feature(scheduling_queue): track events per Pods (#118438)

* feature(sscheduling_queue): track events per Pods

* fix typos

* record events in one slice and make each in-flight Pod to refer it

* fix: use Pop() in test before AddUnschedulableIfNotPresent to register in-flight Pods

* eliminate MakeNextPodFuncs

* call Done inside the scheduling queue

* fix comment

* implement done() not to require lock in it

* fix UTs

* improve the receivedEvents implementation based on suggestions

* call DonePod when we don't call AddUnschedulableIfNotPresent

* fix UT

* use queuehint to filter out events for in-flight Pods

* fix based on suggestion from aldo

* fix based on suggestion from Wei

* rename lastEventBefore → previousEvent

* fix based on suggestion

* address comments from aldo

* fix based on the suggestion from Abdullah

* gate in-flight Pods logic by the SchedulingQueueHints feature gate

pkg/scheduler/internal/queue/scheduling_queue.go

@@ -27,6 +27,7 @@ limitations under the License.
 package queue
 
 import (
+	"container/list"
 	"context"
 	"fmt"
 	"math/rand"
@@ -104,6 +105,9 @@ type SchedulingQueue interface {
 	// Pop removes the head of the queue and returns it. It blocks if the
 	// queue is empty and waits until a new item is added to the queue.
 	Pop() (*framework.QueuedPodInfo, error)
+	// Done must be called for pod returned by Pop. This allows the queue to
+	// keep track of which pods are currently being processed.
+	Done(types.UID)
 	Update(logger klog.Logger, oldPod, newPod *v1.Pod) error
 	Delete(pod *v1.Pod) error
 	// TODO(sanposhiho): move all PreEnqueueCkeck to Requeue and delete it from this parameter eventually.
@@ -158,6 +162,13 @@ type PriorityQueue struct {
 
 	cond sync.Cond
 
+	// inFlightPods holds the UID of all pods which have been popped out for which Done
+	// hasn't been called yet - in other words, all pods that are currently being
+	// processed (being scheduled, in permit, or in the binding cycle).
+	inFlightPods map[types.UID]inFlightPod
+	// receivedEvents holds the events received by the scheduling queue.
+	receivedEvents *list.List
+
 	// activeQ is heap structure that scheduler actively looks at to find pods to
 	// schedule. Head of heap is the highest priority pod.
 	activeQ *heap.Heap
@@ -173,6 +184,7 @@ type PriorityQueue struct {
 	// received a move request. Unschedulable pods in and before this scheduling
 	// cycle will be put back to activeQueue if we were trying to schedule them
 	// when we received move request.
+	// TODO: this will be removed after SchedulingQueueHint goes to stable and the feature gate is removed.
 	moveRequestCycle int64
 
 	// preEnqueuePluginMap is keyed with profile name, valued with registered preEnqueue plugins.
@@ -189,6 +201,9 @@ type PriorityQueue struct {
 	metricsRecorder metrics.MetricAsyncRecorder
 	// pluginMetricsSamplePercent is the percentage of plugin metrics to be sampled.
 	pluginMetricsSamplePercent int
+
+	// isSchedulingQueueHintEnabled indicates whether the feature gate for the scheduling queue is enabled.
+	isSchedulingQueueHintEnabled bool
 }
 
 // QueueingHintFunction is the wrapper of QueueingHintFn that has PluginName.
@@ -197,6 +212,25 @@ type QueueingHintFunction struct {
 	QueueingHintFn framework.QueueingHintFn
 }
 
+type inFlightPod struct {
+	// previousEvent is the latest observed event when the pod is popped.
+	previousEvent *list.Element
+}
+
+// clusterEvent has the event and involved objects.
+type clusterEvent struct {
+	event framework.ClusterEvent
+	// oldObj is the object that involved this event.
+	oldObj interface{}
+	// newObj is the object that involved this event.
+	newObj interface{}
+
+	// inFlightPodsNum is the counter of pods referring to this cluster event.
+	// It is initialized with the number of Pods being scheduled when the event is received,
+	// and is decremented when the scheduling for those Pods are Done().
+	inFlightPodsNum int
+}
+
 type priorityQueueOptions struct {
 	clock                             clock.Clock
 	podInitialBackoffDuration         time.Duration
@@ -330,11 +364,14 @@ func NewPriorityQueue(
 		podMaxInUnschedulablePodsDuration: options.podMaxInUnschedulablePodsDuration,
 		activeQ:                           heap.NewWithRecorder(podInfoKeyFunc, comp, metrics.NewActivePodsRecorder()),
 		unschedulablePods:                 newUnschedulablePods(metrics.NewUnschedulablePodsRecorder(), metrics.NewGatedPodsRecorder()),
-		moveRequestCycle:                  -1,
+		inFlightPods:                      make(map[types.UID]inFlightPod),
+		receivedEvents:                    list.New(),
 		preEnqueuePluginMap:               options.preEnqueuePluginMap,
 		queueingHintMap:                   options.queueingHintMap,
 		metricsRecorder:                   options.metricsRecorder,
 		pluginMetricsSamplePercent:        options.pluginMetricsSamplePercent,
+		moveRequestCycle:                  -1,
+		isSchedulingQueueHintEnabled:      utilfeature.DefaultFeatureGate.Enabled(features.SchedulerQueueingHints),
 	}
 	pq.cond.L = &pq.lock
 	pq.podBackoffQ = heap.NewWithRecorder(podInfoKeyFunc, pq.podsCompareBackoffCompleted, metrics.NewBackoffPodsRecorder())
@@ -567,25 +604,67 @@ func (p *PriorityQueue) SchedulingCycle() int64 {
 	return p.schedulingCycle
 }
 
-// AddUnschedulableIfNotPresent inserts a pod that cannot be scheduled into
+// determineSchedulingHintForInFlightPod looks at the unschedulable plugins of the given Pod
+// and determines the scheduling hint for this Pod while checking the events that happened during in-flight.
+func (p *PriorityQueue) determineSchedulingHintForInFlightPod(logger klog.Logger, pInfo *framework.QueuedPodInfo, podSchedulingCycle int64) framework.QueueingHint {
+	if len(pInfo.UnschedulablePlugins) == 0 {
+		// When there is no unschedulable plugin, we cannot have a guess which event makes this Pod schedulable.
+		// Here, we use the latest requestCycle so that this Pod won't be stuck in the unschedulable pod pool for a long time.
+		if p.receivedEvents.Len() != 0 {
+			return framework.QueueAfterBackoff
+		}
+		return framework.QueueSkip
+	}
+
+	inFlightPod, ok := p.inFlightPods[pInfo.Pod.UID]
+	if !ok {
+		// It shouldn't reach here unless there is a bug somewhere.
+		// But, set podSchedulingCycle to moveRequestCycle
+		// so that this Pod won't stuck in the unschedulable pod pool.
+		logger.Error(nil, "In flight Pod isn't found in the scheduling queue. If you see this error log, it's likely a bug in the scheduler.", "pod", klog.KObj(pInfo.Pod))
+		return framework.QueueAfterBackoff
+	}
+
+	// AddUnschedulableIfNotPresent is called with the Pod at the end of scheduling or binding.
+	// So, given pInfo should have been Pop()ed before,
+	// we can assume pInfo must be recorded in inFlightPods.
+	// check if there is an event that makes this Pod schedulable based on pInfo.UnschedulablePlugins.
+	event := p.receivedEvents.Front()
+	if inFlightPod.previousEvent != nil {
+		// only check events that happened after the Pod was popped.
+		event = inFlightPod.previousEvent.Next()
+	}
+	schedulingHint := framework.QueueSkip
+	for ; event != nil; event = event.Next() {
+		e := event.Value.(*clusterEvent)
+
+		hint := p.isPodWorthRequeuing(logger, pInfo, e.event, e.oldObj, e.newObj)
+		if hint == framework.QueueSkip {
+			continue
+		}
+
+		if hint == framework.QueueImmediately {
+			// QueueImmediately is the strongest opinion, we don't need to check other events.
+			schedulingHint = framework.QueueImmediately
+			break
+		}
+		if hint == framework.QueueAfterBackoff {
+			// replace schedulingHint with QueueAfterBackoff,
+			// but continue to check other events because we may find it QueueImmediately with other events.
+			schedulingHint = framework.QueueAfterBackoff
+		}
+	}
+	return schedulingHint
+}
+
+// addUnschedulableIfNotPresentWithoutQueueingHint inserts a pod that cannot be scheduled into
 // the queue, unless it is already in the queue. Normally, PriorityQueue puts
 // unschedulable pods in `unschedulablePods`. But if there has been a recent move
 // request, then the pod is put in `podBackoffQ`.
-func (p *PriorityQueue) AddUnschedulableIfNotPresent(logger klog.Logger, pInfo *framework.QueuedPodInfo, podSchedulingCycle int64) error {
+// TODO: This function is called only when p.isSchedulingQueueHintEnabled is false,
-	p.lock.Lock()
+// and this will be removed after SchedulingQueueHint goes to stable and the feature gate is removed.
-	defer p.lock.Unlock()
+func (p *PriorityQueue) addUnschedulableWithoutQueueingHint(logger klog.Logger, pInfo *framework.QueuedPodInfo, podSchedulingCycle int64) error {
 	pod := pInfo.Pod
-	if p.unschedulablePods.get(pod) != nil {
-		return fmt.Errorf("Pod %v is already present in unschedulable queue", klog.KObj(pod))
-	}
-
-	if _, exists, _ := p.activeQ.Get(pInfo); exists {
-		return fmt.Errorf("Pod %v is already present in the active queue", klog.KObj(pod))
-	}
-	if _, exists, _ := p.podBackoffQ.Get(pInfo); exists {
-		return fmt.Errorf("Pod %v is already present in the backoff queue", klog.KObj(pod))
-	}
-
 	// Refresh the timestamp since the pod is re-added.
 	pInfo.Timestamp = p.clock.Now()
 
@@ -610,6 +689,54 @@ func (p *PriorityQueue) AddUnschedulableIfNotPresent(logger klog.Logger, pInfo *
 	return nil
 }
 
+// AddUnschedulableIfNotPresent inserts a pod that cannot be scheduled into
+// the queue, unless it is already in the queue. Normally, PriorityQueue puts
+// unschedulable pods in `unschedulablePods`. But if there has been a recent move
+// request, then the pod is put in `podBackoffQ`.
+func (p *PriorityQueue) AddUnschedulableIfNotPresent(logger klog.Logger, pInfo *framework.QueuedPodInfo, podSchedulingCycle int64) error {
+	p.lock.Lock()
+	defer p.lock.Unlock()
+
+	// In any case, this Pod will be moved back to the queue and we should call Done.
+	defer p.done(pInfo.Pod.UID)
+
+	pod := pInfo.Pod
+	if p.unschedulablePods.get(pod) != nil {
+		return fmt.Errorf("Pod %v is already present in unschedulable queue", klog.KObj(pod))
+	}
+
+	if _, exists, _ := p.activeQ.Get(pInfo); exists {
+		return fmt.Errorf("Pod %v is already present in the active queue", klog.KObj(pod))
+	}
+	if _, exists, _ := p.podBackoffQ.Get(pInfo); exists {
+		return fmt.Errorf("Pod %v is already present in the backoff queue", klog.KObj(pod))
+	}
+
+	if !p.isSchedulingQueueHintEnabled {
+		// fall back to the old behavior which doesn't depend on the queueing hint.
+		return p.addUnschedulableWithoutQueueingHint(logger, pInfo, podSchedulingCycle)
+	}
+
+	// Refresh the timestamp since the pod is re-added.
+	pInfo.Timestamp = p.clock.Now()
+
+	// If a move request has been received, move it to the BackoffQ, otherwise move
+	// it to unschedulablePods.
+	for plugin := range pInfo.UnschedulablePlugins {
+		metrics.UnschedulableReason(plugin, pInfo.Pod.Spec.SchedulerName).Inc()
+	}
+
+	// Based on isPodWorthRequeuing(), we check whether this Pod may change its scheduling result by any of events that happened during scheduling.
+	schedulingHint := p.determineSchedulingHintForInFlightPod(logger, pInfo, podSchedulingCycle)
+
+	// In this case, we try to requeue this Pod to activeQ/backoffQ.
+	queue := p.requeuePodViaQueueingHint(logger, pInfo, schedulingHint, ScheduleAttemptFailure)
+	logger.V(6).Info("Pod moved to an internal scheduling queue", "pod", klog.KObj(pod), "event", ScheduleAttemptFailure, "queue", queue, "schedulingCycle", podSchedulingCycle)
+
+	p.addNominatedPodUnlocked(logger, pInfo.PodInfo, nil)
+	return nil
+}
+
 // flushBackoffQCompleted Moves all pods from backoffQ which have completed backoff in to activeQ
 func (p *PriorityQueue) flushBackoffQCompleted(logger klog.Logger) {
 	p.lock.Lock()
@@ -685,9 +812,74 @@ func (p *PriorityQueue) Pop() (*framework.QueuedPodInfo, error) {
 	pInfo := obj.(*framework.QueuedPodInfo)
 	pInfo.Attempts++
 	p.schedulingCycle++
+	// In flight, no move request yet.
+	if p.isSchedulingQueueHintEnabled {
+		p.inFlightPods[pInfo.Pod.UID] = inFlightPod{
+			previousEvent: p.receivedEvents.Back(),
+		}
+	}
+
+	for plugin := range pInfo.UnschedulablePlugins {
+		metrics.UnschedulableReason(plugin, pInfo.Pod.Spec.SchedulerName).Dec()
+	}
+
 	return pInfo, nil
 }
 
+// Done must be called for pod returned by Pop. This allows the queue to
+// keep track of which pods are currently being processed.
+func (p *PriorityQueue) Done(pod types.UID) {
+	p.lock.Lock()
+	defer p.lock.Unlock()
+
+	p.done(pod)
+}
+
+func (p *PriorityQueue) done(pod types.UID) {
+	if !p.isSchedulingQueueHintEnabled {
+		// do nothing if schedulingQueueHint is disabled.
+		// In that case, we don't have inFlightPods and receivedEvents.
+		return
+	}
+	inFlightPod, ok := p.inFlightPods[pod]
+	if !ok {
+		// This Pod is already done()ed.
+		return
+	}
+	delete(p.inFlightPods, pod)
+
+	// remove events which is only referred from this Pod
+	// so that the receivedEvents map doesn't grow infinitely.
+
+	// Find the event that we should start.
+	// case1. If the previousEvent is nil, it means no receivedEvents when this Pod's scheduling started.
+	//        We start from the first event in the receivedEvents.
+	// case2. If the previousEvent is not nil, but the inFlightPodsNum is 0,
+	//        this previousEvent is removed from the list already.
+	//        We start from the first event in the receivedEvents.
+	event := p.receivedEvents.Front()
+	if inFlightPod.previousEvent != nil && inFlightPod.previousEvent.Value.(*clusterEvent).inFlightPodsNum != 0 {
+		// case3. If the previousEvent is not nil, and the inFlightPodsNum is not 0,
+		//        we can start from the next event of the previousEvent.
+		event = inFlightPod.previousEvent.Next()
+	}
+
+	for event != nil {
+		e := event.Value.(*clusterEvent)
+		// decrement inFlightPodsNum on events that happened after the Pod is popped.
+		e.inFlightPodsNum--
+		if e.inFlightPodsNum <= 0 {
+			// remove the event from the list if no Pod refers to it.
+			eventToDelete := event
+			// we need to take next event before removal.
+			event = event.Next()
+			p.receivedEvents.Remove(eventToDelete)
+			continue
+		}
+		event = event.Next()
+	}
+}
+
 // isPodUpdated checks if the pod is updated in a way that it may have become
 // schedulable. It drops status of the pod and compares it with old version,
 // except for pod.status.resourceClaimStatuses: changing that may have an
@@ -853,7 +1045,7 @@ func (p *PriorityQueue) MoveAllToActiveOrBackoffQueue(logger klog.Logger, event
 func (p *PriorityQueue) requeuePodViaQueueingHint(logger klog.Logger, pInfo *framework.QueuedPodInfo, schedulingHint framework.QueueingHint, event string) string {
 	if schedulingHint == framework.QueueSkip {
 		p.unschedulablePods.addOrUpdate(pInfo)
-		metrics.SchedulerQueueIncomingPods.WithLabelValues("unschedulable", ScheduleAttemptFailure).Inc()
+		metrics.SchedulerQueueIncomingPods.WithLabelValues("unschedulable", event).Inc()
 		return unschedulablePods
 	}
 
@@ -907,7 +1099,22 @@ func (p *PriorityQueue) movePodsToActiveOrBackoffQueue(logger klog.Logger, podIn
 			activated = true
 		}
 	}
+
 	p.moveRequestCycle = p.schedulingCycle
+
+	// (no need to check the feature gate because there is always no p.inFlightPods when the feature is disabled.)
+	if len(p.inFlightPods) != 0 {
+		// AddUnschedulableIfNotPresent might get called for in-flight Pods later, and in
+		// AddUnschedulableIfNotPresent we need to know whether events were
+		// observed while scheduling them.
+		p.receivedEvents.PushBack(&clusterEvent{
+			event:           event,
+			inFlightPodsNum: len(p.inFlightPods),
+			oldObj:          oldObj,
+			newObj:          newObj,
+		})
+	}
+
 	if activated {
 		p.cond.Broadcast()
 	}
@@ -1233,24 +1440,6 @@ func newPodNominator(podLister listersv1.PodLister) *nominator {
 	}
 }
 
-// MakeNextPodFunc returns a function to retrieve the next pod from a given
-// scheduling queue
-func MakeNextPodFunc(logger klog.Logger, queue SchedulingQueue) func() *framework.QueuedPodInfo {
-	return func() *framework.QueuedPodInfo {
-		podInfo, err := queue.Pop()
-		if err == nil && podInfo != nil {
-			logger.V(4).Info("About to try and schedule pod", "pod", klog.KObj(podInfo.Pod))
-			for plugin := range podInfo.UnschedulablePlugins {
-				metrics.UnschedulableReason(plugin, podInfo.Pod.Spec.SchedulerName).Dec()
-			}
-			return podInfo
-		} else if err != nil {
-			logger.Error(err, "Error while retrieving next pod from scheduling queue")
-		}
-		return nil
-	}
-}
-
 func podInfoKeyFunc(obj interface{}) (string, error) {
 	return cache.MetaNamespaceKeyFunc(obj.(*framework.QueuedPodInfo).Pod)
 }

pkg/scheduler/internal/queue/scheduling_queue_test.go

@@ -17,6 +17,7 @@ limitations under the License.
 package queue
 
 import (
+	"container/list"
 	"context"
 	"fmt"
 	"math"
@@ -32,12 +33,15 @@ import (
 	"k8s.io/apimachinery/pkg/runtime"
 	"k8s.io/apimachinery/pkg/types"
 	"k8s.io/apimachinery/pkg/util/sets"
+	utilfeature "k8s.io/apiserver/pkg/util/feature"
 	"k8s.io/client-go/informers"
 	"k8s.io/client-go/kubernetes/fake"
+	featuregatetesting "k8s.io/component-base/featuregate/testing"
 	"k8s.io/component-base/metrics/testutil"
 	"k8s.io/klog/v2"
 	"k8s.io/klog/v2/ktesting"
 	podutil "k8s.io/kubernetes/pkg/api/v1/pod"
+	"k8s.io/kubernetes/pkg/features"
 	"k8s.io/kubernetes/pkg/scheduler/framework"
 	"k8s.io/kubernetes/pkg/scheduler/framework/plugins/queuesort"
 	"k8s.io/kubernetes/pkg/scheduler/metrics"
@@ -175,14 +179,454 @@ func TestPriorityQueue_AddWithReversePriorityLessFunc(t *testing.T) {
 	}
 }
 
+func clusterEventsToList(clusterEvents []*clusterEvent) *list.List {
+	l := list.New()
+	for _, event := range clusterEvents {
+		l.PushBack(event)
+	}
+	return l
+}
+
+func listToClusterEvents(l *list.List) []*clusterEvent {
+	clusterEvents := []*clusterEvent{}
+	for e := l.Front(); e != nil; e = e.Next() {
+		clusterEvents = append(clusterEvents, e.Value.(*clusterEvent))
+	}
+	return clusterEvents
+}
+
+func Test_InFlightPods(t *testing.T) {
+	pod := st.MakePod().Name("targetpod").UID("pod1").Obj()
+	pod2 := st.MakePod().Name("targetpod2").UID("pod2").Obj()
+	pod3 := st.MakePod().Name("targetpod3").UID("pod3").Obj()
+
+	type action struct {
+		// ONLY ONE of the following should be set.
+		eventHappens *framework.ClusterEvent
+		podPopped    *v1.Pod
+		podEnqueued  *framework.QueuedPodInfo
+	}
+
+	tests := []struct {
+		name            string
+		queueingHintMap QueueingHintMapPerProfile
+		// initialPods is the initial Pods in the activeQ.
+		initialPods                  []*v1.Pod
+		actions                      []action
+		wantInFlightPods             map[types.UID]inFlightPod
+		wantActiveQPodNames          []string
+		wantBackoffQPodNames         []string
+		wantUnschedPodPoolPodNames   []string
+		wantReceivedEvents           *list.List
+		isSchedulingQueueHintEnabled bool
+	}{
+		{
+			name:        "when SchedulingQueueHint is disabled, inFlightPods and receivedEvents should be empty",
+			initialPods: []*v1.Pod{pod},
+			actions: []action{
+				// This Pod shouldn't be added to inFlightPods because SchedulingQueueHint is disabled.
+				{podPopped: pod},
+				// This event shouldn't be added to receivedEvents because SchedulingQueueHint is disabled.
+				{eventHappens: &PvAdd},
+			},
+			wantInFlightPods:   map[types.UID]inFlightPod{},
+			wantReceivedEvents: clusterEventsToList([]*clusterEvent{}),
+		},
+		{
+			name:        "when SchedulingQueueHint is disabled, which queue to enqueue Pod should be decided without SchedulingQueueHint",
+			initialPods: []*v1.Pod{pod},
+			actions: []action{
+				{podPopped: pod},
+				{eventHappens: &AssignedPodAdd},
+				{podEnqueued: newQueuedPodInfoForLookup(pod, "fooPlugin1")},
+			},
+			wantBackoffQPodNames: []string{"targetpod"},
+			wantInFlightPods:     map[types.UID]inFlightPod{},
+			wantReceivedEvents:   list.New(),
+			queueingHintMap: QueueingHintMapPerProfile{
+				"": {
+					// This hint fn tells that this event doesn't make a Pod schedulable.
+					// However, this QueueingHintFn will be ignored actually because SchedulingQueueHint is disabled.
+					AssignedPodAdd: {
+						{
+							PluginName:     "fooPlugin1",
+							QueueingHintFn: queueHintReturnQueueSkip,
+						},
+					},
+				},
+			},
+		},
+		{
+			name:                         "Pod is registered in inFlightPods with no previousEvent if Pod is popped from activeQ while no receivedEvents",
+			isSchedulingQueueHintEnabled: true,
+			initialPods:                  []*v1.Pod{pod},
+			actions: []action{
+				// This won't be added to receivedEvents because no inFlightPods at this point.
+				{eventHappens: &PvcAdd},
+				// This Pod has no previousEvent because no receivedEvents at this point.
+				{podPopped: pod},
+				{eventHappens: &PvAdd},
+			},
+			wantInFlightPods: map[types.UID]inFlightPod{
+				"pod1": {
+					// no previousEvent
+				},
+			},
+			wantReceivedEvents: clusterEventsToList([]*clusterEvent{
+				{event: PvAdd, inFlightPodsNum: 1},
+			}),
+		},
+		{
+			name:                         "Pod, registered in inFlightPods with no previousEvent, is enqueued back to activeQ",
+			isSchedulingQueueHintEnabled: true,
+			initialPods:                  []*v1.Pod{pod, pod2},
+			actions: []action{
+				// This won't be added to receivedEvents because no inFlightPods at this point.
+				{eventHappens: &PvcAdd},
+				// This Pod has no previousEvent because no receivedEvents at this point.
+				{podPopped: pod},
+				{eventHappens: &PvAdd},
+				{podPopped: pod2},
+				{eventHappens: &NodeAdd},
+				{podEnqueued: newQueuedPodInfoForLookup(pod)},
+			},
+			wantBackoffQPodNames: []string{"targetpod"},
+			wantInFlightPods: map[types.UID]inFlightPod{
+				"pod2": {
+					// When pod is enqueued back to queue, inFlightPodsNum in previousEvent is also updated to 0.
+					previousEvent: &list.Element{Value: &clusterEvent{event: PvAdd, inFlightPodsNum: 0}},
+				},
+			},
+			wantReceivedEvents: clusterEventsToList([]*clusterEvent{
+				// event: PvAdd is removed when pod is enqueued back to queue.
+				{event: NodeAdd, inFlightPodsNum: 1}, // inFlightPodsNum is updated from 2 to 1.
+			}),
+		},
+		{
+			name:                         "Pod registered in inFlightPods with previousEvent with inFlightPodsNum:0 is enqueued back to activeQ",
+			isSchedulingQueueHintEnabled: true,
+			initialPods:                  []*v1.Pod{pod, pod2},
+			actions: []action{
+				// This won't be added to receivedEvents because no inFlightPods at this point.
+				{eventHappens: &PvcAdd},
+				// This Pod has no previousEvent because no receivedEvents at this point.
+				{podPopped: pod},
+				{eventHappens: &PvAdd},
+				{podPopped: pod2},
+				{eventHappens: &NodeAdd},
+				{podEnqueued: newQueuedPodInfoForLookup(pod)},
+				{eventHappens: &CSINodeUpdate},
+				// pod2 is registered in inFlightPods with previousEvent with inFlightPodsNum:0.
+				{podEnqueued: newQueuedPodInfoForLookup(pod2)},
+			},
+			wantBackoffQPodNames: []string{"targetpod", "targetpod2"},
+			wantInFlightPods:     map[types.UID]inFlightPod{},
+			wantReceivedEvents:   clusterEventsToList([]*clusterEvent{
+				// all events are correctly cleaned up.
+			}),
+		},
+		{
+			name:                         "Pod registered in inFlightPods with previousEvent with inFlightPodsNum:non-zero is enqueued back to activeQ",
+			isSchedulingQueueHintEnabled: true,
+			initialPods:                  []*v1.Pod{pod, pod2, pod3},
+			actions: []action{
+				// This won't be added to receivedEvents because no inFlightPods at this point.
+				{eventHappens: &PvcAdd},
+				// This Pod has no previousEvent because no receivedEvents at this point.
+				{podPopped: pod},
+				{eventHappens: &PvAdd},
+				// This Pod will get previousEvent (PvAdd).
+				{podPopped: pod2},
+				{eventHappens: &NodeAdd},
+				// This Pod will get previousEvent (NodeAdd).
+				// This Pod won't be requeued again.
+				{podPopped: pod3},
+				{eventHappens: &AssignedPodAdd},
+				// pod2 is registered in inFlightPods with previousEvent with inFlightPodsNum:non-zero.
+				{podEnqueued: newQueuedPodInfoForLookup(pod2)},
+			},
+			wantBackoffQPodNames: []string{"targetpod2"},
+			wantInFlightPods: map[types.UID]inFlightPod{
+				"pod1": {
+					// no previousEvent
+				},
+				"pod3": {
+					previousEvent: &list.Element{Value: &clusterEvent{event: NodeAdd, inFlightPodsNum: 1}},
+				},
+			},
+			wantReceivedEvents: clusterEventsToList([]*clusterEvent{
+				{event: PvAdd, inFlightPodsNum: 1},
+				{event: NodeAdd, inFlightPodsNum: 1},
+				{event: AssignedPodAdd, inFlightPodsNum: 2},
+			}),
+		},
+		{
+			name:                         "events before popping Pod are ignored",
+			isSchedulingQueueHintEnabled: true,
+			initialPods:                  []*v1.Pod{pod},
+			actions: []action{
+				{eventHappens: &WildCardEvent},
+				{podPopped: pod},
+				{eventHappens: &AssignedPodAdd},
+				{podEnqueued: newQueuedPodInfoForLookup(pod, "fooPlugin1")},
+			},
+			wantUnschedPodPoolPodNames: []string{"targetpod"},
+			wantInFlightPods:           map[types.UID]inFlightPod{},
+			wantReceivedEvents:         list.New(),
+			queueingHintMap: QueueingHintMapPerProfile{
+				"": {
+					// fooPlugin1 has a queueing hint function for AssignedPodAdd,
+					// but hint fn tells that this event doesn't make a Pod scheudlable.
+					AssignedPodAdd: {
+						{
+							PluginName:     "fooPlugin1",
+							QueueingHintFn: queueHintReturnQueueSkip,
+						},
+					},
+				},
+			},
+		},
+		{
+			name:                         "pod is enqueued to backoff if no failed plugin",
+			isSchedulingQueueHintEnabled: true,
+			initialPods:                  []*v1.Pod{pod},
+			actions: []action{
+				{podPopped: pod},
+				{eventHappens: &AssignedPodAdd},
+				{podEnqueued: newQueuedPodInfoForLookup(pod)},
+			},
+			wantBackoffQPodNames: []string{"targetpod"},
+			wantInFlightPods:     map[types.UID]inFlightPod{},
+			wantReceivedEvents:   list.New(),
+			queueingHintMap: QueueingHintMapPerProfile{
+				"": {
+					// It will be ignored because no failed plugin.
+					AssignedPodAdd: {
+						{
+							PluginName:     "fooPlugin1",
+							QueueingHintFn: queueHintReturnQueueImmediately,
+						},
+					},
+				},
+			},
+		},
+		{
+			name:                         "pod is enqueued to unschedulable pod pool if no events that can make the pod schedulable",
+			isSchedulingQueueHintEnabled: true,
+			initialPods:                  []*v1.Pod{pod},
+			actions: []action{
+				{podPopped: pod},
+				{eventHappens: &NodeAdd},
+				{podEnqueued: newQueuedPodInfoForLookup(pod, "fooPlugin1")},
+			},
+			wantUnschedPodPoolPodNames: []string{"targetpod"},
+			wantInFlightPods:           map[types.UID]inFlightPod{},
+			wantReceivedEvents:         list.New(),
+			queueingHintMap: QueueingHintMapPerProfile{
+				"": {
+					// fooPlugin1 has no queueing hint function for NodeAdd.
+					AssignedPodAdd: {
+						{
+							// It will be ignored because the event is not NodeAdd.
+							PluginName:     "fooPlugin1",
+							QueueingHintFn: queueHintReturnQueueImmediately,
+						},
+					},
+				},
+			},
+		},
+		{
+			name:                         "pod is enqueued to unschedulable pod pool because the failed plugin has a hint fn but it returns QueueSkip",
+			isSchedulingQueueHintEnabled: true,
+			initialPods:                  []*v1.Pod{pod},
+			actions: []action{
+				{podPopped: pod},
+				{eventHappens: &AssignedPodAdd},
+				{podEnqueued: newQueuedPodInfoForLookup(pod, "fooPlugin1")},
+			},
+			wantUnschedPodPoolPodNames: []string{"targetpod"},
+			wantInFlightPods:           map[types.UID]inFlightPod{},
+			wantReceivedEvents:         list.New(),
+			queueingHintMap: QueueingHintMapPerProfile{
+				"": {
+					// fooPlugin1 has a queueing hint function for AssignedPodAdd,
+					// but hint fn tells that this event doesn't make a Pod scheudlable.
+					AssignedPodAdd: {
+						{
+							PluginName:     "fooPlugin1",
+							QueueingHintFn: queueHintReturnQueueSkip,
+						},
+					},
+				},
+			},
+		},
+		{
+			name:                         "pod is enqueued to activeQ because the failed plugin has a hint fn and it returns QueueImmediately",
+			isSchedulingQueueHintEnabled: true,
+			initialPods:                  []*v1.Pod{pod},
+			actions: []action{
+				{podPopped: pod},
+				{eventHappens: &AssignedPodAdd},
+				{podEnqueued: newQueuedPodInfoForLookup(pod, "fooPlugin1", "fooPlugin2", "fooPlugin3")},
+			},
+			wantActiveQPodNames: []string{"targetpod"},
+			wantInFlightPods:    map[types.UID]inFlightPod{},
+			wantReceivedEvents:  list.New(),
+			queueingHintMap: QueueingHintMapPerProfile{
+				"": {
+					AssignedPodAdd: {
+						{
+							// it will be ignored because the hint fn returns QueueSkip that is weaker than queueHintReturnQueueImmediately from fooPlugin1.
+							PluginName:     "fooPlugin3",
+							QueueingHintFn: queueHintReturnQueueSkip,
+						},
+						{
+							// it will be ignored because the hint fn returns QueueAfterBackoff that is weaker than queueHintReturnQueueImmediately from fooPlugin1.
+							PluginName:     "fooPlugin2",
+							QueueingHintFn: queueHintReturnQueueAfterBackoff,
+						},
+						{
+							// The hint fn tells that this event makes a Pod scheudlable immediately.
+							PluginName:     "fooPlugin1",
+							QueueingHintFn: queueHintReturnQueueImmediately,
+						},
+					},
+				},
+			},
+		},
+		{
+			name:                         "pod is enqueued to backoffQ because the failed plugin has a hint fn and it returns QueueAfterBackoff",
+			isSchedulingQueueHintEnabled: true,
+			initialPods:                  []*v1.Pod{pod},
+			actions: []action{
+				{podPopped: pod},
+				{eventHappens: &AssignedPodAdd},
+				{podEnqueued: newQueuedPodInfoForLookup(pod, "fooPlugin1", "fooPlugin2")},
+			},
+			wantBackoffQPodNames: []string{"targetpod"},
+			wantInFlightPods:     map[types.UID]inFlightPod{},
+			wantReceivedEvents:   list.New(),
+			queueingHintMap: QueueingHintMapPerProfile{
+				"": {
+					AssignedPodAdd: {
+						{
+							// it will be ignored because the hint fn returns QueueSkip that is weaker than queueHintReturnQueueAfterBackoff from fooPlugin1.
+							PluginName:     "fooPlugin2",
+							QueueingHintFn: queueHintReturnQueueSkip,
+						},
+						{
+							// The hint fn tells that this event makes a Pod scheudlable.
+							PluginName:     "fooPlugin1",
+							QueueingHintFn: queueHintReturnQueueAfterBackoff,
+						},
+					},
+				},
+			},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			defer featuregatetesting.SetFeatureGateDuringTest(t, utilfeature.DefaultFeatureGate, features.SchedulerQueueingHints, test.isSchedulingQueueHintEnabled)()
+			logger, ctx := ktesting.NewTestContext(t)
+			ctx, cancel := context.WithCancel(ctx)
+			defer cancel()
+			obj := make([]runtime.Object, 0, len(test.initialPods))
+			for _, p := range test.initialPods {
+				obj = append(obj, p)
+			}
+			q := NewTestQueueWithObjects(ctx, newDefaultQueueSort(), obj, WithQueueingHintMapPerProfile(test.queueingHintMap))
+
+			for _, p := range test.initialPods {
+				q.Add(logger, p)
+			}
+
+			for _, action := range test.actions {
+				switch {
+				case action.podPopped != nil:
+					p, err := q.Pop()
+					if err != nil {
+						t.Fatalf("Pop failed: %v", err)
+					}
+					if p.Pod.UID != action.podPopped.UID {
+						t.Errorf("Unexpected popped pod: %v", p)
+					}
+					continue
+				case action.eventHappens != nil:
+					q.MoveAllToActiveOrBackoffQueue(logger, *action.eventHappens, nil, nil, nil)
+				case action.podEnqueued != nil:
+					q.AddUnschedulableIfNotPresent(logger, action.podEnqueued, q.SchedulingCycle())
+				}
+			}
+
+			if diff := cmp.Diff(test.wantInFlightPods, q.inFlightPods, cmp.AllowUnexported(inFlightPod{}, list.Element{}, clusterEvent{}), cmpopts.IgnoreFields(list.Element{}, "next", "prev", "list")); diff != "" {
+				t.Errorf("Unexpected diff in inFlightPods (-want, +got):\n%s", diff)
+			}
+
+			if diff := cmp.Diff(listToClusterEvents(test.wantReceivedEvents), listToClusterEvents(q.receivedEvents), cmp.AllowUnexported(clusterEvent{})); diff != "" {
+				t.Errorf("Unexpected diff in receivedEvents (-want, +got):\n%s", diff)
+			}
+
+			if test.wantActiveQPodNames != nil {
+				rawPodInfos := q.activeQ.List()
+				if len(rawPodInfos) != len(test.wantActiveQPodNames) {
+					diff := cmp.Diff(test.wantActiveQPodNames, rawPodInfos, cmpopts.SortSlices(func(a, b interface{}) bool {
+						return a.(framework.PodInfo).Pod.Name < b.(framework.PodInfo).Pod.Name
+					}))
+					t.Fatalf("Length of activeQ is not expected. Got %v, want %v.\n%s", len(rawPodInfos), len(test.wantActiveQPodNames), diff)
+				}
+
+				wantPodNames := sets.New(test.wantActiveQPodNames...)
+				for _, rawPodInfo := range rawPodInfos {
+					podGotFromActiveQ := rawPodInfo.(*framework.QueuedPodInfo).Pod
+					if !wantPodNames.Has(podGotFromActiveQ.Name) {
+						t.Fatalf("Pod %v was not expected to be in the activeQ.", podGotFromActiveQ.Name)
+					}
+				}
+			}
+
+			if test.wantBackoffQPodNames != nil {
+				rawPodInfos := q.podBackoffQ.List()
+				if len(rawPodInfos) != len(test.wantBackoffQPodNames) {
+					diff := cmp.Diff(test.wantBackoffQPodNames, rawPodInfos, cmpopts.SortSlices(func(a, b interface{}) bool {
+						return a.(framework.PodInfo).Pod.Name < b.(framework.PodInfo).Pod.Name
+					}))
+					t.Fatalf("Length of backoffQ is not expected. Got %v, want %v.\n%s", len(rawPodInfos), len(test.wantBackoffQPodNames), diff)
+				}
+
+				wantPodNames := sets.New(test.wantBackoffQPodNames...)
+				for _, rawPodInfo := range rawPodInfos {
+					podGotFromBackoffQ := rawPodInfo.(*framework.QueuedPodInfo).Pod
+					if !wantPodNames.Has(podGotFromBackoffQ.Name) {
+						t.Fatalf("Pod %v was not expected to be in the backoffQ.", podGotFromBackoffQ.Name)
+					}
+				}
+			}
+
+			for _, podName := range test.wantUnschedPodPoolPodNames {
+				p := getUnschedulablePod(q, &st.MakePod().Name(podName).Pod)
+				if p == nil {
+					t.Fatalf("Pod %v was not found in the unschedulablePods.", podName)
+				}
+			}
+		})
+	}
+}
+
 func TestPriorityQueue_AddUnschedulableIfNotPresent(t *testing.T) {
 	objs := []runtime.Object{highPriNominatedPodInfo.Pod, unschedulablePodInfo.Pod}
 	logger, ctx := ktesting.NewTestContext(t)
 	ctx, cancel := context.WithCancel(ctx)
 	defer cancel()
 	q := NewTestQueueWithObjects(ctx, newDefaultQueueSort(), objs)
+	// insert unschedulablePodInfo and pop right after that
+	// because the scheduling queue records unschedulablePod as in-flight Pod.
+	q.Add(logger, unschedulablePodInfo.Pod)
+	if p, err := q.Pop(); err != nil || p.Pod != unschedulablePodInfo.Pod {
+		t.Errorf("Expected: %v after Pop, but got: %v", unschedulablePodInfo.Pod.Name, p.Pod.Name)
+	}
+
 	q.Add(logger, highPriNominatedPodInfo.Pod)
-	q.AddUnschedulableIfNotPresent(logger, newQueuedPodInfoForLookup(highPriNominatedPodInfo.Pod), q.SchedulingCycle()) // Must not add anything.
 	q.AddUnschedulableIfNotPresent(logger, newQueuedPodInfoForLookup(unschedulablePodInfo.Pod), q.SchedulingCycle())
 	expectedNominatedPods := &nominator{
 		nominatedPodToNode: map[types.UID]string{
@@ -202,6 +646,7 @@ func TestPriorityQueue_AddUnschedulableIfNotPresent(t *testing.T) {
 	if len(q.nominator.nominatedPods) != 1 {
 		t.Errorf("Expected nomindatePods to have one element: %v", q.nominator)
 	}
+	// unschedulablePodInfo is inserted to unschedulable pod pool because no events happened during scheduling.
 	if getUnschedulablePod(q, unschedulablePodInfo.Pod) != unschedulablePodInfo.Pod {
 		t.Errorf("Pod %v was not found in the unschedulablePods.", unschedulablePodInfo.Pod.Name)
 	}
@@ -235,7 +680,7 @@ func TestPriorityQueue_AddUnschedulableIfNotPresent_Backoff(t *testing.T) {
 	}
 
 	// move all pods to active queue when we were trying to schedule them
-	q.MoveAllToActiveOrBackoffQueue(logger, TestEvent, nil, nil, nil)
+	q.MoveAllToActiveOrBackoffQueue(logger, WildCardEvent, nil, nil, nil)
 	oldCycle := q.SchedulingCycle()
 
 	firstPod, _ := q.Pop()
@@ -298,6 +743,7 @@ func TestPriorityQueue_Update(t *testing.T) {
 	ctx, cancel := context.WithCancel(ctx)
 	defer cancel()
 	q := NewTestQueueWithObjects(ctx, newDefaultQueueSort(), objs, WithClock(c))
+	// add highPriorityPodInfo to activeQ.
 	q.Update(logger, nil, highPriorityPodInfo.Pod)
 	if _, exists, _ := q.activeQ.Get(newQueuedPodInfoForLookup(highPriorityPodInfo.Pod)); !exists {
 		t.Errorf("Expected %v to be added to activeQ.", highPriorityPodInfo.Pod.Name)
@@ -344,8 +790,11 @@ func TestPriorityQueue_Update(t *testing.T) {
 		t.Errorf("Expected: %v after Pop, but got: %v", medPriorityPodInfo.Pod.Name, podGotFromBackoffQ.Name)
 	}
 
-	// updating a pod which is in unschedulable queue, and it is still backing off,
+	// To simulate the pod is failed in scheduling in the real world, Pop() the pod from activeQ before testing AddUnschedulableIfNotPresent.
-	// we will move it to backoff queue
+	q.activeQ.Add(podInfo)
+	if p, err := q.Pop(); err != nil || p.Pod != medPriorityPodInfo.Pod {
+		t.Errorf("Expected: %v after Pop, but got: %v", medPriorityPodInfo.Pod.Name, p.Pod.Name)
+	}
 	q.AddUnschedulableIfNotPresent(logger, q.newQueuedPodInfo(medPriorityPodInfo.Pod), q.SchedulingCycle())
 	if len(q.unschedulablePods.podInfoMap) != 1 {
 		t.Error("Expected unschedulablePods to be 1.")
@@ -739,6 +1188,10 @@ func TestPriorityQueue_MoveAllToActiveOrBackoffQueueWithQueueingHint(t *testing.
 			cl := testingclock.NewFakeClock(now)
 			q := NewTestQueue(ctx, newDefaultQueueSort(), WithQueueingHintMapPerProfile(m), WithClock(cl))
 			// add to unsched pod pool
+			q.activeQ.Add(q.newQueuedPodInfo(test.podInfo.Pod))
+			if p, err := q.Pop(); err != nil || p.Pod != test.podInfo.Pod {
+				t.Errorf("Expected: %v after Pop, but got: %v", test.podInfo.Pod.Name, p.Pod.Name)
+			}
 			q.AddUnschedulableIfNotPresent(logger, test.podInfo, q.SchedulingCycle())
 
 			cl.Step(test.duration)
@@ -773,22 +1226,43 @@ func TestPriorityQueue_MoveAllToActiveOrBackoffQueue(t *testing.T) {
 		},
 	}
 	q := NewTestQueue(ctx, newDefaultQueueSort(), WithClock(c), WithQueueingHintMapPerProfile(m))
-	q.Add(logger, medPriorityPodInfo.Pod)
+	// To simulate the pod is failed in scheduling in the real world, Pop() the pod from activeQ before AddUnschedulableIfNotPresent()s below.
+	q.activeQ.Add(q.newQueuedPodInfo(unschedulablePodInfo.Pod))
+	if p, err := q.Pop(); err != nil || p.Pod != unschedulablePodInfo.Pod {
+		t.Errorf("Expected: %v after Pop, but got: %v", unschedulablePodInfo.Pod.Name, p.Pod.Name)
+	}
+	q.activeQ.Add(q.newQueuedPodInfo(highPriorityPodInfo.Pod))
+	if p, err := q.Pop(); err != nil || p.Pod != highPriorityPodInfo.Pod {
+		t.Errorf("Expected: %v after Pop, but got: %v", highPriorityPodInfo.Pod.Name, p.Pod.Name)
+	}
 	q.AddUnschedulableIfNotPresent(logger, q.newQueuedPodInfo(unschedulablePodInfo.Pod, "fooPlugin"), q.SchedulingCycle())
 	q.AddUnschedulableIfNotPresent(logger, q.newQueuedPodInfo(highPriorityPodInfo.Pod, "fooPlugin"), q.SchedulingCycle())
 	// Construct a Pod, but don't associate its scheduler failure to any plugin
 	hpp1 := highPriorityPodInfo.Pod.DeepCopy()
 	hpp1.Name = "hpp1"
+	q.activeQ.Add(q.newQueuedPodInfo(hpp1))
+	if p, err := q.Pop(); err != nil || p.Pod != hpp1 {
+		t.Errorf("Expected: %v after Pop, but got: %v", hpp1, p.Pod.Name)
+	}
 	q.AddUnschedulableIfNotPresent(logger, q.newQueuedPodInfo(hpp1), q.SchedulingCycle())
 	// Construct another Pod, and associate its scheduler failure to plugin "barPlugin".
 	hpp2 := highPriorityPodInfo.Pod.DeepCopy()
 	hpp2.Name = "hpp2"
+	q.activeQ.Add(q.newQueuedPodInfo(hpp2))
+	if p, err := q.Pop(); err != nil || p.Pod != hpp2 {
+		t.Errorf("Expected: %v after Pop, but got: %v", hpp2, p.Pod.Name)
+	}
 	q.AddUnschedulableIfNotPresent(logger, q.newQueuedPodInfo(hpp2, "barPlugin"), q.SchedulingCycle())
 	// Pods is still backing off, move the pod into backoffQ.
 	q.MoveAllToActiveOrBackoffQueue(logger, NodeAdd, nil, nil, nil)
+	q.Add(logger, medPriorityPodInfo.Pod)
 	if q.activeQ.Len() != 1 {
 		t.Errorf("Expected 1 item to be in activeQ, but got: %v", q.activeQ.Len())
 	}
+	// Pop out the medPriorityPodInfo in activeQ.
+	if p, err := q.Pop(); err != nil || p.Pod != medPriorityPodInfo.Pod {
+		t.Errorf("Expected: %v after Pop, but got: %v", medPriorityPodInfo.Pod, p.Pod.Name)
+	}
 	// hpp2 won't be moved.
 	if q.podBackoffQ.Len() != 3 {
 		t.Fatalf("Expected 3 items to be in podBackoffQ, but got: %v", q.podBackoffQ.Len())
@@ -800,9 +1274,22 @@ func TestPriorityQueue_MoveAllToActiveOrBackoffQueue(t *testing.T) {
 	}
 
 	q.schedulingCycle++
+	q.activeQ.Add(q.newQueuedPodInfo(unschedulablePodInfo.Pod))
+	if p, err := q.Pop(); err != nil || p.Pod != unschedulablePodInfo.Pod {
+		t.Errorf("Expected: %v after Pop, but got: %v", unschedulablePodInfo.Pod.Name, p.Pod.Name)
+	}
+	q.activeQ.Add(q.newQueuedPodInfo(highPriorityPodInfo.Pod))
+	if p, err := q.Pop(); err != nil || p.Pod != highPriorityPodInfo.Pod {
+		t.Errorf("Expected: %v after Pop, but got: %v", highPriorityPodInfo.Pod.Name, p.Pod.Name)
+	}
+	q.activeQ.Add(q.newQueuedPodInfo(hpp1))
+	if p, err := q.Pop(); err != nil || p.Pod != hpp1 {
+		t.Errorf("Expected: %v after Pop, but got: %v", hpp1, p.Pod.Name)
+	}
 	q.AddUnschedulableIfNotPresent(logger, q.newQueuedPodInfo(unschedulablePodInfo.Pod, "fooPlugin"), q.SchedulingCycle())
 	q.AddUnschedulableIfNotPresent(logger, q.newQueuedPodInfo(highPriorityPodInfo.Pod, "fooPlugin"), q.SchedulingCycle())
 	q.AddUnschedulableIfNotPresent(logger, q.newQueuedPodInfo(hpp1), q.SchedulingCycle())
+	q.Add(logger, medPriorityPodInfo.Pod)
 	for _, pod := range []*v1.Pod{unschedulablePodInfo.Pod, highPriorityPodInfo.Pod, hpp1, hpp2} {
 		if q.unschedulablePods.get(pod) == nil {
 			t.Errorf("Expected %v in the unschedulablePods", pod.Name)
@@ -829,7 +1316,7 @@ func TestPriorityQueue_AssignedPodAdded(t *testing.T) {
 	ctx, cancel := context.WithCancel(ctx)
 	defer cancel()
 
-	affinityPod := st.MakePod().Name("afp").Namespace("ns1").UID("upns1").Annotation("annot2", "val2").Priority(mediumPriority).NominatedNodeName("node1").PodAffinityExists("service", "region", st.PodAffinityWithRequiredReq).Obj()
+	affinityPod := st.MakePod().Name("afp").Namespace("ns1").UID("afp").Annotation("annot2", "val2").Priority(mediumPriority).NominatedNodeName("node1").PodAffinityExists("service", "region", st.PodAffinityWithRequiredReq).Obj()
 	labelPod := st.MakePod().Name("lbp").Namespace(affinityPod.Namespace).Label("service", "securityscan").Node("node1").Obj()
 
 	c := testingclock.NewFakeClock(time.Now())
@@ -841,8 +1328,16 @@ func TestPriorityQueue_AssignedPodAdded(t *testing.T) {
 		},
 	}
 	q := NewTestQueue(ctx, newDefaultQueueSort(), WithClock(c), WithQueueingHintMapPerProfile(m))
+	// To simulate the pod is failed in scheduling in the real world, Pop() the pod from activeQ before AddUnschedulableIfNotPresent()s below.
+	q.activeQ.Add(q.newQueuedPodInfo(unschedulablePodInfo.Pod))
+	if p, err := q.Pop(); err != nil || p.Pod != unschedulablePodInfo.Pod {
+		t.Errorf("Expected: %v after Pop, but got: %v", unschedulablePodInfo.Pod.Name, p.Pod.Name)
+	}
+	q.activeQ.Add(q.newQueuedPodInfo(affinityPod))
+	if p, err := q.Pop(); err != nil || p.Pod != affinityPod {
+		t.Errorf("Expected: %v after Pop, but got: %v", affinityPod.Name, p.Pod.Name)
+	}
 	q.Add(logger, medPriorityPodInfo.Pod)
-	// Add a couple of pods to the unschedulablePods.
 	q.AddUnschedulableIfNotPresent(logger, q.newQueuedPodInfo(unschedulablePodInfo.Pod, "fakePlugin"), q.SchedulingCycle())
 	q.AddUnschedulableIfNotPresent(logger, q.newQueuedPodInfo(affinityPod, "fakePlugin"), q.SchedulingCycle())
 
@@ -955,6 +1450,15 @@ func TestPriorityQueue_PendingPods(t *testing.T) {
 	ctx, cancel := context.WithCancel(ctx)
 	defer cancel()
 	q := NewTestQueue(ctx, newDefaultQueueSort())
+	// To simulate the pod is failed in scheduling in the real world, Pop() the pod from activeQ before AddUnschedulableIfNotPresent()s below.
+	q.activeQ.Add(q.newQueuedPodInfo(unschedulablePodInfo.Pod))
+	if p, err := q.Pop(); err != nil || p.Pod != unschedulablePodInfo.Pod {
+		t.Errorf("Expected: %v after Pop, but got: %v", unschedulablePodInfo.Pod.Name, p.Pod.Name)
+	}
+	q.activeQ.Add(q.newQueuedPodInfo(highPriorityPodInfo.Pod))
+	if p, err := q.Pop(); err != nil || p.Pod != highPriorityPodInfo.Pod {
+		t.Errorf("Expected: %v after Pop, but got: %v", highPriorityPodInfo.Pod.Name, p.Pod.Name)
+	}
 	q.Add(logger, medPriorityPodInfo.Pod)
 	q.AddUnschedulableIfNotPresent(logger, q.newQueuedPodInfo(unschedulablePodInfo.Pod), q.SchedulingCycle())
 	q.AddUnschedulableIfNotPresent(logger, q.newQueuedPodInfo(highPriorityPodInfo.Pod), q.SchedulingCycle())
@@ -1287,6 +1791,11 @@ func TestPodFailedSchedulingMultipleTimesDoesNotBlockNewerPod(t *testing.T) {
 		Message: "fake scheduling failure",
 	})
 
+	// To simulate the pod is failed in scheduling in the real world, Pop() the pod from activeQ before AddUnschedulableIfNotPresent() below.
+	q.activeQ.Add(q.newQueuedPodInfo(unschedulablePod))
+	if p, err := q.Pop(); err != nil || p.Pod != unschedulablePod {
+		t.Errorf("Expected: %v after Pop, but got: %v", unschedulablePod.Name, p.Pod.Name)
+	}
 	// Put in the unschedulable queue
 	q.AddUnschedulableIfNotPresent(logger, newQueuedPodInfoForLookup(unschedulablePod), q.SchedulingCycle())
 	// Move clock to make the unschedulable pods complete backoff.
@@ -1411,6 +1920,15 @@ func TestHighPriorityFlushUnschedulablePodsLeftover(t *testing.T) {
 		Message: "fake scheduling failure",
 	})
 
+	// To simulate the pod is failed in scheduling in the real world, Pop() the pod from activeQ before AddUnschedulableIfNotPresent()s below.
+	q.activeQ.Add(q.newQueuedPodInfo(highPod))
+	if p, err := q.Pop(); err != nil || p.Pod != highPod {
+		t.Errorf("Expected: %v after Pop, but got: %v", highPod.Name, p.Pod.Name)
+	}
+	q.activeQ.Add(q.newQueuedPodInfo(midPod))
+	if p, err := q.Pop(); err != nil || p.Pod != midPod {
+		t.Errorf("Expected: %v after Pop, but got: %v", midPod.Name, p.Pod.Name)
+	}
 	q.AddUnschedulableIfNotPresent(logger, q.newQueuedPodInfo(highPod, "fakePlugin"), q.SchedulingCycle())
 	q.AddUnschedulableIfNotPresent(logger, q.newQueuedPodInfo(midPod, "fakePlugin"), q.SchedulingCycle())
 	c.Step(DefaultPodMaxInUnschedulablePodsDuration + time.Second)
@@ -1516,10 +2034,16 @@ var (
 		queue.Add(logger, pInfo.Pod)
 	}
 	addUnschedulablePodBackToUnschedulablePods = func(logger klog.Logger, queue *PriorityQueue, pInfo *framework.QueuedPodInfo) {
-		queue.AddUnschedulableIfNotPresent(logger, pInfo, 0)
+		// To simulate the pod is failed in scheduling in the real world, Pop() the pod from activeQ before AddUnschedulableIfNotPresent() below.
+		queue.activeQ.Add(queue.newQueuedPodInfo(pInfo.Pod))
+		if p, err := queue.Pop(); err != nil || p.Pod != pInfo.Pod {
+			panic(fmt.Sprintf("Expected: %v after Pop, but got: %v", pInfo.Pod.Name, p.Pod.Name))
+		}
+
+		queue.AddUnschedulableIfNotPresent(logger, pInfo, 1)
 	}
 	addUnschedulablePodBackToBackoffQ = func(logger klog.Logger, queue *PriorityQueue, pInfo *framework.QueuedPodInfo) {
-		queue.AddUnschedulableIfNotPresent(logger, pInfo, -1)
+		queue.AddUnschedulableIfNotPresent(logger, pInfo, 1)
 	}
 	addPodActiveQ = func(logger klog.Logger, queue *PriorityQueue, pInfo *framework.QueuedPodInfo) {
 		queue.activeQ.Add(pInfo)
@@ -2050,6 +2574,7 @@ func TestPerPodSchedulingMetrics(t *testing.T) {
 
 func TestIncomingPodsMetrics(t *testing.T) {
 	timestamp := time.Now()
+	unschedulablePlg := "unschedulable_plugin"
 	metrics.Register()
 	var pInfos = make([]*framework.QueuedPodInfo, 0, 3)
 	for i := 1; i <= 3; i++ {
@@ -2057,6 +2582,7 @@ func TestIncomingPodsMetrics(t *testing.T) {
 			PodInfo: mustNewTestPodInfo(t,
 				st.MakePod().Name(fmt.Sprintf("test-pod-%d", i)).Namespace(fmt.Sprintf("ns%d", i)).UID(fmt.Sprintf("tp-%d", i)).Obj()),
 			Timestamp:            timestamp,
+			UnschedulablePlugins: sets.New(unschedulablePlg),
 		}
 		pInfos = append(pInfos, p)
 	}
@@ -2261,6 +2787,11 @@ func TestMoveAllToActiveOrBackoffQueue_PreEnqueueChecks(t *testing.T) {
 			defer cancel()
 			q := NewTestQueue(ctx, newDefaultQueueSort())
 			for i, podInfo := range tt.podInfos {
+				// To simulate the pod is failed in scheduling in the real world, Pop() the pod from activeQ before AddUnschedulableIfNotPresent() below.
+				q.activeQ.Add(q.newQueuedPodInfo(podInfo.Pod))
+				if p, err := q.Pop(); err != nil || p.Pod != podInfo.Pod {
+					t.Errorf("Expected: %v after Pop, but got: %v", podInfo.Pod.Name, p.Pod.Name)
+				}
 				q.AddUnschedulableIfNotPresent(logger, podInfo, q.schedulingCycle)
 				// NOTE: On Windows, time.Now() is not as precise, 2 consecutive calls may return the same timestamp,
 				// resulting in 0 time delta / latency. This will cause the pods to be backed off in a random

pkg/scheduler/schedule_one.go

@@ -66,12 +66,19 @@ const (
 // scheduleOne does the entire scheduling workflow for a single pod. It is serialized on the scheduling algorithm's host fitting.
 func (sched *Scheduler) scheduleOne(ctx context.Context) {
 	logger := klog.FromContext(ctx)
-	podInfo := sched.NextPod()
+	podInfo, err := sched.NextPod()
+	if err != nil {
+		logger.Error(err, "Error while retrieving next pod from scheduling queue")
+		return
+	}
 	// pod could be nil when schedulerQueue is closed
 	if podInfo == nil || podInfo.Pod == nil {
 		return
 	}
+
 	pod := podInfo.Pod
+	logger.V(4).Info("About to try and schedule pod", "pod", klog.KObj(pod))
+
 	fwk, err := sched.frameworkForPod(pod)
 	if err != nil {
 		// This shouldn't happen, because we only accept for scheduling the pods
@@ -115,6 +122,9 @@ func (sched *Scheduler) scheduleOne(ctx context.Context) {
 		if !status.IsSuccess() {
 			sched.handleBindingCycleError(bindingCycleCtx, state, fwk, assumedPodInfo, start, scheduleResult, status)
 		}
+		// Usually, DonePod is called inside the scheduling queue,
+		// but in this case, we need to call it here because this Pod won't go back to the scheduling queue.
+		sched.SchedulingQueue.Done(assumedPodInfo.Pod.UID)
 	}()
 }
 
@@ -922,6 +932,16 @@ func getAttemptsLabel(p *framework.QueuedPodInfo) string {
 // handleSchedulingFailure records an event for the pod that indicates the
 // pod has failed to schedule. Also, update the pod condition and nominated node name if set.
 func (sched *Scheduler) handleSchedulingFailure(ctx context.Context, fwk framework.Framework, podInfo *framework.QueuedPodInfo, status *framework.Status, nominatingInfo *framework.NominatingInfo, start time.Time) {
+	calledDone := false
+	defer func() {
+		if !calledDone {
+			// Basically, AddUnschedulableIfNotPresent calls DonePod internally.
+			// But, AddUnschedulableIfNotPresent isn't called in some corner cases.
+			// Here, we call DonePod explicitly to avoid leaking the pod.
+			sched.SchedulingQueue.Done(podInfo.Pod.UID)
+		}
+	}()
+
 	logger := klog.FromContext(ctx)
 	reason := v1.PodReasonSchedulerError
 	if status.IsUnschedulable() {
@@ -967,11 +987,13 @@ func (sched *Scheduler) handleSchedulingFailure(ctx context.Context, fwk framewo
 	cachedPod, e := podLister.Pods(pod.Namespace).Get(pod.Name)
 	if e != nil {
 		logger.Info("Pod doesn't exist in informer cache", "pod", klog.KObj(pod), "err", e)
+		// We need to call DonePod here because we don't call AddUnschedulableIfNotPresent in this case.
 	} else {
 		// In the case of extender, the pod may have been bound successfully, but timed out returning its response to the scheduler.
 		// It could result in the live version to carry .spec.nodeName, and that's inconsistent with the internal-queued version.
 		if len(cachedPod.Spec.NodeName) != 0 {
 			logger.Info("Pod has been assigned to node. Abort adding it back to queue.", "pod", klog.KObj(pod), "node", cachedPod.Spec.NodeName)
+			// We need to call DonePod here because we don't call AddUnschedulableIfNotPresent in this case.
 		} else {
 			// As <cachedPod> is from SharedInformer, we need to do a DeepCopy() here.
 			// ignore this err since apiserver doesn't properly validate affinity terms
@@ -980,6 +1002,7 @@ func (sched *Scheduler) handleSchedulingFailure(ctx context.Context, fwk framewo
 			if err := sched.SchedulingQueue.AddUnschedulableIfNotPresent(logger, podInfo, sched.SchedulingQueue.SchedulingCycle()); err != nil {
 				logger.Error(err, "Error occurred")
 			}
+			calledDone = true
 		}
 	}
 

pkg/scheduler/schedule_one_test.go

@@ -765,8 +765,8 @@ func TestSchedulerScheduleOne(t *testing.T) {
 			sched := &Scheduler{
 				Cache:  cache,
 				client: client,
-				NextPod: func() *framework.QueuedPodInfo {
+				NextPod: func() (*framework.QueuedPodInfo, error) {
-					return &framework.QueuedPodInfo{PodInfo: mustNewPodInfo(t, item.sendPod)}
+					return &framework.QueuedPodInfo{PodInfo: mustNewPodInfo(t, item.sendPod)}, nil
 				},
 				SchedulingQueue: internalqueue.NewTestQueue(ctx, nil),
 				Profiles:        profile.Map{testSchedulerName: fwk},
@@ -3228,8 +3228,8 @@ func setupTestScheduler(ctx context.Context, t *testing.T, queuedPodStore *clien
 		client:                   client,
 		nodeInfoSnapshot:         internalcache.NewEmptySnapshot(),
 		percentageOfNodesToScore: schedulerapi.DefaultPercentageOfNodesToScore,
-		NextPod: func() *framework.QueuedPodInfo {
+		NextPod: func() (*framework.QueuedPodInfo, error) {
-			return &framework.QueuedPodInfo{PodInfo: mustNewPodInfo(t, clientcache.Pop(queuedPodStore).(*v1.Pod))}
+			return &framework.QueuedPodInfo{PodInfo: mustNewPodInfo(t, clientcache.Pop(queuedPodStore).(*v1.Pod))}, nil
 		},
 		SchedulingQueue: schedulingQueue,
 		Profiles:        profile.Map{testSchedulerName: fwk},

pkg/scheduler/scheduler.go

@@ -71,7 +71,7 @@ type Scheduler struct {
 	// is available. We don't use a channel for this, because scheduling
 	// a pod may take some amount of time and we don't want pods to get
 	// stale while they sit in a channel.
-	NextPod func() *framework.QueuedPodInfo
+	NextPod func() (*framework.QueuedPodInfo, error)
 
 	// FailureHandler is called upon a scheduling failure.
 	FailureHandler FailureHandlerFn
@@ -346,12 +346,12 @@ func New(ctx context.Context,
 		nodeInfoSnapshot:         snapshot,
 		percentageOfNodesToScore: options.percentageOfNodesToScore,
 		Extenders:                extenders,
-		NextPod:                  internalqueue.MakeNextPodFunc(logger, podQueue),
 		StopEverything:           stopEverything,
 		SchedulingQueue:          podQueue,
 		Profiles:                 profiles,
 		logger:                   logger,
 	}
+	sched.NextPod = podQueue.Pop
 	sched.applyDefaultHandlers()
 
 	if err = addAllEventHandlers(sched, informerFactory, dynInformerFactory, unionedGVKs(queueingHintsPerProfile)); err != nil {

test/integration/scheduler/preemption/preemption_test.go

@@ -1477,13 +1477,13 @@ func initTestPreferNominatedNode(t *testing.T, nsPrefix string, opts ...schedule
 	testutils.SyncSchedulerInformerFactory(testCtx)
 	// wraps the NextPod() method to make it appear the preemption has been done already and the nominated node has been set.
 	f := testCtx.Scheduler.NextPod
-	testCtx.Scheduler.NextPod = func() (podInfo *framework.QueuedPodInfo) {
+	testCtx.Scheduler.NextPod = func() (*framework.QueuedPodInfo, error) {
-		podInfo = f()
+		podInfo, _ := f()
 		// Scheduler.Next() may return nil when scheduler is shutting down.
 		if podInfo != nil {
 			podInfo.Pod.Status.NominatedNodeName = "node-1"
 		}
-		return podInfo
+		return podInfo, nil
 	}
 	go testCtx.Scheduler.Run(testCtx.Ctx)
 	return testCtx

test/integration/util/util.go

@@ -1097,7 +1097,7 @@ func NextPodOrDie(t *testing.T, testCtx *TestContext) *schedulerframework.Queued
 	// NextPod() is a blocking operation. Wrap it in timeout() to avoid relying on
 	// default go testing timeout (10m) to abort.
 	if err := timeout(testCtx.Ctx, time.Second*5, func() {
-		podInfo = testCtx.Scheduler.NextPod()
+		podInfo, _ = testCtx.Scheduler.NextPod()
 	}); err != nil {
 		t.Fatalf("Timed out waiting for the Pod to be popped: %v", err)
 	}
@@ -1112,7 +1112,7 @@ func NextPod(t *testing.T, testCtx *TestContext) *schedulerframework.QueuedPodIn
 	// NextPod() is a blocking operation. Wrap it in timeout() to avoid relying on
 	// default go testing timeout (10m) to abort.
 	if err := timeout(testCtx.Ctx, time.Second*5, func() {
-		podInfo = testCtx.Scheduler.NextPod()
+		podInfo, _ = testCtx.Scheduler.NextPod()
 	}); err != nil {
 		return nil
 	}