[Coscheduling] CalculateAssignedPods cost too much time

[GreenHand]

PodGroup manager will try every node and every pod in CalculateAssignedPods()

scheduler-plugins/pkg/coscheduling/core/core.go

Lines 246 to 264 in cd3e4fb

 // CalculateAssignedPods returns the number of pods that has been assigned nodes: assumed or bound. 
 func (pgMgr *PodGroupManager) CalculateAssignedPods(podGroupName, namespace string) int { 
 	nodeInfos, err := pgMgr.snapshotSharedLister.NodeInfos().List() 
 	if err != nil { 
 		klog.ErrorS(err, "Cannot get nodeInfos from frameworkHandle") 
 		return 0 
 	} 
 	var count int 
 	for _, nodeInfo := range nodeInfos { 
 		for _, podInfo := range nodeInfo.Pods { 
 			pod := podInfo.Pod 
 			if util.GetPodGroupLabel(pod) == podGroupName && pod.Namespace == namespace && pod.Spec.NodeName != "" { 
 				count++ 
 			} 
 		} 
 	} 
  
 	return count 
 } 

When there are 5k or more nodes and 50000+ pods in cluster, CalculateAssignedPods() will cost 30+ms.
We should cache the number of assigned pods to save time in scheduling cycle.

[GreenHand]

/assign