fix(metrics): clear forward occupancy on idle (#33562)

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

python/sglang/srt/managers/scheduler.py

@@ -3904,9 +3904,6 @@ class Scheduler(
         # reset token ratio
         self.new_token_ratio_tracker.reset()
 
-        # reset device timer window so idle time isn't counted
-        self.metrics_reporter.reset_device_timer_window()
-
         # Publish the idle state so /get_loads and DP balancing do not see stale load.
         self.publish_load_snapshot(force=True)
 

python/sglang/srt/managers/scheduler_components/metrics_reporter.py

@@ -2,6 +2,7 @@ from __future__ import annotations
 
 import dataclasses
 import logging
+import math
 import tempfile
 import time
 from collections import defaultdict
@@ -1080,7 +1081,7 @@ class SchedulerMetricsReporter:
             # the gauge. Readers sample it asynchronously, and the window
             # boundary can phase-lock with the decode-log cadence, turning a
             # one-tick NaN into NaN on every log line. NaN is published only
-            # when truly stale (reset_device_timer_window after idle).
+            # when truly stale (_reset_device_timer_window after idle).
             self._device_timer_window_start = now
             self._device_timer_window_gpu_time = 0.0
         else:
@@ -1093,13 +1094,20 @@ class SchedulerMetricsReporter:
         if self._device_timer_window_batch_count >= self.decode_log_interval:
             self._device_timer_window_batch_count = 0
 
-    def reset_device_timer_window(self):
+    def _reset_device_timer_window(self):
+        """Exclude idle time and invalidate the last forward-occupancy sample."""
         if ENABLE_METRICS_DEVICE_TIMER:
             self._device_timer_window_batch_count = 0
             self.fwd_occupancy = float("nan")
+            self.stats.fwd_occupancy = float("nan")
 
     def _maybe_log_idle_metrics(self):
-        """Collect and log metrics every 30 seconds during idle."""
+        """Reset forward timing and publish idle metrics when needed."""
+        # Preserve the transition so the rate limit cannot leave a finite idle gauge.
+        is_fwd_occupancy_stale = ENABLE_METRICS_DEVICE_TIMER and not math.isnan(
+            self.stats.fwd_occupancy
+        )
+        self._reset_device_timer_window()
         if not self.current_scheduler_metrics_enabled:
             return
         # The running-reqs gauge holds the last batch report until the next
@@ -1111,6 +1119,7 @@ class SchedulerMetricsReporter:
         )
         if (
             not gauge_stale
+            and not is_fwd_occupancy_stale
             and time.perf_counter() <= self.metrics_collector.last_log_time + 30
         ):
             return