Merge pull request #77559 from ahg-g/permit-extension-point

Implement the permit extension point in scheduler.

pkg/scheduler/framework/v1alpha1/BUILD

@@ -7,6 +7,7 @@ go_library(
         "framework.go",
         "interface.go",
         "registry.go",
+        "waiting_pods_map.go",
     ],
     importpath = "k8s.io/kubernetes/pkg/scheduler/framework/v1alpha1",
     visibility = ["//visibility:public"],
@@ -14,6 +15,7 @@ go_library(
         "//pkg/scheduler/internal/cache:go_default_library",
         "//staging/src/k8s.io/api/core/v1:go_default_library",
         "//staging/src/k8s.io/apimachinery/pkg/runtime:go_default_library",
+        "//staging/src/k8s.io/apimachinery/pkg/types:go_default_library",
         "//vendor/k8s.io/klog:go_default_library",
     ],
 )

pkg/scheduler/framework/v1alpha1/framework.go

@@ -18,9 +18,11 @@ package v1alpha1
 
 import (
 	"fmt"
+	"time"
 
 	"k8s.io/api/core/v1"
 	"k8s.io/apimachinery/pkg/runtime"
+	"k8s.io/apimachinery/pkg/types"
 	"k8s.io/klog"
 	"k8s.io/kubernetes/pkg/scheduler/internal/cache"
 )
@@ -30,12 +32,19 @@ import (
 type framework struct {
 	registry         Registry
 	nodeInfoSnapshot *cache.NodeInfoSnapshot
+	waitingPods      *waitingPodsMap
 	plugins          map[string]Plugin // a map of initialized plugins. Plugin name:plugin instance.
 	reservePlugins   []ReservePlugin
 	prebindPlugins   []PrebindPlugin
 	unreservePlugins []UnreservePlugin
+	permitPlugins    []PermitPlugin
 }
 
+const (
+	// Specifies the maximum timeout a permit plugin can return.
+	maxTimeout time.Duration = 15 * time.Minute
+)
+
 var _ = Framework(&framework{})
 
 // NewFramework initializes plugins given the configuration and the registry.
@@ -44,6 +53,7 @@ func NewFramework(r Registry, _ *runtime.Unknown) (Framework, error) {
 		registry:         r,
 		nodeInfoSnapshot: cache.NewNodeInfoSnapshot(),
 		plugins:          make(map[string]Plugin),
+		waitingPods:      newWaitingPodsMap(),
 	}
 
 	// TODO: The framework needs to read the scheduler config and initialize only
@@ -68,6 +78,9 @@ func NewFramework(r Registry, _ *runtime.Unknown) (Framework, error) {
 		if up, ok := p.(UnreservePlugin); ok {
 			f.unreservePlugins = append(f.unreservePlugins, up)
 		}
+		if pr, ok := p.(PermitPlugin); ok {
+			f.permitPlugins = append(f.permitPlugins, pr)
+		}
 	}
 	return f, nil
 }
@@ -117,6 +130,69 @@ func (f *framework) RunUnreservePlugins(
 	}
 }
 
+// RunPermitPlugins runs the set of configured permit plugins. If any of these
+// plugins returns a status other than "Success" or "Wait", it does not continue
+// running the remaining plugins and returns an error. Otherwise, if any of the
+// plugins returns "Wait", then this function will block for the timeout period
+// returned by the plugin, if the time expires, then it will return an error.
+// Note that if multiple plugins asked to wait, then we wait for the minimum
+// timeout duration.
+func (f *framework) RunPermitPlugins(
+	pc *PluginContext, pod *v1.Pod, nodeName string) *Status {
+	timeout := maxTimeout
+	statusCode := Success
+	for _, pl := range f.permitPlugins {
+		status, d := pl.Permit(pc, pod, nodeName)
+		if !status.IsSuccess() {
+			if status.Code() == Unschedulable {
+				msg := fmt.Sprintf("rejected by %v at permit: %v", pl.Name(), status.Message())
+				klog.V(4).Infof(msg)
+				return NewStatus(status.Code(), msg)
+			}
+			if status.Code() == Wait {
+				// Use the minimum timeout duration.
+				if timeout > d {
+					timeout = d
+				}
+				statusCode = Wait
+			} else {
+				msg := fmt.Sprintf("error while running %v permit plugin for pod %v: %v", pl.Name(), pod.Name, status.Message())
+				klog.Error(msg)
+				return NewStatus(Error, msg)
+			}
+		}
+	}
+
+	// We now wait for the minimum duration if at least one plugin asked to
+	// wait (and no plugin rejected the pod)
+	if statusCode == Wait {
+		w := newWaitingPod(pod)
+		f.waitingPods.add(w)
+		defer f.waitingPods.remove(pod.UID)
+		timer := time.NewTimer(timeout)
+		klog.V(4).Infof("waiting for %v for pod %v at permit", timeout, pod.Name)
+		select {
+		case <-timer.C:
+			msg := fmt.Sprintf("pod %v rejected due to timeout after waiting %v at permit", pod.Name, timeout)
+			klog.V(4).Infof(msg)
+			return NewStatus(Unschedulable, msg)
+		case s := <-w.s:
+			if !s.IsSuccess() {
+				if s.Code() == Unschedulable {
+					msg := fmt.Sprintf("rejected while waiting at permit: %v", s.Message())
+					klog.V(4).Infof(msg)
+					return NewStatus(s.Code(), msg)
+				}
+				msg := fmt.Sprintf("error received while waiting at permit for pod %v: %v", pod.Name, s.Message())
+				klog.Error(msg)
+				return NewStatus(Error, msg)
+			}
+		}
+	}
+
+	return nil
+}
+
 // NodeInfoSnapshot returns the latest NodeInfo snapshot. The snapshot
 // is taken at the beginning of a scheduling cycle and remains unchanged until a
 // pod finishes "Reserve". There is no guarantee that the information remains
@@ -124,3 +200,13 @@ func (f *framework) RunUnreservePlugins(
 func (f *framework) NodeInfoSnapshot() *cache.NodeInfoSnapshot {
 	return f.nodeInfoSnapshot
 }
+
+// IterateOverWaitingPods acquires a read lock and iterates over the WaitingPods map.
+func (f *framework) IterateOverWaitingPods(callback func(WaitingPod)) {
+	f.waitingPods.iterate(callback)
+}
+
+// GetWaitingPod returns a reference to a WaitingPod given its UID.
+func (f *framework) GetWaitingPod(uid types.UID) WaitingPod {
+	return f.waitingPods.get(uid)
+}

pkg/scheduler/framework/v1alpha1/interface.go

@@ -20,8 +20,10 @@ package v1alpha1
 
 import (
 	"errors"
+	"time"
 
 	"k8s.io/api/core/v1"
+	"k8s.io/apimachinery/pkg/types"
 	internalcache "k8s.io/kubernetes/pkg/scheduler/internal/cache"
 )
 
@@ -38,6 +40,8 @@ const (
 	// Unschedulable is used when a plugin finds a pod unschedulable.
 	// The accompanying status message should explain why the pod is unschedulable.
 	Unschedulable Code = 2
+	// Wait is used when a permit plugin finds a pod scheduling should wait.
+	Wait Code = 3
 )
 
 // Status indicates the result of running a plugin. It consists of a code and a
@@ -86,6 +90,18 @@ func NewStatus(code Code, msg string) *Status {
 	}
 }
 
+// WaitingPod represents a pod currently waiting in the permit phase.
+type WaitingPod interface {
+	// GetPod returns a reference to the waiting pod.
+	GetPod() *v1.Pod
+	// Allow the waiting pod to be scheduled. Returns true if the allow signal was
+	// successfully delivered, false otherwise.
+	Allow() bool
+	// Reject declares the waiting pod unschedulable. Returns true if the allow signal
+	// was successfully delivered, false otherwise.
+	Reject(msg string) bool
+}
+
 // Plugin is the parent type for all the scheduling framework plugins.
 type Plugin interface {
 	Name() string
@@ -105,7 +121,7 @@ type ReservePlugin interface {
 }
 
 // PrebindPlugin is an interface that must be implemented by "prebind" plugins.
-// These plugins are called before a pod being scheduled
+// These plugins are called before a pod being scheduled.
 type PrebindPlugin interface {
 	Plugin
 	// Prebind is called before binding a pod. All prebind plugins must return
@@ -124,6 +140,19 @@ type UnreservePlugin interface {
 	Unreserve(pc *PluginContext, p *v1.Pod, nodeName string)
 }
 
+// PermitPlugin is an interface that must be implemented by "permit" plugins.
+// These plugins are called before a pod is bound to a node.
+type PermitPlugin interface {
+	Plugin
+	// Permit is called before binding a pod (and before prebind plugins). Permit
+	// plugins are used to prevent or delay the binding of a Pod. A permit plugin
+	// must return success or wait with timeout duration, or the pod will be rejected.
+	// The pod will also be rejected if the wait timeout or the pod is rejected while
+	// waiting. Note that if the plugin returns "wait", the framework will wait only
+	// after running the remaining plugins given that no other plugin rejects the pod.
+	Permit(pc *PluginContext, p *v1.Pod, nodeName string) (*Status, time.Duration)
+}
+
 // Framework manages the set of plugins in use by the scheduling framework.
 // Configured plugins are called at specified points in a scheduling context.
 type Framework interface {
@@ -142,6 +171,15 @@ type Framework interface {
 
 	// RunUnreservePlugins runs the set of configured unreserve plugins.
 	RunUnreservePlugins(pc *PluginContext, pod *v1.Pod, nodeName string)
+
+	// RunPermitPlugins runs the set of configured permit plugins. If any of these
+	// plugins returns a status other than "Success" or "Wait", it does not continue
+	// running the remaining plugins and returns an error. Otherwise, if any of the
+	// plugins returns "Wait", then this function will block for the timeout period
+	// returned by the plugin, if the time expires, then it will return an error.
+	// Note that if multiple plugins asked to wait, then we wait for the minimum
+	// timeout duration.
+	RunPermitPlugins(pc *PluginContext, pod *v1.Pod, nodeName string) *Status
 }
 
 // FrameworkHandle provides data and some tools that plugins can use. It is
@@ -153,4 +191,10 @@ type FrameworkHandle interface {
 	// a pod finishes "Reserve" point. There is no guarantee that the information
 	// remains unchanged in the binding phase of scheduling.
 	NodeInfoSnapshot() *internalcache.NodeInfoSnapshot
+
+	// IterateOverWaitingPods acquires a read lock and iterates over the WaitingPods map.
+	IterateOverWaitingPods(callback func(WaitingPod))
+
+	// GetWaitingPod returns a waiting pod given its UID.
+	GetWaitingPod(uid types.UID) WaitingPod
 }

pkg/scheduler/framework/v1alpha1/waiting_pods_map.go

@@ -0,0 +1,109 @@
+/*
+Copyright 2019 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package v1alpha1
+
+import (
+	"sync"
+
+	"k8s.io/api/core/v1"
+	"k8s.io/apimachinery/pkg/types"
+)
+
+// waitingPodsMap a thread-safe map used to maintain pods waiting in the permit phase.
+type waitingPodsMap struct {
+	pods map[types.UID]WaitingPod
+	mu   sync.RWMutex
+}
+
+// newWaitingPodsMap returns a new waitingPodsMap.
+func newWaitingPodsMap() *waitingPodsMap {
+	return &waitingPodsMap{
+		pods: make(map[types.UID]WaitingPod),
+	}
+}
+
+// add a new WaitingPod to the map.
+func (m *waitingPodsMap) add(wp WaitingPod) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	m.pods[wp.GetPod().UID] = wp
+}
+
+// remove a WaitingPod from the map.
+func (m *waitingPodsMap) remove(uid types.UID) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	delete(m.pods, uid)
+}
+
+// get a WaitingPod from the map.
+func (m *waitingPodsMap) get(uid types.UID) WaitingPod {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+	return m.pods[uid]
+
+}
+
+// iterate acquires a read lock and iterates over the WaitingPods map.
+func (m *waitingPodsMap) iterate(callback func(WaitingPod)) {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+	for _, v := range m.pods {
+		callback(v)
+	}
+}
+
+// waitingPod represents a pod waiting in the permit phase.
+type waitingPod struct {
+	pod *v1.Pod
+	s   chan *Status
+}
+
+// newWaitingPod returns a new waitingPod instance.
+func newWaitingPod(pod *v1.Pod) *waitingPod {
+	return &waitingPod{
+		pod: pod,
+		s:   make(chan *Status),
+	}
+}
+
+// GetPod returns a reference to the waiting pod.
+func (w *waitingPod) GetPod() *v1.Pod {
+	return w.pod
+}
+
+// Allow the waiting pod to be scheduled. Returns true if the allow signal was
+// successfully delivered, false otherwise.
+func (w *waitingPod) Allow() bool {
+	select {
+	case w.s <- NewStatus(Success, ""):
+		return true
+	default:
+		return false
+	}
+}
+
+// Reject declares the waiting pod unschedulable. Returns true if the allow signal
+// was successfully delivered, false otherwise.
+func (w *waitingPod) Reject(msg string) bool {
+	select {
+	case w.s <- NewStatus(Unschedulable, msg):
+		return true
+	default:
+		return false
+	}
+}

pkg/scheduler/scheduler.go

@@ -533,6 +533,25 @@ func (sched *Scheduler) scheduleOne() {
 			}
 		}
 
+		// Run "permit" plugins.
+		permitStatus := fwk.RunPermitPlugins(pluginContext, assumedPod, scheduleResult.SuggestedHost)
+		if !permitStatus.IsSuccess() {
+			var reason string
+			if permitStatus.Code() == framework.Unschedulable {
+				reason = v1.PodReasonUnschedulable
+			} else {
+				metrics.PodScheduleErrors.Inc()
+				reason = SchedulerError
+			}
+			if forgetErr := sched.Cache().ForgetPod(assumedPod); forgetErr != nil {
+				klog.Errorf("scheduler cache ForgetPod failed: %v", forgetErr)
+			}
+			sched.recordSchedulingFailure(assumedPod, permitStatus.AsError(), reason, permitStatus.Message())
+			// trigger un-reserve plugins to clean up state associated with the reserved Pod
+			fwk.RunUnreservePlugins(pluginContext, assumedPod, scheduleResult.SuggestedHost)
+			return
+		}
+
 		// Run "prebind" plugins.
 		prebindStatus := fwk.RunPrebindPlugins(pluginContext, assumedPod, scheduleResult.SuggestedHost)
 		if !prebindStatus.IsSuccess() {

test/integration/scheduler/framework_test.go

@@ -30,12 +30,18 @@ import (
 // TesterPlugin is common ancestor for a test plugin that allows injection of
 // failures and some other test functionalities.
 type TesterPlugin struct {
-	numReserveCalled   int
+	numReserveCalled    int
-	numPrebindCalled   int
+	numPrebindCalled    int
-	numUnreserveCalled int
+	numUnreserveCalled  int
-	failReserve        bool
+	failReserve         bool
-	failPrebind        bool
+	failPrebind         bool
-	rejectPrebind      bool
+	rejectPrebind       bool
+	numPermitCalled     int
+	failPermit          bool
+	rejectPermit        bool
+	timeoutPermit       bool
+	waitAndRejectPermit bool
+	waitAndAllowPermit  bool
 }
 
 type ReservePlugin struct {
@@ -50,15 +56,22 @@ type UnreservePlugin struct {
 	TesterPlugin
 }
 
+type PermitPlugin struct {
+	TesterPlugin
+	fh framework.FrameworkHandle
+}
+
 const (
 	reservePluginName   = "reserve-plugin"
 	prebindPluginName   = "prebind-plugin"
 	unreservePluginName = "unreserve-plugin"
+	permitPluginName    = "permit-plugin"
 )
 
 var _ = framework.ReservePlugin(&ReservePlugin{})
 var _ = framework.PrebindPlugin(&PrebindPlugin{})
 var _ = framework.UnreservePlugin(&UnreservePlugin{})
+var _ = framework.PermitPlugin(&PermitPlugin{})
 
 // Name returns name of the plugin.
 func (rp *ReservePlugin) Name() string {
@@ -134,6 +147,55 @@ func NewUnreservePlugin(_ *runtime.Unknown, _ framework.FrameworkHandle) (framew
 	return unresPlugin, nil
 }
 
+var perPlugin = &PermitPlugin{}
+
+// Name returns name of the plugin.
+func (pp *PermitPlugin) Name() string {
+	return permitPluginName
+}
+
+// Permit implements the permit test plugin.
+func (pp *PermitPlugin) Permit(pc *framework.PluginContext, pod *v1.Pod, nodeName string) (*framework.Status, time.Duration) {
+	pp.numPermitCalled++
+	if pp.failPermit {
+		return framework.NewStatus(framework.Error, fmt.Sprintf("injecting failure for pod %v", pod.Name)), 0
+	}
+	if pp.rejectPermit {
+		return framework.NewStatus(framework.Unschedulable, fmt.Sprintf("reject pod %v", pod.Name)), 0
+	}
+	if pp.timeoutPermit {
+		return framework.NewStatus(framework.Wait, ""), 3 * time.Second
+	}
+	if pp.waitAndRejectPermit || pp.waitAndAllowPermit {
+		if pod.Name == "waiting-pod" {
+			return framework.NewStatus(framework.Wait, ""), 30 * time.Second
+		}
+		// This is the signalling pod, wait until the waiting-pod is actually waiting and then either reject or allow it.
+		wait.Poll(10*time.Millisecond, 30*time.Second, func() (bool, error) {
+			w := false
+			pp.fh.IterateOverWaitingPods(func(wp framework.WaitingPod) { w = true })
+			return w, nil
+		})
+		if pp.waitAndRejectPermit {
+			pp.fh.IterateOverWaitingPods(func(wp framework.WaitingPod) {
+				wp.Reject(fmt.Sprintf("reject pod %v", wp.GetPod().Name))
+			})
+			return framework.NewStatus(framework.Unschedulable, fmt.Sprintf("reject pod %v", pod.Name)), 0
+		}
+		if pp.waitAndAllowPermit {
+			pp.fh.IterateOverWaitingPods(func(wp framework.WaitingPod) { wp.Allow() })
+			return nil, 0
+		}
+	}
+	return nil, 0
+}
+
+// NewPermitPlugin is the factory for permit plugin.
+func NewPermitPlugin(_ *runtime.Unknown, fh framework.FrameworkHandle) (framework.Plugin, error) {
+	perPlugin.fh = fh
+	return perPlugin, nil
+}
+
 // TestReservePlugin tests invocation of reserve plugins.
 func TestReservePlugin(t *testing.T) {
 	// Create a plugin registry for testing. Register only a reserve plugin.
@@ -181,7 +243,7 @@ func TestReservePlugin(t *testing.T) {
 
 // TestPrebindPlugin tests invocation of prebind plugins.
 func TestPrebindPlugin(t *testing.T) {
-	// Create a plugin registry for testing. Register only a reserve plugin.
+	// Create a plugin registry for testing. Register only a prebind plugin.
 	registry := framework.Registry{prebindPluginName: NewPrebindPlugin}
 
 	// Create the master and the scheduler with the test plugin set.
@@ -336,3 +398,169 @@ func TestUnreservePlugin(t *testing.T) {
 		cleanupPods(cs, t, []*v1.Pod{pod})
 	}
 }
+
+// TestPermitPlugin tests invocation of permit plugins.
+func TestPermitPlugin(t *testing.T) {
+	// Create a plugin registry for testing. Register only a permit plugin.
+	registry := framework.Registry{permitPluginName: NewPermitPlugin}
+
+	// Create the master and the scheduler with the test plugin set.
+	context := initTestSchedulerWithOptions(t,
+		initTestMaster(t, "permit-plugin", nil),
+		false, nil, registry, false, time.Second)
+	defer cleanupTest(t, context)
+
+	cs := context.clientSet
+	// Add a few nodes.
+	_, err := createNodes(cs, "test-node", nil, 2)
+	if err != nil {
+		t.Fatalf("Cannot create nodes: %v", err)
+	}
+
+	tests := []struct {
+		fail    bool
+		reject  bool
+		timeout bool
+	}{
+		{
+			fail:    false,
+			reject:  false,
+			timeout: false,
+		},
+		{
+			fail:    true,
+			reject:  false,
+			timeout: false,
+		},
+		{
+			fail:    false,
+			reject:  true,
+			timeout: false,
+		},
+		{
+			fail:    true,
+			reject:  true,
+			timeout: false,
+		},
+		{
+			fail:    false,
+			reject:  false,
+			timeout: true,
+		},
+		{
+			fail:    false,
+			reject:  false,
+			timeout: true,
+		},
+	}
+
+	for i, test := range tests {
+		perPlugin.failPermit = test.fail
+		perPlugin.rejectPermit = test.reject
+		perPlugin.timeoutPermit = test.timeout
+		perPlugin.waitAndRejectPermit = false
+		perPlugin.waitAndAllowPermit = false
+		// Create a best effort pod.
+		pod, err := createPausePod(cs,
+			initPausePod(cs, &pausePodConfig{Name: "test-pod", Namespace: context.ns.Name}))
+		if err != nil {
+			t.Errorf("Error while creating a test pod: %v", err)
+		}
+		if test.fail {
+			if err = wait.Poll(10*time.Millisecond, 30*time.Second, podSchedulingError(cs, pod.Namespace, pod.Name)); err != nil {
+				t.Errorf("test #%v: Expected a scheduling error, but didn't get it. error: %v", i, err)
+			}
+		} else {
+			if test.reject || test.timeout {
+				if err = waitForPodUnschedulable(cs, pod); err != nil {
+					t.Errorf("test #%v: Didn't expect the pod to be scheduled. error: %v", i, err)
+				}
+			} else {
+				if err = waitForPodToSchedule(cs, pod); err != nil {
+					t.Errorf("test #%v: Expected the pod to be scheduled. error: %v", i, err)
+				}
+			}
+		}
+
+		if perPlugin.numPermitCalled == 0 {
+			t.Errorf("Expected the permit plugin to be called.")
+		}
+
+		cleanupPods(cs, t, []*v1.Pod{pod})
+	}
+}
+
+// TestCoSchedulingWithPermitPlugin tests invocation of permit plugins.
+func TestCoSchedulingWithPermitPlugin(t *testing.T) {
+	// Create a plugin registry for testing. Register only a permit plugin.
+	registry := framework.Registry{permitPluginName: NewPermitPlugin}
+
+	// Create the master and the scheduler with the test plugin set.
+	context := initTestSchedulerWithOptions(t,
+		initTestMaster(t, "permit-plugin", nil),
+		false, nil, registry, false, time.Second)
+	defer cleanupTest(t, context)
+
+	cs := context.clientSet
+	// Add a few nodes.
+	_, err := createNodes(cs, "test-node", nil, 2)
+	if err != nil {
+		t.Fatalf("Cannot create nodes: %v", err)
+	}
+
+	tests := []struct {
+		waitReject bool
+		waitAllow  bool
+	}{
+		{
+			waitReject: true,
+			waitAllow:  false,
+		},
+		{
+			waitReject: false,
+			waitAllow:  true,
+		},
+	}
+
+	for i, test := range tests {
+		perPlugin.failPermit = false
+		perPlugin.rejectPermit = false
+		perPlugin.timeoutPermit = false
+		perPlugin.waitAndRejectPermit = test.waitReject
+		perPlugin.waitAndAllowPermit = test.waitAllow
+
+		// Create two pods.
+		waitingPod, err := createPausePod(cs,
+			initPausePod(cs, &pausePodConfig{Name: "waiting-pod", Namespace: context.ns.Name}))
+		if err != nil {
+			t.Errorf("Error while creating the waiting pod: %v", err)
+		}
+		signallingPod, err := createPausePod(cs,
+			initPausePod(cs, &pausePodConfig{Name: "signalling-pod", Namespace: context.ns.Name}))
+		if err != nil {
+			t.Errorf("Error while creating the signalling pod: %v", err)
+		}
+
+		if test.waitReject {
+			if err = waitForPodUnschedulable(cs, waitingPod); err != nil {
+				t.Errorf("test #%v: Didn't expect the waiting pod to be scheduled. error: %v", i, err)
+			}
+			if err = waitForPodUnschedulable(cs, signallingPod); err != nil {
+				t.Errorf("test #%v: Didn't expect the signalling pod to be scheduled. error: %v", i, err)
+			}
+		} else {
+			if err = waitForPodToSchedule(cs, waitingPod); err != nil {
+				t.Errorf("test #%v: Expected the waiting pod to be scheduled. error: %v", i, err)
+			}
+			if err = waitForPodToSchedule(cs, signallingPod); err != nil {
+				t.Errorf("test #%v: Expected the signalling pod to be scheduled. error: %v", i, err)
+			}
+		}
+
+		if perPlugin.numPermitCalled == 0 {
+			t.Errorf("Expected the permit plugin to be called.")
+		}
+
+		cleanupPods(cs, t, []*v1.Pod{waitingPod, signallingPod})
+	}
+}