Reduce Pool contention in cacher

Author: wojtek-t

staging/src/k8s.io/apiserver/pkg/storage/cacher/cacher.go

@@ -186,6 +186,9 @@ type Cacher struct {
 	stopped  bool
 	stopCh   chan struct{}
 	stopWg   sync.WaitGroup
+
+	// Used to avoid unnecessary allocations in underlying watchers.
+	timer *time.Timer
 }
 
 // NewCacherFromConfig creates a new Cacher responsible for servicing WATCH and LIST requests from
@@ -227,6 +230,7 @@ func NewCacherFromConfig(config Config) *Cacher {
 		// and there are no guarantees on the order that they will stop.
 		// So we will be simply closing the channel, and synchronizing on the WaitGroup.
 		stopCh: stopCh,
+		timer:  time.NewTimer(time.Duration(0)),
 	}
 	watchCache.SetOnEvent(cacher.processEvent)
 	go cacher.dispatchEvents()
@@ -242,6 +246,14 @@ func NewCacherFromConfig(config Config) *Cacher {
 			}, time.Second, stopCh,
 		)
 	}()
+
+	// Ensure that timer is stopped.
+	if !cacher.timer.Stop() {
+		// Consume triggered (but not yet received) timer event
+		// so that future reuse does not get a spurious timeout.
+		<-cacher.timer.C
+	}
+
 	return cacher
 }
 
@@ -621,13 +633,13 @@ func (c *Cacher) dispatchEvent(event *watchCacheEvent) {
 	defer c.Unlock()
 	// Iterate over "allWatchers" no matter what the trigger function is.
 	for _, watcher := range c.watchers.allWatchers {
-		watcher.add(event, c.dispatchTimeoutBudget)
+		watcher.add(event, c.timer, c.dispatchTimeoutBudget)
 	}
 	if supported {
 		// Iterate over watchers interested in the given values of the trigger.
 		for _, triggerValue := range triggerValues {
 			for _, watcher := range c.watchers.valueWatchers[triggerValue] {
-				watcher.add(event, c.dispatchTimeoutBudget)
+				watcher.add(event, c.timer, c.dispatchTimeoutBudget)
 			}
 		}
 	} else {
@@ -640,7 +652,7 @@ func (c *Cacher) dispatchEvent(event *watchCacheEvent) {
 		// Iterate over watchers interested in exact values for all values.
 		for _, watchers := range c.watchers.valueWatchers {
 			for _, watcher := range watchers {
-				watcher.add(event, c.dispatchTimeoutBudget)
+				watcher.add(event, c.timer, c.dispatchTimeoutBudget)
 			}
 		}
 	}
@@ -826,9 +838,7 @@ func (c *cacheWatcher) stop() {
 	}
 }
 
-var timerPool sync.Pool
-
-func (c *cacheWatcher) add(event *watchCacheEvent, budget *timeBudget) {
+func (c *cacheWatcher) add(event *watchCacheEvent, timer *time.Timer, budget *timeBudget) {
 	// Try to send the event immediately, without blocking.
 	select {
 	case c.input <- event:
@@ -842,23 +852,16 @@ func (c *cacheWatcher) add(event *watchCacheEvent, budget *timeBudget) {
 	startTime := time.Now()
 	timeout := budget.takeAvailable()
 
-	t, ok := timerPool.Get().(*time.Timer)
-	if ok {
-		t.Reset(timeout)
-	} else {
-		t = time.NewTimer(timeout)
-	}
-	defer timerPool.Put(t)
+	timer.Reset(timeout)
 
 	select {
 	case c.input <- event:
-		stopped := t.Stop()
-		if !stopped {
+		if !timer.Stop() {
 			// Consume triggered (but not yet received) timer event
 			// so that future reuse does not get a spurious timeout.
-			<-t.C
+			<-timer.C
 		}
-	case <-t.C:
+	case <-timer.C:
 		// This means that we couldn't send event to that watcher.
 		// Since we don't want to block on it infinitely,
 		// we simply terminate it.