Add stream label to TTFT metrics (#32363)

Co-authored-by: Jialin Ouyang <Jialin.Ouyang@gmail.com>

python/sglang/srt/managers/tokenizer_manager.py

@@ -2501,7 +2501,9 @@ class TokenizerManager(TokenizerControlMixin, TokenizerManagerScoreMixin):
             state.ttft_observed = True
             state.last_completion_tokens = completion_tokens
             self.metrics_collector.observe_time_to_first_token(
-                labels, state.time_stats.get_first_token_latency()
+                labels,
+                state.time_stats.get_first_token_latency(),
+                stream=getattr(state.obj, "stream", False),
             )
         else:
             num_new_tokens = completion_tokens - state.last_completion_tokens

python/sglang/srt/observability/metrics_collector.py

@@ -1630,7 +1630,8 @@ class TokenizerMetricsCollector(_StatLoggerDIMixin):
         self.histogram_time_to_first_token = Histogram(
             name="sglang:time_to_first_token_seconds",
             documentation="Histogram of time to first token in seconds.",
-            labelnames=labels.keys(),
+            # "stream" splits streaming vs non-streaming requests.
+            labelnames=[*labels.keys(), "stream"],
             buckets=bucket_time_to_first_token,
         )
 
@@ -1701,11 +1702,15 @@ class TokenizerMetricsCollector(_StatLoggerDIMixin):
             float(generation_tokens)
         )
 
-    def observe_time_to_first_token(self, labels: Dict[str, str], value: float):
+    def observe_time_to_first_token(
-        self.histogram_time_to_first_token.labels(**labels).observe(value)
+        self, labels: Dict[str, str], value: float, *, stream: bool
+    ):
+        self.histogram_time_to_first_token.labels(
+            **labels, stream="true" if stream else "false"
+        ).observe(value)
 
     def check_time_to_first_token_straggler(self, value: float) -> bool:
-        his = self.histogram_time_to_first_token.labels(**self.labels)
+        his = self.histogram_time_to_first_token.labels(**self.labels, stream="true")
         total_observations = sum(bucket._value for bucket in his._buckets)
         if total_observations < 100:
             return False