[Misc] Raise error when using encoder/decoder model with cpu backend (#8355)

vllm/utils.py

@@ -82,6 +82,9 @@ STR_NOT_IMPL_ENC_DEC_PROMPT_ADAPTER = ("Prompt adapters are not "
                                        "currently supported with encoder/"
                                        "decoder models.")
 
+STR_NOT_IMPL_ENC_DEC_CPU = ("CPU is not currently supported with "
+                            "encoder/decoder models.")
+
 # Efficiently import all enc/dec error strings
 # rather than having to import all of the above
 STR_NOT_IMPL_ENC_DEC_ERR_STRS = {
@@ -97,6 +100,7 @@ STR_NOT_IMPL_ENC_DEC_ERR_STRS = {
     "STR_NOT_IMPL_ENC_DEC_CUDA_GRAPH": STR_NOT_IMPL_ENC_DEC_CUDAGRAPH,
     "STR_NOT_IMPL_ENC_DEC_BACKEND": STR_NOT_IMPL_ENC_DEC_BACKEND,
     "STR_NOT_IMPL_ENC_DEC_PROMPT_ADAPTER": STR_NOT_IMPL_ENC_DEC_PROMPT_ADAPTER,
+    "STR_NOT_IMPL_ENC_DEC_CPU": STR_NOT_IMPL_ENC_DEC_CPU
 }
 
 # Constants related to forcing the attention backend selection

vllm/worker/cpu_model_runner.py

@@ -15,7 +15,7 @@ from vllm.model_executor.model_loader import get_model
 from vllm.multimodal import (MULTIMODAL_REGISTRY, BatchedTensorInputs,
                              MultiModalInputs)
 from vllm.sequence import IntermediateTensors, SequenceGroupMetadata
-from vllm.utils import make_tensor_with_pad
+from vllm.utils import STR_NOT_IMPL_ENC_DEC_ERR_STRS, make_tensor_with_pad
 from vllm.worker.model_runner_base import (
     ModelRunnerBase, ModelRunnerInputBase,
     _add_attn_metadata_broadcastable_dict,
@@ -121,6 +121,10 @@ class CPUModelRunner(ModelRunnerBase[CPUModelInput]):
         # Lazy initialization.
         self.model: nn.Module  # Set after init_Model
 
+        if self.model_config.is_encoder_decoder_model:
+            raise NotImplementedError(
+                STR_NOT_IMPL_ENC_DEC_ERR_STRS['STR_NOT_IMPL_ENC_DEC_CPU'])
+
     def load_model(self) -> None:
         self.model = get_model(model_config=self.model_config,
                                load_config=self.load_config,