stats: add busy_duration stats (#4179)

tokio/src/runtime/stats/stats.rs

@@ -1,6 +1,9 @@
 //! This file contains the types necessary to collect various types of stats.
 use crate::loom::sync::atomic::{AtomicU64, Ordering::Relaxed};
 
+use std::convert::TryFrom;
+use std::time::{Duration, Instant};
+
 /// This type contains methods to retrieve stats from a Tokio runtime.
 #[derive(Debug)]
 pub struct RuntimeStats {
@@ -14,6 +17,10 @@ pub struct WorkerStats {
     park_count: AtomicU64,
     steal_count: AtomicU64,
     poll_count: AtomicU64,
+    busy_duration_min: AtomicU64,
+    busy_duration_max: AtomicU64,
+    busy_duration_last: AtomicU64,
+    busy_duration_total: AtomicU64,
 }
 
 impl RuntimeStats {
@@ -24,6 +31,10 @@ impl RuntimeStats {
                 park_count: AtomicU64::new(0),
                 steal_count: AtomicU64::new(0),
                 poll_count: AtomicU64::new(0),
+                busy_duration_min: AtomicU64::new(0),
+                busy_duration_max: AtomicU64::new(0),
+                busy_duration_last: AtomicU64::new(0),
+                busy_duration_total: AtomicU64::new(0),
             });
         }
 
@@ -54,13 +65,43 @@ impl WorkerStats {
     pub fn poll_count(&self) -> u64 {
         self.poll_count.load(Relaxed)
     }
+
+    /// Returns the duration for which the runtime was busy last time it was busy.
+    pub fn busy_duration_last(&self) -> Duration {
+        Duration::from_nanos(self.busy_duration_last.load(Relaxed))
+    }
+
+    /// Returns the total amount of time this worker has been busy for.
+    pub fn busy_duration_total(&self) -> Duration {
+        Duration::from_nanos(self.busy_duration_total.load(Relaxed))
+    }
+
+    /// Returns the smallest busy duration since the last 16 parks.
+    pub fn busy_duration_min(&self) -> Duration {
+        Duration::from_nanos(self.busy_duration_min.load(Relaxed))
+    }
+
+    /// Returns the largest busy duration since the last 16 parks.
+    pub fn busy_duration_max(&self) -> Duration {
+        Duration::from_nanos(self.busy_duration_max.load(Relaxed))
+    }
 }
 
 pub(crate) struct WorkerStatsBatcher {
     my_index: usize,
     park_count: u64,
     steal_count: u64,
     poll_count: u64,
+    /// The last 16 busy durations in nanoseconds.
+    ///
+    /// This array is set to contain the same value 16 times after the first
+    /// iteration. Since we only publish the min, max and last value in the
+    /// array, then this gives the correct result.
+    busy_duration: [u64; 16],
+    busy_duration_i: usize,
+    /// The total busy duration in nanoseconds.
+    busy_duration_total: u64,
+    last_resume_time: Instant,
 }
 
 impl WorkerStatsBatcher {
@@ -70,6 +111,10 @@ impl WorkerStatsBatcher {
             park_count: 0,
             steal_count: 0,
             poll_count: 0,
+            busy_duration: [0; 16],
+            busy_duration_i: usize::MAX,
+            busy_duration_total: 0,
+            last_resume_time: Instant::now(),
         }
     }
     pub(crate) fn submit(&mut self, to: &RuntimeStats) {
@@ -78,13 +123,46 @@ impl WorkerStatsBatcher {
         worker.park_count.store(self.park_count, Relaxed);
         worker.steal_count.store(self.steal_count, Relaxed);
         worker.poll_count.store(self.poll_count, Relaxed);
+
+        let mut min = u64::MAX;
+        let mut max = 0;
+        let last = self.busy_duration[self.busy_duration_i % 16];
+        for &val in &self.busy_duration {
+            if val <= min {
+                min = val;
+            }
+            if val >= max {
+                max = val;
+            }
+        }
+        worker.busy_duration_min.store(min, Relaxed);
+        worker.busy_duration_max.store(max, Relaxed);
+        worker.busy_duration_last.store(last, Relaxed);
+        worker
+            .busy_duration_total
+            .store(self.busy_duration_total, Relaxed);
     }
 
     pub(crate) fn about_to_park(&mut self) {
         self.park_count += 1;
+
+        let busy_duration = self.last_resume_time.elapsed();
+        let busy_duration = u64::try_from(busy_duration.as_nanos()).unwrap_or(u64::MAX);
+        self.busy_duration_total += busy_duration;
+        if self.busy_duration_i == usize::MAX {
+            // We are parking for the first time. Set array to contain current
+            // duration in every slot.
+            self.busy_duration_i = 0;
+            self.busy_duration = [busy_duration; 16];
+        } else {
+            self.busy_duration_i = (self.busy_duration_i + 1) % 16;
+            self.busy_duration[self.busy_duration_i] = busy_duration;
+        }
     }
 
-    pub(crate) fn returned_from_park(&mut self) {}
+    pub(crate) fn returned_from_park(&mut self) {
+        self.last_resume_time = Instant::now();
+    }
 
     #[cfg(feature = "rt-multi-thread")]
     pub(crate) fn incr_steal_count(&mut self, by: u16) {