR_CUDA_GRAPH: int = 16
+    VLLM_FLASH_ATTN_MAX_NUM_SPLITS_FOR_CUDA_GRAPH: int = 32
     VLLM_RAY_PER_WORKER_GPUS: float = 1.0
     VLLM_RAY_BUNDLE_INDICES: str = ""
     VLLM_CUDART_SO_PATH: Optional[str] = None
@@ -1017,7 +1017,7 @@ environment_variables: dict[str, Callable[[], Any]] = {
     # max number splits for cuda graph decode
     "VLLM_FLASH_ATTN_MAX_NUM_SPLITS_FOR_CUDA_GRAPH":
     lambda: int(os.getenv("VLLM_FLASH_ATTN_MAX_NUM_SPLITS_FOR_CUDA_GRAPH",
-                          "16")),
+                          "32")),
 
     # Number of GPUs per worker in Ray, if it is set to be a fraction,
     # it allows ray to schedule multiple actors on a single GPU,