[Misc] Use public API in benchmark_throughput (#4300)

benchmarks/benchmark_throughput.py

@@ -103,25 +103,22 @@ def run_vllm(
     )
 
     # Add the requests to the engine.
+    prompts = []
+    sampling_params = []
     for prompt, _, output_len in requests:
-        sampling_params = SamplingParams(
+        prompts.append(prompt)
+        sampling_params.append(
+            SamplingParams(
                 n=n,
                 temperature=0.0 if use_beam_search else 1.0,
                 top_p=1.0,
                 use_beam_search=use_beam_search,
                 ignore_eos=True,
                 max_tokens=output_len,
-        )
-        # FIXME(woosuk): Do not use internal method.
-        llm._add_request(
-            prompt=prompt,
-            prompt_token_ids=None,
-            sampling_params=sampling_params,
-        )
+            ))
 
     start = time.perf_counter()
-    # FIXME(woosuk): Do not use internal method.
-    llm._run_engine(use_tqdm=True)
+    llm.generate(prompts, sampling_params, use_tqdm=True)
     end = time.perf_counter()
     return end - start