[Misc] Add quantization config support for speculative model. (#7343)

vllm/config.py

@@ -961,6 +961,7 @@ class SpeculativeConfig:
         target_parallel_config: ParallelConfig,
         target_dtype: str,
         speculative_model: Optional[str],
+        speculative_model_quantization: Optional[str],
         speculative_draft_tensor_parallel_size: Optional[int],
         num_speculative_tokens: Optional[int],
         speculative_max_model_len: Optional[int],
@@ -989,6 +990,9 @@ class SpeculativeConfig:
             target_dtype (str): The data type used for the target model.
             speculative_model (Optional[str]): The name of the speculative
                 model, if provided.
+            speculative_model_quantization (Optional[str]): Quantization method
+                that was used to quantize the speculative model weights. If
+                None, we assume the model weights are not quantized.
             speculative_draft_tensor_parallel_size (Optional[int]): The degree
                 of the tensor parallelism for the draft model.
             num_speculative_tokens (Optional[int]): The number of speculative
@@ -1056,11 +1060,11 @@ class SpeculativeConfig:
                 "Speculative decoding requires usage of the V2 "
                 "block manager. Enable it with --use-v2-block-manager.")
 
-        # TODO: The user should be able to specify revision/quantization/max
-        # model len for the draft model. It is not currently supported.
+        # TODO: The user should be able to specify revision/max model len
+        # for the draft model. It is not currently supported.
         draft_revision = None
         draft_code_revision = None
-        draft_quantization = None
+        draft_quantization = speculative_model_quantization
 
         if speculative_model == "[ngram]":
             if ngram_prompt_lookup_min is None:
@@ -1217,7 +1221,7 @@ class SpeculativeConfig:
         elif speculative_draft_tensor_parallel_size != 1:
             # TODO(wooyeon): allow tp values larger than 1
             raise ValueError(
-                f"{speculative_draft_tensor_parallel_size=} cannot be"
+                f"{speculative_draft_tensor_parallel_size=} cannot be "
                 f"other value than 1")
 
         draft_parallel_config = ParallelConfig(