rebase: bump k8s.io/kubernetes from 1.26.2 to 1.27.2

Bumps [k8s.io/kubernetes](https://github.com/kubernetes/kubernetes) from 1.26.2 to 1.27.2.
- [Release notes](https://github.com/kubernetes/kubernetes/releases)
- [Commits](https://github.com/kubernetes/kubernetes/compare/v1.26.2...v1.27.2)

---
updated-dependencies:
- dependency-name: k8s.io/kubernetes
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

vendor/k8s.io/apiserver/pkg/util/flowcontrol/OWNERS

@@ -0,0 +1,15 @@
+# See the OWNERS docs at https://go.k8s.io/owners
+
+approvers:
+  - lavalamp
+  - deads2k
+  - yue9944882
+  - MikeSpreitzer
+reviewers:
+  - lavalamp
+  - deads2k
+  - yue9944882
+  - MikeSpreitzer
+labels:
+  - sig/api-machinery
+  - area/apiserver

vendor/k8s.io/apiserver/pkg/util/flowcontrol/apf_context.go

@@ -0,0 +1,93 @@
+/*
+Copyright 2021 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package flowcontrol
+
+import (
+	"context"
+	"sync"
+)
+
+type priorityAndFairnessKeyType int
+
+const (
+	// priorityAndFairnessInitializationSignalKey is a key under which
+	// initialization signal function for watch requests is stored
+	// in the context.
+	priorityAndFairnessInitializationSignalKey priorityAndFairnessKeyType = iota
+)
+
+// WithInitializationSignal creates a copy of parent context with
+// priority and fairness initialization signal value.
+func WithInitializationSignal(ctx context.Context, signal InitializationSignal) context.Context {
+	return context.WithValue(ctx, priorityAndFairnessInitializationSignalKey, signal)
+}
+
+// initializationSignalFrom returns an initialization signal function
+// which when called signals that watch initialization has already finished
+// to priority and fairness dispatcher.
+func initializationSignalFrom(ctx context.Context) (InitializationSignal, bool) {
+	signal, ok := ctx.Value(priorityAndFairnessInitializationSignalKey).(InitializationSignal)
+	return signal, ok && signal != nil
+}
+
+// WatchInitialized sends a signal to priority and fairness dispatcher
+// that a given watch request has already been initialized.
+func WatchInitialized(ctx context.Context) {
+	if signal, ok := initializationSignalFrom(ctx); ok {
+		signal.Signal()
+	}
+}
+
+// RequestDelegated informs the priority and fairness dispatcher that
+// a given request has been delegated to an aggregated API
+// server. No-op when priority and fairness is disabled.
+func RequestDelegated(ctx context.Context) {
+	// The watch initialization signal doesn't traverse request
+	// boundaries, so we generously fire it as soon as we know
+	// that the request won't be serviced locally. Safe to call
+	// for non-watch requests.
+	WatchInitialized(ctx)
+}
+
+// InitializationSignal is an interface that allows sending and handling
+// initialization signals.
+type InitializationSignal interface {
+	// Signal notifies the dispatcher about finished initialization.
+	Signal()
+	// Wait waits for the initialization signal.
+	Wait()
+}
+
+type initializationSignal struct {
+	once sync.Once
+	done chan struct{}
+}
+
+func NewInitializationSignal() InitializationSignal {
+	return &initializationSignal{
+		once: sync.Once{},
+		done: make(chan struct{}),
+	}
+}
+
+func (i *initializationSignal) Signal() {
+	i.once.Do(func() { close(i.done) })
+}
+
+func (i *initializationSignal) Wait() {
+	<-i.done
+}

vendor/k8s.io/apiserver/pkg/util/flowcontrol/apf_controller_debug.go

@@ -0,0 +1,265 @@
+/*
+Copyright 2019 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package flowcontrol
+
+import (
+	"fmt"
+	"io"
+	"net/http"
+	"strconv"
+	"strings"
+	"text/tabwriter"
+	"time"
+
+	"k8s.io/apimachinery/pkg/runtime/schema"
+	"k8s.io/apimachinery/pkg/util/runtime"
+	"k8s.io/apiserver/pkg/server/mux"
+)
+
+const (
+	queryIncludeRequestDetails = "includeRequestDetails"
+)
+
+func (cfgCtlr *configController) Install(c *mux.PathRecorderMux) {
+	// TODO(yue9944882): handle "Accept" header properly
+	// debugging dumps a CSV content for three levels of granularity
+	// 1. row per priority-level
+	c.UnlistedHandleFunc("/debug/api_priority_and_fairness/dump_priority_levels", cfgCtlr.dumpPriorityLevels)
+	// 2. row per queue
+	c.UnlistedHandleFunc("/debug/api_priority_and_fairness/dump_queues", cfgCtlr.dumpQueues)
+	// 3. row per request
+	c.UnlistedHandleFunc("/debug/api_priority_and_fairness/dump_requests", cfgCtlr.dumpRequests)
+}
+
+func (cfgCtlr *configController) dumpPriorityLevels(w http.ResponseWriter, r *http.Request) {
+	cfgCtlr.lock.Lock()
+	defer cfgCtlr.lock.Unlock()
+	tabWriter := tabwriter.NewWriter(w, 8, 0, 1, ' ', 0)
+	columnHeaders := []string{
+		"PriorityLevelName", // 1
+		"ActiveQueues",      // 2
+		"IsIdle",            // 3
+		"IsQuiescing",       // 4
+		"WaitingRequests",   // 5
+		"ExecutingRequests", // 6
+	}
+	tabPrint(tabWriter, rowForHeaders(columnHeaders))
+	endLine(tabWriter)
+	for _, plState := range cfgCtlr.priorityLevelStates {
+		if plState.queues == nil {
+			tabPrint(tabWriter, row(
+				plState.pl.Name, // 1
+				"<none>",        // 2
+				"<none>",        // 3
+				"<none>",        // 4
+				"<none>",        // 5
+				"<none>",        // 6
+			))
+			endLine(tabWriter)
+			continue
+		}
+		queueSetDigest := plState.queues.Dump(false)
+		activeQueueNum := 0
+		for _, q := range queueSetDigest.Queues {
+			if len(q.Requests) > 0 {
+				activeQueueNum++
+			}
+		}
+
+		tabPrint(tabWriter, rowForPriorityLevel(
+			plState.pl.Name,          // 1
+			activeQueueNum,           // 2
+			plState.queues.IsIdle(),  // 3
+			plState.quiescing,        // 4
+			queueSetDigest.Waiting,   // 5
+			queueSetDigest.Executing, // 6
+		))
+		endLine(tabWriter)
+	}
+	runtime.HandleError(tabWriter.Flush())
+}
+
+func (cfgCtlr *configController) dumpQueues(w http.ResponseWriter, r *http.Request) {
+	cfgCtlr.lock.Lock()
+	defer cfgCtlr.lock.Unlock()
+	tabWriter := tabwriter.NewWriter(w, 8, 0, 1, ' ', 0)
+	columnHeaders := []string{
+		"PriorityLevelName", // 1
+		"Index",             // 2
+		"PendingRequests",   // 3
+		"ExecutingRequests", // 4
+		"SeatsInUse",        // 5
+		"NextDispatchR",     // 6
+		"InitialSeatsSum",   // 7
+		"MaxSeatsSum",       // 8
+		"TotalWorkSum",      // 9
+	}
+	tabPrint(tabWriter, rowForHeaders(columnHeaders))
+	endLine(tabWriter)
+	for _, plState := range cfgCtlr.priorityLevelStates {
+		if plState.queues == nil {
+			tabPrint(tabWriter, row(
+				plState.pl.Name, // 1
+				"<none>",        // 2
+				"<none>",        // 3
+				"<none>",        // 4
+				"<none>",        // 5
+				"<none>",        // 6
+				"<none>",        // 7
+				"<none>",        // 8
+				"<none>",        // 9
+			))
+			endLine(tabWriter)
+			continue
+		}
+		queueSetDigest := plState.queues.Dump(false)
+		for i, q := range queueSetDigest.Queues {
+			tabPrint(tabWriter, row(
+				plState.pl.Name,                          // 1 - "PriorityLevelName"
+				strconv.Itoa(i),                          // 2 - "Index"
+				strconv.Itoa(len(q.Requests)),            // 3 - "PendingRequests"
+				strconv.Itoa(q.ExecutingRequests),        // 4 - "ExecutingRequests"
+				strconv.Itoa(q.SeatsInUse),               // 5 - "SeatsInUse"
+				q.NextDispatchR,                          // 6 - "NextDispatchR"
+				strconv.Itoa(q.QueueSum.InitialSeatsSum), // 7 - "InitialSeatsSum"
+				strconv.Itoa(q.QueueSum.MaxSeatsSum),     // 8 - "MaxSeatsSum"
+				q.QueueSum.TotalWorkSum,                  // 9 - "TotalWorkSum"
+			))
+			endLine(tabWriter)
+		}
+	}
+	runtime.HandleError(tabWriter.Flush())
+}
+
+func (cfgCtlr *configController) dumpRequests(w http.ResponseWriter, r *http.Request) {
+	cfgCtlr.lock.Lock()
+	defer cfgCtlr.lock.Unlock()
+
+	includeRequestDetails := len(r.URL.Query().Get(queryIncludeRequestDetails)) > 0
+
+	tabWriter := tabwriter.NewWriter(w, 8, 0, 1, ' ', 0)
+	tabPrint(tabWriter, rowForHeaders([]string{
+		"PriorityLevelName",   // 1
+		"FlowSchemaName",      // 2
+		"QueueIndex",          // 3
+		"RequestIndexInQueue", // 4
+		"FlowDistingsher",     // 5
+		"ArriveTime",          // 6
+		"InitialSeats",        // 7
+		"FinalSeats",          // 8
+		"AdditionalLatency",   // 9
+	}))
+	if includeRequestDetails {
+		continueLine(tabWriter)
+		tabPrint(tabWriter, rowForHeaders([]string{
+			"UserName",    // 10
+			"Verb",        // 11
+			"APIPath",     // 12
+			"Namespace",   // 13
+			"Name",        // 14
+			"APIVersion",  // 15
+			"Resource",    // 16
+			"SubResource", // 17
+		}))
+	}
+	endLine(tabWriter)
+	for _, plState := range cfgCtlr.priorityLevelStates {
+		if plState.queues == nil {
+			continue
+		}
+		queueSetDigest := plState.queues.Dump(includeRequestDetails)
+		for iq, q := range queueSetDigest.Queues {
+			for ir, r := range q.Requests {
+				tabPrint(tabWriter, row(
+					plState.pl.Name,     // 1
+					r.MatchedFlowSchema, // 2
+					strconv.Itoa(iq),    // 3
+					strconv.Itoa(ir),    // 4
+					r.FlowDistinguisher, // 5
+					r.ArriveTime.UTC().Format(time.RFC3339Nano),    // 6
+					strconv.Itoa(int(r.WorkEstimate.InitialSeats)), // 7
+					strconv.Itoa(int(r.WorkEstimate.FinalSeats)),   // 8
+					r.WorkEstimate.AdditionalLatency.String(),      // 9
+				))
+				if includeRequestDetails {
+					continueLine(tabWriter)
+					tabPrint(tabWriter, rowForRequestDetails(
+						r.UserName,              // 10
+						r.RequestInfo.Verb,      // 11
+						r.RequestInfo.Path,      // 12
+						r.RequestInfo.Namespace, // 13
+						r.RequestInfo.Name,      // 14
+						schema.GroupVersion{
+							Group:   r.RequestInfo.APIGroup,
+							Version: r.RequestInfo.APIVersion,
+						}.String(), // 15
+						r.RequestInfo.Resource,    // 16
+						r.RequestInfo.Subresource, // 17
+					))
+				}
+				endLine(tabWriter)
+			}
+		}
+	}
+	runtime.HandleError(tabWriter.Flush())
+}
+
+func tabPrint(w io.Writer, row string) {
+	_, err := fmt.Fprint(w, row)
+	runtime.HandleError(err)
+}
+
+func continueLine(w io.Writer) {
+	_, err := fmt.Fprint(w, ",\t")
+	runtime.HandleError(err)
+}
+func endLine(w io.Writer) {
+	_, err := fmt.Fprint(w, "\n")
+	runtime.HandleError(err)
+}
+
+func rowForHeaders(headers []string) string {
+	return row(headers...)
+}
+
+func rowForPriorityLevel(plName string, activeQueues int, isIdle, isQuiescing bool, waitingRequests, executingRequests int) string {
+	return row(
+		plName,
+		strconv.Itoa(activeQueues),
+		strconv.FormatBool(isIdle),
+		strconv.FormatBool(isQuiescing),
+		strconv.Itoa(waitingRequests),
+		strconv.Itoa(executingRequests),
+	)
+}
+
+func rowForRequestDetails(username, verb, path, namespace, name, apiVersion, resource, subResource string) string {
+	return row(
+		username,
+		verb,
+		path,
+		namespace,
+		name,
+		apiVersion,
+		resource,
+		subResource,
+	)
+}
+
+func row(columns ...string) string {
+	return strings.Join(columns, ",\t")
+}

vendor/k8s.io/apiserver/pkg/util/flowcontrol/apf_filter.go

@@ -0,0 +1,197 @@
+/*
+Copyright 2019 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package flowcontrol
+
+import (
+	"context"
+	"strconv"
+	"time"
+
+	"k8s.io/apiserver/pkg/server/httplog"
+	"k8s.io/apiserver/pkg/server/mux"
+	fq "k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing"
+	"k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing/eventclock"
+	fqs "k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing/queueset"
+	"k8s.io/apiserver/pkg/util/flowcontrol/metrics"
+	fcrequest "k8s.io/apiserver/pkg/util/flowcontrol/request"
+	kubeinformers "k8s.io/client-go/informers"
+	"k8s.io/klog/v2"
+	"k8s.io/utils/clock"
+
+	flowcontrol "k8s.io/api/flowcontrol/v1beta3"
+	flowcontrolclient "k8s.io/client-go/kubernetes/typed/flowcontrol/v1beta3"
+)
+
+// ConfigConsumerAsFieldManager is how the config consuminng
+// controller appears in an ObjectMeta ManagedFieldsEntry.Manager
+const ConfigConsumerAsFieldManager = "api-priority-and-fairness-config-consumer-v1"
+
+// Interface defines how the API Priority and Fairness filter interacts with the underlying system.
+type Interface interface {
+	// Handle takes care of queuing and dispatching a request
+	// characterized by the given digest.  The given `noteFn` will be
+	// invoked with the results of request classification.
+	// The given `workEstimator` is called, if at all, after noteFn.
+	// `workEstimator` will be invoked only when the request
+	//  is classified as non 'exempt'.
+	// 'workEstimator', when invoked, must return the
+	// work parameters for the request.
+	// If the request is queued then `queueNoteFn` will be called twice,
+	// first with `true` and then with `false`; otherwise
+	// `queueNoteFn` will not be called at all.  If Handle decides
+	// that the request should be executed then `execute()` will be
+	// invoked once to execute the request; otherwise `execute()` will
+	// not be invoked.
+	// Handle() should never return while execute() is running, even if
+	// ctx is cancelled or times out.
+	Handle(ctx context.Context,
+		requestDigest RequestDigest,
+		noteFn func(fs *flowcontrol.FlowSchema, pl *flowcontrol.PriorityLevelConfiguration, flowDistinguisher string),
+		workEstimator func() fcrequest.WorkEstimate,
+		queueNoteFn fq.QueueNoteFn,
+		execFn func(),
+	)
+
+	// Run monitors config objects from the main apiservers and causes
+	// any needed changes to local behavior.  This method ceases
+	// activity and returns after the given channel is closed.
+	Run(stopCh <-chan struct{}) error
+
+	// Install installs debugging endpoints to the web-server.
+	Install(c *mux.PathRecorderMux)
+
+	// WatchTracker provides the WatchTracker interface.
+	WatchTracker
+}
+
+// This request filter implements https://github.com/kubernetes/enhancements/blob/master/keps/sig-api-machinery/1040-priority-and-fairness/README.md
+
+// New creates a new instance to implement API priority and fairness
+func New(
+	informerFactory kubeinformers.SharedInformerFactory,
+	flowcontrolClient flowcontrolclient.FlowcontrolV1beta3Interface,
+	serverConcurrencyLimit int,
+	requestWaitLimit time.Duration,
+) Interface {
+	clk := eventclock.Real{}
+	return NewTestable(TestableConfig{
+		Name:                   "Controller",
+		Clock:                  clk,
+		AsFieldManager:         ConfigConsumerAsFieldManager,
+		FoundToDangling:        func(found bool) bool { return !found },
+		InformerFactory:        informerFactory,
+		FlowcontrolClient:      flowcontrolClient,
+		ServerConcurrencyLimit: serverConcurrencyLimit,
+		RequestWaitLimit:       requestWaitLimit,
+		ReqsGaugeVec:           metrics.PriorityLevelConcurrencyGaugeVec,
+		ExecSeatsGaugeVec:      metrics.PriorityLevelExecutionSeatsGaugeVec,
+		QueueSetFactory:        fqs.NewQueueSetFactory(clk),
+	})
+}
+
+// TestableConfig carries the parameters to an implementation that is testable
+type TestableConfig struct {
+	// Name of the controller
+	Name string
+
+	// Clock to use in timing deliberate delays
+	Clock clock.PassiveClock
+
+	// AsFieldManager is the string to use in the metadata for
+	// server-side apply.  Normally this is
+	// `ConfigConsumerAsFieldManager`.  This is exposed as a parameter
+	// so that a test of competing controllers can supply different
+	// values.
+	AsFieldManager string
+
+	// FoundToDangling maps the boolean indicating whether a
+	// FlowSchema's referenced PLC exists to the boolean indicating
+	// that FlowSchema's status should indicate a dangling reference.
+	// This is a parameter so that we can write tests of what happens
+	// when servers disagree on that bit of Status.
+	FoundToDangling func(bool) bool
+
+	// InformerFactory to use in building the controller
+	InformerFactory kubeinformers.SharedInformerFactory
+
+	// FlowcontrolClient to use for manipulating config objects
+	FlowcontrolClient flowcontrolclient.FlowcontrolV1beta3Interface
+
+	// ServerConcurrencyLimit for the controller to enforce
+	ServerConcurrencyLimit int
+
+	// RequestWaitLimit configured on the server
+	RequestWaitLimit time.Duration
+
+	// GaugeVec for metrics about requests, broken down by phase and priority_level
+	ReqsGaugeVec metrics.RatioedGaugeVec
+
+	// RatioedGaugePairVec for metrics about seats occupied by all phases of execution
+	ExecSeatsGaugeVec metrics.RatioedGaugeVec
+
+	// QueueSetFactory for the queuing implementation
+	QueueSetFactory fq.QueueSetFactory
+}
+
+// NewTestable is extra flexible to facilitate testing
+func NewTestable(config TestableConfig) Interface {
+	return newTestableController(config)
+}
+
+func (cfgCtlr *configController) Handle(ctx context.Context, requestDigest RequestDigest,
+	noteFn func(fs *flowcontrol.FlowSchema, pl *flowcontrol.PriorityLevelConfiguration, flowDistinguisher string),
+	workEstimator func() fcrequest.WorkEstimate,
+	queueNoteFn fq.QueueNoteFn,
+	execFn func()) {
+	fs, pl, isExempt, req, startWaitingTime := cfgCtlr.startRequest(ctx, requestDigest, noteFn, workEstimator, queueNoteFn)
+	queued := startWaitingTime != time.Time{}
+	if req == nil {
+		if queued {
+			metrics.ObserveWaitingDuration(ctx, pl.Name, fs.Name, strconv.FormatBool(req != nil), time.Since(startWaitingTime))
+		}
+		klog.V(7).Infof("Handle(%#+v) => fsName=%q, distMethod=%#+v, plName=%q, isExempt=%v, reject", requestDigest, fs.Name, fs.Spec.DistinguisherMethod, pl.Name, isExempt)
+		return
+	}
+	klog.V(7).Infof("Handle(%#+v) => fsName=%q, distMethod=%#+v, plName=%q, isExempt=%v, queued=%v", requestDigest, fs.Name, fs.Spec.DistinguisherMethod, pl.Name, isExempt, queued)
+	var executed bool
+	idle, panicking := true, true
+	defer func() {
+		klog.V(7).Infof("Handle(%#+v) => fsName=%q, distMethod=%#+v, plName=%q, isExempt=%v, queued=%v, Finish() => panicking=%v idle=%v",
+			requestDigest, fs.Name, fs.Spec.DistinguisherMethod, pl.Name, isExempt, queued, panicking, idle)
+		if idle {
+			cfgCtlr.maybeReap(pl.Name)
+		}
+	}()
+	idle = req.Finish(func() {
+		if queued {
+			metrics.ObserveWaitingDuration(ctx, pl.Name, fs.Name, strconv.FormatBool(req != nil), time.Since(startWaitingTime))
+		}
+		metrics.AddDispatch(ctx, pl.Name, fs.Name)
+		executed = true
+		startExecutionTime := time.Now()
+		defer func() {
+			executionTime := time.Since(startExecutionTime)
+			httplog.AddKeyValue(ctx, "apf_execution_time", executionTime)
+			metrics.ObserveExecutionDuration(ctx, pl.Name, fs.Name, executionTime)
+		}()
+		execFn()
+	})
+	if queued && !executed {
+		metrics.ObserveWaitingDuration(ctx, pl.Name, fs.Name, strconv.FormatBool(req != nil), time.Since(startWaitingTime))
+	}
+	panicking = false
+}

vendor/k8s.io/apiserver/pkg/util/flowcontrol/conc_alloc.go

@@ -0,0 +1,256 @@
+/*
+Copyright 2022 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package flowcontrol
+
+import (
+	"errors"
+	"fmt"
+	"math"
+	"sort"
+)
+
+// allocProblemItem is one of the classes to which computeConcurrencyAllocation should make an allocation
+type allocProblemItem struct {
+	target     float64
+	lowerBound float64
+	upperBound float64
+}
+
+// relativeAllocItem is like allocProblemItem but with target avoiding zero and the bounds divided by the target
+type relativeAllocItem struct {
+	target             float64
+	relativeLowerBound float64
+	relativeUpperBound float64
+}
+
+// relativeAllocProblem collects together all the classes and holds the result of sorting by increasing bounds.
+// For J <= K, ascendingIndices[J] identifies a bound that is <= the one of ascendingIndices[K].
+// When ascendingIndices[J] = 2*N + 0, this identifies the lower bound of items[N].
+// When ascendingIndices[J] = 2*N + 1, this identifies the upper bound of items[N].
+type relativeAllocProblem struct {
+	items            []relativeAllocItem
+	ascendingIndices []int
+}
+
+// initIndices fills in ascendingIndices and sorts them
+func (rap *relativeAllocProblem) initIndices() *relativeAllocProblem {
+	rap.ascendingIndices = make([]int, len(rap.items)*2)
+	for idx := 0; idx < len(rap.ascendingIndices); idx++ {
+		rap.ascendingIndices[idx] = idx
+	}
+	sort.Sort(rap)
+	return rap
+}
+
+func (rap *relativeAllocProblem) getItemIndex(idx int) (int, bool) {
+	packedIndex := rap.ascendingIndices[idx]
+	itemIndex := packedIndex / 2
+	return itemIndex, packedIndex == itemIndex*2
+}
+
+// decode(J) returns the bound associated with ascendingIndices[J], the associated items index,
+// and a bool indicating whether the bound is the item's lower bound.
+func (rap *relativeAllocProblem) decode(idx int) (float64, int, bool) {
+	itemIdx, lower := rap.getItemIndex(idx)
+	if lower {
+		return rap.items[itemIdx].relativeLowerBound, itemIdx, lower
+	}
+	return rap.items[itemIdx].relativeUpperBound, itemIdx, lower
+}
+
+func (rap *relativeAllocProblem) getProportion(idx int) float64 {
+	prop, _, _ := rap.decode(idx)
+	return prop
+}
+
+func (rap *relativeAllocProblem) Len() int { return len(rap.items) * 2 }
+
+func (rap *relativeAllocProblem) Less(i, j int) bool {
+	return rap.getProportion(i) < rap.getProportion(j)
+}
+
+func (rap *relativeAllocProblem) Swap(i, j int) {
+	rap.ascendingIndices[i], rap.ascendingIndices[j] = rap.ascendingIndices[j], rap.ascendingIndices[i]
+}
+
+// minMax records the minimum and maximum value seen while scanning a set of numbers
+type minMax struct {
+	min float64
+	max float64
+}
+
+// note scans one more number
+func (mm *minMax) note(x float64) {
+	mm.min = math.Min(mm.min, x)
+	mm.max = math.Max(mm.max, x)
+}
+
+const MinTarget = 0.001
+const epsilon = 0.0000001
+
+// computeConcurrencyAllocation returns the unique `allocs []float64`, and
+// an associated `fairProp float64`, that jointly have
+// all of the following properties (to the degree that floating point calculations allow)
+// if possible otherwise returns an error saying why it is impossible.
+// `allocs` sums to `requiredSum`.
+// For each J in [0, len(classes)):
+// (1) `classes[J].lowerBound <= allocs[J] <= classes[J].upperBound` and
+// (2) exactly one of the following is true:
+// (2a) `allocs[J] == fairProp * classes[J].target`,
+// (2b) `allocs[J] == classes[J].lowerBound && classes[J].lowerBound > fairProp * classes[J].target`, or
+// (2c) `allocs[J] == classes[J].upperBound && classes[J].upperBound < fairProp * classes[J].target`.
+// Each allocProblemItem is required to have `target >= lowerBound >= 0` and `upperBound >= lowerBound`.
+// A target smaller than MinTarget is treated as if it were MinTarget.
+func computeConcurrencyAllocation(requiredSum int, classes []allocProblemItem) ([]float64, float64, error) {
+	if requiredSum < 0 {
+		return nil, 0, errors.New("negative sums are not supported")
+	}
+	requiredSumF := float64(requiredSum)
+	var lowSum, highSum, targetSum float64
+	ubRange := minMax{min: float64(math.MaxFloat32)}
+	lbRange := minMax{min: float64(math.MaxFloat32)}
+	relativeItems := make([]relativeAllocItem, len(classes))
+	for idx, item := range classes {
+		target := item.target
+		if item.lowerBound < 0 {
+			return nil, 0, fmt.Errorf("lower bound %d is %v but negative lower bounds are not allowed", idx, item.lowerBound)
+		}
+		if target < item.lowerBound {
+			return nil, 0, fmt.Errorf("target %d is %v, which is below its lower bound of %v", idx, target, item.lowerBound)
+		}
+		if item.upperBound < item.lowerBound {
+			return nil, 0, fmt.Errorf("upper bound %d is %v but should not be less than the lower bound %v", idx, item.upperBound, item.lowerBound)
+		}
+		if target < MinTarget {
+			// tweak this to a non-zero value so avoid dividing by zero
+			target = MinTarget
+		}
+		lowSum += item.lowerBound
+		highSum += item.upperBound
+		targetSum += target
+		relativeItem := relativeAllocItem{
+			target:             target,
+			relativeLowerBound: item.lowerBound / target,
+			relativeUpperBound: item.upperBound / target,
+		}
+		ubRange.note(relativeItem.relativeUpperBound)
+		lbRange.note(relativeItem.relativeLowerBound)
+		relativeItems[idx] = relativeItem
+	}
+	if lbRange.max > 1 {
+		return nil, 0, fmt.Errorf("lbRange.max-1=%v, which is impossible because lbRange.max can not be greater than 1", lbRange.max-1)
+	}
+	if lowSum-requiredSumF > epsilon {
+		return nil, 0, fmt.Errorf("lower bounds sum to %v, which is higher than the required sum of %v", lowSum, requiredSum)
+	}
+	if requiredSumF-highSum > epsilon {
+		return nil, 0, fmt.Errorf("upper bounds sum to %v, which is lower than the required sum of %v", highSum, requiredSum)
+	}
+	ans := make([]float64, len(classes))
+	if requiredSum == 0 {
+		return ans, 0, nil
+	}
+	if lowSum-requiredSumF > -epsilon { // no wiggle room, constrained from below
+		for idx, item := range classes {
+			ans[idx] = item.lowerBound
+		}
+		return ans, lbRange.min, nil
+	}
+	if requiredSumF-highSum > -epsilon { // no wiggle room, constrained from above
+		for idx, item := range classes {
+			ans[idx] = item.upperBound
+		}
+		return ans, ubRange.max, nil
+	}
+	// Now we know the solution is a unique fairProp in [lbRange.min, ubRange.max].
+	// See if the solution does not run into any bounds.
+	fairProp := requiredSumF / targetSum
+	if lbRange.max <= fairProp && fairProp <= ubRange.min { // no bounds matter
+		for idx := range classes {
+			ans[idx] = relativeItems[idx].target * fairProp
+		}
+		return ans, fairProp, nil
+	}
+	// Sadly, some bounds matter.
+	// We find the solution by sorting the bounds and considering progressively
+	// higher values of fairProp, starting from lbRange.min.
+	rap := (&relativeAllocProblem{items: relativeItems}).initIndices()
+	sumSoFar := lowSum
+	fairProp = lbRange.min
+	var sensitiveTargetSum, deltaSensitiveTargetSum float64
+	var numSensitiveClasses, deltaSensitiveClasses int
+	var nextIdx int
+	// `nextIdx` is the next `rap` index to consider.
+	// `sumSoFar` is what the allocs would sum to if the current
+	// value of `fairProp` solves the problem.
+	// If the current value of fairProp were the answer then
+	// `sumSoFar == requiredSum`.
+	// Otherwise the next increment in fairProp involves changing the allocations
+	// of `numSensitiveClasses` classes whose targets sum to `sensitiveTargetSum`;
+	// for the other classes, an upper or lower bound has applied and will continue to apply.
+	// The last increment of nextIdx calls for adding `deltaSensitiveClasses`
+	// to `numSensitiveClasses` and adding `deltaSensitiveTargetSum` to `sensitiveTargetSum`.
+	for sumSoFar < requiredSumF {
+		// There might be more than one bound that is equal to the current value
+		// of fairProp; find all of them because they will all be relevant to
+		// the next change in fairProp.
+		// Set nextBound to the next bound that is NOT equal to fairProp,
+		// and advance nextIdx to the index of that bound.
+		var nextBound float64
+		for {
+			sensitiveTargetSum += deltaSensitiveTargetSum
+			numSensitiveClasses += deltaSensitiveClasses
+			if nextIdx >= rap.Len() {
+				return nil, 0, fmt.Errorf("impossible: ran out of bounds to consider in bound-constrained problem")
+			}
+			var itemIdx int
+			var lower bool
+			nextBound, itemIdx, lower = rap.decode(nextIdx)
+			if lower {
+				deltaSensitiveClasses = 1
+				deltaSensitiveTargetSum = rap.items[itemIdx].target
+			} else {
+				deltaSensitiveClasses = -1
+				deltaSensitiveTargetSum = -rap.items[itemIdx].target
+			}
+			nextIdx++
+			if nextBound > fairProp {
+				break
+			}
+		}
+		// fairProp can increase to nextBound without passing any intermediate bounds.
+		if numSensitiveClasses == 0 {
+			// No classes are affected by the next range of fairProp; skip right past it
+			fairProp = nextBound
+			continue
+		}
+		// See whether fairProp can increase to the solution before passing the next bound.
+		deltaFairProp := (requiredSumF - sumSoFar) / sensitiveTargetSum
+		nextProp := fairProp + deltaFairProp
+		if nextProp <= nextBound {
+			fairProp = nextProp
+			break
+		}
+		// No, fairProp has to increase above nextBound
+		sumSoFar += (nextBound - fairProp) * sensitiveTargetSum
+		fairProp = nextBound
+	}
+	for idx, item := range classes {
+		ans[idx] = math.Max(item.lowerBound, math.Min(item.upperBound, fairProp*relativeItems[idx].target))
+	}
+	return ans, fairProp, nil
+}

vendor/k8s.io/apiserver/pkg/util/flowcontrol/debug/dump.go

@@ -0,0 +1,60 @@
+/*
+Copyright 2016 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package debug
+
+import (
+	"time"
+
+	"k8s.io/apiserver/pkg/endpoints/request"
+	flowcontrolrequest "k8s.io/apiserver/pkg/util/flowcontrol/request"
+)
+
+// QueueSetDump is an instant dump of queue-set.
+type QueueSetDump struct {
+	Queues       []QueueDump
+	Waiting      int
+	Executing    int
+	SeatsInUse   int
+	SeatsWaiting int
+}
+
+// QueueDump is an instant dump of one queue in a queue-set.
+type QueueDump struct {
+	QueueSum          QueueSum
+	Requests          []RequestDump
+	NextDispatchR     string
+	ExecutingRequests int
+	SeatsInUse        int
+}
+
+type QueueSum struct {
+	InitialSeatsSum int
+	MaxSeatsSum     int
+	TotalWorkSum    string
+}
+
+// RequestDump is an instant dump of one requests pending in the queue.
+type RequestDump struct {
+	MatchedFlowSchema string
+	FlowDistinguisher string
+	ArriveTime        time.Time
+	StartTime         time.Time
+	WorkEstimate      flowcontrolrequest.WorkEstimate
+	// request details
+	UserName    string
+	RequestInfo request.RequestInfo
+}

vendor/k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing/eventclock/interface.go

@@ -0,0 +1,47 @@
+/*
+Copyright 2021 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package eventclock
+
+import (
+	"time"
+
+	baseclock "k8s.io/utils/clock"
+)
+
+// EventFunc does some work that needs to be done at or after the
+// given time.
+type EventFunc func(time.Time)
+
+// EventClock is an active clock abstraction for use in code that is
+// testable with a fake clock that itself determines how time may be
+// advanced.  The timing paradigm is invoking EventFuncs rather than
+// synchronizing through channels, so that the fake clock has a handle
+// on when associated activity is done.
+type Interface interface {
+	baseclock.PassiveClock
+
+	// Sleep returns after the given duration (or more).
+	Sleep(d time.Duration)
+
+	// EventAfterDuration invokes the given EventFunc after the given duration (or more),
+	// passing the time when the invocation was launched.
+	EventAfterDuration(f EventFunc, d time.Duration)
+
+	// EventAfterTime invokes the given EventFunc at the given time or later,
+	// passing the time when the invocation was launched.
+	EventAfterTime(f EventFunc, t time.Time)
+}

vendor/k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing/eventclock/real.go

@@ -0,0 +1,44 @@
+/*
+Copyright 2021 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package eventclock
+
+import (
+	"time"
+
+	"k8s.io/utils/clock"
+)
+
+// RealEventClock fires event on real world time
+type Real struct {
+	clock.RealClock
+}
+
+var _ Interface = Real{}
+
+// EventAfterDuration schedules an EventFunc
+func (Real) EventAfterDuration(f EventFunc, d time.Duration) {
+	ch := time.After(d)
+	go func() {
+		t := <-ch
+		f(t)
+	}()
+}
+
+// EventAfterTime schedules an EventFunc
+func (r Real) EventAfterTime(f EventFunc, t time.Time) {
+	r.EventAfterDuration(f, time.Until(t))
+}

vendor/k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing/integrator.go

@@ -0,0 +1,191 @@
+/*
+Copyright 2019 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package fairqueuing
+
+import (
+	"math"
+	"sync"
+	"time"
+
+	fcmetrics "k8s.io/apiserver/pkg/util/flowcontrol/metrics"
+
+	"k8s.io/utils/clock"
+)
+
+// Integrator computes the moments of some variable X over time as
+// read from a particular clock.  The integrals start when the
+// Integrator is created, and ends at the latest operation on the
+// Integrator.
+type Integrator interface {
+	fcmetrics.Gauge
+
+	GetResults() IntegratorResults
+
+	// Return the results of integrating to now, and reset integration to start now
+	Reset() IntegratorResults
+}
+
+// IntegratorResults holds statistical abstracts of the integration
+type IntegratorResults struct {
+	Duration  float64 //seconds
+	Average   float64 //time-weighted
+	Deviation float64 //standard deviation: sqrt(avg((value-avg)^2))
+	Min, Max  float64
+}
+
+// Equal tests for semantic equality.
+// This considers all NaN values to be equal to each other.
+func (x *IntegratorResults) Equal(y *IntegratorResults) bool {
+	return x == y || x != nil && y != nil && x.Duration == y.Duration && x.Min == y.Min && x.Max == y.Max && (x.Average == y.Average || math.IsNaN(x.Average) && math.IsNaN(y.Average)) && (x.Deviation == y.Deviation || math.IsNaN(x.Deviation) && math.IsNaN(y.Deviation))
+}
+
+type integrator struct {
+	name  string
+	clock clock.PassiveClock
+	sync.Mutex
+	lastTime time.Time
+	x        float64
+	moments  Moments
+	min, max float64
+}
+
+// NewNamedIntegrator makes one that uses the given clock and name
+func NewNamedIntegrator(clock clock.PassiveClock, name string) Integrator {
+	return &integrator{
+		name:     name,
+		clock:    clock,
+		lastTime: clock.Now(),
+	}
+}
+
+func (igr *integrator) Set(x float64) {
+	igr.Lock()
+	igr.setLocked(x)
+	igr.Unlock()
+}
+
+func (igr *integrator) Add(deltaX float64) {
+	igr.Lock()
+	igr.setLocked(igr.x + deltaX)
+	igr.Unlock()
+}
+
+func (igr *integrator) Inc() {
+	igr.Add(1)
+}
+
+func (igr *integrator) Dec() {
+	igr.Add(-1)
+}
+
+func (igr *integrator) SetToCurrentTime() {
+	igr.Set(float64(time.Now().UnixNano()))
+}
+
+func (igr *integrator) setLocked(x float64) {
+	igr.updateLocked()
+	igr.x = x
+	if x < igr.min {
+		igr.min = x
+	}
+	if x > igr.max {
+		igr.max = x
+	}
+}
+
+func (igr *integrator) updateLocked() {
+	now := igr.clock.Now()
+	dt := now.Sub(igr.lastTime).Seconds()
+	igr.lastTime = now
+	igr.moments = igr.moments.Add(ConstantMoments(dt, igr.x))
+}
+
+func (igr *integrator) GetResults() IntegratorResults {
+	igr.Lock()
+	defer igr.Unlock()
+	return igr.getResultsLocked()
+}
+
+func (igr *integrator) Reset() IntegratorResults {
+	igr.Lock()
+	defer igr.Unlock()
+	results := igr.getResultsLocked()
+	igr.moments = Moments{}
+	igr.min = igr.x
+	igr.max = igr.x
+	return results
+}
+
+func (igr *integrator) getResultsLocked() (results IntegratorResults) {
+	igr.updateLocked()
+	results.Min, results.Max = igr.min, igr.max
+	results.Duration = igr.moments.ElapsedSeconds
+	results.Average, results.Deviation = igr.moments.AvgAndStdDev()
+	return
+}
+
+// Moments are the integrals of the 0, 1, and 2 powers of some
+// variable X over some range of time.
+type Moments struct {
+	ElapsedSeconds float64 // integral of dt
+	IntegralX      float64 // integral of x dt
+	IntegralXX     float64 // integral of x*x dt
+}
+
+// ConstantMoments is for a constant X
+func ConstantMoments(dt, x float64) Moments {
+	return Moments{
+		ElapsedSeconds: dt,
+		IntegralX:      x * dt,
+		IntegralXX:     x * x * dt,
+	}
+}
+
+// Add combines over two ranges of time
+func (igr Moments) Add(ogr Moments) Moments {
+	return Moments{
+		ElapsedSeconds: igr.ElapsedSeconds + ogr.ElapsedSeconds,
+		IntegralX:      igr.IntegralX + ogr.IntegralX,
+		IntegralXX:     igr.IntegralXX + ogr.IntegralXX,
+	}
+}
+
+// Sub finds the difference between a range of time and a subrange
+func (igr Moments) Sub(ogr Moments) Moments {
+	return Moments{
+		ElapsedSeconds: igr.ElapsedSeconds - ogr.ElapsedSeconds,
+		IntegralX:      igr.IntegralX - ogr.IntegralX,
+		IntegralXX:     igr.IntegralXX - ogr.IntegralXX,
+	}
+}
+
+// AvgAndStdDev returns the average and standard devation
+func (igr Moments) AvgAndStdDev() (float64, float64) {
+	if igr.ElapsedSeconds <= 0 {
+		return math.NaN(), math.NaN()
+	}
+	avg := igr.IntegralX / igr.ElapsedSeconds
+	// standard deviation is sqrt( average( (x - xbar)^2 ) )
+	// = sqrt( Integral( x^2 + xbar^2 -2*x*xbar dt ) / Duration )
+	// = sqrt( ( Integral( x^2 dt ) + Duration * xbar^2 - 2*xbar*Integral(x dt) ) / Duration)
+	// = sqrt( Integral(x^2 dt)/Duration - xbar^2 )
+	variance := igr.IntegralXX/igr.ElapsedSeconds - avg*avg
+	if variance >= 0 {
+		return avg, math.Sqrt(variance)
+	}
+	return avg, math.NaN()
+}

vendor/k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing/interface.go

@@ -0,0 +1,136 @@
+/*
+Copyright 2019 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package fairqueuing
+
+import (
+	"context"
+	"time"
+
+	"k8s.io/apiserver/pkg/util/flowcontrol/debug"
+	"k8s.io/apiserver/pkg/util/flowcontrol/metrics"
+	"k8s.io/apiserver/pkg/util/flowcontrol/request"
+)
+
+// QueueSetFactory is used to create QueueSet objects.  Creation, like
+// config update, is done in two phases: the first phase consumes the
+// QueuingConfig and the second consumes the DispatchingConfig.  They
+// are separated so that errors from the first phase can be found
+// before committing to a concurrency allotment for the second.
+type QueueSetFactory interface {
+	// BeginConstruction does the first phase of creating a QueueSet.
+	// The RatioedGaugePair observes number of requests,
+	// execution covering just the regular phase.
+	// The RatioedGauge observes number of seats occupied through all phases of execution.
+	// The Gauge observes the seat demand (executing + queued seats).
+	BeginConstruction(QueuingConfig, metrics.RatioedGaugePair, metrics.RatioedGauge, metrics.Gauge) (QueueSetCompleter, error)
+}
+
+// QueueSetCompleter finishes the two-step process of creating or
+// reconfiguring a QueueSet
+type QueueSetCompleter interface {
+	// Complete returns a QueueSet configured by the given
+	// dispatching configuration.
+	Complete(DispatchingConfig) QueueSet
+}
+
+// QueueSet is the abstraction for the queuing and dispatching
+// functionality of one non-exempt priority level.  It covers the
+// functionality described in the "Assignment to a Queue", "Queuing",
+// and "Dispatching" sections of
+// https://github.com/kubernetes/enhancements/blob/master/keps/sig-api-machinery/1040-priority-and-fairness/README.md
+// .  Some day we may have connections between priority levels, but
+// today is not that day.
+type QueueSet interface {
+	// BeginConfigChange starts the two-step process of updating the
+	// configuration.  No change is made until Complete is called.  If
+	// `C := X.BeginConstruction(q)` then `C.Complete(d)` returns the
+	// same value `X`.  If the QueuingConfig's DesiredNumQueues field
+	// is zero then the other queuing-specific config parameters are
+	// not changed, so that the queues continue draining as before.
+	// In any case, reconfiguration does not discard any queue unless
+	// and until it is undesired and empty.
+	BeginConfigChange(QueuingConfig) (QueueSetCompleter, error)
+
+	// IsIdle returns a bool indicating whether the QueueSet was idle
+	// at the moment of the return.  Idle means the QueueSet has zero
+	// requests queued and zero executing.  This bit can change only
+	// (1) during a call to StartRequest and (2) during a call to
+	// Request::Finish.  In the latter case idleness can only change
+	// from false to true.
+	IsIdle() bool
+
+	// StartRequest begins the process of handling a request.  If the
+	// request gets queued and the number of queues is greater than 1
+	// then StartRequest uses the given hashValue as the source of
+	// entropy as it shuffle-shards the request into a queue.  The
+	// descr1 and descr2 values play no role in the logic but appear
+	// in log messages.  This method always returns quickly (without
+	// waiting for the request to be dequeued).  If this method
+	// returns a nil Request value then caller should reject the
+	// request and the returned bool indicates whether the QueueSet
+	// was idle at the moment of the return.  Otherwise idle==false
+	// and the client must call the Finish method of the Request
+	// exactly once.
+	StartRequest(ctx context.Context, width *request.WorkEstimate, hashValue uint64, flowDistinguisher, fsName string, descr1, descr2 interface{}, queueNoteFn QueueNoteFn) (req Request, idle bool)
+
+	// Dump saves and returns the instant internal state of the queue-set.
+	// Note that dumping process will stop the queue-set from proceeding
+	// any requests.
+	// For debugging only.
+	Dump(includeRequestDetails bool) debug.QueueSetDump
+}
+
+// QueueNoteFn is called when a request enters and leaves a queue
+type QueueNoteFn func(inQueue bool)
+
+// Request represents the remainder of the handling of one request
+type Request interface {
+	// Finish determines whether to execute or reject the request and
+	// invokes `execute` if the decision is to execute the request.
+	// The returned `idle bool` value indicates whether the QueueSet
+	// was idle when the value was calculated, but might no longer be
+	// accurate by the time the client examines that value.
+	Finish(execute func()) (idle bool)
+}
+
+// QueuingConfig defines the configuration of the queuing aspect of a QueueSet.
+type QueuingConfig struct {
+	// Name is used to identify a queue set, allowing for descriptive information about its intended use
+	Name string
+
+	// DesiredNumQueues is the number of queues that the API says
+	// should exist now.  This may be zero, in which case
+	// QueueLengthLimit, HandSize, and RequestWaitLimit are ignored.
+	DesiredNumQueues int
+
+	// QueueLengthLimit is the maximum number of requests that may be waiting in a given queue at a time
+	QueueLengthLimit int
+
+	// HandSize is a parameter of shuffle sharding.  Upon arrival of a request, a queue is chosen by randomly
+	// dealing a "hand" of this many queues and then picking one of minimum length.
+	HandSize int
+
+	// RequestWaitLimit is the maximum amount of time that a request may wait in a queue.
+	// If, by the end of that time, the request has not been dispatched then it is rejected.
+	RequestWaitLimit time.Duration
+}
+
+// DispatchingConfig defines the configuration of the dispatching aspect of a QueueSet.
+type DispatchingConfig struct {
+	// ConcurrencyLimit is the maximum number of requests of this QueueSet that may be executing at a time
+	ConcurrencyLimit int
+}

vendor/k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing/promise/interface.go

@@ -0,0 +1,34 @@
+/*
+Copyright 2019 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package promise
+
+// WriteOnce represents a variable that is initially not set and can
+// be set once and is readable.  This is the common meaning for
+// "promise".
+type WriteOnce interface {
+	// Get reads the current value of this variable.  If this
+	// variable is not set yet then this call blocks until this
+	// variable gets a value.
+	Get() interface{}
+
+	// Set normally writes a value into this variable, unblocks every
+	// goroutine waiting for this variable to have a value, and
+	// returns true.  In the unhappy case that this variable is
+	// already set, this method returns false without modifying the
+	// variable's value.
+	Set(interface{}) bool
+}

vendor/k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing/promise/promise.go

@@ -0,0 +1,70 @@
+/*
+Copyright 2019 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package promise
+
+import (
+	"sync"
+)
+
+// promise implements the WriteOnce interface.
+type promise struct {
+	doneCh  <-chan struct{}
+	doneVal interface{}
+	setCh   chan struct{}
+	onceler sync.Once
+	value   interface{}
+}
+
+var _ WriteOnce = &promise{}
+
+// NewWriteOnce makes a new thread-safe WriteOnce.
+//
+// If `initial` is non-nil then that value is Set at creation time.
+//
+// If a `Get` is waiting soon after `doneCh` becomes selectable (which
+// never happens for the nil channel) then `Set(doneVal)` effectively
+// happens at that time.
+func NewWriteOnce(initial interface{}, doneCh <-chan struct{}, doneVal interface{}) WriteOnce {
+	p := &promise{
+		doneCh:  doneCh,
+		doneVal: doneVal,
+		setCh:   make(chan struct{}),
+	}
+	if initial != nil {
+		p.Set(initial)
+	}
+	return p
+}
+
+func (p *promise) Get() interface{} {
+	select {
+	case <-p.setCh:
+	case <-p.doneCh:
+		p.Set(p.doneVal)
+	}
+	return p.value
+}
+
+func (p *promise) Set(value interface{}) bool {
+	var ans bool
+	p.onceler.Do(func() {
+		p.value = value
+		close(p.setCh)
+		ans = true
+	})
+	return ans
+}

vendor/k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing/queueset/doc.go

@@ -0,0 +1,119 @@
+/*
+Copyright 2019 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// Package queueset implements a technique called "fair queuing for
+// server requests".  One QueueSet is a set of queues operating
+// according to this technique.
+//
+// Fair queuing for server requests is inspired by the fair queuing
+// technique from the world of networking.  You can find a good paper
+// on that at https://dl.acm.org/citation.cfm?doid=75247.75248 or
+// http://people.csail.mit.edu/imcgraw/links/research/pubs/networks/WFQ.pdf
+// and there is an implementation outline in the Wikipedia article at
+// https://en.wikipedia.org/wiki/Fair_queuing .
+//
+// Fair queuing for server requests differs from traditional fair
+// queuing in three ways: (1) we are dispatching application layer
+// requests to a server rather than transmitting packets on a network
+// link, (2) multiple requests can be executing at once, and (3) the
+// service time (execution duration) is not known until the execution
+// completes.
+//
+// The first two differences can easily be handled by straightforward
+// adaptation of the concept called "R(t)" in the original paper and
+// "virtual time" in the implementation outline. In that
+// implementation outline, the notation now() is used to mean reading
+// the virtual clock. In the original paper’s terms, "R(t)" is the
+// number of "rounds" that have been completed at real time t ---
+// where a round consists of virtually transmitting one bit from every
+// non-empty queue in the router (regardless of which queue holds the
+// packet that is really being transmitted at the moment); in this
+// conception, a packet is considered to be "in" its queue until the
+// packet’s transmission is finished. For our problem, we can define a
+// round to be giving one nanosecond of CPU to every non-empty queue
+// in the apiserver (where emptiness is judged based on both queued
+// and executing requests from that queue), and define R(t) = (server
+// start time) + (1 ns) * (number of rounds since server start). Let
+// us write NEQ(t) for that number of non-empty queues in the
+// apiserver at time t.  Let us also write C for the concurrency
+// limit.  In the original paper, the partial derivative of R(t) with
+// respect to t is
+//
+//	1 / NEQ(t) .
+//
+// To generalize from transmitting one packet at a time to executing C
+// requests at a time, that derivative becomes
+//
+//	C / NEQ(t) .
+//
+// However, sometimes there are fewer than C requests available to
+// execute.  For a given queue "q", let us also write "reqs(q, t)" for
+// the number of requests of that queue that are executing at that
+// time.  The total number of requests executing is sum[over q]
+// reqs(q, t) and if that is less than C then virtual time is not
+// advancing as fast as it would if all C seats were occupied; in this
+// case the numerator of the quotient in that derivative should be
+// adjusted proportionally.  Putting it all together for fair queing
+// for server requests: at a particular time t, the partial derivative
+// of R(t) with respect to t is
+//
+//	min( C, sum[over q] reqs(q, t) ) / NEQ(t) .
+//
+// In terms of the implementation outline, this is the rate at which
+// virtual time is advancing at time t (in virtual nanoseconds per
+// real nanosecond). Where the networking implementation outline adds
+// packet size to a virtual time, in our version this corresponds to
+// adding a service time (i.e., duration) to virtual time.
+//
+// The third difference is handled by modifying the algorithm to
+// dispatch based on an initial guess at the request’s service time
+// (duration) and then make the corresponding adjustments once the
+// request’s actual service time is known. This is similar, although
+// not exactly isomorphic, to the original paper’s adjustment by
+// `$\delta$` for the sake of promptness.
+//
+// For implementation simplicity (see below), let us use the same
+// initial service time guess for every request; call that duration
+// G. A good choice might be the service time limit (1
+// minute). Different guesses will give slightly different dynamics,
+// but any positive number can be used for G without ruining the
+// long-term behavior.
+//
+// As in ordinary fair queuing, there is a bound on divergence from
+// the ideal. In plain fair queuing the bound is one packet; in our
+// version it is C requests.
+//
+// To support efficiently making the necessary adjustments once a
+// request’s actual service time is known, the virtual finish time of
+// a request and the last virtual finish time of a queue are not
+// represented directly but instead computed from queue length,
+// request position in the queue, and an alternate state variable that
+// holds the queue’s virtual start time. While the queue is empty and
+// has no requests executing: the value of its virtual start time
+// variable is ignored and its last virtual finish time is considered
+// to be in the virtual past. When a request arrives to an empty queue
+// with no requests executing, the queue’s virtual start time is set
+// to the current virtual time. The virtual finish time of request
+// number J in the queue (counting from J=1 for the head) is J * G +
+// (queue's virtual start time). While the queue is non-empty: the
+// last virtual finish time of the queue is the virtual finish time of
+// the last request in the queue. While the queue is empty and has a
+// request executing: the last virtual finish time is the queue’s
+// virtual start time. When a request is dequeued for service the
+// queue’s virtual start time is advanced by G. When a request
+// finishes being served, and the actual service time was S, the
+// queue’s virtual start time is decremented by G - S.
+package queueset

vendor/k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing/queueset/fifo_list.go

@@ -0,0 +1,156 @@
+/*
+Copyright 2021 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package queueset
+
+import (
+	"container/list"
+)
+
+// removeFromFIFOFunc removes a designated element from the list
+// if that element is in the list.
+// The complexity of the runtime cost is O(1).
+// The returned value is the element removed, if indeed one was removed,
+// otherwise `nil`.
+type removeFromFIFOFunc func() *request
+
+// walkFunc is called for each request in the list in the
+// oldest -> newest order.
+// ok: if walkFunc returns false then the iteration stops immediately.
+// walkFunc may remove the given request from the fifo,
+// but may not mutate the fifo in any othe way.
+type walkFunc func(*request) (ok bool)
+
+// Internal interface to abstract out the implementation details
+// of the underlying list used to maintain the requests.
+//
+// Note that a fifo, including the removeFromFIFOFuncs returned from Enqueue,
+// is not safe for concurrent use by multiple goroutines.
+type fifo interface {
+	// Enqueue enqueues the specified request into the list and
+	// returns a removeFromFIFOFunc function that can be used to remove the
+	// request from the list
+	Enqueue(*request) removeFromFIFOFunc
+
+	// Dequeue pulls out the oldest request from the list.
+	Dequeue() (*request, bool)
+
+	// Peek returns the oldest request without removing it.
+	Peek() (*request, bool)
+
+	// Length returns the number of requests in the list.
+	Length() int
+
+	// QueueSum returns the sum of initial seats, final seats, and
+	// additional latency aggregated from all requests in this queue.
+	QueueSum() queueSum
+
+	// Walk iterates through the list in order of oldest -> newest
+	// and executes the specified walkFunc for each request in that order.
+	//
+	// if the specified walkFunc returns false the Walk function
+	// stops the walk an returns immediately.
+	Walk(walkFunc)
+}
+
+// the FIFO list implementation is not safe for concurrent use by multiple
+// goroutines.
+type requestFIFO struct {
+	*list.List
+
+	sum queueSum
+}
+
+func newRequestFIFO() fifo {
+	return &requestFIFO{
+		List: list.New(),
+	}
+}
+
+func (l *requestFIFO) Length() int {
+	return l.Len()
+}
+
+func (l *requestFIFO) QueueSum() queueSum {
+	return l.sum
+}
+
+func (l *requestFIFO) Enqueue(req *request) removeFromFIFOFunc {
+	e := l.PushBack(req)
+	addToQueueSum(&l.sum, req)
+
+	return func() *request {
+		if e.Value == nil {
+			return nil
+		}
+		l.Remove(e)
+		e.Value = nil
+		deductFromQueueSum(&l.sum, req)
+		return req
+	}
+}
+
+func (l *requestFIFO) Dequeue() (*request, bool) {
+	return l.getFirst(true)
+}
+
+func (l *requestFIFO) Peek() (*request, bool) {
+	return l.getFirst(false)
+}
+
+func (l *requestFIFO) getFirst(remove bool) (*request, bool) {
+	e := l.Front()
+	if e == nil {
+		return nil, false
+	}
+
+	if remove {
+		defer func() {
+			l.Remove(e)
+			e.Value = nil
+		}()
+	}
+
+	request, ok := e.Value.(*request)
+	if remove && ok {
+		deductFromQueueSum(&l.sum, request)
+	}
+	return request, ok
+}
+
+func (l *requestFIFO) Walk(f walkFunc) {
+	var next *list.Element
+	for current := l.Front(); current != nil; current = next {
+		next = current.Next() // f is allowed to remove current
+		if r, ok := current.Value.(*request); ok {
+			if !f(r) {
+				return
+			}
+		}
+	}
+}
+
+func addToQueueSum(sum *queueSum, req *request) {
+	sum.InitialSeatsSum += req.InitialSeats()
+	sum.MaxSeatsSum += req.MaxSeats()
+	sum.TotalWorkSum += req.totalWork()
+}
+
+func deductFromQueueSum(sum *queueSum, req *request) {
+	sum.InitialSeatsSum -= req.InitialSeats()
+	sum.MaxSeatsSum -= req.MaxSeats()
+	sum.TotalWorkSum -= req.totalWork()
+}

vendor/k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing/queueset/types.go

@@ -0,0 +1,183 @@
+/*
+Copyright 2019 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package queueset
+
+import (
+	"context"
+	"time"
+
+	genericrequest "k8s.io/apiserver/pkg/endpoints/request"
+	"k8s.io/apiserver/pkg/util/flowcontrol/debug"
+	fq "k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing"
+	"k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing/promise"
+	fcrequest "k8s.io/apiserver/pkg/util/flowcontrol/request"
+)
+
+// request is a temporary container for "requests" with additional
+// tracking fields required for QueueSet functionality.
+type request struct {
+	ctx context.Context
+
+	qs *queueSet
+
+	flowDistinguisher string
+	fsName            string
+
+	// The relevant queue.  Is nil if this request did not go through
+	// a queue.
+	queue *queue
+
+	// estimated amount of work of the request
+	workEstimate completedWorkEstimate
+
+	// decision gets set to a `requestDecision` indicating what to do
+	// with this request.  It gets set exactly once, when the request
+	// is removed from its queue.  The value will be decisionReject,
+	// decisionCancel, or decisionExecute.
+	//
+	// decision.Set is called with the queueSet locked.
+	// decision.Get is called without the queueSet locked.
+	decision promise.WriteOnce
+
+	// arrivalTime is the real time when the request entered this system
+	arrivalTime time.Time
+
+	// descr1 and descr2 are not used in any logic but they appear in
+	// log messages
+	descr1, descr2 interface{}
+
+	queueNoteFn fq.QueueNoteFn
+
+	// The preceding fields are filled in at creation and not modified since;
+	// the following fields may be modified later and must only be accessed while
+	// holding the queueSet's lock.
+
+	// Removes this request from its queue. If the request is not put into a
+	// a queue it will be nil.
+	removeFromQueueLocked removeFromFIFOFunc
+
+	// arrivalR is R(arrivalTime).  R is, confusingly, also called "virtual time".
+	// This field is meaningful only while the request is waiting in the virtual world.
+	arrivalR fcrequest.SeatSeconds
+
+	// startTime is the real time when the request began executing
+	startTime time.Time
+
+	// Indicates whether client has called Request::Wait()
+	waitStarted bool
+}
+
+type completedWorkEstimate struct {
+	fcrequest.WorkEstimate
+	totalWork fcrequest.SeatSeconds // initial plus final work
+	finalWork fcrequest.SeatSeconds // only final work
+}
+
+// queue is a sequence of requests that have arrived but not yet finished
+// execution in both the real and virtual worlds.
+type queue struct {
+	// The requests not yet executing in the real world are stored in a FIFO list.
+	requests fifo
+
+	// nextDispatchR is the R progress meter reading at
+	// which the next request will be dispatched in the virtual world.
+	nextDispatchR fcrequest.SeatSeconds
+
+	// requestsExecuting is the count in the real world.
+	requestsExecuting int
+
+	// index is the position of this queue among those in its queueSet.
+	index int
+
+	// seatsInUse is the total number of "seats" currently occupied
+	// by all the requests that are currently executing in this queue.
+	seatsInUse int
+}
+
+// queueSum tracks the sum of initial seats, max seats, and
+// totalWork from all requests in a given queue
+type queueSum struct {
+	// InitialSeatsSum is the sum of InitialSeats
+	// associated with all requests in a given queue.
+	InitialSeatsSum int
+
+	// MaxSeatsSum is the sum of MaxSeats
+	// associated with all requests in a given queue.
+	MaxSeatsSum int
+
+	// TotalWorkSum is the sum of totalWork of the waiting requests
+	TotalWorkSum fcrequest.SeatSeconds
+}
+
+func (req *request) totalWork() fcrequest.SeatSeconds {
+	return req.workEstimate.totalWork
+}
+
+func (qs *queueSet) completeWorkEstimate(we *fcrequest.WorkEstimate) completedWorkEstimate {
+	finalWork := qs.computeFinalWork(we)
+	return completedWorkEstimate{
+		WorkEstimate: *we,
+		totalWork:    qs.computeInitialWork(we) + finalWork,
+		finalWork:    finalWork,
+	}
+}
+
+func (qs *queueSet) computeInitialWork(we *fcrequest.WorkEstimate) fcrequest.SeatSeconds {
+	return fcrequest.SeatsTimesDuration(float64(we.InitialSeats), qs.estimatedServiceDuration)
+}
+
+func (qs *queueSet) computeFinalWork(we *fcrequest.WorkEstimate) fcrequest.SeatSeconds {
+	return fcrequest.SeatsTimesDuration(float64(we.FinalSeats), we.AdditionalLatency)
+}
+
+func (q *queue) dumpLocked(includeDetails bool) debug.QueueDump {
+	digest := make([]debug.RequestDump, q.requests.Length())
+	i := 0
+	q.requests.Walk(func(r *request) bool {
+		// dump requests.
+		digest[i].MatchedFlowSchema = r.fsName
+		digest[i].FlowDistinguisher = r.flowDistinguisher
+		digest[i].ArriveTime = r.arrivalTime
+		digest[i].StartTime = r.startTime
+		digest[i].WorkEstimate = r.workEstimate.WorkEstimate
+		if includeDetails {
+			userInfo, _ := genericrequest.UserFrom(r.ctx)
+			digest[i].UserName = userInfo.GetName()
+			requestInfo, ok := genericrequest.RequestInfoFrom(r.ctx)
+			if ok {
+				digest[i].RequestInfo = *requestInfo
+			}
+		}
+		i++
+		return true
+	})
+
+	sum := q.requests.QueueSum()
+	queueSum := debug.QueueSum{
+		InitialSeatsSum: sum.InitialSeatsSum,
+		MaxSeatsSum:     sum.MaxSeatsSum,
+		TotalWorkSum:    sum.TotalWorkSum.String(),
+	}
+
+	return debug.QueueDump{
+		NextDispatchR:     q.nextDispatchR.String(),
+		Requests:          digest,
+		ExecutingRequests: q.requestsExecuting,
+		SeatsInUse:        q.seatsInUse,
+		QueueSum:          queueSum,
+	}
+}

vendor/k8s.io/apiserver/pkg/util/flowcontrol/format/formatting.go

@@ -0,0 +1,231 @@
+/*
+Copyright 2019 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package format
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+
+	flowcontrol "k8s.io/api/flowcontrol/v1beta3"
+	"k8s.io/apiserver/pkg/authentication/user"
+	"k8s.io/apiserver/pkg/endpoints/request"
+)
+
+// This file provides an easy way to mark a value for formatting to
+// `%s` in full detail IF it is printed but without costing a lot of
+// CPU or memory if the value is NOT printed.  The API Priority and
+// Fairness API objects are formatted into JSON.  The other types of
+// objects here are formatted into golang source.
+
+// Stringer marks the given value for custom formatting by this package.
+type Stringer struct{ val interface{} }
+
+// Fmt marks the given value for custom formatting by this package.
+func Fmt(val interface{}) Stringer {
+	return Stringer{val}
+}
+
+// String formats to a string in full detail
+func (sr Stringer) String() string {
+	if sr.val == nil {
+		return "nil"
+	}
+	switch typed := sr.val.(type) {
+	case *flowcontrol.FlowSchema,
+		flowcontrol.FlowSchema,
+		flowcontrol.FlowSchemaSpec,
+		flowcontrol.FlowDistinguisherMethod,
+		*flowcontrol.FlowDistinguisherMethod,
+		*flowcontrol.PolicyRulesWithSubjects,
+		flowcontrol.PolicyRulesWithSubjects,
+		flowcontrol.Subject,
+		flowcontrol.ResourcePolicyRule,
+		flowcontrol.NonResourcePolicyRule,
+		flowcontrol.FlowSchemaCondition,
+		*flowcontrol.PriorityLevelConfiguration,
+		flowcontrol.PriorityLevelConfiguration,
+		flowcontrol.PriorityLevelConfigurationSpec,
+		*flowcontrol.LimitedPriorityLevelConfiguration,
+		flowcontrol.LimitedPriorityLevelConfiguration,
+		flowcontrol.LimitResponse,
+		*flowcontrol.QueuingConfiguration,
+		flowcontrol.QueuingConfiguration:
+		return ToJSON(sr.val)
+	case []user.Info:
+		return FmtUsers(typed)
+	case []*request.RequestInfo:
+		return FmtRequests(typed)
+	default:
+		return fmt.Sprintf("%#+v", sr.val)
+	}
+}
+
+// ToJSON converts using encoding/json and handles errors by
+// formatting them
+func ToJSON(val interface{}) string {
+	bs, err := json.Marshal(val)
+	str := string(bs)
+	if err != nil {
+		str = str + "<" + err.Error() + ">"
+	}
+	return str
+}
+
+// FmtPriorityLevelConfiguration returns a golang source expression
+// equivalent to the given value
+func FmtPriorityLevelConfiguration(pl *flowcontrol.PriorityLevelConfiguration) string {
+	if pl == nil {
+		return "nil"
+	}
+	var buf bytes.Buffer
+	buf.WriteString(fmt.Sprintf("&flowcontrolv1beta3.PriorityLevelConfiguration{ObjectMeta: %#+v, Spec: ",
+		pl.ObjectMeta))
+	BufferPriorityLevelConfigurationSpec(&buf, &pl.Spec)
+	buf.WriteString(fmt.Sprintf(", Status: %#+v}", pl.Status))
+	return buf.String()
+}
+
+// FmtPriorityLevelConfigurationSpec returns a golang source
+// expression equivalent to the given value
+func FmtPriorityLevelConfigurationSpec(plSpec *flowcontrol.PriorityLevelConfigurationSpec) string {
+	var buf bytes.Buffer
+	BufferPriorityLevelConfigurationSpec(&buf, plSpec)
+	return buf.String()
+}
+
+// BufferPriorityLevelConfigurationSpec writes a golang source
+// expression for the given value to the given buffer
+func BufferPriorityLevelConfigurationSpec(buf *bytes.Buffer, plSpec *flowcontrol.PriorityLevelConfigurationSpec) {
+	buf.WriteString(fmt.Sprintf("flowcontrolv1beta3.PriorityLevelConfigurationSpec{Type: %#v", plSpec.Type))
+	if plSpec.Limited != nil {
+		buf.WriteString(fmt.Sprintf(", Limited: &flowcontrol.LimitedPriorityLevelConfiguration{NominalConcurrencyShares:%d, LimitResponse:flowcontrol.LimitResponse{Type:%#v", plSpec.Limited.NominalConcurrencyShares, plSpec.Limited.LimitResponse.Type))
+		if plSpec.Limited.LimitResponse.Queuing != nil {
+			buf.WriteString(fmt.Sprintf(", Queuing:&%#+v", *plSpec.Limited.LimitResponse.Queuing))
+		}
+		buf.WriteString(" } }")
+	}
+	buf.WriteString("}")
+}
+
+// FmtFlowSchema produces a golang source expression of the value.
+func FmtFlowSchema(fs *flowcontrol.FlowSchema) string {
+	if fs == nil {
+		return "nil"
+	}
+	var buf bytes.Buffer
+	buf.WriteString(fmt.Sprintf("&flowcontrolv1beta3.FlowSchema{ObjectMeta: %#+v, Spec: ",
+		fs.ObjectMeta))
+	BufferFlowSchemaSpec(&buf, &fs.Spec)
+	buf.WriteString(fmt.Sprintf(", Status: %#+v}", fs.Status))
+	return buf.String()
+}
+
+// FmtFlowSchemaSpec produces a golang source expression equivalent to
+// the given spec
+func FmtFlowSchemaSpec(fsSpec *flowcontrol.FlowSchemaSpec) string {
+	var buf bytes.Buffer
+	BufferFlowSchemaSpec(&buf, fsSpec)
+	return buf.String()
+}
+
+// BufferFlowSchemaSpec writes a golang source expression for the
+// given value to the given buffer
+func BufferFlowSchemaSpec(buf *bytes.Buffer, fsSpec *flowcontrol.FlowSchemaSpec) {
+	buf.WriteString(fmt.Sprintf("flowcontrolv1beta3.FlowSchemaSpec{PriorityLevelConfiguration: %#+v, MatchingPrecedence: %d, DistinguisherMethod: ",
+		fsSpec.PriorityLevelConfiguration,
+		fsSpec.MatchingPrecedence))
+	if fsSpec.DistinguisherMethod == nil {
+		buf.WriteString("nil")
+	} else {
+		buf.WriteString(fmt.Sprintf("&%#+v", *fsSpec.DistinguisherMethod))
+	}
+	buf.WriteString(", Rules: []flowcontrol.PolicyRulesWithSubjects{")
+	for idx, rule := range fsSpec.Rules {
+		if idx > 0 {
+			buf.WriteString(", ")
+		}
+		BufferFmtPolicyRulesWithSubjectsSlim(buf, rule)
+	}
+	buf.WriteString("}}")
+}
+
+// FmtPolicyRulesWithSubjects produces a golang source expression of the value.
+func FmtPolicyRulesWithSubjects(rule flowcontrol.PolicyRulesWithSubjects) string {
+	return "flowcontrolv1beta3.PolicyRulesWithSubjects" + FmtPolicyRulesWithSubjectsSlim(rule)
+}
+
+// FmtPolicyRulesWithSubjectsSlim produces a golang source expression
+// of the value but without the leading type name.  See above for an
+// example context where this is useful.
+func FmtPolicyRulesWithSubjectsSlim(rule flowcontrol.PolicyRulesWithSubjects) string {
+	var buf bytes.Buffer
+	BufferFmtPolicyRulesWithSubjectsSlim(&buf, rule)
+	return buf.String()
+}
+
+// BufferFmtPolicyRulesWithSubjectsSlim writes a golang source
+// expression for the given value to the given buffer but excludes the
+// leading type name
+func BufferFmtPolicyRulesWithSubjectsSlim(buf *bytes.Buffer, rule flowcontrol.PolicyRulesWithSubjects) {
+	buf.WriteString("{Subjects: []flowcontrolv1beta3.Subject{")
+	for jdx, subj := range rule.Subjects {
+		if jdx > 0 {
+			buf.WriteString(", ")
+		}
+		buf.WriteString(fmt.Sprintf("{Kind: %q", subj.Kind))
+		if subj.User != nil {
+			buf.WriteString(fmt.Sprintf(", User: &%#+v", *subj.User))
+		}
+		if subj.Group != nil {
+			buf.WriteString(fmt.Sprintf(", Group: &%#+v", *subj.Group))
+		}
+		if subj.ServiceAccount != nil {
+			buf.WriteString(fmt.Sprintf(", ServiceAccount: &%#+v", *subj.ServiceAccount))
+		}
+		buf.WriteString("}")
+	}
+	buf.WriteString(fmt.Sprintf("}, ResourceRules: %#+v, NonResourceRules: %#+v}", rule.ResourceRules, rule.NonResourceRules))
+}
+
+// FmtUsers produces a golang source expression of the value.
+func FmtUsers(list []user.Info) string {
+	var buf bytes.Buffer
+	buf.WriteString("[]user.Info{")
+	for idx, member := range list {
+		if idx > 0 {
+			buf.WriteString(", ")
+		}
+		buf.WriteString(fmt.Sprintf("%#+v", member))
+	}
+	buf.WriteString("}")
+	return buf.String()
+}
+
+// FmtRequests produces a golang source expression of the value.
+func FmtRequests(list []*request.RequestInfo) string {
+	var buf bytes.Buffer
+	buf.WriteString("[]*request.RequestInfo{")
+	for idx, member := range list {
+		if idx > 0 {
+			buf.WriteString(", ")
+		}
+		buf.WriteString(fmt.Sprintf("%#+v", member))
+	}
+	buf.WriteString("}")
+	return buf.String()
+}

vendor/k8s.io/apiserver/pkg/util/flowcontrol/formatting.go

@@ -0,0 +1,40 @@
+/*
+Copyright 2019 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package flowcontrol
+
+import (
+	"fmt"
+
+	fcfmt "k8s.io/apiserver/pkg/util/flowcontrol/format"
+)
+
+var _ fmt.GoStringer = RequestDigest{}
+
+// GoString produces a golang source expression of the value.
+func (rd RequestDigest) GoString() string {
+	return fmt.Sprintf("RequestDigest{RequestInfo: %#+v, User: %#+v}", rd.RequestInfo, rd.User)
+}
+
+var _ fmt.GoStringer = (*priorityLevelState)(nil)
+
+// GoString produces a golang source expression of the value.
+func (pls *priorityLevelState) GoString() string {
+	if pls == nil {
+		return "nil"
+	}
+	return fmt.Sprintf("&priorityLevelState{pl:%s, qsCompleter:%#+v, queues:%#+v, quiescing:%#v, numPending:%d}", fcfmt.Fmt(pls.pl), pls.qsCompleter, pls.queues, pls.quiescing, pls.numPending)
+}

vendor/k8s.io/apiserver/pkg/util/flowcontrol/metrics/interface.go

@@ -0,0 +1,67 @@
+/*
+Copyright 2019 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package metrics
+
+// Gauge is the methods of a gauge that are used by instrumented code.
+type Gauge interface {
+	Set(float64)
+	Inc()
+	Dec()
+	Add(float64)
+	SetToCurrentTime()
+}
+
+// RatioedGauge tracks ratios.
+// The numerator is set/changed through the Gauge methods,
+// and the denominator can be updated through the SetDenominator method.
+// A ratio is tracked whenever the numerator or denominator is set/changed.
+type RatioedGauge interface {
+	Gauge
+
+	// SetDenominator sets the denominator to use until it is changed again
+	SetDenominator(float64)
+}
+
+// RatioedGaugeVec creates related observers that are
+// differentiated by a series of label values
+type RatioedGaugeVec interface {
+	// NewForLabelValuesSafe makes a new vector member for the given tuple of label values,
+	// initialized with the given numerator and denominator.
+	// Unlike the usual Vec WithLabelValues method, this is intended to be called only
+	// once per vector member (at the start of its lifecycle).
+	// The "Safe" part is saying that the returned object will function properly after metric registration
+	// even if this method is called before registration.
+	NewForLabelValuesSafe(initialNumerator, initialDenominator float64, labelValues []string) RatioedGauge
+}
+
+//////////////////////////////// Pairs ////////////////////////////////
+//
+// API Priority and Fairness tends to use RatioedGaugeVec members in pairs,
+// one for requests waiting in a queue and one for requests being executed.
+// The following definitions are a convenience layer that adds support for that
+// particular pattern of usage.
+
+// RatioedGaugePair is a corresponding pair of gauges, one for the
+// number of requests waiting in queue(s) and one for the number of
+// requests being executed.
+type RatioedGaugePair struct {
+	// RequestsWaiting is given observations of the number of currently queued requests
+	RequestsWaiting RatioedGauge
+
+	// RequestsExecuting is given observations of the number of requests currently executing
+	RequestsExecuting RatioedGauge
+}

vendor/k8s.io/apiserver/pkg/util/flowcontrol/metrics/metrics.go

@@ -0,0 +1,600 @@
+/*
+Copyright 2019 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package metrics
+
+import (
+	"context"
+	"strconv"
+	"strings"
+	"sync"
+	"time"
+
+	epmetrics "k8s.io/apiserver/pkg/endpoints/metrics"
+	apirequest "k8s.io/apiserver/pkg/endpoints/request"
+	compbasemetrics "k8s.io/component-base/metrics"
+	"k8s.io/component-base/metrics/legacyregistry"
+	basemetricstestutil "k8s.io/component-base/metrics/testutil"
+)
+
+const (
+	namespace = "apiserver"
+	subsystem = "flowcontrol"
+)
+
+const (
+	requestKind         = "request_kind"
+	priorityLevel       = "priority_level"
+	flowSchema          = "flow_schema"
+	phase               = "phase"
+	LabelNamePhase      = "phase"
+	LabelValueWaiting   = "waiting"
+	LabelValueExecuting = "executing"
+)
+
+var (
+	queueLengthBuckets            = []float64{0, 10, 25, 50, 100, 250, 500, 1000}
+	requestDurationSecondsBuckets = []float64{0, 0.005, 0.02, 0.05, 0.1, 0.2, 0.5, 1, 2, 5, 10, 30}
+)
+
+var registerMetrics sync.Once
+
+// Register all metrics.
+func Register() {
+	registerMetrics.Do(func() {
+		for _, metric := range metrics {
+			legacyregistry.MustRegister(metric)
+		}
+	})
+}
+
+type resettable interface {
+	Reset()
+}
+
+// Reset all resettable metrics to zero
+func Reset() {
+	for _, metric := range metrics {
+		if rm, ok := metric.(resettable); ok {
+			rm.Reset()
+		}
+	}
+}
+
+// GatherAndCompare the given metrics with the given Prometheus syntax expected value
+func GatherAndCompare(expected string, metricNames ...string) error {
+	return basemetricstestutil.GatherAndCompare(legacyregistry.DefaultGatherer, strings.NewReader(expected), metricNames...)
+}
+
+// Registerables is a slice of Registerable
+type Registerables []compbasemetrics.Registerable
+
+// Append adds more
+func (rs Registerables) Append(more ...compbasemetrics.Registerable) Registerables {
+	return append(rs, more...)
+}
+
+var (
+	apiserverRejectedRequestsTotal = compbasemetrics.NewCounterVec(
+		&compbasemetrics.CounterOpts{
+			Namespace:      namespace,
+			Subsystem:      subsystem,
+			Name:           "rejected_requests_total",
+			Help:           "Number of requests rejected by API Priority and Fairness subsystem",
+			StabilityLevel: compbasemetrics.ALPHA,
+		},
+		[]string{priorityLevel, flowSchema, "reason"},
+	)
+	apiserverDispatchedRequestsTotal = compbasemetrics.NewCounterVec(
+		&compbasemetrics.CounterOpts{
+			Namespace:      namespace,
+			Subsystem:      subsystem,
+			Name:           "dispatched_requests_total",
+			Help:           "Number of requests executed by API Priority and Fairness subsystem",
+			StabilityLevel: compbasemetrics.ALPHA,
+		},
+		[]string{priorityLevel, flowSchema},
+	)
+	// PriorityLevelExecutionSeatsGaugeVec creates observers of seats occupied throughout execution for priority levels
+	PriorityLevelExecutionSeatsGaugeVec = NewTimingRatioHistogramVec(
+		&compbasemetrics.TimingHistogramOpts{
+			Namespace: namespace,
+			Subsystem: subsystem,
+			Name:      "priority_level_seat_utilization",
+			Help:      "Observations, at the end of every nanosecond, of utilization of seats for any stage of execution (but only initial stage for WATCHes)",
+			// Buckets for both 0.99 and 1.0 mean PromQL's histogram_quantile will reveal saturation
+			Buckets:        []float64{0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.95, 0.99, 1},
+			ConstLabels:    map[string]string{phase: "executing"},
+			StabilityLevel: compbasemetrics.ALPHA,
+		},
+		priorityLevel,
+	)
+	// PriorityLevelConcurrencyGaugeVec creates gauges of concurrency broken down by phase, priority level
+	PriorityLevelConcurrencyGaugeVec = NewTimingRatioHistogramVec(
+		&compbasemetrics.TimingHistogramOpts{
+			Namespace: namespace,
+			Subsystem: subsystem,
+			Name:      "priority_level_request_utilization",
+			Help:      "Observations, at the end of every nanosecond, of number of requests (as a fraction of the relevant limit) waiting or in any stage of execution (but only initial stage for WATCHes)",
+			// For executing: the denominator will be seats, so this metric will skew low.
+			// For waiting: total queue capacity is generally quite generous, so this metric will skew low.
+			Buckets:        []float64{0, 0.001, 0.003, 0.01, 0.03, 0.1, 0.25, 0.5, 0.75, 1},
+			StabilityLevel: compbasemetrics.ALPHA,
+		},
+		LabelNamePhase, priorityLevel,
+	)
+	// readWriteConcurrencyGaugeVec creates ratioed gauges of requests/limit broken down by phase and mutating vs readonly
+	readWriteConcurrencyGaugeVec = NewTimingRatioHistogramVec(
+		&compbasemetrics.TimingHistogramOpts{
+			Namespace: namespace,
+			Subsystem: subsystem,
+			Name:      "read_vs_write_current_requests",
+			Help:      "Observations, at the end of every nanosecond, of the number of requests (as a fraction of the relevant limit) waiting or in regular stage of execution",
+			// This metric will skew low for the same reason as the priority level metrics
+			// and also because APF has a combined limit for mutating and readonly.
+			Buckets:        []float64{0, 0.001, 0.01, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.95, 0.99, 1},
+			StabilityLevel: compbasemetrics.ALPHA,
+		},
+		LabelNamePhase, requestKind,
+	)
+	apiserverCurrentR = compbasemetrics.NewGaugeVec(
+		&compbasemetrics.GaugeOpts{
+			Namespace:      namespace,
+			Subsystem:      subsystem,
+			Name:           "current_r",
+			Help:           "R(time of last change)",
+			StabilityLevel: compbasemetrics.ALPHA,
+		},
+		[]string{priorityLevel},
+	)
+	apiserverDispatchR = compbasemetrics.NewGaugeVec(
+		&compbasemetrics.GaugeOpts{
+			Namespace:      namespace,
+			Subsystem:      subsystem,
+			Name:           "dispatch_r",
+			Help:           "R(time of last dispatch)",
+			StabilityLevel: compbasemetrics.ALPHA,
+		},
+		[]string{priorityLevel},
+	)
+	apiserverLatestS = compbasemetrics.NewGaugeVec(
+		&compbasemetrics.GaugeOpts{
+			Namespace:      namespace,
+			Subsystem:      subsystem,
+			Name:           "latest_s",
+			Help:           "S(most recently dispatched request)",
+			StabilityLevel: compbasemetrics.ALPHA,
+		},
+		[]string{priorityLevel},
+	)
+	apiserverNextSBounds = compbasemetrics.NewGaugeVec(
+		&compbasemetrics.GaugeOpts{
+			Namespace:      namespace,
+			Subsystem:      subsystem,
+			Name:           "next_s_bounds",
+			Help:           "min and max, over queues, of S(oldest waiting request in queue)",
+			StabilityLevel: compbasemetrics.ALPHA,
+		},
+		[]string{priorityLevel, "bound"},
+	)
+	apiserverNextDiscountedSBounds = compbasemetrics.NewGaugeVec(
+		&compbasemetrics.GaugeOpts{
+			Namespace:      namespace,
+			Subsystem:      subsystem,
+			Name:           "next_discounted_s_bounds",
+			Help:           "min and max, over queues, of S(oldest waiting request in queue) - estimated work in progress",
+			StabilityLevel: compbasemetrics.ALPHA,
+		},
+		[]string{priorityLevel, "bound"},
+	)
+	apiserverCurrentInqueueRequests = compbasemetrics.NewGaugeVec(
+		&compbasemetrics.GaugeOpts{
+			Namespace:      namespace,
+			Subsystem:      subsystem,
+			Name:           "current_inqueue_requests",
+			Help:           "Number of requests currently pending in queues of the API Priority and Fairness subsystem",
+			StabilityLevel: compbasemetrics.ALPHA,
+		},
+		[]string{priorityLevel, flowSchema},
+	)
+	apiserverRequestQueueLength = compbasemetrics.NewHistogramVec(
+		&compbasemetrics.HistogramOpts{
+			Namespace:      namespace,
+			Subsystem:      subsystem,
+			Name:           "request_queue_length_after_enqueue",
+			Help:           "Length of queue in the API Priority and Fairness subsystem, as seen by each request after it is enqueued",
+			Buckets:        queueLengthBuckets,
+			StabilityLevel: compbasemetrics.ALPHA,
+		},
+		[]string{priorityLevel, flowSchema},
+	)
+	apiserverRequestConcurrencyLimit = compbasemetrics.NewGaugeVec(
+		&compbasemetrics.GaugeOpts{
+			Namespace:      namespace,
+			Subsystem:      subsystem,
+			Name:           "request_concurrency_limit",
+			Help:           "Shared concurrency limit in the API Priority and Fairness subsystem",
+			StabilityLevel: compbasemetrics.ALPHA,
+		},
+		[]string{priorityLevel},
+	)
+	apiserverCurrentExecutingRequests = compbasemetrics.NewGaugeVec(
+		&compbasemetrics.GaugeOpts{
+			Namespace:      namespace,
+			Subsystem:      subsystem,
+			Name:           "current_executing_requests",
+			Help:           "Number of requests in initial (for a WATCH) or any (for a non-WATCH) execution stage in the API Priority and Fairness subsystem",
+			StabilityLevel: compbasemetrics.ALPHA,
+		},
+		[]string{priorityLevel, flowSchema},
+	)
+	apiserverRequestConcurrencyInUse = compbasemetrics.NewGaugeVec(
+		&compbasemetrics.GaugeOpts{
+			Namespace:      namespace,
+			Subsystem:      subsystem,
+			Name:           "request_concurrency_in_use",
+			Help:           "Concurrency (number of seats) occupied by the currently executing (initial stage for a WATCH, any stage otherwise) requests in the API Priority and Fairness subsystem",
+			StabilityLevel: compbasemetrics.ALPHA,
+		},
+		[]string{priorityLevel, flowSchema},
+	)
+	apiserverRequestWaitingSeconds = compbasemetrics.NewHistogramVec(
+		&compbasemetrics.HistogramOpts{
+			Namespace:      namespace,
+			Subsystem:      subsystem,
+			Name:           "request_wait_duration_seconds",
+			Help:           "Length of time a request spent waiting in its queue",
+			Buckets:        requestDurationSecondsBuckets,
+			StabilityLevel: compbasemetrics.ALPHA,
+		},
+		[]string{priorityLevel, flowSchema, "execute"},
+	)
+	apiserverRequestExecutionSeconds = compbasemetrics.NewHistogramVec(
+		&compbasemetrics.HistogramOpts{
+			Namespace:      namespace,
+			Subsystem:      subsystem,
+			Name:           "request_execution_seconds",
+			Help:           "Duration of initial stage (for a WATCH) or any (for a non-WATCH) stage of request execution in the API Priority and Fairness subsystem",
+			Buckets:        requestDurationSecondsBuckets,
+			StabilityLevel: compbasemetrics.ALPHA,
+		},
+		[]string{priorityLevel, flowSchema, "type"},
+	)
+	watchCountSamples = compbasemetrics.NewHistogramVec(
+		&compbasemetrics.HistogramOpts{
+			Namespace:      namespace,
+			Subsystem:      subsystem,
+			Name:           "watch_count_samples",
+			Help:           "count of watchers for mutating requests in API Priority and Fairness",
+			Buckets:        []float64{0, 1, 10, 100, 1000, 10000},
+			StabilityLevel: compbasemetrics.ALPHA,
+		},
+		[]string{priorityLevel, flowSchema},
+	)
+	apiserverEpochAdvances = compbasemetrics.NewCounterVec(
+		&compbasemetrics.CounterOpts{
+			Namespace:      namespace,
+			Subsystem:      subsystem,
+			Name:           "epoch_advance_total",
+			Help:           "Number of times the queueset's progress meter jumped backward",
+			StabilityLevel: compbasemetrics.ALPHA,
+		},
+		[]string{priorityLevel, "success"},
+	)
+	apiserverWorkEstimatedSeats = compbasemetrics.NewHistogramVec(
+		&compbasemetrics.HistogramOpts{
+			Namespace: namespace,
+			Subsystem: subsystem,
+			Name:      "work_estimated_seats",
+			Help:      "Number of estimated seats (maximum of initial and final seats) associated with requests in API Priority and Fairness",
+			// the upper bound comes from the maximum number of seats a request
+			// can occupy which is currently set at 10.
+			Buckets:        []float64{1, 2, 4, 10},
+			StabilityLevel: compbasemetrics.ALPHA,
+		},
+		[]string{priorityLevel, flowSchema},
+	)
+	apiserverDispatchWithNoAccommodation = compbasemetrics.NewCounterVec(
+		&compbasemetrics.CounterOpts{
+			Namespace:      namespace,
+			Subsystem:      subsystem,
+			Name:           "request_dispatch_no_accommodation_total",
+			Help:           "Number of times a dispatch attempt resulted in a non accommodation due to lack of available seats",
+			StabilityLevel: compbasemetrics.ALPHA,
+		},
+		[]string{priorityLevel, flowSchema},
+	)
+	apiserverNominalConcurrencyLimits = compbasemetrics.NewGaugeVec(
+		&compbasemetrics.GaugeOpts{
+			Namespace:      namespace,
+			Subsystem:      subsystem,
+			Name:           "nominal_limit_seats",
+			Help:           "Nominal number of execution seats configured for each priority level",
+			StabilityLevel: compbasemetrics.ALPHA,
+		},
+		[]string{priorityLevel},
+	)
+	apiserverMinimumConcurrencyLimits = compbasemetrics.NewGaugeVec(
+		&compbasemetrics.GaugeOpts{
+			Namespace:      namespace,
+			Subsystem:      subsystem,
+			Name:           "lower_limit_seats",
+			Help:           "Configured lower bound on number of execution seats available to each priority level",
+			StabilityLevel: compbasemetrics.ALPHA,
+		},
+		[]string{priorityLevel},
+	)
+	apiserverMaximumConcurrencyLimits = compbasemetrics.NewGaugeVec(
+		&compbasemetrics.GaugeOpts{
+			Namespace:      namespace,
+			Subsystem:      subsystem,
+			Name:           "upper_limit_seats",
+			Help:           "Configured upper bound on number of execution seats available to each priority level",
+			StabilityLevel: compbasemetrics.ALPHA,
+		},
+		[]string{priorityLevel},
+	)
+	ApiserverSeatDemands = NewTimingRatioHistogramVec(
+		&compbasemetrics.TimingHistogramOpts{
+			Namespace: namespace,
+			Subsystem: subsystem,
+			Name:      "demand_seats",
+			Help:      "Observations, at the end of every nanosecond, of (the number of seats each priority level could use) / (nominal number of seats for that level)",
+			// Rationale for the bucket boundaries:
+			// For 0--1, evenly spaced and not too many;
+			// For 1--2, roughly powers of sqrt(sqrt(2));
+			// For 2--6, roughly powers of sqrt(2);
+			// We need coverage over 1, but do not want too many buckets.
+			Buckets:        []float64{0.2, 0.4, 0.6, 0.8, 1, 1.2, 1.4, 1.7, 2, 2.8, 4, 6},
+			StabilityLevel: compbasemetrics.ALPHA,
+		},
+		priorityLevel,
+	)
+	apiserverSeatDemandHighWatermarks = compbasemetrics.NewGaugeVec(
+		&compbasemetrics.GaugeOpts{
+			Namespace:      namespace,
+			Subsystem:      subsystem,
+			Name:           "demand_seats_high_watermark",
+			Help:           "High watermark, over last adjustment period, of demand_seats",
+			StabilityLevel: compbasemetrics.ALPHA,
+		},
+		[]string{priorityLevel},
+	)
+	apiserverSeatDemandAverages = compbasemetrics.NewGaugeVec(
+		&compbasemetrics.GaugeOpts{
+			Namespace:      namespace,
+			Subsystem:      subsystem,
+			Name:           "demand_seats_average",
+			Help:           "Time-weighted average, over last adjustment period, of demand_seats",
+			StabilityLevel: compbasemetrics.ALPHA,
+		},
+		[]string{priorityLevel},
+	)
+	apiserverSeatDemandStandardDeviations = compbasemetrics.NewGaugeVec(
+		&compbasemetrics.GaugeOpts{
+			Namespace:      namespace,
+			Subsystem:      subsystem,
+			Name:           "demand_seats_stdev",
+			Help:           "Time-weighted standard deviation, over last adjustment period, of demand_seats",
+			StabilityLevel: compbasemetrics.ALPHA,
+		},
+		[]string{priorityLevel},
+	)
+	apiserverSeatDemandSmootheds = compbasemetrics.NewGaugeVec(
+		&compbasemetrics.GaugeOpts{
+			Namespace:      namespace,
+			Subsystem:      subsystem,
+			Name:           "demand_seats_smoothed",
+			Help:           "Smoothed seat demands",
+			StabilityLevel: compbasemetrics.ALPHA,
+		},
+		[]string{priorityLevel},
+	)
+	apiserverSeatDemandTargets = compbasemetrics.NewGaugeVec(
+		&compbasemetrics.GaugeOpts{
+			Namespace:      namespace,
+			Subsystem:      subsystem,
+			Name:           "target_seats",
+			Help:           "Seat allocation targets",
+			StabilityLevel: compbasemetrics.ALPHA,
+		},
+		[]string{priorityLevel},
+	)
+	apiserverFairFracs = compbasemetrics.NewGauge(
+		&compbasemetrics.GaugeOpts{
+			Namespace:      namespace,
+			Subsystem:      subsystem,
+			Name:           "seat_fair_frac",
+			Help:           "Fair fraction of server's concurrency to allocate to each priority level that can use it",
+			StabilityLevel: compbasemetrics.ALPHA,
+		})
+	apiserverCurrentConcurrencyLimits = compbasemetrics.NewGaugeVec(
+		&compbasemetrics.GaugeOpts{
+			Namespace:      namespace,
+			Subsystem:      subsystem,
+			Name:           "current_limit_seats",
+			Help:           "current derived number of execution seats available to each priority level",
+			StabilityLevel: compbasemetrics.ALPHA,
+		},
+		[]string{priorityLevel},
+	)
+
+	metrics = Registerables{
+		apiserverRejectedRequestsTotal,
+		apiserverDispatchedRequestsTotal,
+		apiserverCurrentR,
+		apiserverDispatchR,
+		apiserverLatestS,
+		apiserverNextSBounds,
+		apiserverNextDiscountedSBounds,
+		apiserverCurrentInqueueRequests,
+		apiserverRequestQueueLength,
+		apiserverRequestConcurrencyLimit,
+		apiserverRequestConcurrencyInUse,
+		apiserverCurrentExecutingRequests,
+		apiserverRequestWaitingSeconds,
+		apiserverRequestExecutionSeconds,
+		watchCountSamples,
+		apiserverEpochAdvances,
+		apiserverWorkEstimatedSeats,
+		apiserverDispatchWithNoAccommodation,
+		apiserverNominalConcurrencyLimits,
+		apiserverMinimumConcurrencyLimits,
+		apiserverMaximumConcurrencyLimits,
+		apiserverSeatDemandHighWatermarks,
+		apiserverSeatDemandAverages,
+		apiserverSeatDemandStandardDeviations,
+		apiserverSeatDemandSmootheds,
+		apiserverSeatDemandTargets,
+		apiserverFairFracs,
+		apiserverCurrentConcurrencyLimits,
+	}.
+		Append(PriorityLevelExecutionSeatsGaugeVec.metrics()...).
+		Append(PriorityLevelConcurrencyGaugeVec.metrics()...).
+		Append(readWriteConcurrencyGaugeVec.metrics()...).
+		Append(ApiserverSeatDemands.metrics()...)
+)
+
+type indexOnce struct {
+	labelValues []string
+	once        sync.Once
+	gauge       RatioedGauge
+}
+
+func (io *indexOnce) getGauge() RatioedGauge {
+	io.once.Do(func() {
+		io.gauge = readWriteConcurrencyGaugeVec.NewForLabelValuesSafe(0, 1, io.labelValues)
+	})
+	return io.gauge
+}
+
+var waitingReadonly = indexOnce{labelValues: []string{LabelValueWaiting, epmetrics.ReadOnlyKind}}
+var executingReadonly = indexOnce{labelValues: []string{LabelValueExecuting, epmetrics.ReadOnlyKind}}
+var waitingMutating = indexOnce{labelValues: []string{LabelValueWaiting, epmetrics.MutatingKind}}
+var executingMutating = indexOnce{labelValues: []string{LabelValueExecuting, epmetrics.MutatingKind}}
+
+// GetWaitingReadonlyConcurrency returns the gauge of number of readonly requests waiting / limit on those.
+var GetWaitingReadonlyConcurrency = waitingReadonly.getGauge
+
+// GetExecutingReadonlyConcurrency returns the gauge of number of executing readonly requests / limit on those.
+var GetExecutingReadonlyConcurrency = executingReadonly.getGauge
+
+// GetWaitingMutatingConcurrency returns the gauge of number of mutating requests waiting / limit on those.
+var GetWaitingMutatingConcurrency = waitingMutating.getGauge
+
+// GetExecutingMutatingConcurrency returns the gauge of number of executing mutating requests / limit on those.
+var GetExecutingMutatingConcurrency = executingMutating.getGauge
+
+// AddRequestsInQueues adds the given delta to the gauge of the # of requests in the queues of the specified flowSchema and priorityLevel
+func AddRequestsInQueues(ctx context.Context, priorityLevel, flowSchema string, delta int) {
+	apiserverCurrentInqueueRequests.WithLabelValues(priorityLevel, flowSchema).Add(float64(delta))
+}
+
+// AddRequestsExecuting adds the given delta to the gauge of executing requests of the given flowSchema and priorityLevel
+func AddRequestsExecuting(ctx context.Context, priorityLevel, flowSchema string, delta int) {
+	apiserverCurrentExecutingRequests.WithLabelValues(priorityLevel, flowSchema).Add(float64(delta))
+}
+
+// SetCurrentR sets the current-R (virtualTime) gauge for the given priority level
+func SetCurrentR(priorityLevel string, r float64) {
+	apiserverCurrentR.WithLabelValues(priorityLevel).Set(r)
+}
+
+// SetLatestS sets the latest-S (virtual time of dispatched request) gauge for the given priority level
+func SetDispatchMetrics(priorityLevel string, r, s, sMin, sMax, discountedSMin, discountedSMax float64) {
+	apiserverDispatchR.WithLabelValues(priorityLevel).Set(r)
+	apiserverLatestS.WithLabelValues(priorityLevel).Set(s)
+	apiserverNextSBounds.WithLabelValues(priorityLevel, "min").Set(sMin)
+	apiserverNextSBounds.WithLabelValues(priorityLevel, "max").Set(sMax)
+	apiserverNextDiscountedSBounds.WithLabelValues(priorityLevel, "min").Set(discountedSMin)
+	apiserverNextDiscountedSBounds.WithLabelValues(priorityLevel, "max").Set(discountedSMax)
+}
+
+// AddRequestConcurrencyInUse adds the given delta to the gauge of concurrency in use by
+// the currently executing requests of the given flowSchema and priorityLevel
+func AddRequestConcurrencyInUse(priorityLevel, flowSchema string, delta int) {
+	apiserverRequestConcurrencyInUse.WithLabelValues(priorityLevel, flowSchema).Add(float64(delta))
+}
+
+// AddReject increments the # of rejected requests for flow control
+func AddReject(ctx context.Context, priorityLevel, flowSchema, reason string) {
+	apiserverRejectedRequestsTotal.WithContext(ctx).WithLabelValues(priorityLevel, flowSchema, reason).Add(1)
+}
+
+// AddDispatch increments the # of dispatched requests for flow control
+func AddDispatch(ctx context.Context, priorityLevel, flowSchema string) {
+	apiserverDispatchedRequestsTotal.WithContext(ctx).WithLabelValues(priorityLevel, flowSchema).Add(1)
+}
+
+// ObserveQueueLength observes the queue length for flow control
+func ObserveQueueLength(ctx context.Context, priorityLevel, flowSchema string, length int) {
+	apiserverRequestQueueLength.WithContext(ctx).WithLabelValues(priorityLevel, flowSchema).Observe(float64(length))
+}
+
+// ObserveWaitingDuration observes the queue length for flow control
+func ObserveWaitingDuration(ctx context.Context, priorityLevel, flowSchema, execute string, waitTime time.Duration) {
+	apiserverRequestWaitingSeconds.WithContext(ctx).WithLabelValues(priorityLevel, flowSchema, execute).Observe(waitTime.Seconds())
+}
+
+// ObserveExecutionDuration observes the execution duration for flow control
+func ObserveExecutionDuration(ctx context.Context, priorityLevel, flowSchema string, executionTime time.Duration) {
+	reqType := "regular"
+	if requestInfo, ok := apirequest.RequestInfoFrom(ctx); ok && requestInfo.Verb == "watch" {
+		reqType = requestInfo.Verb
+	}
+	apiserverRequestExecutionSeconds.WithContext(ctx).WithLabelValues(priorityLevel, flowSchema, reqType).Observe(executionTime.Seconds())
+}
+
+// ObserveWatchCount notes a sampling of a watch count
+func ObserveWatchCount(ctx context.Context, priorityLevel, flowSchema string, count int) {
+	watchCountSamples.WithLabelValues(priorityLevel, flowSchema).Observe(float64(count))
+}
+
+// AddEpochAdvance notes an advance of the progress meter baseline for a given priority level
+func AddEpochAdvance(ctx context.Context, priorityLevel string, success bool) {
+	apiserverEpochAdvances.WithContext(ctx).WithLabelValues(priorityLevel, strconv.FormatBool(success)).Inc()
+}
+
+// ObserveWorkEstimatedSeats notes a sampling of estimated seats associated with a request
+func ObserveWorkEstimatedSeats(priorityLevel, flowSchema string, seats int) {
+	apiserverWorkEstimatedSeats.WithLabelValues(priorityLevel, flowSchema).Observe(float64(seats))
+}
+
+// AddDispatchWithNoAccommodation keeps track of number of times dispatch attempt results
+// in a non accommodation due to lack of available seats.
+func AddDispatchWithNoAccommodation(priorityLevel, flowSchema string) {
+	apiserverDispatchWithNoAccommodation.WithLabelValues(priorityLevel, flowSchema).Inc()
+}
+
+func SetPriorityLevelConfiguration(priorityLevel string, nominalCL, minCL, maxCL int) {
+	apiserverRequestConcurrencyLimit.WithLabelValues(priorityLevel).Set(float64(nominalCL))
+	apiserverNominalConcurrencyLimits.WithLabelValues(priorityLevel).Set(float64(nominalCL))
+	apiserverMinimumConcurrencyLimits.WithLabelValues(priorityLevel).Set(float64(minCL))
+	apiserverMaximumConcurrencyLimits.WithLabelValues(priorityLevel).Set(float64(maxCL))
+}
+
+func NotePriorityLevelConcurrencyAdjustment(priorityLevel string, seatDemandHWM, seatDemandAvg, seatDemandStdev, seatDemandSmoothed, seatDemandTarget float64, currentCL int) {
+	apiserverSeatDemandHighWatermarks.WithLabelValues(priorityLevel).Set(seatDemandHWM)
+	apiserverSeatDemandAverages.WithLabelValues(priorityLevel).Set(seatDemandAvg)
+	apiserverSeatDemandStandardDeviations.WithLabelValues(priorityLevel).Set(seatDemandStdev)
+	apiserverSeatDemandSmootheds.WithLabelValues(priorityLevel).Set(seatDemandSmoothed)
+	apiserverSeatDemandTargets.WithLabelValues(priorityLevel).Set(seatDemandTarget)
+	apiserverCurrentConcurrencyLimits.WithLabelValues(priorityLevel).Set(float64(currentCL))
+}
+
+func SetFairFrac(fairFrac float64) {
+	apiserverFairFracs.Set(fairFrac)
+}

vendor/k8s.io/apiserver/pkg/util/flowcontrol/metrics/timing_ratio_histogram.go

@@ -0,0 +1,225 @@
+/*
+Copyright 2022 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package metrics
+
+import (
+	"context"
+	"sync"
+	"time"
+
+	compbasemetrics "k8s.io/component-base/metrics"
+	"k8s.io/klog/v2"
+)
+
+// TimingRatioHistogram is essentially a gauge for a ratio where the client
+// independently controls the numerator and denominator.
+// When scraped it produces a histogram of samples of the ratio
+// taken at the end of every nanosecond.
+// `*TimingRatioHistogram` implements both Registerable and RatioedGauge.
+type TimingRatioHistogram struct {
+	// The implementation is layered on TimingHistogram,
+	// adding the division by an occasionally adjusted denominator.
+
+	// Registerable is the registerable aspect.
+	// That is the registerable aspect of the underlying TimingHistogram.
+	compbasemetrics.Registerable
+
+	// timingRatioHistogramInner implements the RatioedGauge aspect.
+	timingRatioHistogramInner
+}
+
+// TimingRatioHistogramOpts is the constructor parameters of a TimingRatioHistogram.
+// The `TimingHistogramOpts.InitialValue` is the initial numerator.
+type TimingRatioHistogramOpts struct {
+	compbasemetrics.TimingHistogramOpts
+	InitialDenominator float64
+}
+
+// timingRatioHistogramInner implements the instrumentation aspect
+type timingRatioHistogramInner struct {
+	nowFunc         func() time.Time
+	getGaugeOfRatio func() Gauge
+	sync.Mutex
+	// access only with mutex locked
+	numerator, denominator float64
+}
+
+var _ RatioedGauge = &timingRatioHistogramInner{}
+var _ RatioedGauge = &TimingRatioHistogram{}
+var _ compbasemetrics.Registerable = &TimingRatioHistogram{}
+
+// NewTimingHistogram returns an object which is TimingHistogram-like. However, nothing
+// will be measured until the histogram is registered in at least one registry.
+func NewTimingRatioHistogram(opts *TimingRatioHistogramOpts) *TimingRatioHistogram {
+	return NewTestableTimingRatioHistogram(time.Now, opts)
+}
+
+// NewTestableTimingHistogram adds injection of the clock
+func NewTestableTimingRatioHistogram(nowFunc func() time.Time, opts *TimingRatioHistogramOpts) *TimingRatioHistogram {
+	ratioedOpts := opts.TimingHistogramOpts
+	ratioedOpts.InitialValue /= opts.InitialDenominator
+	th := compbasemetrics.NewTestableTimingHistogram(nowFunc, &ratioedOpts)
+	return &TimingRatioHistogram{
+		Registerable: th,
+		timingRatioHistogramInner: timingRatioHistogramInner{
+			nowFunc:         nowFunc,
+			getGaugeOfRatio: func() Gauge { return th },
+			numerator:       opts.InitialValue,
+			denominator:     opts.InitialDenominator,
+		}}
+}
+
+func (trh *timingRatioHistogramInner) Set(numerator float64) {
+	trh.Lock()
+	defer trh.Unlock()
+	trh.numerator = numerator
+	ratio := numerator / trh.denominator
+	trh.getGaugeOfRatio().Set(ratio)
+}
+
+func (trh *timingRatioHistogramInner) Add(deltaNumerator float64) {
+	trh.Lock()
+	defer trh.Unlock()
+	numerator := trh.numerator + deltaNumerator
+	trh.numerator = numerator
+	ratio := numerator / trh.denominator
+	trh.getGaugeOfRatio().Set(ratio)
+}
+
+func (trh *timingRatioHistogramInner) Sub(deltaNumerator float64) {
+	trh.Add(-deltaNumerator)
+}
+
+func (trh *timingRatioHistogramInner) Inc() {
+	trh.Add(1)
+}
+
+func (trh *timingRatioHistogramInner) Dec() {
+	trh.Add(-1)
+}
+
+func (trh *timingRatioHistogramInner) SetToCurrentTime() {
+	trh.Set(float64(trh.nowFunc().Sub(time.Unix(0, 0))))
+}
+
+func (trh *timingRatioHistogramInner) SetDenominator(denominator float64) {
+	trh.Lock()
+	defer trh.Unlock()
+	trh.denominator = denominator
+	ratio := trh.numerator / denominator
+	trh.getGaugeOfRatio().Set(ratio)
+}
+
+// WithContext allows the normal TimingHistogram metric to pass in context.
+// The context is no-op at the current level of development.
+func (trh *timingRatioHistogramInner) WithContext(ctx context.Context) RatioedGauge {
+	return trh
+}
+
+// TimingRatioHistogramVec is a collection of TimingRatioHistograms that differ
+// only in label values.
+// `*TimingRatioHistogramVec` implements both Registerable and RatioedGaugeVec.
+type TimingRatioHistogramVec struct {
+	// promote only the Registerable methods
+	compbasemetrics.Registerable
+	// delegate is TimingHistograms of the ratio
+	delegate compbasemetrics.GaugeVecMetric
+}
+
+var _ RatioedGaugeVec = &TimingRatioHistogramVec{}
+var _ compbasemetrics.Registerable = &TimingRatioHistogramVec{}
+
+// NewTimingHistogramVec constructs a new vector.
+// `opts.InitialValue` is the initial ratio, but this applies
+// only for the tiny period of time until NewForLabelValuesSafe sets
+// the ratio based on the given initial numerator and denominator.
+// Thus there is a tiny splinter of time during member construction when
+// its underlying TimingHistogram is given the initial numerator rather than
+// the initial ratio (which is obviously a non-issue when both are zero).
+// Note the difficulties associated with extracting a member
+// before registering the vector.
+func NewTimingRatioHistogramVec(opts *compbasemetrics.TimingHistogramOpts, labelNames ...string) *TimingRatioHistogramVec {
+	return NewTestableTimingRatioHistogramVec(time.Now, opts, labelNames...)
+}
+
+// NewTestableTimingHistogramVec adds injection of the clock.
+func NewTestableTimingRatioHistogramVec(nowFunc func() time.Time, opts *compbasemetrics.TimingHistogramOpts, labelNames ...string) *TimingRatioHistogramVec {
+	delegate := compbasemetrics.NewTestableTimingHistogramVec(nowFunc, opts, labelNames)
+	return &TimingRatioHistogramVec{
+		Registerable: delegate,
+		delegate:     delegate,
+	}
+}
+
+func (v *TimingRatioHistogramVec) metrics() Registerables {
+	return Registerables{v}
+}
+
+// NewForLabelValuesChecked will return an error if this vec is not hidden and not yet registered
+// or there is a syntactic problem with the labelValues.
+func (v *TimingRatioHistogramVec) NewForLabelValuesChecked(initialNumerator, initialDenominator float64, labelValues []string) (RatioedGauge, error) {
+	underMember, err := v.delegate.WithLabelValuesChecked(labelValues...)
+	if err != nil {
+		return noopRatioed{}, err
+	}
+	underMember.Set(initialNumerator / initialDenominator)
+	return &timingRatioHistogramInner{
+		getGaugeOfRatio: func() Gauge { return underMember },
+		numerator:       initialNumerator,
+		denominator:     initialDenominator,
+	}, nil
+}
+
+// NewForLabelValuesSafe is the same as NewForLabelValuesChecked in cases where that does not
+// return an error.  When the unsafe version returns an error due to the vector not being
+// registered yet, the safe version returns an object that implements its methods
+// by looking up the relevant vector member in each call (thus getting a non-noop after registration).
+// In the other error cases the object returned here is a noop.
+func (v *TimingRatioHistogramVec) NewForLabelValuesSafe(initialNumerator, initialDenominator float64, labelValues []string) RatioedGauge {
+	tro, err := v.NewForLabelValuesChecked(initialNumerator, initialDenominator, labelValues)
+	if err == nil {
+		klog.V(3).InfoS("TimingRatioHistogramVec.NewForLabelValuesSafe hit the efficient case", "fqName", v.FQName(), "labelValues", labelValues)
+		return tro
+	}
+	if !compbasemetrics.ErrIsNotRegistered(err) {
+		klog.ErrorS(err, "Failed to extract TimingRatioHistogramVec member, using noop instead", "vectorname", v.FQName(), "labelValues", labelValues)
+		return tro
+	}
+	klog.V(3).InfoS("TimingRatioHistogramVec.NewForLabelValuesSafe hit the inefficient case", "fqName", v.FQName(), "labelValues", labelValues)
+	// At this point we know v.NewForLabelValuesChecked(..) returns a permanent noop,
+	// which we precisely want to avoid using.  Instead, make our own gauge that
+	// fetches the element on every Set.
+	return &timingRatioHistogramInner{
+		getGaugeOfRatio: func() Gauge { return v.delegate.WithLabelValues(labelValues...) },
+		numerator:       initialNumerator,
+		denominator:     initialDenominator,
+	}
+}
+
+type noopRatioed struct{}
+
+func (noopRatioed) Set(float64)            {}
+func (noopRatioed) Add(float64)            {}
+func (noopRatioed) Sub(float64)            {}
+func (noopRatioed) Inc()                   {}
+func (noopRatioed) Dec()                   {}
+func (noopRatioed) SetToCurrentTime()      {}
+func (noopRatioed) SetDenominator(float64) {}
+
+func (v *TimingRatioHistogramVec) Reset() {
+	v.delegate.Reset()
+}

vendor/k8s.io/apiserver/pkg/util/flowcontrol/metrics/union_gauge.go

@@ -0,0 +1,56 @@
+/*
+Copyright 2022 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package metrics
+
+type unionGauge []Gauge
+
+var _ Gauge = unionGauge(nil)
+
+// NewUnionGauge constructs a Gauge that delegates to all of the given Gauges
+func NewUnionGauge(elts ...Gauge) Gauge {
+	return unionGauge(elts)
+}
+
+func (ug unionGauge) Set(x float64) {
+	for _, gauge := range ug {
+		gauge.Set(x)
+	}
+}
+
+func (ug unionGauge) Add(x float64) {
+	for _, gauge := range ug {
+		gauge.Add(x)
+	}
+}
+
+func (ug unionGauge) Inc() {
+	for _, gauge := range ug {
+		gauge.Inc()
+	}
+}
+
+func (ug unionGauge) Dec() {
+	for _, gauge := range ug {
+		gauge.Dec()
+	}
+}
+
+func (ug unionGauge) SetToCurrentTime() {
+	for _, gauge := range ug {
+		gauge.SetToCurrentTime()
+	}
+}

vendor/k8s.io/apiserver/pkg/util/flowcontrol/metrics/vec_element_pair.go

@@ -0,0 +1,25 @@
+/*
+Copyright 2019 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package metrics
+
+// RatioedGaugeVecPhasedElementPair extracts a pair of elements that differ in handling phase
+func RatioedGaugeVecPhasedElementPair(vec RatioedGaugeVec, initialWaitingDenominator, initialExecutingDenominator float64, labelValues []string) RatioedGaugePair {
+	return RatioedGaugePair{
+		RequestsWaiting:   vec.NewForLabelValuesSafe(0, initialWaitingDenominator, append([]string{LabelValueWaiting}, labelValues...)),
+		RequestsExecuting: vec.NewForLabelValuesSafe(0, initialExecutingDenominator, append([]string{LabelValueExecuting}, labelValues...)),
+	}
+}

vendor/k8s.io/apiserver/pkg/util/flowcontrol/request/config.go

@@ -0,0 +1,92 @@
+/*
+Copyright 2022 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package request
+
+import (
+	"time"
+
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+)
+
+const (
+	minimumSeats                = 1
+	maximumSeats                = 10
+	objectsPerSeat              = 100.0
+	watchesPerSeat              = 10.0
+	enableMutatingWorkEstimator = true
+)
+
+var eventAdditionalDuration = 5 * time.Millisecond
+
+// WorkEstimatorConfig holds work estimator parameters.
+type WorkEstimatorConfig struct {
+	*ListWorkEstimatorConfig     `json:"listWorkEstimatorConfig,omitempty"`
+	*MutatingWorkEstimatorConfig `json:"mutatingWorkEstimatorConfig,omitempty"`
+
+	// MinimumSeats is the minimum number of seats a request must occupy.
+	MinimumSeats uint64 `json:"minimumSeats,omitempty"`
+	// MaximumSeats is the maximum number of seats a request can occupy
+	//
+	// NOTE: work_estimate_seats_samples metric uses the value of maximumSeats
+	// as the upper bound, so when we change maximumSeats we should also
+	// update the buckets of the metric.
+	MaximumSeats uint64 `json:"maximumSeats,omitempty"`
+}
+
+// ListWorkEstimatorConfig holds work estimator parameters related to list requests.
+type ListWorkEstimatorConfig struct {
+	ObjectsPerSeat float64 `json:"objectsPerSeat,omitempty"`
+}
+
+// MutatingWorkEstimatorConfig holds work estimator
+// parameters related to watches of mutating objects.
+type MutatingWorkEstimatorConfig struct {
+	// TODO(wojtekt): Remove it once we tune the algorithm to not fail
+	// scalability tests.
+	Enabled                 bool            `json:"enable,omitempty"`
+	EventAdditionalDuration metav1.Duration `json:"eventAdditionalDurationMs,omitempty"`
+	WatchesPerSeat          float64         `json:"watchesPerSeat,omitempty"`
+}
+
+// DefaultWorkEstimatorConfig creates a new WorkEstimatorConfig with default values.
+func DefaultWorkEstimatorConfig() *WorkEstimatorConfig {
+	return &WorkEstimatorConfig{
+		MinimumSeats:                minimumSeats,
+		MaximumSeats:                maximumSeats,
+		ListWorkEstimatorConfig:     defaultListWorkEstimatorConfig(),
+		MutatingWorkEstimatorConfig: defaultMutatingWorkEstimatorConfig(),
+	}
+}
+
+// defaultListWorkEstimatorConfig creates a new ListWorkEstimatorConfig with default values.
+func defaultListWorkEstimatorConfig() *ListWorkEstimatorConfig {
+	return &ListWorkEstimatorConfig{ObjectsPerSeat: objectsPerSeat}
+}
+
+// defaultMutatingWorkEstimatorConfig creates a new MutatingWorkEstimatorConfig with default values.
+func defaultMutatingWorkEstimatorConfig() *MutatingWorkEstimatorConfig {
+	return &MutatingWorkEstimatorConfig{
+		Enabled:                 enableMutatingWorkEstimator,
+		EventAdditionalDuration: metav1.Duration{Duration: eventAdditionalDuration},
+		WatchesPerSeat:          watchesPerSeat,
+	}
+}
+
+// eventAdditionalDuration converts eventAdditionalDurationMs to a time.Duration type.
+func (c *MutatingWorkEstimatorConfig) eventAdditionalDuration() time.Duration {
+	return c.EventAdditionalDuration.Duration
+}

vendor/k8s.io/apiserver/pkg/util/flowcontrol/request/list_work_estimator.go

@@ -0,0 +1,154 @@
+/*
+Copyright 2021 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package request
+
+import (
+	"math"
+	"net/http"
+	"net/url"
+
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/runtime/schema"
+	apirequest "k8s.io/apiserver/pkg/endpoints/request"
+	"k8s.io/apiserver/pkg/features"
+	utilfeature "k8s.io/apiserver/pkg/util/feature"
+	"k8s.io/klog/v2"
+)
+
+func newListWorkEstimator(countFn objectCountGetterFunc, config *WorkEstimatorConfig) WorkEstimatorFunc {
+	estimator := &listWorkEstimator{
+		config:        config,
+		countGetterFn: countFn,
+	}
+	return estimator.estimate
+}
+
+type listWorkEstimator struct {
+	config        *WorkEstimatorConfig
+	countGetterFn objectCountGetterFunc
+}
+
+func (e *listWorkEstimator) estimate(r *http.Request, flowSchemaName, priorityLevelName string) WorkEstimate {
+	requestInfo, ok := apirequest.RequestInfoFrom(r.Context())
+	if !ok {
+		// no RequestInfo should never happen, but to be on the safe side
+		// let's return maximumSeats
+		return WorkEstimate{InitialSeats: e.config.MaximumSeats}
+	}
+
+	if requestInfo.Name != "" {
+		// Requests with metadata.name specified are usually executed as get
+		// requests in storage layer so their width should be 1.
+		// Example of such list requests:
+		// /apis/certificates.k8s.io/v1/certificatesigningrequests?fieldSelector=metadata.name%3Dcsr-xxs4m
+		// /api/v1/namespaces/test/configmaps?fieldSelector=metadata.name%3Dbig-deployment-1&limit=500&resourceVersion=0
+		return WorkEstimate{InitialSeats: e.config.MinimumSeats}
+	}
+
+	query := r.URL.Query()
+	listOptions := metav1.ListOptions{}
+	if err := metav1.Convert_url_Values_To_v1_ListOptions(&query, &listOptions, nil); err != nil {
+		klog.ErrorS(err, "Failed to convert options while estimating work for the list request")
+
+		// This request is destined to fail in the validation layer,
+		// return maximumSeats for this request to be consistent.
+		return WorkEstimate{InitialSeats: e.config.MaximumSeats}
+	}
+	isListFromCache := !shouldListFromStorage(query, &listOptions)
+
+	numStored, err := e.countGetterFn(key(requestInfo))
+	switch {
+	case err == ObjectCountStaleErr:
+		// object count going stale is indicative of degradation, so we should
+		// be conservative here and allocate maximum seats to this list request.
+		// NOTE: if a CRD is removed, its count will go stale first and then the
+		// pruner will eventually remove the CRD from the cache.
+		return WorkEstimate{InitialSeats: e.config.MaximumSeats}
+	case err == ObjectCountNotFoundErr:
+		// there are multiple scenarios in which we can see this error:
+		//  a. the type is truly unknown, a typo on the caller's part.
+		//  b. the count has gone stale for too long and the pruner
+		//     has removed the type from the cache.
+		//  c. the type is an aggregated resource that is served by a
+		//     different apiserver (thus its object count is not updated)
+		// we don't have a way to distinguish between those situations.
+		// However, in case c, the request is delegated to a different apiserver,
+		// and thus its cost for our server is minimal. To avoid the situation
+		// when aggregated API calls are overestimated, we allocate the minimum
+		// possible seats (see #109106 as an example when being more conservative
+		// led to problems).
+		return WorkEstimate{InitialSeats: e.config.MinimumSeats}
+	case err != nil:
+		// we should never be here since Get returns either ObjectCountStaleErr or
+		// ObjectCountNotFoundErr, return maximumSeats to be on the safe side.
+		klog.ErrorS(err, "Unexpected error from object count tracker")
+		return WorkEstimate{InitialSeats: e.config.MaximumSeats}
+	}
+
+	limit := numStored
+	if utilfeature.DefaultFeatureGate.Enabled(features.APIListChunking) && listOptions.Limit > 0 &&
+		listOptions.Limit < numStored {
+		limit = listOptions.Limit
+	}
+
+	var estimatedObjectsToBeProcessed int64
+
+	switch {
+	case isListFromCache:
+		// TODO: For resources that implement indexes at the watchcache level,
+		//  we need to adjust the cost accordingly
+		estimatedObjectsToBeProcessed = numStored
+	case listOptions.FieldSelector != "" || listOptions.LabelSelector != "":
+		estimatedObjectsToBeProcessed = numStored + limit
+	default:
+		estimatedObjectsToBeProcessed = 2 * limit
+	}
+
+	// for now, our rough estimate is to allocate one seat to each 100 obejcts that
+	// will be processed by the list request.
+	// we will come up with a different formula for the transformation function and/or
+	// fine tune this number in future iteratons.
+	seats := uint64(math.Ceil(float64(estimatedObjectsToBeProcessed) / e.config.ObjectsPerSeat))
+
+	// make sure we never return a seat of zero
+	if seats < e.config.MinimumSeats {
+		seats = e.config.MinimumSeats
+	}
+	if seats > e.config.MaximumSeats {
+		seats = e.config.MaximumSeats
+	}
+	return WorkEstimate{InitialSeats: seats}
+}
+
+func key(requestInfo *apirequest.RequestInfo) string {
+	groupResource := &schema.GroupResource{
+		Group:    requestInfo.APIGroup,
+		Resource: requestInfo.Resource,
+	}
+	return groupResource.String()
+}
+
+// NOTICE: Keep in sync with shouldDelegateList function in
+//
+//	staging/src/k8s.io/apiserver/pkg/storage/cacher/cacher.go
+func shouldListFromStorage(query url.Values, opts *metav1.ListOptions) bool {
+	resourceVersion := opts.ResourceVersion
+	pagingEnabled := utilfeature.DefaultFeatureGate.Enabled(features.APIListChunking)
+	hasContinuation := pagingEnabled && len(opts.Continue) > 0
+	hasLimit := pagingEnabled && opts.Limit > 0 && resourceVersion != "0"
+	return resourceVersion == "" || hasContinuation || hasLimit || opts.ResourceVersionMatch == metav1.ResourceVersionMatchExact
+}

vendor/k8s.io/apiserver/pkg/util/flowcontrol/request/mutating_work_estimator.go

@@ -0,0 +1,149 @@
+/*
+Copyright 2021 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package request
+
+import (
+	"math"
+	"net/http"
+	"time"
+
+	apirequest "k8s.io/apiserver/pkg/endpoints/request"
+	"k8s.io/apiserver/pkg/util/flowcontrol/metrics"
+)
+
+func newMutatingWorkEstimator(countFn watchCountGetterFunc, config *WorkEstimatorConfig) WorkEstimatorFunc {
+	estimator := &mutatingWorkEstimator{
+		config:  config,
+		countFn: countFn,
+	}
+	return estimator.estimate
+}
+
+type mutatingWorkEstimator struct {
+	config  *WorkEstimatorConfig
+	countFn watchCountGetterFunc
+}
+
+func (e *mutatingWorkEstimator) estimate(r *http.Request, flowSchemaName, priorityLevelName string) WorkEstimate {
+	// TODO(wojtekt): Remove once we tune the algorithm to not fail
+	// scalability tests.
+	if !e.config.Enabled {
+		return WorkEstimate{
+			InitialSeats: 1,
+		}
+	}
+
+	requestInfo, ok := apirequest.RequestInfoFrom(r.Context())
+	if !ok {
+		// no RequestInfo should never happen, but to be on the safe side
+		// let's return a large value.
+		return WorkEstimate{
+			InitialSeats:      1,
+			FinalSeats:        e.config.MaximumSeats,
+			AdditionalLatency: e.config.eventAdditionalDuration(),
+		}
+	}
+
+	if isRequestExemptFromWatchEvents(requestInfo) {
+		return WorkEstimate{
+			InitialSeats:      e.config.MinimumSeats,
+			FinalSeats:        0,
+			AdditionalLatency: time.Duration(0),
+		}
+	}
+
+	watchCount := e.countFn(requestInfo)
+	metrics.ObserveWatchCount(r.Context(), priorityLevelName, flowSchemaName, watchCount)
+
+	// The cost of the request associated with the watchers of that event
+	// consists of three parts:
+	// - cost of going through the event change logic
+	// - cost of serialization of the event
+	// - cost of processing an event object for each watcher (e.g. filtering,
+	//     sending data over network)
+	// We're starting simple to get some operational experience with it and
+	// we will work on tuning the algorithm later. Given that the actual work
+	// associated with processing watch events is happening in multiple
+	// goroutines (proportional to the number of watchers) that are all
+	// resumed at once, as a starting point we assume that each such goroutine
+	// is taking 1/Nth of a seat for M milliseconds.
+	// We allow the accounting of that work in P&F to be reshaped into another
+	// rectangle of equal area for practical reasons.
+	var finalSeats uint64
+	var additionalLatency time.Duration
+
+	// TODO: Make this unconditional after we tune the algorithm better.
+	//   Technically, there is an overhead connected to processing an event after
+	//   the request finishes even if there is a small number of watches.
+	//   However, until we tune the estimation we want to stay on the safe side
+	//   an avoid introducing additional latency for almost every single request.
+	if watchCount >= int(e.config.WatchesPerSeat) {
+		// TODO: As described in the KEP, we should take into account that not all
+		//   events are equal and try to estimate the cost of a single event based on
+		//   some historical data about size of events.
+		finalSeats = uint64(math.Ceil(float64(watchCount) / e.config.WatchesPerSeat))
+		finalWork := SeatsTimesDuration(float64(finalSeats), e.config.eventAdditionalDuration())
+
+		// While processing individual events is highly parallel,
+		// the design/implementation of P&F has a couple limitations that
+		// make using this assumption in the P&F implementation very
+		// inefficient because:
+		// - we reserve max(initialSeats, finalSeats) for time of executing
+		//   both phases of the request
+		// - even more importantly, when a given `wide` request is the one to
+		//   be dispatched, we are not dispatching any other request until
+		//   we accumulate enough seats to dispatch the nominated one, even
+		//   if currently unoccupied seats would allow for dispatching some
+		//   other requests in the meantime
+		// As a consequence of these, the wider the request, the more capacity
+		// will effectively be blocked and unused during dispatching and
+		// executing this request.
+		//
+		// To mitigate the impact of it, we're capping the maximum number of
+		// seats that can be assigned to a given request. Thanks to it:
+		// 1) we reduce the amount of seat-seconds that are "wasted" during
+		//    dispatching and executing initial phase of the request
+		// 2) we are not changing the finalWork estimate - just potentially
+		//    reshaping it to be narrower and longer. As long as the maximum
+		//    seats setting will prevent dispatching too many requests at once
+		//    to prevent overloading kube-apiserver (and/or etcd or the VM or
+		//    a physical machine it is running on), we believe the relaxed
+		//    version should be good enough to achieve the P&F goals.
+		//
+		// TODO: Confirm that the current cap of maximumSeats allow us to
+		//   achieve the above.
+		if finalSeats > e.config.MaximumSeats {
+			finalSeats = e.config.MaximumSeats
+		}
+		additionalLatency = finalWork.DurationPerSeat(float64(finalSeats))
+	}
+
+	return WorkEstimate{
+		InitialSeats:      1,
+		FinalSeats:        finalSeats,
+		AdditionalLatency: additionalLatency,
+	}
+}
+
+func isRequestExemptFromWatchEvents(requestInfo *apirequest.RequestInfo) bool {
+	// Creating token for service account does not produce any event,
+	// but still serviceaccounts can have multiple watchers.
+	if requestInfo.Resource == "serviceaccounts" && requestInfo.Subresource == "token" {
+		return true
+	}
+	return false
+}

vendor/k8s.io/apiserver/pkg/util/flowcontrol/request/object_count_tracker.go

@@ -0,0 +1,169 @@
+/*
+Copyright 2021 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package request
+
+import (
+	"errors"
+	"sync"
+	"time"
+
+	"k8s.io/apimachinery/pkg/util/wait"
+	"k8s.io/klog/v2"
+	"k8s.io/utils/clock"
+)
+
+const (
+	// type deletion (it applies mostly to CRD) is not a very frequent
+	// operation so we can afford to prune the cache at a large interval.
+	// at the same time, we also want to make sure that the scalability
+	// tests hit this code path.
+	pruneInterval = 1 * time.Hour
+
+	// the storage layer polls for object count at every 1m interval, we will allow
+	// up to 2-3 transient failures to get the latest count for a given resource.
+	staleTolerationThreshold = 3 * time.Minute
+)
+
+var (
+	// ObjectCountNotFoundErr is returned when the object count for
+	// a given resource is not being tracked.
+	ObjectCountNotFoundErr = errors.New("object count not found for the given resource")
+
+	// ObjectCountStaleErr is returned when the object count for a
+	// given resource has gone stale due to transient failures.
+	ObjectCountStaleErr = errors.New("object count has gone stale for the given resource")
+)
+
+// StorageObjectCountTracker is an interface that is used to keep track of
+// of the total number of objects for each resource.
+// {group}.{resource} is used as the key name to update and retrieve
+// the total number of objects for a given resource.
+type StorageObjectCountTracker interface {
+	// Set is invoked to update the current number of total
+	// objects for the given resource
+	Set(string, int64)
+
+	// Get returns the total number of objects for the given resource.
+	// The following errors are returned:
+	//  - if the count has gone stale for a given resource due to transient
+	//    failures ObjectCountStaleErr is returned.
+	//  - if the given resource is not being tracked then
+	//    ObjectCountNotFoundErr is returned.
+	Get(string) (int64, error)
+
+	// RunUntil starts all the necessary maintenance.
+	RunUntil(stopCh <-chan struct{})
+}
+
+// NewStorageObjectCountTracker returns an instance of
+// StorageObjectCountTracker interface that can be used to
+// keep track of the total number of objects for each resource.
+func NewStorageObjectCountTracker() StorageObjectCountTracker {
+	return &objectCountTracker{
+		clock:  &clock.RealClock{},
+		counts: map[string]*timestampedCount{},
+	}
+}
+
+// timestampedCount stores the count of a given resource with a last updated
+// timestamp so we can prune it after it goes stale for certain threshold.
+type timestampedCount struct {
+	count         int64
+	lastUpdatedAt time.Time
+}
+
+// objectCountTracker implements StorageObjectCountTracker with
+// reader/writer mutual exclusion lock.
+type objectCountTracker struct {
+	clock clock.PassiveClock
+
+	lock   sync.RWMutex
+	counts map[string]*timestampedCount
+}
+
+func (t *objectCountTracker) Set(groupResource string, count int64) {
+	if count <= -1 {
+		// a value of -1 indicates that the 'Count' call failed to contact
+		// the storage layer, in most cases this error can be transient.
+		// we will continue to work with the count that is in the cache
+		// up to a certain threshold defined by staleTolerationThreshold.
+		// in case this becomes a non transient error then the count for
+		// the given resource will will eventually be removed from
+		// the cache by the pruner.
+		return
+	}
+
+	now := t.clock.Now()
+
+	// lock for writing
+	t.lock.Lock()
+	defer t.lock.Unlock()
+
+	if item, ok := t.counts[groupResource]; ok {
+		item.count = count
+		item.lastUpdatedAt = now
+		return
+	}
+
+	t.counts[groupResource] = &timestampedCount{
+		count:         count,
+		lastUpdatedAt: now,
+	}
+}
+
+func (t *objectCountTracker) Get(groupResource string) (int64, error) {
+	staleThreshold := t.clock.Now().Add(-staleTolerationThreshold)
+
+	t.lock.RLock()
+	defer t.lock.RUnlock()
+
+	if item, ok := t.counts[groupResource]; ok {
+		if item.lastUpdatedAt.Before(staleThreshold) {
+			return item.count, ObjectCountStaleErr
+		}
+		return item.count, nil
+	}
+	return 0, ObjectCountNotFoundErr
+}
+
+// RunUntil runs all the necessary maintenance.
+func (t *objectCountTracker) RunUntil(stopCh <-chan struct{}) {
+	wait.PollUntil(
+		pruneInterval,
+		func() (bool, error) {
+			// always prune at every pruneInterval
+			return false, t.prune(pruneInterval)
+		}, stopCh)
+	klog.InfoS("StorageObjectCountTracker pruner is exiting")
+}
+
+func (t *objectCountTracker) prune(threshold time.Duration) error {
+	oldestLastUpdatedAtAllowed := t.clock.Now().Add(-threshold)
+
+	// lock for writing
+	t.lock.Lock()
+	defer t.lock.Unlock()
+
+	for groupResource, count := range t.counts {
+		if count.lastUpdatedAt.After(oldestLastUpdatedAtAllowed) {
+			continue
+		}
+		delete(t.counts, groupResource)
+	}
+
+	return nil
+}

vendor/k8s.io/apiserver/pkg/util/flowcontrol/request/seat_seconds.go

@@ -0,0 +1,65 @@
+/*
+Copyright 2021 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package request
+
+import (
+	"fmt"
+	"math"
+	"time"
+)
+
+// SeatSeconds is a measure of work, in units of seat-seconds, using a fixed-point representation.
+// `SeatSeconds(n)` represents `n/ssScale` seat-seconds.
+// The `ssScale` constant is private to the implementation here,
+// no other code should use it.
+type SeatSeconds uint64
+
+// MaxSeatsSeconds is the maximum representable value of SeatSeconds
+const MaxSeatSeconds = SeatSeconds(math.MaxUint64)
+
+// MinSeatSeconds is the lowest representable value of SeatSeconds
+const MinSeatSeconds = SeatSeconds(0)
+
+// SeatsTimeDuration produces the SeatSeconds value for the given factors.
+// This is intended only to produce small values, increments in work
+// rather than amount of work done since process start.
+func SeatsTimesDuration(seats float64, duration time.Duration) SeatSeconds {
+	return SeatSeconds(math.Round(seats * float64(duration/time.Nanosecond) / (1e9 / ssScale)))
+}
+
+// ToFloat converts to a floating-point representation.
+// This conversion may lose precision.
+func (ss SeatSeconds) ToFloat() float64 {
+	return float64(ss) / ssScale
+}
+
+// DurationPerSeat returns duration per seat.
+// This division may lose precision.
+func (ss SeatSeconds) DurationPerSeat(seats float64) time.Duration {
+	return time.Duration(float64(ss) / seats * (float64(time.Second) / ssScale))
+}
+
+// String converts to a string.
+// This is suitable for large as well as small values.
+func (ss SeatSeconds) String() string {
+	const div = SeatSeconds(ssScale)
+	quo := ss / div
+	rem := ss - quo*div
+	return fmt.Sprintf("%d.%08dss", quo, rem)
+}
+
+const ssScale = 1e8

vendor/k8s.io/apiserver/pkg/util/flowcontrol/request/width.go

@@ -0,0 +1,113 @@
+/*
+Copyright 2021 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package request
+
+import (
+	"fmt"
+	"net/http"
+	"time"
+
+	apirequest "k8s.io/apiserver/pkg/endpoints/request"
+	"k8s.io/klog/v2"
+)
+
+// WorkEstimate carries three of the four parameters that determine the work in a request.
+// The fourth parameter is the duration of the initial phase of execution.
+type WorkEstimate struct {
+	// InitialSeats is the number of seats occupied while the server is
+	// executing this request.
+	InitialSeats uint64
+
+	// FinalSeats is the number of seats occupied at the end,
+	// during the AdditionalLatency.
+	FinalSeats uint64
+
+	// AdditionalLatency specifies the additional duration the seats allocated
+	// to this request must be reserved after the given request had finished.
+	// AdditionalLatency should not have any impact on the user experience, the
+	// caller must not experience this additional latency.
+	AdditionalLatency time.Duration
+}
+
+// MaxSeats returns the maximum number of seats the request occupies over the
+// phases of being served.
+func (we *WorkEstimate) MaxSeats() int {
+	if we.InitialSeats >= we.FinalSeats {
+		return int(we.InitialSeats)
+	}
+
+	return int(we.FinalSeats)
+}
+
+// objectCountGetterFunc represents a function that gets the total
+// number of objects for a given resource.
+type objectCountGetterFunc func(string) (int64, error)
+
+// watchCountGetterFunc represents a function that gets the total
+// number of watchers potentially interested in a given request.
+type watchCountGetterFunc func(*apirequest.RequestInfo) int
+
+// NewWorkEstimator estimates the work that will be done by a given request,
+// if no WorkEstimatorFunc matches the given request then the default
+// work estimate of 1 seat is allocated to the request.
+func NewWorkEstimator(objectCountFn objectCountGetterFunc, watchCountFn watchCountGetterFunc, config *WorkEstimatorConfig) WorkEstimatorFunc {
+	estimator := &workEstimator{
+		minimumSeats:          config.MinimumSeats,
+		maximumSeats:          config.MaximumSeats,
+		listWorkEstimator:     newListWorkEstimator(objectCountFn, config),
+		mutatingWorkEstimator: newMutatingWorkEstimator(watchCountFn, config),
+	}
+	return estimator.estimate
+}
+
+// WorkEstimatorFunc returns the estimated work of a given request.
+// This function will be used by the Priority & Fairness filter to
+// estimate the work of of incoming requests.
+type WorkEstimatorFunc func(request *http.Request, flowSchemaName, priorityLevelName string) WorkEstimate
+
+func (e WorkEstimatorFunc) EstimateWork(r *http.Request, flowSchemaName, priorityLevelName string) WorkEstimate {
+	return e(r, flowSchemaName, priorityLevelName)
+}
+
+type workEstimator struct {
+	// the minimum number of seats a request must occupy
+	minimumSeats uint64
+	// the maximum number of seats a request can occupy
+	maximumSeats uint64
+	// listWorkEstimator estimates work for list request(s)
+	listWorkEstimator WorkEstimatorFunc
+	// mutatingWorkEstimator calculates the width of mutating request(s)
+	mutatingWorkEstimator WorkEstimatorFunc
+}
+
+func (e *workEstimator) estimate(r *http.Request, flowSchemaName, priorityLevelName string) WorkEstimate {
+	requestInfo, ok := apirequest.RequestInfoFrom(r.Context())
+	if !ok {
+		klog.ErrorS(fmt.Errorf("no RequestInfo found in context"), "Failed to estimate work for the request", "URI", r.RequestURI)
+		// no RequestInfo should never happen, but to be on the safe side let's return maximumSeats
+		return WorkEstimate{InitialSeats: e.maximumSeats}
+	}
+
+	switch requestInfo.Verb {
+	case "list":
+		return e.listWorkEstimator.EstimateWork(r, flowSchemaName, priorityLevelName)
+	case "create", "update", "patch", "delete":
+		return e.mutatingWorkEstimator.EstimateWork(r, flowSchemaName, priorityLevelName)
+	}
+
+	return WorkEstimate{InitialSeats: e.minimumSeats}
+}

vendor/k8s.io/apiserver/pkg/util/flowcontrol/rule.go

@@ -0,0 +1,203 @@
+/*
+Copyright 2019 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package flowcontrol
+
+import (
+	"strings"
+
+	flowcontrol "k8s.io/api/flowcontrol/v1beta3"
+	"k8s.io/apiserver/pkg/authentication/serviceaccount"
+	"k8s.io/apiserver/pkg/authentication/user"
+	"k8s.io/apiserver/pkg/endpoints/request"
+)
+
+// Tests whether a given request and FlowSchema match.  Nobody mutates
+// either input.
+func matchesFlowSchema(digest RequestDigest, flowSchema *flowcontrol.FlowSchema) bool {
+	for _, policyRule := range flowSchema.Spec.Rules {
+		if matchesPolicyRule(digest, &policyRule) {
+			return true
+		}
+	}
+	return false
+}
+
+func matchesPolicyRule(digest RequestDigest, policyRule *flowcontrol.PolicyRulesWithSubjects) bool {
+	if !matchesASubject(digest.User, policyRule.Subjects) {
+		return false
+	}
+	if digest.RequestInfo.IsResourceRequest {
+		return matchesAResourceRule(digest.RequestInfo, policyRule.ResourceRules)
+	}
+	return matchesANonResourceRule(digest.RequestInfo, policyRule.NonResourceRules)
+}
+
+func matchesASubject(user user.Info, subjects []flowcontrol.Subject) bool {
+	for _, subject := range subjects {
+		if matchesSubject(user, subject) {
+			return true
+		}
+	}
+	return false
+}
+
+func matchesSubject(user user.Info, subject flowcontrol.Subject) bool {
+	switch subject.Kind {
+	case flowcontrol.SubjectKindUser:
+		return subject.User != nil && (subject.User.Name == flowcontrol.NameAll || subject.User.Name == user.GetName())
+	case flowcontrol.SubjectKindGroup:
+		if subject.Group == nil {
+			return false
+		}
+		seek := subject.Group.Name
+		if seek == "*" {
+			return true
+		}
+		for _, userGroup := range user.GetGroups() {
+			if userGroup == seek {
+				return true
+			}
+		}
+		return false
+	case flowcontrol.SubjectKindServiceAccount:
+		if subject.ServiceAccount == nil {
+			return false
+		}
+		if subject.ServiceAccount.Name == flowcontrol.NameAll {
+			return serviceAccountMatchesNamespace(subject.ServiceAccount.Namespace, user.GetName())
+		}
+		return serviceaccount.MatchesUsername(subject.ServiceAccount.Namespace, subject.ServiceAccount.Name, user.GetName())
+	default:
+		return false
+	}
+}
+
+// serviceAccountMatchesNamespace checks whether the provided service account username matches the namespace, without
+// allocating. Use this when checking a service account namespace against a known string.
+// This is copied from `k8s.io/apiserver/pkg/authentication/serviceaccount::MatchesUsername` and simplified to not check the name part.
+func serviceAccountMatchesNamespace(namespace string, username string) bool {
+	const (
+		ServiceAccountUsernamePrefix    = "system:serviceaccount:"
+		ServiceAccountUsernameSeparator = ":"
+	)
+	if !strings.HasPrefix(username, ServiceAccountUsernamePrefix) {
+		return false
+	}
+	username = username[len(ServiceAccountUsernamePrefix):]
+
+	if !strings.HasPrefix(username, namespace) {
+		return false
+	}
+	username = username[len(namespace):]
+
+	return strings.HasPrefix(username, ServiceAccountUsernameSeparator)
+}
+
+func matchesAResourceRule(ri *request.RequestInfo, rules []flowcontrol.ResourcePolicyRule) bool {
+	for _, rr := range rules {
+		if matchesResourcePolicyRule(ri, rr) {
+			return true
+		}
+	}
+	return false
+}
+
+func matchesResourcePolicyRule(ri *request.RequestInfo, policyRule flowcontrol.ResourcePolicyRule) bool {
+	if !matchPolicyRuleVerb(policyRule.Verbs, ri.Verb) {
+		return false
+	}
+	if !matchPolicyRuleResource(policyRule.Resources, ri.Resource, ri.Subresource) {
+		return false
+	}
+	if !matchPolicyRuleAPIGroup(policyRule.APIGroups, ri.APIGroup) {
+		return false
+	}
+	if len(ri.Namespace) == 0 {
+		return policyRule.ClusterScope
+	}
+	return containsString(ri.Namespace, policyRule.Namespaces, flowcontrol.NamespaceEvery)
+}
+
+func matchesANonResourceRule(ri *request.RequestInfo, rules []flowcontrol.NonResourcePolicyRule) bool {
+	for _, rr := range rules {
+		if matchesNonResourcePolicyRule(ri, rr) {
+			return true
+		}
+	}
+	return false
+}
+
+func matchesNonResourcePolicyRule(ri *request.RequestInfo, policyRule flowcontrol.NonResourcePolicyRule) bool {
+	if !matchPolicyRuleVerb(policyRule.Verbs, ri.Verb) {
+		return false
+	}
+	return matchPolicyRuleNonResourceURL(policyRule.NonResourceURLs, ri.Path)
+}
+
+func matchPolicyRuleVerb(policyRuleVerbs []string, requestVerb string) bool {
+	return containsString(requestVerb, policyRuleVerbs, flowcontrol.VerbAll)
+}
+
+func matchPolicyRuleNonResourceURL(policyRuleRequestURLs []string, requestPath string) bool {
+	for _, rulePath := range policyRuleRequestURLs {
+		if rulePath == flowcontrol.NonResourceAll || rulePath == requestPath {
+			return true
+		}
+		rulePrefix := strings.TrimSuffix(rulePath, "*")
+		if !strings.HasSuffix(rulePrefix, "/") {
+			rulePrefix = rulePrefix + "/"
+		}
+		if strings.HasPrefix(requestPath, rulePrefix) {
+			return true
+		}
+	}
+	return false
+}
+
+func matchPolicyRuleAPIGroup(policyRuleAPIGroups []string, requestAPIGroup string) bool {
+	return containsString(requestAPIGroup, policyRuleAPIGroups, flowcontrol.APIGroupAll)
+}
+
+func rsJoin(requestResource, requestSubresource string) string {
+	seekString := requestResource
+	if requestSubresource != "" {
+		seekString = requestResource + "/" + requestSubresource
+	}
+	return seekString
+}
+
+func matchPolicyRuleResource(policyRuleRequestResources []string, requestResource, requestSubresource string) bool {
+	return containsString(rsJoin(requestResource, requestSubresource), policyRuleRequestResources, flowcontrol.ResourceAll)
+}
+
+// containsString returns true if either `x` or `wildcard` is in
+// `list`.  The wildcard is not a pattern to match against `x`; rather
+// the presence of the wildcard in the list is the caller's way of
+// saying that all values of `x` should match the list.  This function
+// assumes that if `wildcard` is in `list` then it is the only member
+// of the list, which is enforced by validation.
+func containsString(x string, list []string, wildcard string) bool {
+	if len(list) == 1 && list[0] == wildcard {
+		return true
+	}
+	for _, y := range list {
+		if x == y {
+			return true
+		}
+	}
+	return false
+}

vendor/k8s.io/apiserver/pkg/util/flowcontrol/watch_tracker.go

@@ -0,0 +1,234 @@
+/*
+Copyright 2021 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package flowcontrol
+
+import (
+	"net/http"
+	"sync"
+
+	metainternalversion "k8s.io/apimachinery/pkg/apis/meta/internalversion"
+	"k8s.io/apimachinery/pkg/apis/meta/internalversion/scheme"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/util/sets"
+	"k8s.io/apiserver/pkg/endpoints/request"
+
+	"k8s.io/klog/v2"
+)
+
+// readOnlyVerbs contains verbs for read-only requests.
+var readOnlyVerbs = sets.NewString("get", "list", "watch", "proxy")
+
+// watchIdentifier identifies group of watches that are similar.
+// As described in the "Priority and Fairness" KEP, we consider
+// watches similar if they have the same resourceType, namespace
+// and name. We ignore selectors as they have to be evaluated
+// when processing an even anyway.
+//
+// TODO: For now we only track the number of watches registered
+// in our kube-apiserver. Eventually we should consider sharing
+// this information with other kube-apiserver as described in the
+// KEP, but this isn't part of the first version.
+type watchIdentifier struct {
+	apiGroup  string
+	resource  string
+	namespace string
+	name      string
+}
+
+// ForgetWatchFunc is a function that should be called to forget
+// the previously registered watch from the watch tracker.
+type ForgetWatchFunc func()
+
+// WatchTracker is an interface that allows tracking the number
+// of watches in the system for the purpose of estimating the
+// cost of incoming mutating requests.
+type WatchTracker interface {
+	// RegisterWatch reqisters a watch based on the provided http.Request
+	// in the tracker. It returns the function that should be called
+	// to forget the watcher once it is finished.
+	RegisterWatch(r *http.Request) ForgetWatchFunc
+
+	// GetInterestedWatchCount returns the number of watches that are
+	// potentially interested in a request with a given RequestInfo
+	// for the purpose of estimating cost of that request.
+	GetInterestedWatchCount(requestInfo *request.RequestInfo) int
+}
+
+// builtinIndexes represents of set of indexes registered in
+// watchcache that are indexing watches and increase speed of
+// their processing.
+// We define the indexes as a map from a resource to the path
+// to the field in the object on which the index is built.
+type builtinIndexes map[string]string
+
+func getBuiltinIndexes() builtinIndexes {
+	// The only existing indexes as of now are:
+	// - spec.nodeName for pods
+	// - metadata.Name for nodes, secrets and configmaps
+	// However, we can ignore the latter, because the requestInfo.Name
+	// is set for them (i.e. we already catch them correctly).
+	return map[string]string{
+		"pods": "spec.nodeName",
+	}
+}
+
+// watchTracker tracks the number of watches in the system for
+// the purpose of estimating the cost of incoming mutating requests.
+type watchTracker struct {
+	// indexes represents a set of registered indexes.
+	// It can't change after creation.
+	indexes builtinIndexes
+
+	lock       sync.Mutex
+	watchCount map[watchIdentifier]int
+}
+
+func NewWatchTracker() WatchTracker {
+	return &watchTracker{
+		indexes:    getBuiltinIndexes(),
+		watchCount: make(map[watchIdentifier]int),
+	}
+}
+
+const (
+	unsetValue = "<unset>"
+)
+
+func getIndexValue(r *http.Request, field string) string {
+	opts := metainternalversion.ListOptions{}
+	if err := scheme.ParameterCodec.DecodeParameters(r.URL.Query(), metav1.SchemeGroupVersion, &opts); err != nil {
+		klog.Warningf("Couldn't parse list options for %v: %v", r.URL.Query(), err)
+		return unsetValue
+	}
+	if opts.FieldSelector == nil {
+		return unsetValue
+	}
+	if value, ok := opts.FieldSelector.RequiresExactMatch(field); ok {
+		return value
+	}
+	return unsetValue
+}
+
+type indexValue struct {
+	resource string
+	value    string
+}
+
+// RegisterWatch implements WatchTracker interface.
+func (w *watchTracker) RegisterWatch(r *http.Request) ForgetWatchFunc {
+	requestInfo, ok := request.RequestInfoFrom(r.Context())
+	if !ok || requestInfo == nil || requestInfo.Verb != "watch" {
+		return nil
+	}
+
+	var index *indexValue
+	if indexField, ok := w.indexes[requestInfo.Resource]; ok {
+		index = &indexValue{
+			resource: requestInfo.Resource,
+			value:    getIndexValue(r, indexField),
+		}
+	}
+
+	identifier := &watchIdentifier{
+		apiGroup:  requestInfo.APIGroup,
+		resource:  requestInfo.Resource,
+		namespace: requestInfo.Namespace,
+		name:      requestInfo.Name,
+	}
+
+	w.lock.Lock()
+	defer w.lock.Unlock()
+	w.updateIndexLocked(identifier, index, 1)
+	return w.forgetWatch(identifier, index)
+}
+
+func (w *watchTracker) updateIndexLocked(identifier *watchIdentifier, index *indexValue, incr int) {
+	if index == nil {
+		w.watchCount[*identifier] += incr
+	} else {
+		// For resources with defined index, for a given watch event we are
+		// only processing the watchers that:
+		// (a) do not specify field selector for an index field
+		// (b) do specify field selector with the value equal to the value
+		//     coming from the processed object
+		//
+		// TODO(wojtek-t): For the sake of making progress and initially
+		// simplifying the implementation, we approximate (b) for all values
+		// as the value for an empty string. The assumption we're making here
+		// is that the difference between the actual number of watchers that
+		// will be processed, i.e. (a)+(b) above and the one from our
+		// approximation i.e. (a)+[(b) for field value of ""] will be small.
+		// This seem to be true in almost all production clusters, which makes
+		// it a reasonable first step simplification to unblock progres on it.
+		if index.value == unsetValue || index.value == "" {
+			w.watchCount[*identifier] += incr
+		}
+	}
+}
+
+func (w *watchTracker) forgetWatch(identifier *watchIdentifier, index *indexValue) ForgetWatchFunc {
+	return func() {
+		w.lock.Lock()
+		defer w.lock.Unlock()
+
+		w.updateIndexLocked(identifier, index, -1)
+		if w.watchCount[*identifier] == 0 {
+			delete(w.watchCount, *identifier)
+		}
+	}
+}
+
+// GetInterestedWatchCount implements WatchTracker interface.
+//
+// TODO(wojtek-t): As of now, requestInfo for object creation (POST) doesn't
+//
+//	contain the Name field set. Figure out if we can somehow get it for the
+//	more accurate cost estimation.
+//
+// TODO(wojtek-t): Figure out how to approach DELETECOLLECTION calls.
+func (w *watchTracker) GetInterestedWatchCount(requestInfo *request.RequestInfo) int {
+	if requestInfo == nil || readOnlyVerbs.Has(requestInfo.Verb) {
+		return 0
+	}
+
+	result := 0
+	// The watches that we're interested in include:
+	// - watches for all objects of a resource type (no namespace and name specified)
+	// - watches for all objects of a resource type in the same namespace (no name specified)
+	// - watched interested in this particular object
+	identifier := &watchIdentifier{
+		apiGroup: requestInfo.APIGroup,
+		resource: requestInfo.Resource,
+	}
+
+	w.lock.Lock()
+	defer w.lock.Unlock()
+
+	result += w.watchCount[*identifier]
+
+	if requestInfo.Namespace != "" {
+		identifier.namespace = requestInfo.Namespace
+		result += w.watchCount[*identifier]
+	}
+
+	if requestInfo.Name != "" {
+		identifier.name = requestInfo.Name
+		result += w.watchCount[*identifier]
+	}
+
+	return result
+}