Implement scheduler.util.backoff as a queue

We are going to use PodBackoff for controlling backoff when adding
unschedulable pods back to the active scheduling queue. In order to do
this more easily, limit the interface for PodBackoff to only this struct
(rather than exposing BackoffEntry) and change the backing expiry
implementation to be queue based.

pkg/scheduler/factory/factory.go

@@ -1493,8 +1493,7 @@ func (c *configFactory) MakeDefaultErrorFunc(backoff *util.PodBackoff, podQueue
 			// to run on a node, scheduler takes the pod into account when running
 			// predicates for the node.
 			if !util.PodPriorityEnabled() {
-				entry := backoff.GetEntry(podID)
-				if !entry.TryWait(backoff.MaxDuration()) {
+				if !backoff.TryBackoffAndWait(podID) {
 					klog.Warningf("Request for pod %v already in flight, abandoning", podID)
 					return
 				}

pkg/scheduler/util/BUILD

@@ -11,7 +11,6 @@ go_test(
     srcs = [
         "backoff_utils_test.go",
         "heap_test.go",
-        "testutil_test.go",
         "utils_test.go",
     ],
     embed = [":go_default_library"],
@@ -28,7 +27,6 @@ go_library(
     srcs = [
         "backoff_utils.go",
         "heap.go",
-        "testutil.go",
         "utils.go",
     ],
     importpath = "k8s.io/kubernetes/pkg/scheduler/util",

pkg/scheduler/util/backoff_utils.go

@@ -37,10 +37,11 @@ func (realClock) Now() time.Time {
 	return time.Now()
 }
 
-// BackoffEntry is single threaded.  in particular, it only allows a single action to be waiting on backoff at a time.
-// It is expected that all users will only use the public TryWait(...) method
+// backoffEntry is single threaded.  in particular, it only allows a single action to be waiting on backoff at a time.
 // It is also not safe to copy this object.
-type BackoffEntry struct {
+type backoffEntry struct {
+	initialized bool
+	podName     ktypes.NamespacedName
 	backoff     time.Duration
 	lastUpdate  time.Time
 	reqInFlight int32
@@ -48,45 +49,46 @@ type BackoffEntry struct {
 
 // tryLock attempts to acquire a lock via atomic compare and swap.
 // returns true if the lock was acquired, false otherwise
-func (b *BackoffEntry) tryLock() bool {
+func (b *backoffEntry) tryLock() bool {
 	return atomic.CompareAndSwapInt32(&b.reqInFlight, 0, 1)
 }
 
 // unlock returns the lock.  panics if the lock isn't held
-func (b *BackoffEntry) unlock() {
+func (b *backoffEntry) unlock() {
 	if !atomic.CompareAndSwapInt32(&b.reqInFlight, 1, 0) {
 		panic(fmt.Sprintf("unexpected state on unlocking: %+v", b))
 	}
 }
 
-// TryWait tries to acquire the backoff lock, maxDuration is the maximum allowed period to wait for.
-func (b *BackoffEntry) TryWait(maxDuration time.Duration) bool {
-	if !b.tryLock() {
-		return false
-	}
-	defer b.unlock()
-	b.wait(maxDuration)
-	return true
+// backoffTime returns the Time when a backoffEntry completes backoff
+func (b *backoffEntry) backoffTime() time.Time {
+	return b.lastUpdate.Add(b.backoff)
 }
 
-func (b *BackoffEntry) getBackoff(maxDuration time.Duration) time.Duration {
-	duration := b.backoff
-	newDuration := time.Duration(duration) * 2
+// getBackoff returns the duration until this entry completes backoff
+func (b *backoffEntry) getBackoff(maxDuration time.Duration) time.Duration {
+	if !b.initialized {
+		b.initialized = true
+		return b.backoff
+	}
+	newDuration := b.backoff * 2
 	if newDuration > maxDuration {
 		newDuration = maxDuration
 	}
 	b.backoff = newDuration
-	klog.V(4).Infof("Backing off %s", duration.String())
-	return duration
+	klog.V(4).Infof("Backing off %s", newDuration.String())
+	return newDuration
 }
 
-func (b *BackoffEntry) wait(maxDuration time.Duration) {
+// backoffAndWait Blocks until this entry has completed backoff
+func (b *backoffEntry) backoffAndWait(maxDuration time.Duration) {
 	time.Sleep(b.getBackoff(maxDuration))
 }
 
 // PodBackoff is used to restart a pod with back-off delay.
 type PodBackoff struct {
-	perPodBackoff   map[ktypes.NamespacedName]*BackoffEntry
+	// expiryQ stores backoffEntry orderedy by lastUpdate until they reach maxDuration and are GC'd
+	expiryQ         *Heap
 	lock            sync.Mutex
 	clock           clock
 	defaultDuration time.Duration
@@ -111,24 +113,54 @@ func CreatePodBackoff(defaultDuration, maxDuration time.Duration) *PodBackoff {
 // CreatePodBackoffWithClock creates a pod back-off object by default duration, max duration and clock.
 func CreatePodBackoffWithClock(defaultDuration, maxDuration time.Duration, clock clock) *PodBackoff {
 	return &PodBackoff{
-		perPodBackoff:   map[ktypes.NamespacedName]*BackoffEntry{},
+		expiryQ:         NewHeap(backoffEntryKeyFunc, backoffEntryCompareUpdate),
 		clock:           clock,
 		defaultDuration: defaultDuration,
 		maxDuration:     maxDuration,
 	}
 }
 
-// GetEntry returns a back-off entry by Pod ID.
-func (p *PodBackoff) GetEntry(podID ktypes.NamespacedName) *BackoffEntry {
+// getEntry returns the backoffEntry for a given podID
+func (p *PodBackoff) getEntry(podID ktypes.NamespacedName) *backoffEntry {
+	entry, exists, _ := p.expiryQ.GetByKey(podID.String())
+	var be *backoffEntry
+	if !exists {
+		be = &backoffEntry{
+			initialized: false,
+			podName:     podID,
+			backoff:     p.defaultDuration,
+		}
+		p.expiryQ.Update(be)
+	} else {
+		be = entry.(*backoffEntry)
+	}
+	return be
+}
+
+// BackoffPod updates the backoff for a podId and returns the duration until backoff completion
+func (p *PodBackoff) BackoffPod(podID ktypes.NamespacedName) time.Duration {
 	p.lock.Lock()
 	defer p.lock.Unlock()
-	entry, ok := p.perPodBackoff[podID]
-	if !ok {
-		entry = &BackoffEntry{backoff: p.defaultDuration}
-		p.perPodBackoff[podID] = entry
-	}
+	entry := p.getEntry(podID)
 	entry.lastUpdate = p.clock.Now()
-	return entry
+	p.expiryQ.Update(entry)
+	return entry.getBackoff(p.maxDuration)
+}
+
+// TryBackoffAndWait tries to acquire the backoff lock
+func (p *PodBackoff) TryBackoffAndWait(podID ktypes.NamespacedName) bool {
+	p.lock.Lock()
+	entry := p.getEntry(podID)
+
+	if !entry.tryLock() {
+		p.lock.Unlock()
+		return false
+	}
+	defer entry.unlock()
+	duration := entry.getBackoff(p.maxDuration)
+	p.lock.Unlock()
+	time.Sleep(duration)
+	return true
 }
 
 // Gc execute garbage collection on the pod back-off.
@@ -136,9 +168,30 @@ func (p *PodBackoff) Gc() {
 	p.lock.Lock()
 	defer p.lock.Unlock()
 	now := p.clock.Now()
-	for podID, entry := range p.perPodBackoff {
-		if now.Sub(entry.lastUpdate) > p.maxDuration {
-			delete(p.perPodBackoff, podID)
+	var be *backoffEntry
+	for {
+		entry := p.expiryQ.Peek()
+		if entry == nil {
+			break
+		}
+		be = entry.(*backoffEntry)
+		if now.Sub(be.lastUpdate) > p.maxDuration {
+			p.expiryQ.Pop()
+		} else {
+			break
 		}
 	}
 }
+
+// backoffEntryKeyFunc is the keying function used for mapping a backoffEntry to string for heap
+func backoffEntryKeyFunc(b interface{}) (string, error) {
+	be := b.(*backoffEntry)
+	return be.podName.String(), nil
+}
+
+// backoffEntryCompareUpdate returns true when b1's backoff time is before b2's
+func backoffEntryCompareUpdate(b1, b2 interface{}) bool {
+	be1 := b1.(*backoffEntry)
+	be2 := b2.(*backoffEntry)
+	return be1.lastUpdate.Before(be2.lastUpdate)
+}

pkg/scheduler/util/backoff_utils_test.go

@@ -64,7 +64,7 @@ func TestBackoff(t *testing.T) {
 	}
 
 	for _, test := range tests {
-		duration := backoff.GetEntry(test.podID).getBackoff(backoff.maxDuration)
+		duration := backoff.BackoffPod(test.podID)
 		if duration != test.expectedDuration {
 			t.Errorf("expected: %s, got %s for %s", test.expectedDuration.String(), duration.String(), test.podID)
 		}
@@ -72,14 +72,15 @@ func TestBackoff(t *testing.T) {
 		backoff.Gc()
 	}
 	fooID := ktypes.NamespacedName{Namespace: "default", Name: "foo"}
-	backoff.perPodBackoff[fooID].backoff = 60 * time.Second
-	duration := backoff.GetEntry(fooID).getBackoff(backoff.maxDuration)
+	be := backoff.getEntry(fooID)
+	be.backoff = 60 * time.Second
+	duration := backoff.BackoffPod(fooID)
 	if duration != 60*time.Second {
 		t.Errorf("expected: 60, got %s", duration.String())
 	}
 	// Verify that we split on namespaces correctly, same name, different namespace
 	fooID.Namespace = "other"
-	duration = backoff.GetEntry(fooID).getBackoff(backoff.maxDuration)
+	duration = backoff.BackoffPod(fooID)
 	if duration != 1*time.Second {
 		t.Errorf("expected: 1, got %s", duration.String())
 	}

pkg/scheduler/util/heap.go

@@ -113,6 +113,14 @@ func (h *heapData) Pop() interface{} {
 	return item.obj
 }
 
+// Peek is supposed to be called by heap.Peek only.
+func (h *heapData) Peek() interface{} {
+	if len(h.queue) > 0 {
+		return h.items[h.queue[0]].obj
+	}
+	return nil
+}
+
 // Heap is a producer/consumer queue that implements a heap data structure.
 // It can be used to implement priority queues and similar data structures.
 type Heap struct {
@@ -169,7 +177,12 @@ func (h *Heap) Delete(obj interface{}) error {
 	return fmt.Errorf("object not found")
 }
 
-// Pop returns the head of the heap.
+// Peek returns the head of the heap without removing it.
+func (h *Heap) Peek() interface{} {
+	return h.data.Peek()
+}
+
+// Pop returns the head of the heap and removes it.
 func (h *Heap) Pop() (interface{}, error) {
 	obj := heap.Pop(h.data)
 	if obj != nil {