Add metrics for speculative decoding (acceptance rate, average acceptance length) (#11441)

python/sglang/srt/metrics/collector.py

@@ -127,6 +127,7 @@ class SchedulerStats:
 
     # Speculative decoding
     spec_accept_length: float = 0.0
+    spec_accept_rate: float = 0.0
 
     # Retract
     num_retracted_reqs: int = 0
@@ -220,6 +221,12 @@ class SchedulerMetricsCollector:
             labelnames=labels.keys(),
             multiprocess_mode="mostrecent",
         )
+        self.spec_accept_rate = Gauge(
+            name="sglang:spec_accept_rate",
+            documentation="The average acceptance rate of speculative decoding (`accepted tokens / total draft tokens` in batch).",
+            labelnames=labels.keys(),
+            multiprocess_mode="mostrecent",
+        )
 
         # Retract
         self.num_retracted_reqs = Gauge(
@@ -520,6 +527,7 @@ class SchedulerMetricsCollector:
 
         # Speculative decoding
         self._log_gauge(self.spec_accept_length, stats.spec_accept_length)
+        self._log_gauge(self.spec_accept_rate, stats.spec_accept_rate)
 
         # PD disaggregation
         self._log_gauge(