[Bugfix] Fix vllm bench serve to count multimodal tokens in "total input tokens" (#38654)

Signed-off-by: Matthias Gehre <matthias.gehre@amd.com>

vllm/benchmarks/lib/endpoint_request_func.py

@@ -237,6 +237,8 @@ async def async_request_openai_completions(
                                 generated_text += text or ""
                             elif usage := data.get("usage"):
                                 output.output_tokens = usage.get("completion_tokens")
+                                if (pt := usage.get("prompt_tokens")) is not None:
+                                    output.prompt_len = pt
                 if first_chunk_received:
                     output.success = True
                 else:
@@ -358,6 +360,8 @@ async def async_request_openai_chat_completions(
                                 generated_text += content or ""
                             elif usage := data.get("usage"):
                                 output.output_tokens = usage.get("completion_tokens")
+                                if (pt := usage.get("prompt_tokens")) is not None:
+                                    output.prompt_len = pt
 
                             most_recent_timestamp = timestamp
 

vllm/benchmarks/serve.py

@@ -439,7 +439,7 @@ def calculate_metrics(
                         ).input_ids
                     )
             actual_output_lens.append(output_len)
-            total_input += input_requests[i].prompt_len
+            total_input += outputs[i].prompt_len
             tpot = 0
             if output_len > 1:
                 latency_minus_ttft = outputs[i].latency - outputs[i].ttft