v0.34.0_1

src/metrics/vhost.rs

@@ -62,12 +62,25 @@ impl VhostMetrics {
                 Err(observed) => current = observed,
             }
         }
-        for (index, threshold) in DURATION_BUCKETS_US.iter().enumerate() {
-            if micros <= *threshold {
-                self.buckets[index].fetch_add(1, Ordering::Relaxed);
+        // Write exactly one exclusive histogram bin per exchange. Prometheus
+        // cumulative le=... buckets are reconstructed only when scraped.
+        // This removes up to 11 contended atomics for short 1 KiB responses.
+        let bucket = DURATION_BUCKETS_US.partition_point(|threshold| micros > *threshold);
+        self.buckets[bucket].fetch_add(1, Ordering::Relaxed);
+    }
+
+    /// A scrape-consistent cumulative representation of exclusive bins. The
+    /// sum of atomic snapshots is monotonic and the final count includes +Inf.
+    pub fn duration_histogram(&self) -> ([u64; DURATION_BUCKETS_US.len()], u64) {
+        let mut cumulative = [0u64; DURATION_BUCKETS_US.len()];
+        let mut count = 0u64;
+        for (index, bin) in self.buckets.iter().enumerate() {
+            count = count.saturating_add(bin.load(Ordering::Relaxed));
+            if index < DURATION_BUCKETS_US.len() {
+                cumulative[index] = count;
             }
         }
-        self.buckets[DURATION_BUCKETS_US.len()].fetch_add(1, Ordering::Relaxed);
+        (cumulative, count)
     }
 
     pub fn view(&self) -> VhostMetricsView {

src/metrics/vhost/tests.rs

@@ -1,5 +1,23 @@
 mod vhost_tests {
     use super::*;
+    #[test]
+    fn exclusive_bins_reconstruct_exact_prometheus_cumulative_boundaries() {
+        let m = VhostMetrics::default();
+        m.active.store(5, Ordering::Relaxed);
+        for micros in [1, 5_000, 5_001, 25_000, 5_000_001] {
+            m.complete(200, false, std::time::Duration::from_micros(micros), 0, 1040);
+        }
+        let (cumulative, total) = m.duration_histogram();
+        assert_eq!(total, 5);
+        assert_eq!(cumulative, [2, 3, 4, 4, 4, 4, 4, 4, 4, 4]);
+        assert_eq!(n(&m.buckets[0]), 2);
+        assert_eq!(n(&m.buckets[1]), 1);
+        assert_eq!(n(&m.buckets[2]), 1);
+        assert_eq!(n(&m.buckets[10]), 1);
+        assert_eq!(n(&m.completed), 5);
+        assert_eq!(n(&m.active), 0);
+    }
+
     #[test]
     fn streaming_completion_and_histogram() {
         let m = VhostMetrics::default();
@@ -10,7 +28,12 @@ mod vhost_tests {
         assert_eq!(n(&m.status[4]), 1);
         assert_eq!(n(&m.buckets[1]), 0);
         assert_eq!(n(&m.buckets[2]), 1);
-        assert_eq!(n(&m.buckets[10]), 1);
+        assert_eq!(n(&m.buckets[10]), 0); // exclusive +Inf bin
+        let (buckets, count) = m.duration_histogram();
+        assert_eq!(buckets[1], 0);
+        assert_eq!(buckets[2], 1);
+        assert_eq!(buckets[9], 1);
+        assert_eq!(count, 1);
         let view = m.view();
         assert_eq!(view.requests, 0);
         assert_eq!(view.completed, 1);