Replace time.time() to time.perf_counter() for benchmarking. (#6178)

Signed-off-by: Lifu Huang <lifu.hlf@gmail.com>

benchmark/multi_turn_chat/bench_sglang.py

@@ -27,7 +27,7 @@ def main(args):
 
     backend = select_sglang_backend(args)
 
-    tic = time.time()
+    tic = time.perf_counter()
     states = multi_turns.run_batch(
         multi_qas,
         temperature=0,
@@ -35,7 +35,7 @@ def main(args):
         num_threads=args.parallel,
         progress_bar=True,
     )
-    latency = time.time() - tic
+    latency = time.perf_counter() - tic
 
     print(f"Latency: {latency:.3f}")