[Hardware][Intel] Add CPU inference backend (#3634)

Co-authored-by: Kunshang Ji <kunshang.ji@intel.com>
Co-authored-by: Yuan Zhou <yuan.zhou@intel.com>

vllm/attention/selector.py

@@ -5,7 +5,7 @@ import torch
 
 from vllm.attention.backends.abstract import AttentionBackend
 from vllm.logger import init_logger
-from vllm.utils import is_hip
+from vllm.utils import is_cpu, is_hip
 
 logger = init_logger(__name__)
 
@@ -17,6 +17,10 @@ def get_attn_backend(dtype: torch.dtype) -> Type[AttentionBackend]:
         from vllm.attention.backends.flash_attn import (  # noqa: F401
             FlashAttentionBackend)
         return FlashAttentionBackend
+    elif is_cpu():
+        logger.info("Using Torch SDPA backend.")
+        from vllm.attention.backends.torch_sdpa import TorchSDPABackend
+        return TorchSDPABackend
     else:
         logger.info("Using XFormers backend.")
         from vllm.attention.backends.xformers import (  # noqa: F401
@@ -29,6 +33,8 @@ def _can_use_flash_attn(dtype: torch.dtype) -> bool:
         # AMD GPUs.
         logger.info("Cannot use FlashAttention backend for AMD GPUs.")
         return False
+    if is_cpu():
+        return False
     if torch.cuda.get_device_capability()[0] < 8:
         # Volta and Turing NVIDIA GPUs.
         logger.info("Cannot use FlashAttention backend for Volta and Turing "