[Fix] Add model sequence length into model config (#575)

vllm/config.py

@@ -109,6 +109,26 @@ class ModelConfig:
         total_num_attention_heads = self.hf_config.num_attention_heads
         return total_num_attention_heads // parallel_config.tensor_parallel_size
 
+    def get_max_model_len(self) -> int:
+        max_model_len = float("inf")
+        possible_keys = [
+            # OPT
+            "max_position_embeddings",
+            # GPT-2
+            "n_positions",
+            # MPT
+            "max_seq_len",
+            # Others
+            "max_sequence_length",
+            "max_seq_length",
+            "seq_len",
+        ]
+        for key in possible_keys:
+            max_len_key = getattr(self.hf_config, key, None)
+            if max_len_key is not None:
+                max_model_len = min(max_model_len, max_len_key)
+        return max_model_len
+
     def get_num_layers(self, parallel_config: "ParallelConfig") -> int:
         total_num_hidden_layers = self.hf_config.num_hidden_layers
         return total_num_hidden_layers // parallel_config.pipeline_parallel_size

vllm/engine/arg_utils.py

@@ -155,10 +155,9 @@ class EngineArgs:
         parallel_config = ParallelConfig(self.pipeline_parallel_size,
                                          self.tensor_parallel_size,
                                          self.worker_use_ray)
-        max_model_len = getattr(model_config.hf_config,
-                                'max_position_embeddings', float('inf'))
         scheduler_config = SchedulerConfig(self.max_num_batched_tokens,
-                                           self.max_num_seqs, max_model_len)
+                                           self.max_num_seqs,
+                                           model_config.get_max_model_len())
         return model_config, cache_config, parallel_config, scheduler_config
 
 

vllm/entrypoints/openai/api_server.py

@@ -107,25 +107,14 @@ async def get_gen_prompt(request) -> str:
     return prompt
 
 
-async def check_length(request, prompt, model_config):
-    if hasattr(model_config.hf_config, "max_sequence_length"):
-        context_len = model_config.hf_config.max_sequence_length
-    elif hasattr(model_config.hf_config, "seq_length"):
-        context_len = model_config.hf_config.seq_length
-    elif hasattr(model_config.hf_config, "max_position_embeddings"):
-        context_len = model_config.hf_config.max_position_embeddings
-    elif hasattr(model_config.hf_config, "seq_length"):
-        context_len = model_config.hf_config.seq_length
-    else:
-        context_len = 2048
-
+async def check_length(request, prompt):
     input_ids = tokenizer(prompt).input_ids
     token_num = len(input_ids)
 
-    if token_num + request.max_tokens > context_len:
+    if token_num + request.max_tokens > max_model_len:
         return create_error_response(
             HTTPStatus.BAD_REQUEST,
-            f"This model's maximum context length is {context_len} tokens. "
+            f"This model's maximum context length is {max_model_len} tokens. "
             f"However, you requested {request.max_tokens + token_num} tokens "
             f"({token_num} in the messages, "
             f"{request.max_tokens} in the completion). "
@@ -194,7 +183,7 @@ async def create_chat_completion(raw_request: Request):
                                      "logit_bias is not currently supported")
 
     prompt = await get_gen_prompt(request)
-    error_check_ret = await check_length(request, prompt, engine_model_config)
+    error_check_ret = await check_length(request, prompt)
     if error_check_ret is not None:
         return error_check_ret
 
@@ -591,6 +580,7 @@ if __name__ == "__main__":
     engine_args = AsyncEngineArgs.from_cli_args(args)
     engine = AsyncLLMEngine.from_engine_args(engine_args)
     engine_model_config = asyncio.run(engine.get_model_config())
+    max_model_len = engine_model_config.get_max_model_len()
 
     # A separate tokenizer to map token IDs to strings.
     tokenizer = get_tokenizer(engine_args.tokenizer,