Pick pods for preemption based on StartTime of pods when priorities are equal

pkg/scheduler/core/extender_test.go

@@ -197,7 +197,7 @@ func (f *FakeExtender) selectVictimsOnNodeByExtender(
 	// and get cached node info by given node name.
 	nodeInfoCopy := f.cachedNodeNameToInfo[node.GetName()].Clone()
 
-	potentialVictims := util.SortableList{CompFunc: util.HigherPriorityPod}
+	potentialVictims := util.SortableList{CompFunc: util.MoreImportantPod}
 
 	removePod := func(rp *v1.Pod) {
 		nodeInfoCopy.RemovePod(rp)

pkg/scheduler/core/generic_scheduler.go

@@ -1046,7 +1046,7 @@ func selectVictimsOnNode(
 	if nodeInfo == nil {
 		return nil, 0, false
 	}
-	potentialVictims := util.SortableList{CompFunc: util.HigherPriorityPod}
+	potentialVictims := util.SortableList{CompFunc: util.MoreImportantPod}
 	nodeInfoCopy := nodeInfo.Clone()
 
 	removePod := func(rp *v1.Pod) {

pkg/scheduler/core/generic_scheduler_test.go

@@ -947,6 +947,19 @@ func TestSelectNodesForPreemption(t *testing.T) {
 			expected: map[string]map[string]bool{"machine1": {"b": true, "c": true}},
 		},
 		{
+			name:       "mixed priority pods are preempted, pick later StartTime one when priorities are equal",
+			predicates: map[string]algorithmpredicates.FitPredicate{"matches": algorithmpredicates.PodFitsResources},
+			nodes:      []string{"machine1", "machine2"},
+			pod:        &v1.Pod{ObjectMeta: metav1.ObjectMeta{Name: "machine1", UID: types.UID("machine1")}, Spec: v1.PodSpec{Containers: largeContainers, Priority: &highPriority}},
+			pods: []*v1.Pod{
+				{ObjectMeta: metav1.ObjectMeta{Name: "a", UID: types.UID("a")}, Spec: v1.PodSpec{Containers: smallContainers, Priority: &lowPriority, NodeName: "machine1"}, Status: v1.PodStatus{StartTime: &startTime20190107}},
+				{ObjectMeta: metav1.ObjectMeta{Name: "b", UID: types.UID("b")}, Spec: v1.PodSpec{Containers: smallContainers, Priority: &lowPriority, NodeName: "machine1"}, Status: v1.PodStatus{StartTime: &startTime20190106}},
+				{ObjectMeta: metav1.ObjectMeta{Name: "c", UID: types.UID("c")}, Spec: v1.PodSpec{Containers: mediumContainers, Priority: &midPriority, NodeName: "machine1"}, Status: v1.PodStatus{StartTime: &startTime20190105}},
+				{ObjectMeta: metav1.ObjectMeta{Name: "d", UID: types.UID("d")}, Spec: v1.PodSpec{Containers: smallContainers, Priority: &highPriority, NodeName: "machine1"}, Status: v1.PodStatus{StartTime: &startTime20190104}},
+				{ObjectMeta: metav1.ObjectMeta{Name: "e", UID: types.UID("e")}, Spec: v1.PodSpec{Containers: largeContainers, Priority: &highPriority, NodeName: "machine2"}, Status: v1.PodStatus{StartTime: &startTime20190103}}},
+			expected: map[string]map[string]bool{"machine1": {"a": true, "c": true}},
+		},
+		{
 			name:       "pod with anti-affinity is preempted",
 			predicates: map[string]algorithmpredicates.FitPredicate{"matches": algorithmpredicates.PodFitsResources},
 			nodes:      []string{"machine1", "machine2"},

pkg/scheduler/util/utils.go

@@ -134,9 +134,15 @@ func (l *SortableList) Sort() {
 	sort.Sort(l)
 }
 
-// HigherPriorityPod return true when priority of the first pod is higher than
-// the second one. It takes arguments of the type "interface{}" to be used with
-// SortableList, but expects those arguments to be *v1.Pod.
-func HigherPriorityPod(pod1, pod2 interface{}) bool {
-	return GetPodPriority(pod1.(*v1.Pod)) > GetPodPriority(pod2.(*v1.Pod))
+// MoreImportantPod return true when priority of the first pod is higher than
+// the second one. If two pods' priorities are equal, compare their StartTime.
+// It takes arguments of the type "interface{}" to be used with SortableList,
+// but expects those arguments to be *v1.Pod.
+func MoreImportantPod(pod1, pod2 interface{}) bool {
+	p1 := GetPodPriority(pod1.(*v1.Pod))
+	p2 := GetPodPriority(pod2.(*v1.Pod))
+	if p1 != p2 {
+		return p1 > p2
+	}
+	return GetPodStartTime(pod1.(*v1.Pod)).Before(GetPodStartTime(pod2.(*v1.Pod)))
 }