From 22d33baca2c0c639cfd45c48e99803e56c3efa74 Mon Sep 17 00:00:00 2001
From: Nick Hill <nhill@redhat.com>
Date: Wed, 19 Mar 2025 14:04:41 -0700
Subject: [PATCH] [FrontEnd][Perf] `merge_async_iterators` fast-path for
 single-prompt requests (#15150)

Signed-off-by: Nick Hill <nhill@redhat.com>
---
 vllm/utils.py | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/vllm/utils.py b/vllm/utils.py
index 79787303af5bc..9bc081890bcb7 100644
--- a/vllm/utils.py
+++ b/vllm/utils.py
@@ -411,6 +411,11 @@ async def merge_async_iterators(
     When it yields, it yields a tuple (i, item) where i is the index of the
     iterator that yields the item.
     """
+    if len(iterators) == 1:
+        # Fast-path single iterator case.
+        async for item in iterators[0]:
+            yield 0, item
+        return
 
     loop = asyncio.get_running_loop()