fix[ROCm]: Remove unconditional aiter import (#32902)

Signed-off-by: rabi <ramishra@redhat.com>

vllm/_aiter_ops.py

@@ -31,7 +31,12 @@ IS_AITER_FOUND = is_aiter_found()
 
 
 def is_aiter_found_and_supported() -> bool:
-    if current_platform.is_rocm() and IS_AITER_FOUND:
+    """Check if AITER is available AND enabled via environment variable.
+
+    Checks: platform (ROCm), device arch (gfx9), library existence,
+    and VLLM_ROCM_USE_AITER env variable.
+    """
+    if current_platform.is_rocm() and IS_AITER_FOUND and envs.VLLM_ROCM_USE_AITER:
         from vllm.platforms.rocm import on_gfx9
 
         return on_gfx9()
@@ -40,13 +45,11 @@ def is_aiter_found_and_supported() -> bool:
 
 def if_aiter_supported(func: Callable) -> Callable:
     """Decorator that only executes the function if
-    ROCm AITER package is supported on gfx9 archs.
+    ROCm AITER package is supported and enabled on gfx9 archs.
     """
 
     @functools.wraps(func)
     def wrapper(*args, **kwargs):
-        # checks the platform, device arch and aiter library existence.
-
         if is_aiter_found_and_supported():
             return func(*args, **kwargs)
 
@@ -63,6 +66,11 @@ if is_aiter_found_and_supported():
     from aiter import dtypes
 
     AITER_FP8_DTYPE = dtypes.fp8
+else:
+    # Placeholder when AITER is disabled - prevents NameError during module load.
+    # Note: When AITER is disabled, ops are not registered, so fake implementations
+    # referencing this variable won't actually be called at runtime.
+    AITER_FP8_DTYPE = _FP8_DTYPE
 
 
 def _rocm_aiter_fused_moe_impl(

vllm/v1/attention/backends/rocm_aiter_fa.py

@@ -32,10 +32,11 @@ from vllm.v1.kv_cache_interface import AttentionSpec
 _PARTITION_SIZE_ROCM = 256
 _CP_TOKENS_PER_ITER_ROCM = 32 * 1024
 if current_platform.is_rocm():
-    import aiter
-
     from vllm.triton_utils import tl, triton
 
+    if rocm_aiter_ops.is_enabled():
+        import aiter
+
     def block_size(x, head_dim):
         return min(65536 // x.element_size(), triton.next_power_of_2(head_dim))
 

vllm/v1/spec_decode/eagle.py

@@ -183,7 +183,9 @@ class SpecDecodeBaseProposer:
                 RocmAttentionMetadata,
             ]
             # ROCM_AITER_FA is an optional backend
-            if find_spec(
+            from vllm._aiter_ops import rocm_aiter_ops
+
+            if rocm_aiter_ops.is_enabled() and find_spec(
                 AttentionBackendEnum.ROCM_AITER_FA.get_path(include_classname=False)
             ):
                 from vllm.v1.attention.backends.rocm_aiter_fa import (