create an ordered list of nodes instead of iterating over the tree

pkg/scheduler/core/generic_scheduler.go

@@ -187,16 +187,15 @@ func (g *genericScheduler) Schedule(ctx context.Context, state *framework.CycleS
 	}
 	trace.Step("Running prefilter plugins done")
 
-	numNodes := g.cache.NodeTree().NumNodes()
-	if numNodes == 0 {
-		return result, ErrNoNodesAvailable
-	}
-
 	if err := g.snapshot(); err != nil {
 		return result, err
 	}
 	trace.Step("Snapshoting scheduler cache and node infos done")
 
+	if len(g.nodeInfoSnapshot.NodeInfoList) == 0 {
+		return result, ErrNoNodesAvailable
+	}
+
 	startPredicateEvalTime := time.Now()
 	filteredNodes, failedPredicateMap, filteredNodesStatuses, err := g.findNodesThatFit(ctx, state, pod)
 	if err != nil {
@@ -213,7 +212,7 @@ func (g *genericScheduler) Schedule(ctx context.Context, state *framework.CycleS
 	if len(filteredNodes) == 0 {
 		return result, &FitError{
 			Pod:                   pod,
-			NumAllNodes:           numNodes,
+			NumAllNodes:           len(g.nodeInfoSnapshot.NodeInfoList),
 			FailedPredicates:      failedPredicateMap,
 			FilteredNodesStatuses: filteredNodesStatuses,
 		}
@@ -460,13 +459,13 @@ func (g *genericScheduler) findNodesThatFit(ctx context.Context, state *framewor
 	if len(g.predicates) == 0 && !g.framework.HasFilterPlugins() {
 		filtered = g.nodeInfoSnapshot.ListNodes()
 	} else {
-		allNodes := int32(g.cache.NodeTree().NumNodes())
+		allNodes := int32(len(g.nodeInfoSnapshot.NodeInfoList))
 		numNodesToFind := g.numFeasibleNodesToFind(allNodes)
 
 		// Create filtered list with enough space to avoid growing it
 		// and allow assigning.
 		filtered = make([]*v1.Node, numNodesToFind)
-		errs := errors.MessageCountMap{}
+		errCh := util.NewErrorChannel()
 		var (
 			predicateResultLock sync.Mutex
 			filteredLen         int32
@@ -479,20 +478,17 @@ func (g *genericScheduler) findNodesThatFit(ctx context.Context, state *framewor
 		state.Write(migration.PredicatesStateKey, &migration.PredicatesStateData{Reference: meta})
 
 		checkNode := func(i int) {
-			nodeName := g.cache.NodeTree().Next()
-
+			nodeInfo := g.nodeInfoSnapshot.NodeInfoList[i]
 			fits, failedPredicates, status, err := g.podFitsOnNode(
 				ctx,
 				state,
 				pod,
 				meta,
-				g.nodeInfoSnapshot.NodeInfoMap[nodeName],
+				nodeInfo,
 				g.alwaysCheckAllPredicates,
 			)
 			if err != nil {
-				predicateResultLock.Lock()
-				errs[err.Error()]++
-				predicateResultLock.Unlock()
+				errCh.SendErrorWithCancel(err, cancel)
 				return
 			}
 			if fits {
@@ -501,15 +497,15 @@ func (g *genericScheduler) findNodesThatFit(ctx context.Context, state *framewor
 					cancel()
 					atomic.AddInt32(&filteredLen, -1)
 				} else {
-					filtered[length-1] = g.nodeInfoSnapshot.NodeInfoMap[nodeName].Node()
+					filtered[length-1] = nodeInfo.Node()
 				}
 			} else {
 				predicateResultLock.Lock()
 				if !status.IsSuccess() {
-					filteredNodesStatuses[nodeName] = status
+					filteredNodesStatuses[nodeInfo.Node().Name] = status
 				}
 				if len(failedPredicates) != 0 {
-					failedPredicateMap[nodeName] = failedPredicates
+					failedPredicateMap[nodeInfo.Node().Name] = failedPredicates
 				}
 				predicateResultLock.Unlock()
 			}
@@ -520,8 +516,8 @@ func (g *genericScheduler) findNodesThatFit(ctx context.Context, state *framewor
 		workqueue.ParallelizeUntil(ctx, 16, int(allNodes), checkNode)
 
 		filtered = filtered[:filteredLen]
-		if len(errs) > 0 {
-			return []*v1.Node{}, FailedPredicateMap{}, framework.NodeToStatusMap{}, errors.CreateAggregateFromMessageCountMap(errs)
+		if err := errCh.ReceiveError(); err != nil {
+			return []*v1.Node{}, FailedPredicateMap{}, framework.NodeToStatusMap{}, err
 		}
 	}
 

pkg/scheduler/internal/cache/cache.go

@@ -74,7 +74,7 @@ type schedulerCache struct {
 	// headNode points to the most recently updated NodeInfo in "nodes". It is the
 	// head of the linked list.
 	headNode *nodeInfoListItem
-	nodeTree *NodeTree
+	nodeTree *nodeTree
 	// A map from image name to its imageState.
 	imageStates map[string]*imageState
 }
@@ -238,6 +238,17 @@ func (cache *schedulerCache) UpdateNodeInfoSnapshot(nodeSnapshot *schedulernodei
 			}
 		}
 	}
+
+	// Take a snapshot of the nodes order in the tree
+	nodeSnapshot.NodeInfoList = make([]*schedulernodeinfo.NodeInfo, 0, cache.nodeTree.numNodes)
+	for i := 0; i < cache.nodeTree.numNodes; i++ {
+		nodeName := cache.nodeTree.next()
+		if n := nodeSnapshot.NodeInfoMap[nodeName]; n != nil {
+			nodeSnapshot.NodeInfoList = append(nodeSnapshot.NodeInfoList, n)
+		} else {
+			klog.Errorf("node %q exist in nodeTree but not in NodeInfoMap, this should not happen.", nodeName)
+		}
+	}
 	return nil
 }
 
@@ -516,7 +527,7 @@ func (cache *schedulerCache) AddNode(node *v1.Node) error {
 	}
 	cache.moveNodeInfoToHead(node.Name)
 
-	cache.nodeTree.AddNode(node)
+	cache.nodeTree.addNode(node)
 	cache.addNodeImageStates(node, n.info)
 	return n.info.SetNode(node)
 }
@@ -534,7 +545,7 @@ func (cache *schedulerCache) UpdateNode(oldNode, newNode *v1.Node) error {
 	}
 	cache.moveNodeInfoToHead(newNode.Name)
 
-	cache.nodeTree.UpdateNode(oldNode, newNode)
+	cache.nodeTree.updateNode(oldNode, newNode)
 	cache.addNodeImageStates(newNode, n.info)
 	return n.info.SetNode(newNode)
 }
@@ -560,7 +571,7 @@ func (cache *schedulerCache) RemoveNode(node *v1.Node) error {
 		cache.moveNodeInfoToHead(node.Name)
 	}
 
-	if err := cache.nodeTree.RemoveNode(node); err != nil {
+	if err := cache.nodeTree.removeNode(node); err != nil {
 		return err
 	}
 	cache.removeNodeImageStates(node)
@@ -688,10 +699,6 @@ func (cache *schedulerCache) expirePod(key string, ps *podState) error {
 	return nil
 }
 
-func (cache *schedulerCache) NodeTree() *NodeTree {
-	return cache.nodeTree
-}
-
 // GetNodeInfo returns cached data for the node name.
 func (cache *schedulerCache) GetNodeInfo(nodeName string) (*v1.Node, error) {
 	cache.mu.RLock()

pkg/scheduler/internal/cache/cache_test.go

@@ -1066,7 +1066,7 @@ func TestNodeOperators(t *testing.T) {
 		if !found {
 			t.Errorf("Failed to find node %v in internalcache.", node.Name)
 		}
-		if cache.nodeTree.NumNodes() != 1 || cache.nodeTree.Next() != node.Name {
+		if cache.nodeTree.numNodes != 1 || cache.nodeTree.next() != node.Name {
 			t.Errorf("cache.nodeTree is not updated correctly after adding node: %v", node.Name)
 		}
 
@@ -1109,7 +1109,7 @@ func TestNodeOperators(t *testing.T) {
 			t.Errorf("Failed to update node in schedulernodeinfo:\n got: %+v \nexpected: %+v", got, expected)
 		}
 		// Check nodeTree after update
-		if cache.nodeTree.NumNodes() != 1 || cache.nodeTree.Next() != node.Name {
+		if cache.nodeTree.numNodes != 1 || cache.nodeTree.next() != node.Name {
 			t.Errorf("unexpected cache.nodeTree after updating node: %v", node.Name)
 		}
 
@@ -1120,7 +1120,7 @@ func TestNodeOperators(t *testing.T) {
 		}
 		// Check nodeTree after remove. The node should be removed from the nodeTree even if there are
 		// still pods on it.
-		if cache.nodeTree.NumNodes() != 0 || cache.nodeTree.Next() != "" {
+		if cache.nodeTree.numNodes != 0 || cache.nodeTree.next() != "" {
 			t.Errorf("unexpected cache.nodeTree after removing node: %v", node.Name)
 		}
 	}

pkg/scheduler/internal/cache/fake/fake_cache.go

@@ -103,9 +103,6 @@ func (c *Cache) Snapshot() *internalcache.Snapshot {
 	return &internalcache.Snapshot{}
 }
 
-// NodeTree is a fake method for testing.
-func (c *Cache) NodeTree() *internalcache.NodeTree { return nil }
-
 // GetNodeInfo is a fake method for testing.
 func (c *Cache) GetNodeInfo(nodeName string) (*v1.Node, error) {
 	return nil, nil
@@ -120,3 +117,8 @@ func (c *Cache) ListNodes() []*v1.Node {
 func (c *Cache) GetCSINodeInfo(nodeName string) (*storagev1beta1.CSINode, error) {
 	return nil, nil
 }
+
+// NumNodes is a fake method for testing.
+func (c *Cache) NumNodes() int {
+	return 0
+}

pkg/scheduler/internal/cache/interface.go

@@ -119,9 +119,6 @@ type Cache interface {
 
 	// Snapshot takes a snapshot on current cache
 	Snapshot() *Snapshot
-
-	// NodeTree returns a node tree structure
-	NodeTree() *NodeTree
 }
 
 // Snapshot is a snapshot of cache state

pkg/scheduler/internal/cache/node_tree.go

@@ -18,22 +18,21 @@ package cache
 
 import (
 	"fmt"
-	"sync"
 
 	"k8s.io/api/core/v1"
-	utilnode "k8s.io/kubernetes/pkg/util/node"
-
 	"k8s.io/klog"
+	utilnode "k8s.io/kubernetes/pkg/util/node"
 )
 
-// NodeTree is a tree-like data structure that holds node names in each zone. Zone names are
+// nodeTree is a tree-like data structure that holds node names in each zone. Zone names are
 // keys to "NodeTree.tree" and values of "NodeTree.tree" are arrays of node names.
-type NodeTree struct {
+// NodeTree is NOT thread-safe, any concurrent updates/reads from it must be synchronized by the caller.
+// It is used only by schedulerCache, and should stay as such.
+type nodeTree struct {
 	tree      map[string]*nodeArray // a map from zone (region-zone) to an array of nodes in the zone.
 	zones     []string              // a list of all the zones in the tree (keys)
 	zoneIndex int
 	numNodes  int
-	mu        sync.RWMutex
 }
 
 // nodeArray is a struct that has nodes that are in a zone.
@@ -58,8 +57,8 @@ func (na *nodeArray) next() (nodeName string, exhausted bool) {
 }
 
 // newNodeTree creates a NodeTree from nodes.
-func newNodeTree(nodes []*v1.Node) *NodeTree {
-	nt := &NodeTree{
+func newNodeTree(nodes []*v1.Node) *nodeTree {
+	nt := &nodeTree{
 		tree: make(map[string]*nodeArray),
 	}
 	for _, n := range nodes {
@@ -68,15 +67,9 @@ func newNodeTree(nodes []*v1.Node) *NodeTree {
 	return nt
 }
 
-// AddNode adds a node and its corresponding zone to the tree. If the zone already exists, the node
+// addNode adds a node and its corresponding zone to the tree. If the zone already exists, the node
 // is added to the array of nodes in that zone.
-func (nt *NodeTree) AddNode(n *v1.Node) {
-	nt.mu.Lock()
-	defer nt.mu.Unlock()
-	nt.addNode(n)
-}
-
-func (nt *NodeTree) addNode(n *v1.Node) {
+func (nt *nodeTree) addNode(n *v1.Node) {
 	zone := utilnode.GetZoneKey(n)
 	if na, ok := nt.tree[zone]; ok {
 		for _, nodeName := range na.nodes {
@@ -94,14 +87,8 @@ func (nt *NodeTree) addNode(n *v1.Node) {
 	nt.numNodes++
 }
 
-// RemoveNode removes a node from the NodeTree.
-func (nt *NodeTree) RemoveNode(n *v1.Node) error {
-	nt.mu.Lock()
-	defer nt.mu.Unlock()
-	return nt.removeNode(n)
-}
-
-func (nt *NodeTree) removeNode(n *v1.Node) error {
+// removeNode removes a node from the NodeTree.
+func (nt *nodeTree) removeNode(n *v1.Node) error {
 	zone := utilnode.GetZoneKey(n)
 	if na, ok := nt.tree[zone]; ok {
 		for i, nodeName := range na.nodes {
@@ -122,7 +109,7 @@ func (nt *NodeTree) removeNode(n *v1.Node) error {
 
 // removeZone removes a zone from tree.
 // This function must be called while writer locks are hold.
-func (nt *NodeTree) removeZone(zone string) {
+func (nt *nodeTree) removeZone(zone string) {
 	delete(nt.tree, zone)
 	for i, z := range nt.zones {
 		if z == zone {
@@ -132,8 +119,8 @@ func (nt *NodeTree) removeZone(zone string) {
 	}
 }
 
-// UpdateNode updates a node in the NodeTree.
-func (nt *NodeTree) UpdateNode(old, new *v1.Node) {
+// updateNode updates a node in the NodeTree.
+func (nt *nodeTree) updateNode(old, new *v1.Node) {
 	var oldZone string
 	if old != nil {
 		oldZone = utilnode.GetZoneKey(old)
@@ -144,24 +131,20 @@ func (nt *NodeTree) UpdateNode(old, new *v1.Node) {
 	if oldZone == newZone {
 		return
 	}
-	nt.mu.Lock()
-	defer nt.mu.Unlock()
 	nt.removeNode(old) // No error checking. We ignore whether the old node exists or not.
 	nt.addNode(new)
 }
 
-func (nt *NodeTree) resetExhausted() {
+func (nt *nodeTree) resetExhausted() {
 	for _, na := range nt.tree {
 		na.lastIndex = 0
 	}
 	nt.zoneIndex = 0
 }
 
-// Next returns the name of the next node. NodeTree iterates over zones and in each zone iterates
+// next returns the name of the next node. NodeTree iterates over zones and in each zone iterates
 // over nodes in a round robin fashion.
-func (nt *NodeTree) Next() string {
-	nt.mu.Lock()
-	defer nt.mu.Unlock()
+func (nt *nodeTree) next() string {
 	if len(nt.zones) == 0 {
 		return ""
 	}
@@ -185,10 +168,3 @@ func (nt *NodeTree) Next() string {
 		}
 	}
 }
-
-// NumNodes returns the number of nodes.
-func (nt *NodeTree) NumNodes() int {
-	nt.mu.RLock()
-	defer nt.mu.RUnlock()
-	return nt.numNodes
-}

pkg/scheduler/internal/cache/node_tree_test.go

@@ -110,23 +110,23 @@ var allNodes = []*v1.Node{
 		},
 	}}
 
-func verifyNodeTree(t *testing.T, nt *NodeTree, expectedTree map[string]*nodeArray) {
+func verifyNodeTree(t *testing.T, nt *nodeTree, expectedTree map[string]*nodeArray) {
 	expectedNumNodes := int(0)
 	for _, na := range expectedTree {
 		expectedNumNodes += len(na.nodes)
 	}
-	if numNodes := nt.NumNodes(); numNodes != expectedNumNodes {
-		t.Errorf("unexpected NodeTree.numNodes. Expected: %v, Got: %v", expectedNumNodes, numNodes)
+	if numNodes := nt.numNodes; numNodes != expectedNumNodes {
+		t.Errorf("unexpected nodeTree.numNodes. Expected: %v, Got: %v", expectedNumNodes, numNodes)
 	}
 	if !reflect.DeepEqual(nt.tree, expectedTree) {
 		t.Errorf("The node tree is not the same as expected. Expected: %v, Got: %v", expectedTree, nt.tree)
 	}
 	if len(nt.zones) != len(expectedTree) {
-		t.Errorf("Number of zones in NodeTree.zones is not expected. Expected: %v, Got: %v", len(expectedTree), len(nt.zones))
+		t.Errorf("Number of zones in nodeTree.zones is not expected. Expected: %v, Got: %v", len(expectedTree), len(nt.zones))
 	}
 	for _, z := range nt.zones {
 		if _, ok := expectedTree[z]; !ok {
-			t.Errorf("zone %v is not expected to exist in NodeTree.zones", z)
+			t.Errorf("zone %v is not expected to exist in nodeTree.zones", z)
 		}
 	}
 }
@@ -170,7 +170,7 @@ func TestNodeTree_AddNode(t *testing.T) {
 		t.Run(test.name, func(t *testing.T) {
 			nt := newNodeTree(nil)
 			for _, n := range test.nodesToAdd {
-				nt.AddNode(n)
+				nt.addNode(n)
 			}
 			verifyNodeTree(t, nt, test.expectedTree)
 		})
@@ -227,7 +227,7 @@ func TestNodeTree_RemoveNode(t *testing.T) {
 		t.Run(test.name, func(t *testing.T) {
 			nt := newNodeTree(test.existingNodes)
 			for _, n := range test.nodesToRemove {
-				err := nt.RemoveNode(n)
+				err := nt.removeNode(n)
 				if test.expectError == (err == nil) {
 					t.Errorf("unexpected returned error value: %v", err)
 				}
@@ -312,7 +312,7 @@ func TestNodeTree_UpdateNode(t *testing.T) {
 			if oldNode == nil {
 				oldNode = &v1.Node{ObjectMeta: metav1.ObjectMeta{Name: "nonexisting-node"}}
 			}
-			nt.UpdateNode(oldNode, test.nodeToUpdate)
+			nt.updateNode(oldNode, test.nodeToUpdate)
 			verifyNodeTree(t, nt, test.expectedTree)
 		})
 	}
@@ -357,7 +357,7 @@ func TestNodeTree_Next(t *testing.T) {
 
 			var output []string
 			for i := 0; i < test.numRuns; i++ {
-				output = append(output, nt.Next())
+				output = append(output, nt.next())
 			}
 			if !reflect.DeepEqual(output, test.expectedOutput) {
 				t.Errorf("unexpected output. Expected: %v, Got: %v", test.expectedOutput, output)
@@ -423,18 +423,18 @@ func TestNodeTreeMultiOperations(t *testing.T) {
 					if addIndex >= len(test.nodesToAdd) {
 						t.Error("more add operations than nodesToAdd")
 					} else {
-						nt.AddNode(test.nodesToAdd[addIndex])
+						nt.addNode(test.nodesToAdd[addIndex])
 						addIndex++
 					}
 				case "remove":
 					if removeIndex >= len(test.nodesToRemove) {
 						t.Error("more remove operations than nodesToRemove")
 					} else {
-						nt.RemoveNode(test.nodesToRemove[removeIndex])
+						nt.removeNode(test.nodesToRemove[removeIndex])
 						removeIndex++
 					}
 				case "next":
-					output = append(output, nt.Next())
+					output = append(output, nt.next())
 				default:
 					t.Errorf("unknow operation: %v", op)
 				}

pkg/scheduler/nodeinfo/snapshot.go

@@ -20,12 +20,14 @@ import (
 	v1 "k8s.io/api/core/v1"
 )
 
-// Snapshot is a snapshot of cache NodeInfo. The scheduler takes a
-// snapshot at the beginning of each scheduling cycle and uses it for its
-// operations in that cycle.
+// Snapshot is a snapshot of cache NodeInfo and NodeTree order. The scheduler takes a
+// snapshot at the beginning of each scheduling cycle and uses it for its operations in that cycle.
 type Snapshot struct {
+	// NodeInfoMap a map of node name to a snapshot of its NodeInfo.
 	NodeInfoMap map[string]*NodeInfo
-	Generation  int64
+	// NodeInfoList is the list of nodes as ordered in the cache's nodeTree.
+	NodeInfoList []*NodeInfo
+	Generation   int64
 }
 
 // NewSnapshot initializes a Snapshot struct and returns it.
@@ -38,7 +40,7 @@ func NewSnapshot() *Snapshot {
 // ListNodes returns the list of nodes in the snapshot.
 func (s *Snapshot) ListNodes() []*v1.Node {
 	nodes := make([]*v1.Node, 0, len(s.NodeInfoMap))
-	for _, n := range s.NodeInfoMap {
+	for _, n := range s.NodeInfoList {
 		if n != nil && n.node != nil {
 			nodes = append(nodes, n.node)
 		}