[Misc] improve example mlpspeculator and llm_engine_example (#16175)

Signed-off-by: reidliu41 <reid201711@gmail.com>
Co-authored-by: reidliu41 <reid201711@gmail.com>

examples/offline_inference/llm_engine_example.py

 # SPDX-License-Identifier: Apache-2.0
-
+"""
+This file demonstrates using the `LLMEngine`
+for processing prompts with various sampling parameters.
+"""
 import argparse
 
 from vllm import EngineArgs, LLMEngine, RequestOutput, SamplingParams
@@ -26,6 +29,7 @@ def process_requests(engine: LLMEngine,
     """Continuously process a list of prompts and handle the outputs."""
     request_id = 0
 
+    print('-' * 50)
     while test_prompts or engine.has_unfinished_requests():
         if test_prompts:
             prompt, sampling_params = test_prompts.pop(0)
@@ -37,6 +41,7 @@ def process_requests(engine: LLMEngine,
         for request_output in request_outputs:
             if request_output.finished:
                 print(request_output)
+                print('-' * 50)
 
 
 def initialize_engine(args: argparse.Namespace) -> LLMEngine:

examples/offline_inference/mlpspeculator.py

 # SPDX-License-Identifier: Apache-2.0
+"""
+This file demonstrates the usage of text generation with an LLM model,
+comparing the performance with and without speculative decoding.
+
+Note that still not support `v1`:
+VLLM_USE_V1=0 python examples/offline_inference/mlpspeculator.py
+"""
 
 import gc
 import time
@@ -7,7 +14,7 @@ from vllm import LLM, SamplingParams
 
 
 def time_generation(llm: LLM, prompts: list[str],
-                    sampling_params: SamplingParams):
+                    sampling_params: SamplingParams, title: str):
     # Generate texts from the prompts. The output is a list of RequestOutput
     # objects that contain the prompt, generated text, and other information.
     # Warmup first
@@ -16,11 +23,15 @@ def time_generation(llm: LLM, prompts: list[str],
     start = time.time()
     outputs = llm.generate(prompts, sampling_params)
     end = time.time()
-    print((end - start) / sum([len(o.outputs[0].token_ids) for o in outputs]))
+    print("-" * 50)
+    print(title)
+    print("time: ",
+          (end - start) / sum(len(o.outputs[0].token_ids) for o in outputs))
     # Print the outputs.
     for output in outputs:
         generated_text = output.outputs[0].text
         print(f"text: {generated_text!r}")
+        print("-" * 50)
 
 
 if __name__ == "__main__":
@@ -41,8 +52,7 @@ if __name__ == "__main__":
     # Create an LLM without spec decoding
     llm = LLM(model="meta-llama/Llama-2-13b-chat-hf")
 
-    print("Without speculation")
-    time_generation(llm, prompts, sampling_params)
+    time_generation(llm, prompts, sampling_params, "Without speculation")
 
     del llm
     gc.collect()
@@ -55,5 +65,4 @@ if __name__ == "__main__":
         },
     )
 
-    print("With speculation")
-    time_generation(llm, prompts, sampling_params)
+    time_generation(llm, prompts, sampling_params, "With speculation")