[Bug] Fix decode stats error on output_len 1 (#1585)

python/sglang/bench_latency.py

@@ -340,13 +340,16 @@ def latency_test_run_once(
             rank_print(
                 f"Decode.  latency: {latency:6.5f} s, throughput: {throughput:9.2f} token/s"
             )
-    med_decode_latency = np.median(decode_latencies)
-    med_decode_throughput = batch_size / med_decode_latency
-    rank_print(
-        f"Decode.  median latency: {med_decode_latency:6.5f} s, median throughput: {med_decode_throughput:9.2f} token/s"
-    )
-    measurement_results["median_decode_latency"] = med_decode_latency
-    measurement_results["median_decode_throughput"] = med_decode_throughput
+
+    # record decode timing from 2nd output
+    if output_len > 1:
+        med_decode_latency = np.median(decode_latencies)
+        med_decode_throughput = batch_size / med_decode_latency
+        rank_print(
+            f"Decode.  median latency: {med_decode_latency:6.5f} s, median throughput: {med_decode_throughput:9.2f} token/s"
+        )
+        measurement_results["median_decode_latency"] = med_decode_latency
+        measurement_results["median_decode_throughput"] = med_decode_throughput
 
     throughput = (input_len + output_len) * batch_size / tot_latency
     rank_print(
@@ -382,7 +385,7 @@ def latency_test(
         reqs,
         bench_args.batch_size[0],
         bench_args.input_len[0],
-        4,  # shorter decoding to speed up the warmup
+        8,  # shorter decoding to speed up the warmup
     )
     rank_print("Benchmark ...")