kube-scheduler 调度流程

创建调度器

创建调度器主要是构造调度队列，调度缓存，调度框架和调度算法，以及获取待调度pod和将调度失败pod加入不可调度队列的两个函数。

//pkg/scheduler/factory.go
func (c *Configurator) create() (*Scheduler, error) {
	...
	return &Scheduler{
		//调度缓存
		SchedulerCache:  c.schedulerCache,
		//调度算法
		Algorithm:       algo,
		Extenders:       extenders,
		//调度框架
		Profiles:        profiles,
		//从调度队列获取得调度pod，如果没有则堵塞
		NextPod:         internalqueue.MakeNextPodFunc(podQueue),
		//调度失败后，将pod加入不可调度队列
		Error:           MakeDefaultErrorFunc(c.client, c.informerFactory.Core().V1().Pods().Lister(), podQueue, c.schedulerCache),
		StopEverything:  c.StopEverything,
		//调度队列
		SchedulingQueue: podQueue,
	}, nil
}

调度缓存，调度队列和调度框架在前面文章已经分析过了，还有一个核心功能调度算法，实现也比较简单，只有一个接口函数，如下

type ScheduleAlgorithm interface {
	Schedule(context.Context, []framework.Extender, framework.Framework, *framework.CycleState, *v1.Pod) (scheduleResult ScheduleResult, err error)
}

genericScheduler实现了ScheduleAlgorithm接口，其结构如下

type genericScheduler struct {
	//用来调用cache提供的UpdateSnapshot做快照
	cache                    internalcache.Cache
	//将快照信息保存到nodeInfoSnapshot
	nodeInfoSnapshot         *internalcache.Snapshot
	//每次调度pod时，并不是所有的node都会参与调度，而是通过此变量控制百分百
	percentageOfNodesToScore int32
	//如上面所说，用来保存下一次调度时从哪个node开始调度
	nextStartNodeIndex       int
}

MakeNextPodFunc返回一个函数，用来从调度队列pop待调度pod，如果没有则堵塞

// MakeNextPodFunc returns a function to retrieve the next pod from a given
// scheduling queue
func MakeNextPodFunc(queue SchedulingQueue) func() *framework.QueuedPodInfo {
	return func() *framework.QueuedPodInfo {
		podInfo, err := queue.Pop()
		if err == nil {
			klog.V(4).InfoS("About to try and schedule pod", "pod", klog.KObj(podInfo.Pod))
			return podInfo
		}
		klog.ErrorS(err, "Error while retrieving next pod from scheduling queue")
		return nil
	}
}

MakeDefaultErrorFunc返回一个函数，用来将调度失败的pod加入不可调度队列等待重新调度

// MakeDefaultErrorFunc construct a function to handle pod scheduler error
func MakeDefaultErrorFunc(client clientset.Interface, podLister corelisters.PodLister, podQueue internalqueue.SchedulingQueue, schedulerCache internalcache.Cache) func(*framework.QueuedPodInfo, error) {
	return func(podInfo *framework.QueuedPodInfo, err error) {
		pod := podInfo.Pod
		if err == ErrNoNodesAvailable {
			klog.V(2).InfoS("Unable to schedule pod; no nodes are registered to the cluster; waiting", "pod", klog.KObj(pod))
		} else if fitError, ok := err.(*framework.FitError); ok {
			// Inject UnschedulablePlugins to PodInfo, which will be used later for moving Pods between queues efficiently.
			podInfo.UnschedulablePlugins = fitError.Diagnosis.UnschedulablePlugins
			klog.V(2).InfoS("Unable to schedule pod; no fit; waiting", "pod", klog.KObj(pod), "err", err)
		} else if apierrors.IsNotFound(err) {
			klog.V(2).InfoS("Unable to schedule pod, possibly due to node not found; waiting", "pod", klog.KObj(pod), "err", err)
			if errStatus, ok := err.(apierrors.APIStatus); ok && errStatus.Status().Details.Kind == "node" {
				nodeName := errStatus.Status().Details.Name
				// when node is not found, We do not remove the node right away. Trying again to get
				// the node and if the node is still not found, then remove it from the scheduler cache.
				_, err := client.CoreV1().Nodes().Get(context.TODO(), nodeName, metav1.GetOptions{})
				if err != nil && apierrors.IsNotFound(err) {
					node := v1.Node{ObjectMeta: metav1.ObjectMeta{Name: nodeName}}
					if err := schedulerCache.RemoveNode(&node); err != nil {
						klog.V(4).InfoS("Node is not found; failed to remove it from the cache", "node", node.Name)
					}
				}
			}
		} else {
			klog.ErrorS(err, "Error scheduling pod; retrying", "pod", klog.KObj(pod))
		}

		//如果pod已经被删除了，也就没必要加入不可调度队列了
		// Check if the Pod exists in informer cache.
		cachedPod, err := podLister.Pods(pod.Namespace).Get(pod.Name)
		if err != nil {
			klog.InfoS("Pod doesn't exist in informer cache", "pod", klog.KObj(pod), "err", err)
			return
		}

		// In the case of extender, the pod may have been bound successfully, but timed out returning its response to the scheduler.
		// It could result in the live version to carry .spec.nodeName, and that's inconsistent with the internal-queued version.
		if len(cachedPod.Spec.NodeName) != 0 {
			klog.InfoS("Pod has been assigned to node. Abort adding it back to queue.", "pod", klog.KObj(pod), "node", cachedPod.Spec.NodeName)
			return
		}

		// As  is from SharedInformer, we need to do a DeepCopy() here.
		podInfo.PodInfo = framework.NewPodInfo(cachedPod.DeepCopy())
		//将pod加入不可调度队列
		if err := podQueue.AddUnschedulableIfNotPresent(podInfo, podQueue.SchedulingCycle()); err != nil {
			klog.ErrorS(err, "Error occurred")
		}
	}
}

运行调度器

创建调度器后，执行其Run函数开始进行调度

// Run begins watching and scheduling. It starts scheduling and blocked until the context is done.
func (sched *Scheduler) Run(ctx context.Context) {
	sched.SchedulingQueue.Run()
	//周期调用scheduleOne调度pod
	wait.UntilWithContext(ctx, sched.scheduleOne, 0)
	sched.SchedulingQueue.Close()
}

scheduleOne从待调度队列获取pod，对其执行调度算法Schedule，选择合适的node进行bind，如果调度失败还要执行抢占流程，并加入不可调度队列重新调度

// scheduleOne does the entire scheduling workflow for a single pod. It is serialized on the scheduling algorithm's host fitting.
func (sched *Scheduler) scheduleOne(ctx context.Context) {
	//NextPod()为MakeNextPodFunc返回的函数，用来从调度队列pop出一个待调度pod，如果没有待调度pod，则堵塞等待
	podInfo := sched.NextPod()
	// pod could be nil when schedulerQueue is closed
	if podInfo == nil || podInfo.Pod == nil {
		return
	}
	pod := podInfo.Pod
	fwk, err := sched.frameworkForPod(pod)
	if err != nil {
		// This shouldn't happen, because we only accept for scheduling the pods
		// which specify a scheduler name that matches one of the profiles.
		klog.ErrorS(err, "Error occurred")
		return
	}
	//如下两种特殊情况可不必调度
	//a. pod的DeletionTimestamp自动不为空，即pod被删除了
	//b. pod处于假定状态
	if sched.skipPodSchedule(fwk, pod) {
		return
	}

	klog.V(3).InfoS("Attempting to schedule pod", "pod", klog.KObj(pod))

	// Synchronously attempt to find a fit for the pod.
	start := time.Now()
	//创建CycleState
	state := framework.NewCycleState()
	state.SetRecordPluginMetrics(rand.Intn(100) < pluginMetricsSamplePercent)
	// Initialize an empty podsToActivate struct, which will be filled up by plugins or stay empty.
	podsToActivate := framework.NewPodsToActivate()
	state.Write(framework.PodsToActivateKey, podsToActivate)

	schedulingCycleCtx, cancel := context.WithCancel(ctx)
	defer cancel()
	//执行调度算法，为pod选择一个合适的node，后面具体分析此函数
	scheduleResult, err := sched.Algorithm.Schedule(schedulingCycleCtx, sched.Extenders, fwk, state, pod)
	if err != nil {
		// Schedule() may have failed because the pod would not fit on any host, so we try to
		// preempt, with the expectation that the next time the pod is tried for scheduling it
		// will fit due to the preemption. It is also possible that a different pod will schedule
		// into the resources that were preempted, but this is harmless.
		nominatedNode := ""
		//调度失败，并且失败原因为fitError，这种错误的话执行抢占有可能成功
		if fitError, ok := err.(*framework.FitError); ok {
			//没注册PostFilter插件
			if !fwk.HasPostFilterPlugins() {
				klog.V(3).InfoS("No PostFilter plugins are registered, so no preemption will be performed")
			} else {
				//执行PostFilter扩展点上的插件，目前只有抢占一个插件DefaultPreemption:pkg/scheduler/framework/plugins/defaultpreemption/defaultpreemption.go
				// Run PostFilter plugins to try to make the pod schedulable in a future scheduling cycle.
				result, status := fwk.RunPostFilterPlugins(ctx, state, pod, fitError.Diagnosis.NodeToStatusMap)
				if status.Code() == framework.Error {
					klog.ErrorS(nil, "Status after running PostFilter plugins for pod", "pod", klog.KObj(pod), "status", status)
				} else {
					klog.V(5).InfoS("Status after running PostFilter plugins for pod", "pod", klog.KObj(pod), "status", status)
				}
				//抢占成功，NominatedNodeName为提名node，即此pod很大可能会运行在此node上，为什么是可能？虽然抢占成功了但也有可能被其他高优先级的pod抢占
				if status.IsSuccess() && result != nil {
					nominatedNode = result.NominatedNodeName
				}
			}
			// Pod did not fit anywhere, so it is counted as a failure. If preemption
			// succeeds, the pod should get counted as a success the next time we try to
			// schedule it. (hopefully)
			metrics.PodUnschedulable(fwk.ProfileName(), metrics.SinceInSeconds(start))
		//没有可用的node，抢占也没用
		} else if err == ErrNoNodesAvailable {
			// No nodes available is counted as unschedulable rather than an error.
			metrics.PodUnschedulable(fwk.ProfileName(), metrics.SinceInSeconds(start))
		} else {
			klog.ErrorS(err, "Error selecting node for pod", "pod", klog.KObj(pod))
			metrics.PodScheduleError(fwk.ProfileName(), metrics.SinceInSeconds(start))
		}
		//对调度失败pod的处理，后面会详细看一下此函数
		sched.recordSchedulingFailure(fwk, podInfo, err, v1.PodReasonUnschedulable, nominatedNode)
		//返回，开始调度下一个pod
		return
	}
	metrics.SchedulingAlgorithmLatency.Observe(metrics.SinceInSeconds(start))
	//调度pod成功，告诉cache假定此pod运行在给定的node上，虽然还没有bind到node上，但这样我们继续调度下一个pod而不用等待bind成功
	assumedPodInfo := podInfo.DeepCopy()
	assumedPod := assumedPodInfo.Pod
	// assume modifies `assumedPod` by setting NodeName=scheduleResult.SuggestedHost
	//假定pod
	err = sched.assume(assumedPod, scheduleResult.SuggestedHost)
	if err != nil {
		metrics.PodScheduleError(fwk.ProfileName(), metrics.SinceInSeconds(start))
		// This is most probably result of a BUG in retrying logic.
		// We report an error here so that pod scheduling can be retried.
		// This relies on the fact that Error will check if the pod has been bound
		// to a node and if so will not add it back to the unscheduled pods queue
		// (otherwise this would cause an infinite loop).
		sched.recordSchedulingFailure(fwk, assumedPodInfo, err, SchedulerError, "")
		return
	}

	//执行Reserve扩展点上的插件，比如保存PV
	if sts := fwk.RunReservePluginsReserve(schedulingCycleCtx, state, assumedPod, scheduleResult.SuggestedHost); !sts.IsSuccess() {
		metrics.PodScheduleError(fwk.ProfileName(), metrics.SinceInSeconds(start))
		// trigger un-reserve to clean up state associated with the reserved Pod
		fwk.RunReservePluginsUnreserve(schedulingCycleCtx, state, assumedPod, scheduleResult.SuggestedHost)
		if forgetErr := sched.SchedulerCache.ForgetPod(assumedPod); forgetErr != nil {
			klog.ErrorS(forgetErr, "Scheduler cache ForgetPod failed")
		}
		sched.recordSchedulingFailure(fwk, assumedPodInfo, sts.AsError(), SchedulerError, "")
		return
	}

	//执行Permit扩展点上的插件，目前没插件
	runPermitStatus := fwk.RunPermitPlugins(schedulingCycleCtx, state, assumedPod, scheduleResult.SuggestedHost)
	if runPermitStatus.Code() != framework.Wait && !runPermitStatus.IsSuccess() {
		var reason string
		if runPermitStatus.IsUnschedulable() {
			metrics.PodUnschedulable(fwk.ProfileName(), metrics.SinceInSeconds(start))
			reason = v1.PodReasonUnschedulable
		} else {
			metrics.PodScheduleError(fwk.ProfileName(), metrics.SinceInSeconds(start))
			reason = SchedulerError
		}
		// One of the plugins returned status different than success or wait.
		fwk.RunReservePluginsUnreserve(schedulingCycleCtx, state, assumedPod, scheduleResult.SuggestedHost)
		if forgetErr := sched.SchedulerCache.ForgetPod(assumedPod); forgetErr != nil {
			klog.ErrorS(forgetErr, "Scheduler cache ForgetPod failed")
		}
		sched.recordSchedulingFailure(fwk, assumedPodInfo, runPermitStatus.AsError(), reason, "")
		return
	}

	// At the end of a successful scheduling cycle, pop and move up Pods if needed.
	if len(podsToActivate.Map) != 0 {
		sched.SchedulingQueue.Activate(podsToActivate.Map)
		// Clear the entries after activation.
		podsToActivate.Map = make(map[string]*v1.Pod)
	}

	//执行异步bind流程
	// bind the pod to its host asynchronously (we can do this b/c of the assumption step above).
	go func() {
		bindingCycleCtx, cancel := context.WithCancel(ctx)
		defer cancel()
		metrics.SchedulerGoroutines.WithLabelValues(metrics.Binding).Inc()
		defer metrics.SchedulerGoroutines.WithLabelValues(metrics.Binding).Dec()

		waitOnPermitStatus := fwk.WaitOnPermit(bindingCycleCtx, assumedPod)
		if !waitOnPermitStatus.IsSuccess() {
			...
		}

		// Run "prebind" plugins.
		preBindStatus := fwk.RunPreBindPlugins(bindingCycleCtx, state, assumedPod, scheduleResult.SuggestedHost)
		if !preBindStatus.IsSuccess() {
			metrics.PodScheduleError(fwk.ProfileName(), metrics.SinceInSeconds(start))
			// trigger un-reserve plugins to clean up state associated with the reserved Pod
			fwk.RunReservePluginsUnreserve(bindingCycleCtx, state, assumedPod, scheduleResult.SuggestedHost)
			if forgetErr := sched.SchedulerCache.ForgetPod(assumedPod); forgetErr != nil {
				klog.ErrorS(forgetErr, "scheduler cache ForgetPod failed")
			} else {
				// "Forget"ing an assumed Pod in binding cycle should be treated as a PodDelete event,
				// as the assumed Pod had occupied a certain amount of resources in scheduler cache.
				// TODO(#103853): de-duplicate the logic.
				sched.SchedulingQueue.MoveAllToActiveOrBackoffQueue(internalqueue.AssignedPodDelete, nil)
			}
			sched.recordSchedulingFailure(fwk, assumedPodInfo, preBindStatus.AsError(), SchedulerError, "")
			return
		}

		//执行bind插件
		err := sched.bind(bindingCycleCtx, fwk, assumedPod, scheduleResult.SuggestedHost, state)
		if err != nil {
			metrics.PodScheduleError(fwk.ProfileName(), metrics.SinceInSeconds(start))
			// trigger un-reserve plugins to clean up state associated with the reserved Pod
			fwk.RunReservePluginsUnreserve(bindingCycleCtx, state, assumedPod, scheduleResult.SuggestedHost)
			if err := sched.SchedulerCache.ForgetPod(assumedPod); err != nil {
				klog.ErrorS(err, "scheduler cache ForgetPod failed")
			} else {
				// "Forget"ing an assumed Pod in binding cycle should be treated as a PodDelete event,
				// as the assumed Pod had occupied a certain amount of resources in scheduler cache.
				// TODO(#103853): de-duplicate the logic.
				sched.SchedulingQueue.MoveAllToActiveOrBackoffQueue(internalqueue.AssignedPodDelete, nil)
			}
			sched.recordSchedulingFailure(fwk, assumedPodInfo, fmt.Errorf("binding rejected: %w", err), SchedulerError, "")
		} else {
			// Calculating nodeResourceString can be heavy. Avoid it if klog verbosity is below 2.
			if klog.V(2).Enabled() {
				klog.InfoS("Successfully bound pod to node", "pod", klog.KObj(pod), "node", scheduleResult.SuggestedHost, "evaluatedNodes", scheduleResult.EvaluatedNodes, "feasibleNodes", scheduleResult.FeasibleNodes)
			}
			metrics.PodScheduled(fwk.ProfileName(), metrics.SinceInSeconds(start))
			metrics.PodSchedulingAttempts.Observe(float64(podInfo.Attempts))
			metrics.PodSchedulingDuration.WithLabelValues(getAttemptsLabel(podInfo)).Observe(metrics.SinceInSeconds(podInfo.InitialAttemptTimestamp))

			// Run "postbind" plugins.
			fwk.RunPostBindPlugins(bindingCycleCtx, state, assumedPod, scheduleResult.SuggestedHost)

			// At the end of a successful binding cycle, move up Pods if needed.
			if len(podsToActivate.Map) != 0 {
				sched.SchedulingQueue.Activate(podsToActivate.Map)
				// Unlike the logic in scheduling cycle, we don't bother deleting the entries
				// as `podsToActivate.Map` is no longer consumed.
			}
		}
	}()
}

CycleState
CycleState用在调度周期中，被插件用来保存/获取任意数据，比如PreFilter插件保存某些数据到CycleState中，Filter从CycleState获取这些数据。

type CycleState struct {
	mx      sync.RWMutex
	storage map[StateKey]StateData
	// if recordPluginMetrics is true, PluginExecutionDuration will be recorded for this cycle.
	recordPluginMetrics bool
}

//接口类型，可用来存储任意数据
type StateData interface {
	// Clone is an interface to make a copy of StateData. For performance reasons,
	// clone should make shallow copies for members (e.g., slices or maps) that are not
	// impacted by PreFilter's optional AddPod/RemovePod methods.
	Clone() StateData
}

recordSchedulingFailure
recordSchedulingFailure用来将失败的pod加入不可调度队列，等待下次重新调度，如果是抢占成功的pod，还要更新调度队列，并且向apiserver发起请求，更新pod.Status.NominatedNodeName为nominatedNode

// recordSchedulingFailure records an event for the pod that indicates the
// pod has failed to schedule. Also, update the pod condition and nominated node name if set.
func (sched *Scheduler) recordSchedulingFailure(fwk framework.Framework, podInfo *framework.QueuedPodInfo, err error, reason string, nominatedNode string) {
	//Error为MakeDefaultErrorFunc返回的函数，将pod放入不可调度队列，等待下次重新调度
	sched.Error(podInfo, err)

	// Update the scheduling queue with the nominated pod information. Without
	// this, there would be a race condition between the next scheduling cycle
	// and the time the scheduler receives a Pod Update for the nominated pod.
	// Here we check for nil only for tests.
	if sched.SchedulingQueue != nil {
		//如果nominatedNode不为空，说明抢占成功，则将此pod添加到提名node nominatedNode的nominatedpod中
		sched.SchedulingQueue.AddNominatedPod(podInfo.PodInfo, nominatedNode)
	}

	pod := podInfo.Pod
	msg := truncateMessage(err.Error())
	fwk.EventRecorder().Eventf(pod, nil, v1.EventTypeWarning, "FailedScheduling", "Scheduling", msg)
	//如果nominatedNode不为空，即抢占成功，则设置pod.Status.NominatedNodeName为nominatedNode，向apiserver发起请求更新此字段
	if err := updatePod(sched.client, pod, &v1.PodCondition{
		Type:    v1.PodScheduled,
		Status:  v1.ConditionFalse,
		Reason:  reason,
		Message: err.Error(),
	}, nominatedNode); err != nil {
		klog.ErrorS(err, "Error updating pod", "pod", klog.KObj(pod))
	}
}

assume
assume将假定pod加入cache中，并将pod的信息聚合到node上。
同时如果此pod是抢占pod，还要将抢占信息从cache中删除

// assume signals to the cache that a pod is already in the cache, so that binding can be asynchronous.
// assume modifies `assumed`.
func (sched *Scheduler) assume(assumed *v1.Pod, host string) error {
	// Optimistically assume that the binding will succeed and send it to apiserver
	// in the background.
	// If the binding fails, scheduler will release resources allocated to assumed pod
	// immediately.
	assumed.Spec.NodeName = host

	if err := sched.SchedulerCache.AssumePod(assumed); err != nil {
		klog.ErrorS(err, "Scheduler cache AssumePod failed")
		return err
	}
	// if "assumed" is a nominated pod, we should remove it from internal cache
	if sched.SchedulingQueue != nil {
		sched.SchedulingQueue.DeleteNominatedPodIfExists(assumed)
	}

	return nil
}

Schedule
Schedule从cache获取最新的node信息，调度pod

// Schedule tries to schedule the given pod to one of the nodes in the node list.
// If it succeeds, it will return the name of the node.
// If it fails, it will return a FitError error with reasons.
func (g *genericScheduler) Schedule(ctx context.Context, extenders []framework.Extender, fwk framework.Framework, state *framework.CycleState, pod *v1.Pod) (result ScheduleResult, err error) {
	trace := utiltrace.New("Scheduling", utiltrace.Field{Key: "namespace", Value: pod.Namespace}, utiltrace.Field{Key: "name", Value: pod.Name})
	defer trace.LogIfLong(100 * time.Millisecond)

	//g.cache.UpdateSnapshot(g.nodeInfoSnapshot)对cache中的node信息做快照
	if err := g.snapshot(); err != nil {
		return result, err
	}
	trace.Step("Snapshotting scheduler cache and node infos done")

	//如果node个数为0，则调度失败，返回错误ErrNoNodesAvailable
	if g.nodeInfoSnapshot.NumNodes() == 0 {
		return result, ErrNoNodesAvailable
	}

	//获取通过Filter扩展点上插件的node列表
	feasibleNodes, diagnosis, err := g.findNodesThatFitPod(ctx, extenders, fwk, state, pod)
	if err != nil {
		return result, err
	}
	trace.Step("Computing predicates done")

	//全部过滤失败，返回FitError错误，可执行抢占
	if len(feasibleNodes) == 0 {
		return result, &framework.FitError{
			Pod:         pod,
			NumAllNodes: g.nodeInfoSnapshot.NumNodes(),
			Diagnosis:   diagnosis,
		}
	}

	//只有一个node通过filter，返回即可
	if len(feasibleNodes) == 1 {
		return ScheduleResult{
			SuggestedHost:  feasibleNodes[0].Name,
			EvaluatedNodes: 1 + len(diagnosis.NodeToStatusMap),
			FeasibleNodes:  1,
		}, nil
	}

	//如果有多个node通过了filter，则执行优选，调用prioritizeNodes对他们执行Score插件进行打分
	priorityList, err := prioritizeNodes(ctx, extenders, fwk, state, pod, feasibleNodes)
	if err != nil {
		return result, err
	}
	//分数最高的node即为fitnode
	host, err := g.selectHost(priorityList)
	trace.Step("Prioritizing done")

	return ScheduleResult{
		SuggestedHost:  host,
		EvaluatedNodes: len(feasibleNodes) + len(diagnosis.NodeToStatusMap),
		FeasibleNodes:  len(feasibleNodes),
	}, err
}

findNodesThatFitPod返回适合pod的node列表

func (g *genericScheduler) findNodesThatFitPod(ctx context.Context, extenders []framework.Extender, fwk framework.Framework, state *framework.CycleState, pod *v1.Pod) ([]*v1.Node, framework.Diagnosis, error) {
	diagnosis := framework.Diagnosis{
		NodeToStatusMap:      make(framework.NodeToStatusMap),
		UnschedulablePlugins: sets.NewString(),
	}

	//执行PreFilter扩展点上的插件
	s := fwk.RunPreFilterPlugins(ctx, state, pod)
	//从快照中获取所有的node
	allNodes, err := g.nodeInfoSnapshot.NodeInfos().List()
	...
	//如果pod.Status.NominatedNodeName不为空，说明此pod之前被调度失败并执行抢占成功的pod，再次对NominatedNodeName执行Filter插件，
	//如果key成功，则不用再进行后续流程，直接返回NominatedNodeName即可
	if len(pod.Status.NominatedNodeName) > 0 && feature.DefaultFeatureGate.Enabled(features.PreferNominatedNode) {
		//evaluateNominatedNode调用findNodesThatPassFilters看是否能通过filter
		feasibleNodes, err := g.evaluateNominatedNode(ctx, extenders, pod, fwk, state, diagnosis)
		if err != nil {
			klog.ErrorS(err, "Evaluation failed on nominated node", "pod", klog.KObj(pod), "node", pod.Status.NominatedNodeName)
		}
		// Nominated node passes all the filters, scheduler is good to assign this node to the pod.
		if len(feasibleNodes) != 0 {
			return feasibleNodes, diagnosis, nil
		}
	}
	//返回通过filter的node
	feasibleNodes, err := g.findNodesThatPassFilters(ctx, fwk, state, pod, diagnosis, allNodes)
	if err != nil {
		return nil, diagnosis, err
	}
	...
	return feasibleNodes, diagnosis, nil
}

findNodesThatPassFilters选取指定个数的node执行Filter插件，并返回通过的node列表

// findNodesThatPassFilters finds the nodes that fit the filter plugins.
func (g *genericScheduler) findNodesThatPassFilters(
	ctx context.Context,
	fwk framework.Framework,
	state *framework.CycleState,
	pod *v1.Pod,
	diagnosis framework.Diagnosis,
	nodes []*framework.NodeInfo) ([]*v1.Node, error) {
	//返回此次参与调度的node个数：
	//如果总node个数小于100或者percentageOfNodesToScore为100,则返回总node个数，即所有node都参与调度，
	//否则按照percentageOfNodesToScore指定的百分比选取node个数
	numNodesToFind := g.numFeasibleNodesToFind(int32(len(nodes)))

	// Create feasible list with enough space to avoid growing it
	// and allow assigning.
	feasibleNodes := make([]*v1.Node, numNodesToFind)

	//没有配置Filter插件，则返回所有的可用node feasibleNodes
	if !fwk.HasFilterPlugins() {
		length := len(nodes)
		for i := range feasibleNodes {
			feasibleNodes[i] = nodes[(g.nextStartNodeIndex+i)%length].Node()
		}
		g.nextStartNodeIndex = (g.nextStartNodeIndex + len(feasibleNodes)) % length
		return feasibleNodes, nil
	}

	errCh := parallelize.NewErrorChannel()
	var statusesLock sync.Mutex
	var feasibleNodesLen int32
	ctx, cancel := context.WithCancel(ctx)
	//参数i指的是要处理的数据的索引
	//比如要处理的node个数为160，启动16个协程进行处理，则每个协程要处理10个，
	//第一个协程处理0-15，第二个处理16-31，以此类推
	checkNode := func(i int) {
		// We check the nodes starting from where we left off in the previous scheduling cycle,
		// this is to make sure all nodes have the same chance of being examined across pods.
		nodeInfo := nodes[(g.nextStartNodeIndex+i)%len(nodes)]
		//执行 filter 插件
		status := fwk.RunFilterPluginsWithNominatedPods(ctx, state, pod, nodeInfo)
		if status.Code() == framework.Error {
			errCh.SendErrorWithCancel(status.AsError(), cancel)
			return
		}
		if status.IsSuccess() {
			length := atomic.AddInt32(&feasibleNodesLen, 1)
			if length > numNodesToFind {
				cancel()
				atomic.AddInt32(&feasibleNodesLen, -1)
			} else {
				feasibleNodes[length-1] = nodeInfo.Node()
			}
		} else {
			statusesLock.Lock()
			diagnosis.NodeToStatusMap[nodeInfo.Node().Name] = status
			diagnosis.UnschedulablePlugins.Insert(status.FailedPlugin())
			statusesLock.Unlock()
		}
	}

	beginCheckNode := time.Now()
	statusCode := framework.Success
	defer func() {
		// We record Filter extension point latency here instead of in framework.go because framework.RunFilterPlugins
		// function is called for each node, whereas we want to have an overall latency for all nodes per scheduling cycle.
		// Note that this latency also includes latency for `addNominatedPods`, which calls framework.RunPreFilterAddPod.
		metrics.FrameworkExtensionPointDuration.WithLabelValues(runtime.Filter, statusCode.String(), fwk.ProfileName()).Observe(metrics.SinceInSeconds(beginCheckNode))
	}()

	// Stops searching for more nodes once the configured number of feasible nodes
	// are found.
	//启动16个协程，并行执行checkNode，len(nodes)表示要处理的总个数
	fwk.Parallelizer().Until(ctx, len(nodes), checkNode)
	//处理的node个数为过滤成功的node个数和失败的node个数总和
	processedNodes := int(feasibleNodesLen) + len(diagnosis.NodeToStatusMap)
	//nextStartNodeIndex是下次调度时要处理的node的索引
	//对len(nodes)取模的作用是达到最大值后反转到0
	g.nextStartNodeIndex = (g.nextStartNodeIndex + processedNodes) % len(nodes)

	feasibleNodes = feasibleNodes[:feasibleNodesLen]
	if err := errCh.ReceiveError(); err != nil {
		statusCode = framework.Error
		return nil, err
	}
	return feasibleNodes, nil
}

prioritizeNodes对node执行score插件进行打分

func prioritizeNodes(
	ctx context.Context,
	extenders []framework.Extender,
	fwk framework.Framework,
	state *framework.CycleState,
	pod *v1.Pod,
	nodes []*v1.Node,
) (framework.NodeScoreList, error) {
	// If no priority configs are provided, then all nodes will have a score of one.
	// This is required to generate the priority list in the required format
	//如果没配置score插件，则设置每个node得分为1
	if len(extenders) == 0 && !fwk.HasScorePlugins() {
		result := make(framework.NodeScoreList, 0, len(nodes))
		for i := range nodes {
			result = append(result, framework.NodeScore{
				Name:  nodes[i].Name,
				Score: 1,
			})
		}
		return result, nil
	}

	//执行 prescore 插件
	preScoreStatus := fwk.RunPreScorePlugins(ctx, state, pod, nodes)
	if !preScoreStatus.IsSuccess() {
		return nil, preScoreStatus.AsError()
	}

	//执行 score 插件
	scoresMap, scoreStatus := fwk.RunScorePlugins(ctx, state, pod, nodes)
	if !scoreStatus.IsSuccess() {
		return nil, scoreStatus.AsError()
	}

	//汇总每个node总得分
	result := make(framework.NodeScoreList, 0, len(nodes))

	for i := range nodes {
		result = append(result, framework.NodeScore{Name: nodes[i].Name, Score: 0})
		for j := range scoresMap {
			result[i].Score += scoresMap[j][i].Score
		}
	}

	...

	return result, nil
}

selectHost选择得分最高的node，如果多个node得分相同，则随机选择一个node

func (g *genericScheduler) selectHost(nodeScoreList framework.NodeScoreList) (string, error) {
	if len(nodeScoreList) == 0 {
		return "", fmt.Errorf("empty priorityList")
	}
	maxScore := nodeScoreList[0].Score
	selected := nodeScoreList[0].Name
	cntOfMaxScore := 1
	for _, ns := range nodeScoreList[1:] {
		if ns.Score > maxScore {
			maxScore = ns.Score
			selected = ns.Name
			cntOfMaxScore = 1
		} else if ns.Score == maxScore {
			cntOfMaxScore++
			if rand.Intn(cntOfMaxScore) == 0 {
				// Replace the candidate with probability of 1/cntOfMaxScore
				selected = ns.Name
			}
		}
	}
	return selected, nil
}