[Platform][Refactor] Extract func get_default_attn_backend to Platform

vllm/attention/selector.py

@@ -1,4 +1,3 @@
-import enum
 import os
 from contextlib import contextmanager
 from functools import lru_cache
@@ -9,26 +8,12 @@
 import vllm.envs as envs
 from vllm.attention.backends.abstract import AttentionBackend
 from vllm.logger import init_logger
-from vllm.platforms import current_platform
+from vllm.platforms import _Backend, current_platform
 from vllm.utils import STR_BACKEND_ENV_VAR
 
 logger = init_logger(__name__)
 
 
-class _Backend(enum.Enum):
-    FLASH_ATTN = enum.auto()
-    FLASH_ATTN_VLLM_V1 = enum.auto()
-    XFORMERS = enum.auto()
-    ROCM_FLASH = enum.auto()
-    TORCH_SDPA = enum.auto()
-    OPENVINO = enum.auto()
-    FLASHINFER = enum.auto()
-    HPU_ATTN = enum.auto()
-    PALLAS = enum.auto()
-    IPEX = enum.auto()
-    NO_ATTENTION = enum.auto()
-
-
 def backend_name_to_enum(backend_name: str) -> _Backend:
     assert backend_name is not None
 
@@ -216,40 +201,11 @@ def which_attn_to_use(head_size: int,
         if backend_by_env_var is not None:
             selected_backend = backend_name_to_enum(backend_by_env_var)
 
-    if current_platform.is_cpu():
-        if selected_backend != _Backend.TORCH_SDPA:
-            logger.info("Cannot use %s backend on CPU.", selected_backend)
-        return _Backend.TORCH_SDPA
-
-    if current_platform.is_openvino():
-        if selected_backend != _Backend.OPENVINO:
-            logger.info("Cannot use %s backend on OpenVINO.", selected_backend)
-        return _Backend.OPENVINO
-
-    if current_platform.is_xpu():
-        if selected_backend != _Backend.IPEX:
-            logger.info("Cannot use %s backend on XPU.", selected_backend)
-        return _Backend.IPEX
-
-    if current_platform.is_tpu():
-        if selected_backend != _Backend.PALLAS:
-            logger.info("Cannot use %s backend on TPU.", selected_backend)
-        return _Backend.PALLAS
-
-    if current_platform.is_rocm():
-        # AMD GPUs.
-        selected_backend = (_Backend.ROCM_FLASH if selected_backend
-                            == _Backend.FLASH_ATTN else selected_backend)
-        if selected_backend == _Backend.ROCM_FLASH:
-            if not current_platform.has_device_capability(90):
-                # not Instinct series GPUs.
-                logger.info("flash_attn is not supported on NAVI GPUs.")
-        else:
-            logger.info("%s is not supported in AMD GPUs.", selected_backend)
-        return _Backend.ROCM_FLASH
-
-    if current_platform.is_hpu():
-        return _Backend.HPU_ATTN
+    # get device-specific default attn_backend
+    default_backend = current_platform.get_default_attn_backend(
+        selected_backend)
+    if default_backend is not None:
+        return default_backend
 
     if use_v1:
         return _Backend.FLASH_ATTN_VLLM_V1

vllm/model_executor/models/molmo.py

@@ -13,7 +13,6 @@
 from transformers import PretrainedConfig
 
 from vllm.attention import Attention, AttentionMetadata
-from vllm.attention.selector import _Backend
 from vllm.compilation.decorators import support_torch_compile
 from vllm.config import CacheConfig, VllmConfig
 from vllm.distributed import (get_pp_group, get_tensor_model_parallel_rank,
@@ -38,6 +37,7 @@
 from vllm.model_executor.model_loader.weight_utils import default_weight_loader
 from vllm.multimodal import MULTIMODAL_REGISTRY, MultiModalKwargs
 from vllm.multimodal.utils import cached_get_tokenizer
+from vllm.platforms import _Backend
 from vllm.sequence import (VLLM_TOKEN_ID_ARRAY_TYPE, IntermediateTensors,
                            SequenceData)
 from vllm.transformers_utils.processor import get_processor

vllm/model_executor/models/qwen2_vl.py

@@ -39,7 +39,6 @@
     make_batched_images, make_batched_videos, smart_resize)
 
 from vllm.attention import AttentionMetadata
-from vllm.attention.selector import _Backend
 from vllm.config import VllmConfig
 from vllm.distributed import get_pp_group, parallel_state
 from vllm.distributed import utils as dist_utils
@@ -65,6 +64,7 @@
 from vllm.multimodal.inputs import (MultiModalData, MultiModalDataDict,
                                     MultiModalKwargs)
 from vllm.multimodal.utils import cached_get_tokenizer
+from vllm.platforms import _Backend
 from vllm.sequence import IntermediateTensors, PoolerOutput, SequenceData
 from vllm.transformers_utils.config import uses_mrope
 from vllm.transformers_utils.processor import cached_get_processor

vllm/model_executor/models/utils.py

@@ -9,13 +9,13 @@
 from transformers import PretrainedConfig
 
 import vllm.envs as envs
-from vllm.attention.selector import (_Backend, backend_name_to_enum,
+from vllm.attention.selector import (backend_name_to_enum,
                                      get_global_forced_attn_backend)
 from vllm.config import VllmConfig
 from vllm.logger import init_logger
 from vllm.model_executor.model_loader.weight_utils import default_weight_loader
 from vllm.multimodal import MultiModalPlaceholderMap, NestedTensors
-from vllm.platforms import current_platform
+from vllm.platforms import _Backend, current_platform
 from vllm.sequence import IntermediateTensors
 from vllm.utils import is_pin_memory_available
 

vllm/platforms/__init__.py

@@ -1,3 +1,4 @@
+from .interface import _Backend  # noqa: F401
 from .interface import Platform, PlatformEnum, UnspecifiedPlatform
 
 current_platform: Platform

vllm/platforms/cpu.py

@@ -1,7 +1,11 @@
 import psutil
 import torch
 
-from .interface import Platform, PlatformEnum
+from vllm.logger import init_logger
+
+from .interface import Platform, PlatformEnum, _Backend
+
+logger = init_logger(__name__)
 
 
 class CpuPlatform(Platform):
@@ -11,6 +15,12 @@ class CpuPlatform(Platform):
     def get_device_name(cls, device_id: int = 0) -> str:
         return "cpu"
 
+    @classmethod
+    def get_default_attn_backend(cls, selected_backend: _Backend) -> _Backend:
+        if selected_backend != _Backend.TORCH_SDPA:
+            logger.info("Cannot use %s backend on CPU.", selected_backend)
+        return _Backend.TORCH_SDPA
+
     @classmethod
     def get_device_total_memory(cls, device_id: int = 0) -> int:
         return psutil.virtual_memory().total

vllm/platforms/hpu.py

@@ -1,11 +1,15 @@
 import torch
 
-from .interface import Platform, PlatformEnum
+from .interface import Platform, PlatformEnum, _Backend
 
 
 class HpuPlatform(Platform):
     _enum = PlatformEnum.HPU
 
+    @classmethod
+    def get_default_attn_backend(cls, selected_backend: _Backend) -> _Backend:
+        return _Backend.HPU_ATTN
+
     @staticmethod
     def inference_mode():
         return torch.no_grad()

vllm/platforms/interface.py

@@ -6,6 +6,20 @@
 import torch
 
 
+class _Backend(enum.Enum):
+    FLASH_ATTN = enum.auto()
+    FLASH_ATTN_VLLM_V1 = enum.auto()
+    XFORMERS = enum.auto()
+    ROCM_FLASH = enum.auto()
+    TORCH_SDPA = enum.auto()
+    OPENVINO = enum.auto()
+    FLASHINFER = enum.auto()
+    HPU_ATTN = enum.auto()
+    PALLAS = enum.auto()
+    IPEX = enum.auto()
+    NO_ATTENTION = enum.auto()
+
+
 class PlatformEnum(enum.Enum):
     CUDA = enum.auto()
     ROCM = enum.auto()
@@ -66,6 +80,11 @@ def is_cuda_alike(self) -> bool:
         """Stateless version of :func:`torch.cuda.is_available`."""
         return self._enum in (PlatformEnum.CUDA, PlatformEnum.ROCM)
 
+    @classmethod
+    def get_default_attn_backend(cls, selected_backend: _Backend):
+        """Get the default attention backend of a device."""
+        return None
+
     @classmethod
     def get_device_capability(
         cls,

vllm/platforms/openvino.py

@@ -3,14 +3,20 @@
 import vllm.envs as envs
 from vllm.logger import init_logger
 
-from .interface import Platform, PlatformEnum
+from .interface import Platform, PlatformEnum, _Backend
 
 logger = init_logger(__name__)
 
 
 class OpenVinoPlatform(Platform):
     _enum = PlatformEnum.OPENVINO
 
+    @classmethod
+    def get_default_attn_backend(cls, selected_backend: _Backend) -> _Backend:
+        if selected_backend != _Backend.OPENVINO:
+            logger.info("Cannot use %s backend on OpenVINO.", selected_backend)
+        return _Backend.OPENVINO
+
     @classmethod
     def get_device_name(self, device_id: int = 0) -> str:
         return "openvino"

vllm/platforms/rocm.py

@@ -5,7 +5,7 @@
 
 from vllm.logger import init_logger
 
-from .interface import DeviceCapability, Platform, PlatformEnum
+from .interface import DeviceCapability, Platform, PlatformEnum, _Backend
 
 logger = init_logger(__name__)
 
@@ -19,6 +19,18 @@
 class RocmPlatform(Platform):
     _enum = PlatformEnum.ROCM
 
+    @classmethod
+    def get_default_attn_backend(cls, selected_backend: _Backend) -> _Backend:
+        selected_backend = (_Backend.ROCM_FLASH if selected_backend
+                            == _Backend.FLASH_ATTN else selected_backend)
+        if selected_backend == _Backend.ROCM_FLASH:
+            if not cls.has_device_capability(90):
+                # not Instinct series GPUs.
+                logger.info("flash_attn is not supported on NAVI GPUs.")
+        else:
+            logger.info("%s is not supported in AMD GPUs.", selected_backend)
+        return _Backend.ROCM_FLASH
+
     @classmethod
     @lru_cache(maxsize=8)
     def get_device_capability(cls, device_id: int = 0) -> DeviceCapability:

vllm/platforms/tpu.py

@@ -4,9 +4,10 @@
 
 import vllm.envs as envs
 from vllm.compilation.levels import CompilationLevel
+from vllm.logger import init_logger
 from vllm.plugins import set_torch_compile_backend
 
-from .interface import Platform, PlatformEnum
+from .interface import Platform, PlatformEnum, _Backend
 
 if "VLLM_TORCH_COMPILE_LEVEL" not in os.environ:
     os.environ["VLLM_TORCH_COMPILE_LEVEL"] = str(CompilationLevel.DYNAMO_ONCE)
@@ -16,10 +17,18 @@
 
 set_torch_compile_backend("openxla")
 
+logger = init_logger(__name__)
+
 
 class TpuPlatform(Platform):
     _enum = PlatformEnum.TPU
 
+    @classmethod
+    def get_default_attn_backend(cls, selected_backend: _Backend) -> _Backend:
+        if selected_backend != _Backend.PALLAS:
+            logger.info("Cannot use %s backend on TPU.", selected_backend)
+        return _Backend.PALLAS
+
     @classmethod
     def get_device_name(cls, device_id: int = 0) -> str:
         raise NotImplementedError

vllm/platforms/xpu.py

@@ -1,11 +1,21 @@
 import torch
 
-from .interface import DeviceCapability, Platform, PlatformEnum
+from vllm.logger import init_logger
+
+from .interface import DeviceCapability, Platform, PlatformEnum, _Backend
+
+logger = init_logger(__name__)
 
 
 class XPUPlatform(Platform):
     _enum = PlatformEnum.XPU
 
+    @classmethod
+    def get_default_attn_backend(cls, selected_backend: _Backend) -> _Backend:
+        if selected_backend != _Backend.IPEX:
+            logger.info("Cannot use %s backend on XPU.", selected_backend)
+        return _Backend.IPEX
+
     @staticmethod
     def get_device_capability(device_id: int = 0) -> DeviceCapability:
         major, minor, *_ = torch.xpu.get_device_capability(

vllm/worker/enc_dec_model_runner.py

@@ -8,7 +8,7 @@
 from vllm.attention.backends.abstract import (AttentionBackend,
                                               AttentionMetadata)
 from vllm.attention.backends.utils import PAD_SLOT_ID
-from vllm.attention.selector import (_Backend, get_env_variable_attn_backend,
+from vllm.attention.selector import (get_env_variable_attn_backend,
                                      get_global_forced_attn_backend)
 from vllm.config import VllmConfig
 from vllm.forward_context import set_forward_context
@@ -18,6 +18,7 @@
 from vllm.model_executor.layers.sampler import SamplerOutput
 from vllm.multimodal import (MULTIMODAL_REGISTRY, MultiModalKwargs,
                              MultiModalRegistry)
+from vllm.platforms import _Backend
 from vllm.sampling_params import SamplingParams
 from vllm.sequence import (IntermediateTensors, PoolerOutput,
                            SequenceGroupMetadata)