feat: implement "queue-sort" extension point for scheduling framework

pkg/scheduler/framework/v1alpha1/framework.go

@@ -34,6 +34,7 @@ type framework struct {
 	nodeInfoSnapshot *cache.NodeInfoSnapshot
 	waitingPods      *waitingPodsMap
 	plugins          map[string]Plugin // a map of initialized plugins. Plugin name:plugin instance.
+	queueSortPlugins []QueueSortPlugin
 	reservePlugins   []ReservePlugin
 	prebindPlugins   []PrebindPlugin
 	unreservePlugins []UnreservePlugin
@@ -69,6 +70,10 @@ func NewFramework(r Registry, _ *runtime.Unknown) (Framework, error) {
 		// TODO: For now, we assume any plugins that implements an extension
 		// point wants to be called at that extension point. We should change this
 		// later and add these plugins based on the configuration.
+		if qsp, ok := p.(QueueSortPlugin); ok {
+			f.queueSortPlugins = append(f.queueSortPlugins, qsp)
+		}
+
 		if rp, ok := p.(ReservePlugin); ok {
 			f.reservePlugins = append(f.reservePlugins, rp)
 		}
@@ -85,6 +90,16 @@ func NewFramework(r Registry, _ *runtime.Unknown) (Framework, error) {
 	return f, nil
 }
 
+// QueueSortFunc returns the function to sort pods in scheduling queue
+func (f *framework) QueueSortFunc() LessFunc {
+	if len(f.queueSortPlugins) == 0 {
+		return nil
+	}
+
+	// Only one QueueSort plugin can be enabled.
+	return f.queueSortPlugins[0].Less
+}
+
 // RunPrebindPlugins runs the set of configured prebind plugins. It returns a
 // failure (bool) if any of the plugins returns an error. It also returns an
 // error containing the rejection message or the error occurred in the plugin.

pkg/scheduler/framework/v1alpha1/interface.go

@@ -107,6 +107,25 @@ type Plugin interface {
 	Name() string
 }
 
+// PodInfo is minimum cell in the scheduling queue.
+type PodInfo struct {
+	Pod *v1.Pod
+	// The time pod added to the scheduling queue.
+	Timestamp time.Time
+}
+
+// LessFunc is the function to sort pod info
+type LessFunc func(podInfo1, podInfo2 *PodInfo) bool
+
+// QueueSortPlugin is an interface that must be implemented by "QueueSort" plugins.
+// These plugins are used to sort pods in the scheduling queue. Only one queue sort
+// plugin may be enabled at a time.
+type QueueSortPlugin interface {
+	Plugin
+	// Less are used to sort pods in the scheduling queue.
+	Less(*PodInfo, *PodInfo) bool
+}
+
 // ReservePlugin is an interface for Reserve plugins. These plugins are called
 // at the reservation point. These are meant to update the state of the plugin.
 // This concept used to be called 'assume' in the original scheduler.
@@ -157,6 +176,9 @@ type PermitPlugin interface {
 // Configured plugins are called at specified points in a scheduling context.
 type Framework interface {
 	FrameworkHandle
+	// QueueSortFunc returns the function to sort pods in scheduling queue
+	QueueSortFunc() LessFunc
+
 	// RunPrebindPlugins runs the set of configured prebind plugins. It returns
 	// *Status and its code is set to non-success if any of the plugins returns
 	// anything but Success. If the Status code is "Unschedulable", it is