Introduce more metrics on concurrency

Introduce min, average, and standard deviation for the number of
executing mutating and readOnly requests.

Introduce min, max, average, and standard deviation for the number
waiting and number waiting per priority level.

Later:

Revised to use a series of windows

Use three individuals instead of array of powers

Later:

Add coarse queue count metrics, removed windowed avg and stddev

Add metrics for number of queued mutating and readOnly requests,
to complement metrics for number executing.

Later:

Removed windowed average and standard deviation because consumers can
derive such from integrals of consumer's chosen window.

Also replaced "requestKind" Prometheus label with "request_kind".

Later:

Revised to focus on sampling

Make the clock intrinsic to a TimedObserver

... so that the clock can be read while holding the observer's lock;
otherwise, forward progress is not guaranteed (and violations were
observed in testing).

Bug fixes and histogram buckets revision

SetX1 to 1 when queue length limit is zero, beause dividing by zero is nasty.

Remove obsolete argument in gen_test.go.

Add a bucket boundary at 0 for sample-and-water-mark histograms, to
distinguish zeroes from non-zeros.

This includes adding Integrator test.

Simplified test code.

More pervasively used "ctlr" instead of "ctl" as abbreviation for
"controller".

staging/src/k8s.io/apiserver/pkg/endpoints/metrics/metrics.go

@@ -122,7 +122,7 @@ var (
 			Help:           "Number of requests dropped with 'Try again later' response",
 			StabilityLevel: compbasemetrics.ALPHA,
 		},
-		[]string{"requestKind"},
+		[]string{"request_kind"},
 	)
 	// TLSHandshakeErrors is a number of requests dropped with 'TLS handshake error from' error
 	TLSHandshakeErrors = compbasemetrics.NewCounter(
@@ -166,7 +166,15 @@ var (
 			Help:           "Maximal number of currently used inflight request limit of this apiserver per request kind in last second.",
 			StabilityLevel: compbasemetrics.ALPHA,
 		},
-		[]string{"requestKind"},
+		[]string{"request_kind"},
+	)
+	currentInqueueRequests = compbasemetrics.NewGaugeVec(
+		&compbasemetrics.GaugeOpts{
+			Name:           "apiserver_current_inqueue_requests",
+			Help:           "Maximal number of queued requests in this apiserver per request kind in last second.",
+			StabilityLevel: compbasemetrics.ALPHA,
+		},
+		[]string{"request_kind"},
 	)
 
 	requestTerminationsTotal = compbasemetrics.NewCounterVec(
@@ -191,6 +199,7 @@ var (
 		WatchEvents,
 		WatchEventsSizes,
 		currentInflightRequests,
+		currentInqueueRequests,
 		requestTerminationsTotal,
 	}
 
@@ -231,6 +240,11 @@ const (
 	ReadOnlyKind = "readOnly"
 	// MutatingKind is a string identifying mutating request kind
 	MutatingKind = "mutating"
+
+	// WaitingPhase is the phase value for a request waiting in a queue
+	WaitingPhase = "waiting"
+	// ExecutingPhase is the phase value for an executing request
+	ExecutingPhase = "executing"
 )
 
 const (
@@ -261,9 +275,19 @@ func Reset() {
 	}
 }
 
-func UpdateInflightRequestMetrics(nonmutating, mutating int) {
+// UpdateInflightRequestMetrics reports concurrency metrics classified by
-	currentInflightRequests.WithLabelValues(ReadOnlyKind).Set(float64(nonmutating))
+// mutating vs Readonly.
-	currentInflightRequests.WithLabelValues(MutatingKind).Set(float64(mutating))
+func UpdateInflightRequestMetrics(phase string, nonmutating, mutating int) {
+	for _, kc := range []struct {
+		kind  string
+		count int
+	}{{ReadOnlyKind, nonmutating}, {MutatingKind, mutating}} {
+		if phase == ExecutingPhase {
+			currentInflightRequests.WithLabelValues(kc.kind).Set(float64(kc.count))
+		} else {
+			currentInqueueRequests.WithLabelValues(kc.kind).Set(float64(kc.count))
+		}
+	}
 }
 
 // RecordRequestTermination records that the request was terminated early as part of a resource

staging/src/k8s.io/apiserver/pkg/server/filters/BUILD

@@ -62,6 +62,7 @@ go_library(
         "//staging/src/k8s.io/apiserver/pkg/endpoints/request:go_default_library",
         "//staging/src/k8s.io/apiserver/pkg/server/httplog:go_default_library",
         "//staging/src/k8s.io/apiserver/pkg/util/flowcontrol:go_default_library",
+        "//staging/src/k8s.io/apiserver/pkg/util/flowcontrol/metrics:go_default_library",
         "//staging/src/k8s.io/client-go/kubernetes/scheme:go_default_library",
         "//vendor/k8s.io/klog/v2:go_default_library",
     ],

staging/src/k8s.io/apiserver/pkg/server/filters/maxinflight.go

@@ -27,6 +27,7 @@ import (
 	"k8s.io/apiserver/pkg/authentication/user"
 	"k8s.io/apiserver/pkg/endpoints/metrics"
 	apirequest "k8s.io/apiserver/pkg/endpoints/request"
+	fcmetrics "k8s.io/apiserver/pkg/util/flowcontrol/metrics"
 
 	"k8s.io/klog/v2"
 )
@@ -50,13 +51,17 @@ func handleError(w http.ResponseWriter, r *http.Request, err error) {
 	klog.Errorf(err.Error())
 }
 
-// requestWatermark is used to trak maximal usage of inflight requests.
+// requestWatermark is used to track maximal numbers of requests in a particular phase of handling
 type requestWatermark struct {
+	phase                                string
+	readOnlyObserver, mutatingObserver   fcmetrics.TimedObserver
 	lock                                 sync.Mutex
 	readOnlyWatermark, mutatingWatermark int
 }
 
 func (w *requestWatermark) recordMutating(mutatingVal int) {
+	w.mutatingObserver.Set(float64(mutatingVal))
+
 	w.lock.Lock()
 	defer w.lock.Unlock()
 
@@ -66,6 +71,8 @@ func (w *requestWatermark) recordMutating(mutatingVal int) {
 }
 
 func (w *requestWatermark) recordReadOnly(readOnlyVal int) {
+	w.readOnlyObserver.Set(float64(readOnlyVal))
+
 	w.lock.Lock()
 	defer w.lock.Unlock()
 
@@ -74,9 +81,14 @@ func (w *requestWatermark) recordReadOnly(readOnlyVal int) {
 	}
 }
 
-var watermark = &requestWatermark{}
+// watermark tracks requests being executed (not waiting in a queue)
+var watermark = &requestWatermark{
+	phase:            metrics.ExecutingPhase,
+	readOnlyObserver: fcmetrics.ReadWriteConcurrencyObserverPairGenerator.Generate(1, 1, []string{metrics.ReadOnlyKind}).RequestsExecuting,
+	mutatingObserver: fcmetrics.ReadWriteConcurrencyObserverPairGenerator.Generate(1, 1, []string{metrics.MutatingKind}).RequestsExecuting,
+}
 
-func startRecordingUsage() {
+func startRecordingUsage(watermark *requestWatermark) {
 	go func() {
 		wait.Forever(func() {
 			watermark.lock.Lock()
@@ -86,7 +98,7 @@ func startRecordingUsage() {
 			watermark.mutatingWatermark = 0
 			watermark.lock.Unlock()
 
-			metrics.UpdateInflightRequestMetrics(readOnlyWatermark, mutatingWatermark)
+			metrics.UpdateInflightRequestMetrics(watermark.phase, readOnlyWatermark, mutatingWatermark)
 		}, inflightUsageMetricUpdatePeriod)
 	}()
 }
@@ -100,7 +112,7 @@ func WithMaxInFlightLimit(
 	mutatingLimit int,
 	longRunningRequestCheck apirequest.LongRunningRequestCheck,
 ) http.Handler {
-	startOnce.Do(startRecordingUsage)
+	startOnce.Do(func() { startRecordingUsage(watermark) })
 	if nonMutatingLimit == 0 && mutatingLimit == 0 {
 		return handler
 	}
@@ -108,9 +120,11 @@ func WithMaxInFlightLimit(
 	var mutatingChan chan bool
 	if nonMutatingLimit != 0 {
 		nonMutatingChan = make(chan bool, nonMutatingLimit)
+		watermark.readOnlyObserver.SetX1(float64(nonMutatingLimit))
 	}
 	if mutatingLimit != 0 {
 		mutatingChan = make(chan bool, mutatingLimit)
+		watermark.mutatingObserver.SetX1(float64(mutatingLimit))
 	}
 
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
@@ -141,21 +155,22 @@ func WithMaxInFlightLimit(
 
 			select {
 			case c <- true:
-				var mutatingLen, readOnlyLen int
+				// We note the concurrency level both while the
+				// request is being served and after it is done being
+				// served, because both states contribute to the
+				// sampled stats on concurrency.
 				if isMutatingRequest {
-					mutatingLen = len(mutatingChan)
+					watermark.recordMutating(len(c))
 				} else {
-					readOnlyLen = len(nonMutatingChan)
+					watermark.recordReadOnly(len(c))
 				}
-
 				defer func() {
 					<-c
 					if isMutatingRequest {
-						watermark.recordMutating(mutatingLen)
+						watermark.recordMutating(len(c))
 					} else {
-						watermark.recordReadOnly(readOnlyLen)
+						watermark.recordReadOnly(len(c))
 					}
-
 				}()
 				handler.ServeHTTP(w, r)
 

staging/src/k8s.io/apiserver/pkg/server/filters/priority-and-fairness.go

@@ -24,8 +24,10 @@ import (
 
 	fcv1a1 "k8s.io/api/flowcontrol/v1alpha1"
 	apitypes "k8s.io/apimachinery/pkg/types"
+	epmetrics "k8s.io/apiserver/pkg/endpoints/metrics"
 	apirequest "k8s.io/apiserver/pkg/endpoints/request"
 	utilflowcontrol "k8s.io/apiserver/pkg/util/flowcontrol"
+	fcmetrics "k8s.io/apiserver/pkg/util/flowcontrol/metrics"
 	"k8s.io/klog/v2"
 )
 
@@ -53,7 +55,15 @@ func GetClassification(ctx context.Context) *PriorityAndFairnessClassification {
 	return ctx.Value(priorityAndFairnessKey).(*PriorityAndFairnessClassification)
 }
 
-var atomicMutatingLen, atomicNonMutatingLen int32
+// waitingMark tracks requests waiting rather than being executed
+var waitingMark = &requestWatermark{
+	phase:            epmetrics.WaitingPhase,
+	readOnlyObserver: fcmetrics.ReadWriteConcurrencyObserverPairGenerator.Generate(1, 1, []string{epmetrics.ReadOnlyKind}).RequestsWaiting,
+	mutatingObserver: fcmetrics.ReadWriteConcurrencyObserverPairGenerator.Generate(1, 1, []string{epmetrics.MutatingKind}).RequestsWaiting,
+}
+
+var atomicMutatingExecuting, atomicReadOnlyExecuting int32
+var atomicMutatingWaiting, atomicReadOnlyWaiting int32
 
 // WithPriorityAndFairness limits the number of in-flight
 // requests in a fine-grained way.
@@ -66,7 +76,10 @@ func WithPriorityAndFairness(
 		klog.Warningf("priority and fairness support not found, skipping")
 		return handler
 	}
-	startOnce.Do(startRecordingUsage)
+	startOnce.Do(func() {
+		startRecordingUsage(watermark)
+		startRecordingUsage(waitingMark)
+	})
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		ctx := r.Context()
 		requestInfo, ok := apirequest.RequestInfoFrom(ctx)
@@ -98,22 +111,23 @@ func WithPriorityAndFairness(
 
 		var served bool
 		isMutatingRequest := !nonMutatingRequestVerbs.Has(requestInfo.Verb)
-		execute := func() {
+		noteExecutingDelta := func(delta int32) {
-			var mutatingLen, readOnlyLen int
 			if isMutatingRequest {
-				mutatingLen = int(atomic.AddInt32(&atomicMutatingLen, 1))
+				watermark.recordMutating(int(atomic.AddInt32(&atomicMutatingExecuting, delta)))
 			} else {
-				readOnlyLen = int(atomic.AddInt32(&atomicNonMutatingLen, 1))
+				watermark.recordReadOnly(int(atomic.AddInt32(&atomicReadOnlyExecuting, delta)))
 			}
-			defer func() {
+		}
-				if isMutatingRequest {
+		noteWaitingDelta := func(delta int32) {
-					atomic.AddInt32(&atomicMutatingLen, -11)
+			if isMutatingRequest {
-					watermark.recordMutating(mutatingLen)
+				waitingMark.recordMutating(int(atomic.AddInt32(&atomicMutatingWaiting, delta)))
-				} else {
+			} else {
-					atomic.AddInt32(&atomicNonMutatingLen, -1)
+				waitingMark.recordReadOnly(int(atomic.AddInt32(&atomicReadOnlyWaiting, delta)))
-					watermark.recordReadOnly(readOnlyLen)
+			}
-				}
+		}
-			}()
+		execute := func() {
+			noteExecutingDelta(1)
+			defer noteExecutingDelta(-1)
 			served = true
 			innerCtx := context.WithValue(ctx, priorityAndFairnessKey, classification)
 			innerReq := r.Clone(innerCtx)
@@ -122,10 +136,15 @@ func WithPriorityAndFairness(
 			handler.ServeHTTP(w, innerReq)
 		}
 		digest := utilflowcontrol.RequestDigest{requestInfo, user}
-		fcIfc.Handle(ctx, digest, note, execute)
+		fcIfc.Handle(ctx, digest, note, func(inQueue bool) {
+			if inQueue {
+				noteWaitingDelta(1)
+			} else {
+				noteWaitingDelta(-1)
+			}
+		}, execute)
 		if !served {
 			tooManyRequests(r, w)
-			return
 		}
 
 	})

staging/src/k8s.io/apiserver/pkg/util/flowcontrol/BUILD

@@ -85,6 +85,7 @@ go_test(
         "//staging/src/k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing:go_default_library",
         "//staging/src/k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing/testing:go_default_library",
         "//staging/src/k8s.io/apiserver/pkg/util/flowcontrol/format:go_default_library",
+        "//staging/src/k8s.io/apiserver/pkg/util/flowcontrol/metrics:go_default_library",
         "//staging/src/k8s.io/client-go/informers:go_default_library",
         "//staging/src/k8s.io/client-go/kubernetes/fake:go_default_library",
         "//staging/src/k8s.io/client-go/kubernetes/typed/flowcontrol/v1alpha1:go_default_library",

staging/src/k8s.io/apiserver/pkg/util/flowcontrol/apf_controller.go

@@ -84,7 +84,8 @@ type RequestDigest struct {
 // this type and cfgMeal follow the convention that the suffix
 // "Locked" means that the caller must hold the configController lock.
 type configController struct {
-	queueSetFactory fq.QueueSetFactory
+	queueSetFactory  fq.QueueSetFactory
+	obsPairGenerator metrics.TimedObserverPairGenerator
 
 	// configQueue holds `(interface{})(0)` when the configuration
 	// objects need to be reprocessed.
@@ -144,6 +145,9 @@ type priorityLevelState struct {
 	// number of goroutines between Controller::Match and calling the
 	// returned StartFunction
 	numPending int
+
+	// Observers tracking number waiting, executing
+	obsPair metrics.TimedObserverPair
 }
 
 // NewTestableController is extra flexible to facilitate testing
@@ -152,104 +156,106 @@ func newTestableController(
 	flowcontrolClient fcclientv1a1.FlowcontrolV1alpha1Interface,
 	serverConcurrencyLimit int,
 	requestWaitLimit time.Duration,
+	obsPairGenerator metrics.TimedObserverPairGenerator,
 	queueSetFactory fq.QueueSetFactory,
 ) *configController {
-	cfgCtl := &configController{
+	cfgCtlr := &configController{
 		queueSetFactory:        queueSetFactory,
+		obsPairGenerator:       obsPairGenerator,
 		serverConcurrencyLimit: serverConcurrencyLimit,
 		requestWaitLimit:       requestWaitLimit,
 		flowcontrolClient:      flowcontrolClient,
 		priorityLevelStates:    make(map[string]*priorityLevelState),
 	}
 	klog.V(2).Infof("NewTestableController with serverConcurrencyLimit=%d, requestWaitLimit=%s", serverConcurrencyLimit, requestWaitLimit)
-	cfgCtl.initializeConfigController(informerFactory)
+	cfgCtlr.initializeConfigController(informerFactory)
 	// ensure the data structure reflects the mandatory config
-	cfgCtl.lockAndDigestConfigObjects(nil, nil)
+	cfgCtlr.lockAndDigestConfigObjects(nil, nil)
-	return cfgCtl
+	return cfgCtlr
 }
 
 // initializeConfigController sets up the controller that processes
 // config API objects.
-func (cfgCtl *configController) initializeConfigController(informerFactory kubeinformers.SharedInformerFactory) {
+func (cfgCtlr *configController) initializeConfigController(informerFactory kubeinformers.SharedInformerFactory) {
-	cfgCtl.configQueue = workqueue.NewNamedRateLimitingQueue(workqueue.NewItemExponentialFailureRateLimiter(200*time.Millisecond, 8*time.Hour), "priority_and_fairness_config_queue")
+	cfgCtlr.configQueue = workqueue.NewNamedRateLimitingQueue(workqueue.NewItemExponentialFailureRateLimiter(200*time.Millisecond, 8*time.Hour), "priority_and_fairness_config_queue")
 	fci := informerFactory.Flowcontrol().V1alpha1()
 	pli := fci.PriorityLevelConfigurations()
 	fsi := fci.FlowSchemas()
-	cfgCtl.plLister = pli.Lister()
+	cfgCtlr.plLister = pli.Lister()
-	cfgCtl.plInformerSynced = pli.Informer().HasSynced
+	cfgCtlr.plInformerSynced = pli.Informer().HasSynced
-	cfgCtl.fsLister = fsi.Lister()
+	cfgCtlr.fsLister = fsi.Lister()
-	cfgCtl.fsInformerSynced = fsi.Informer().HasSynced
+	cfgCtlr.fsInformerSynced = fsi.Informer().HasSynced
 	pli.Informer().AddEventHandler(cache.ResourceEventHandlerFuncs{
 		AddFunc: func(obj interface{}) {
 			pl := obj.(*fctypesv1a1.PriorityLevelConfiguration)
 			klog.V(7).Infof("Triggered API priority and fairness config reloading due to creation of PLC %s", pl.Name)
-			cfgCtl.configQueue.Add(0)
+			cfgCtlr.configQueue.Add(0)
 		},
 		UpdateFunc: func(oldObj, newObj interface{}) {
 			newPL := newObj.(*fctypesv1a1.PriorityLevelConfiguration)
 			oldPL := oldObj.(*fctypesv1a1.PriorityLevelConfiguration)
 			if !apiequality.Semantic.DeepEqual(oldPL.Spec, newPL.Spec) {
 				klog.V(7).Infof("Triggered API priority and fairness config reloading due to spec update of PLC %s", newPL.Name)
-				cfgCtl.configQueue.Add(0)
+				cfgCtlr.configQueue.Add(0)
 			}
 		},
 		DeleteFunc: func(obj interface{}) {
 			name, _ := cache.DeletionHandlingMetaNamespaceKeyFunc(obj)
 			klog.V(7).Infof("Triggered API priority and fairness config reloading due to deletion of PLC %s", name)
-			cfgCtl.configQueue.Add(0)
+			cfgCtlr.configQueue.Add(0)
 
 		}})
 	fsi.Informer().AddEventHandler(cache.ResourceEventHandlerFuncs{
 		AddFunc: func(obj interface{}) {
 			fs := obj.(*fctypesv1a1.FlowSchema)
 			klog.V(7).Infof("Triggered API priority and fairness config reloading due to creation of FS %s", fs.Name)
-			cfgCtl.configQueue.Add(0)
+			cfgCtlr.configQueue.Add(0)
 		},
 		UpdateFunc: func(oldObj, newObj interface{}) {
 			newFS := newObj.(*fctypesv1a1.FlowSchema)
 			oldFS := oldObj.(*fctypesv1a1.FlowSchema)
 			if !apiequality.Semantic.DeepEqual(oldFS.Spec, newFS.Spec) {
 				klog.V(7).Infof("Triggered API priority and fairness config reloading due to spec update of FS %s", newFS.Name)
-				cfgCtl.configQueue.Add(0)
+				cfgCtlr.configQueue.Add(0)
 			}
 		},
 		DeleteFunc: func(obj interface{}) {
 			name, _ := cache.DeletionHandlingMetaNamespaceKeyFunc(obj)
 			klog.V(7).Infof("Triggered API priority and fairness config reloading due to deletion of FS %s", name)
-			cfgCtl.configQueue.Add(0)
+			cfgCtlr.configQueue.Add(0)
 
 		}})
 }
 
-func (cfgCtl *configController) Run(stopCh <-chan struct{}) error {
+func (cfgCtlr *configController) Run(stopCh <-chan struct{}) error {
-	defer cfgCtl.configQueue.ShutDown()
+	defer cfgCtlr.configQueue.ShutDown()
 	klog.Info("Starting API Priority and Fairness config controller")
-	if ok := cache.WaitForCacheSync(stopCh, cfgCtl.plInformerSynced, cfgCtl.fsInformerSynced); !ok {
+	if ok := cache.WaitForCacheSync(stopCh, cfgCtlr.plInformerSynced, cfgCtlr.fsInformerSynced); !ok {
 		return fmt.Errorf("Never achieved initial sync")
 	}
 	klog.Info("Running API Priority and Fairness config worker")
-	wait.Until(cfgCtl.runWorker, time.Second, stopCh)
+	wait.Until(cfgCtlr.runWorker, time.Second, stopCh)
 	klog.Info("Shutting down API Priority and Fairness config worker")
 	return nil
 }
 
-func (cfgCtl *configController) runWorker() {
+func (cfgCtlr *configController) runWorker() {
-	for cfgCtl.processNextWorkItem() {
+	for cfgCtlr.processNextWorkItem() {
 	}
 }
 
-func (cfgCtl *configController) processNextWorkItem() bool {
+func (cfgCtlr *configController) processNextWorkItem() bool {
-	obj, shutdown := cfgCtl.configQueue.Get()
+	obj, shutdown := cfgCtlr.configQueue.Get()
 	if shutdown {
 		return false
 	}
 
 	func(obj interface{}) {
-		defer cfgCtl.configQueue.Done(obj)
+		defer cfgCtlr.configQueue.Done(obj)
-		if !cfgCtl.syncOne() {
+		if !cfgCtlr.syncOne() {
-			cfgCtl.configQueue.AddRateLimited(obj)
+			cfgCtlr.configQueue.AddRateLimited(obj)
 		} else {
-			cfgCtl.configQueue.Forget(obj)
+			cfgCtlr.configQueue.Forget(obj)
 		}
 	}(obj)
 
@@ -259,19 +265,19 @@ func (cfgCtl *configController) processNextWorkItem() bool {
 // syncOne attempts to sync all the API Priority and Fairness config
 // objects.  It either succeeds and returns `true` or logs an error
 // and returns `false`.
-func (cfgCtl *configController) syncOne() bool {
+func (cfgCtlr *configController) syncOne() bool {
 	all := labels.Everything()
-	newPLs, err := cfgCtl.plLister.List(all)
+	newPLs, err := cfgCtlr.plLister.List(all)
 	if err != nil {
 		klog.Errorf("Unable to list PriorityLevelConfiguration objects: %s", err.Error())
 		return false
 	}
-	newFSs, err := cfgCtl.fsLister.List(all)
+	newFSs, err := cfgCtlr.fsLister.List(all)
 	if err != nil {
 		klog.Errorf("Unable to list FlowSchema objects: %s", err.Error())
 		return false
 	}
-	err = cfgCtl.digestConfigObjects(newPLs, newFSs)
+	err = cfgCtlr.digestConfigObjects(newPLs, newFSs)
 	if err == nil {
 		return true
 	}
@@ -288,7 +294,7 @@ func (cfgCtl *configController) syncOne() bool {
 // FlowSchemas --- with the work dvided among the passes according to
 // those dependencies.
 type cfgMeal struct {
-	cfgCtl *configController
+	cfgCtlr *configController
 
 	newPLStates map[string]*priorityLevelState
 
@@ -315,9 +321,9 @@ type fsStatusUpdate struct {
 }
 
 // digestConfigObjects is given all the API objects that configure
-// cfgCtl and writes its consequent new configState.
+// cfgCtlr and writes its consequent new configState.
-func (cfgCtl *configController) digestConfigObjects(newPLs []*fctypesv1a1.PriorityLevelConfiguration, newFSs []*fctypesv1a1.FlowSchema) error {
+func (cfgCtlr *configController) digestConfigObjects(newPLs []*fctypesv1a1.PriorityLevelConfiguration, newFSs []*fctypesv1a1.FlowSchema) error {
-	fsStatusUpdates := cfgCtl.lockAndDigestConfigObjects(newPLs, newFSs)
+	fsStatusUpdates := cfgCtlr.lockAndDigestConfigObjects(newPLs, newFSs)
 	var errs []error
 	for _, fsu := range fsStatusUpdates {
 		enc, err := json.Marshal(fsu.condition)
@@ -326,7 +332,7 @@ func (cfgCtl *configController) digestConfigObjects(newPLs []*fctypesv1a1.Priori
 			panic(fmt.Sprintf("Failed to json.Marshall(%#+v): %s", fsu.condition, err.Error()))
 		}
 		klog.V(4).Infof("Writing Condition %s to FlowSchema %s because its previous value was %s", string(enc), fsu.flowSchema.Name, fcfmt.Fmt(fsu.oldValue))
-		_, err = cfgCtl.flowcontrolClient.FlowSchemas().Patch(context.TODO(), fsu.flowSchema.Name, apitypes.StrategicMergePatchType, []byte(fmt.Sprintf(`{"status": {"conditions": [ %s ] } }`, string(enc))), metav1.PatchOptions{FieldManager: "api-priority-and-fairness-config-consumer-v1"}, "status")
+		_, err = cfgCtlr.flowcontrolClient.FlowSchemas().Patch(context.TODO(), fsu.flowSchema.Name, apitypes.StrategicMergePatchType, []byte(fmt.Sprintf(`{"status": {"conditions": [ %s ] } }`, string(enc))), metav1.PatchOptions{FieldManager: "api-priority-and-fairness-config-consumer-v1"}, "status")
 		if err != nil {
 			errs = append(errs, errors.Wrap(err, fmt.Sprintf("failed to set a status.condition for FlowSchema %s", fsu.flowSchema.Name)))
 		}
@@ -337,11 +343,11 @@ func (cfgCtl *configController) digestConfigObjects(newPLs []*fctypesv1a1.Priori
 	return apierrors.NewAggregate(errs)
 }
 
-func (cfgCtl *configController) lockAndDigestConfigObjects(newPLs []*fctypesv1a1.PriorityLevelConfiguration, newFSs []*fctypesv1a1.FlowSchema) []fsStatusUpdate {
+func (cfgCtlr *configController) lockAndDigestConfigObjects(newPLs []*fctypesv1a1.PriorityLevelConfiguration, newFSs []*fctypesv1a1.FlowSchema) []fsStatusUpdate {
-	cfgCtl.lock.Lock()
+	cfgCtlr.lock.Lock()
-	defer cfgCtl.lock.Unlock()
+	defer cfgCtlr.lock.Unlock()
 	meal := cfgMeal{
-		cfgCtl:      cfgCtl,
+		cfgCtlr:     cfgCtlr,
 		newPLStates: make(map[string]*priorityLevelState),
 	}
 
@@ -351,16 +357,16 @@ func (cfgCtl *configController) lockAndDigestConfigObjects(newPLs []*fctypesv1a1
 
 	// Supply missing mandatory PriorityLevelConfiguration objects
 	if !meal.haveExemptPL {
-		meal.imaginePL(fcboot.MandatoryPriorityLevelConfigurationExempt, cfgCtl.requestWaitLimit)
+		meal.imaginePL(fcboot.MandatoryPriorityLevelConfigurationExempt, cfgCtlr.requestWaitLimit)
 	}
 	if !meal.haveCatchAllPL {
-		meal.imaginePL(fcboot.MandatoryPriorityLevelConfigurationCatchAll, cfgCtl.requestWaitLimit)
+		meal.imaginePL(fcboot.MandatoryPriorityLevelConfigurationCatchAll, cfgCtlr.requestWaitLimit)
 	}
 
 	meal.finishQueueSetReconfigsLocked()
 
 	// The new config has been constructed
-	cfgCtl.priorityLevelStates = meal.newPLStates
+	cfgCtlr.priorityLevelStates = meal.newPLStates
 	klog.V(5).Infof("Switched to new API Priority and Fairness configuration")
 	return meal.fsStatusUpdates
 }
@@ -369,11 +375,11 @@ func (cfgCtl *configController) lockAndDigestConfigObjects(newPLs []*fctypesv1a1
 // Pretend broken ones do not exist.
 func (meal *cfgMeal) digestNewPLsLocked(newPLs []*fctypesv1a1.PriorityLevelConfiguration) {
 	for _, pl := range newPLs {
-		state := meal.cfgCtl.priorityLevelStates[pl.Name]
+		state := meal.cfgCtlr.priorityLevelStates[pl.Name]
 		if state == nil {
-			state = &priorityLevelState{}
+			state = &priorityLevelState{obsPair: meal.cfgCtlr.obsPairGenerator.Generate(1, 1, []string{pl.Name})}
 		}
-		qsCompleter, err := qscOfPL(meal.cfgCtl.queueSetFactory, state.queues, pl, meal.cfgCtl.requestWaitLimit)
+		qsCompleter, err := queueSetCompleterForPL(meal.cfgCtlr.queueSetFactory, state.queues, pl, meal.cfgCtlr.requestWaitLimit, state.obsPair)
 		if err != nil {
 			klog.Warningf("Ignoring PriorityLevelConfiguration object %s because its spec (%s) is broken: %s", pl.Name, fcfmt.Fmt(pl.Spec), err)
 			continue
@@ -439,7 +445,7 @@ func (meal *cfgMeal) digestFlowSchemasLocked(newFSs []*fctypesv1a1.FlowSchema) {
 		fsSeq = append(fsSeq, fcboot.MandatoryFlowSchemaCatchAll)
 	}
 
-	meal.cfgCtl.flowSchemas = fsSeq
+	meal.cfgCtlr.flowSchemas = fsSeq
 	if klog.V(5).Enabled() {
 		for _, fs := range fsSeq {
 			klog.Infof("Using FlowSchema %s", fcfmt.Fmt(fs))
@@ -453,7 +459,7 @@ func (meal *cfgMeal) digestFlowSchemasLocked(newFSs []*fctypesv1a1.FlowSchema) {
 // queues, otherwise start the quiescing process if that has not
 // already been started.
 func (meal *cfgMeal) processOldPLsLocked() {
-	for plName, plState := range meal.cfgCtl.priorityLevelStates {
+	for plName, plState := range meal.cfgCtlr.priorityLevelStates {
 		if meal.newPLStates[plName] != nil {
 			// Still desired and already updated
 			continue
@@ -476,9 +482,9 @@ func (meal *cfgMeal) processOldPLsLocked() {
 			}
 		}
 		var err error
-		plState.qsCompleter, err = qscOfPL(meal.cfgCtl.queueSetFactory, plState.queues, plState.pl, meal.cfgCtl.requestWaitLimit)
+		plState.qsCompleter, err = queueSetCompleterForPL(meal.cfgCtlr.queueSetFactory, plState.queues, plState.pl, meal.cfgCtlr.requestWaitLimit, plState.obsPair)
 		if err != nil {
-			// This can not happen because qscOfPL already approved this config
+			// This can not happen because queueSetCompleterForPL already approved this config
 			panic(fmt.Sprintf("%s from name=%q spec=%s", err, plName, fcfmt.Fmt(plState.pl.Spec)))
 		}
 		if plState.pl.Spec.Limited != nil {
@@ -509,7 +515,7 @@ func (meal *cfgMeal) finishQueueSetReconfigsLocked() {
 		// The use of math.Ceil here means that the results might sum
 		// to a little more than serverConcurrencyLimit but the
 		// difference will be negligible.
-		concurrencyLimit := int(math.Ceil(float64(meal.cfgCtl.serverConcurrencyLimit) * float64(plState.pl.Spec.Limited.AssuredConcurrencyShares) / meal.shareSum))
+		concurrencyLimit := int(math.Ceil(float64(meal.cfgCtlr.serverConcurrencyLimit) * float64(plState.pl.Spec.Limited.AssuredConcurrencyShares) / meal.shareSum))
 		metrics.UpdateSharedConcurrencyLimit(plName, concurrencyLimit)
 
 		if plState.queues == nil {
@@ -521,10 +527,11 @@ func (meal *cfgMeal) finishQueueSetReconfigsLocked() {
 	}
 }
 
-// qscOfPL returns a pointer to an appropriate QueuingConfig or nil
+// queueSetCompleterForPL returns an appropriate QueueSetCompleter for the
-// if no limiting is called for.  Returns nil and an error if the given
+// given priority level configuration.  Returns nil if that config
+// does not call for limiting.  Returns nil and an error if the given
 // object is malformed in a way that is a problem for this package.
-func qscOfPL(qsf fq.QueueSetFactory, queues fq.QueueSet, pl *fctypesv1a1.PriorityLevelConfiguration, requestWaitLimit time.Duration) (fq.QueueSetCompleter, error) {
+func queueSetCompleterForPL(qsf fq.QueueSetFactory, queues fq.QueueSet, pl *fctypesv1a1.PriorityLevelConfiguration, requestWaitLimit time.Duration, intPair metrics.TimedObserverPair) (fq.QueueSetCompleter, error) {
 	if (pl.Spec.Type == fctypesv1a1.PriorityLevelEnablementExempt) != (pl.Spec.Limited == nil) {
 		return nil, errors.New("broken union structure at the top")
 	}
@@ -553,7 +560,7 @@ func qscOfPL(qsf fq.QueueSetFactory, queues fq.QueueSet, pl *fctypesv1a1.Priorit
 	if queues != nil {
 		qsc, err = queues.BeginConfigChange(qcQS)
 	} else {
-		qsc, err = qsf.BeginConstruction(qcQS)
+		qsc, err = qsf.BeginConstruction(qcQS, intPair)
 	}
 	if err != nil {
 		err = errors.Wrap(err, fmt.Sprintf("priority level %q has QueuingConfiguration %#+v, which is invalid", pl.Name, qcAPI))
@@ -594,9 +601,11 @@ func (meal *cfgMeal) presyncFlowSchemaStatus(fs *fctypesv1a1.FlowSchema, isDangl
 }
 
 // imaginePL adds a priority level based on one of the mandatory ones
+// that does not actually exist (right now) as a real API object.
 func (meal *cfgMeal) imaginePL(proto *fctypesv1a1.PriorityLevelConfiguration, requestWaitLimit time.Duration) {
 	klog.V(3).Infof("No %s PriorityLevelConfiguration found, imagining one", proto.Name)
-	qsCompleter, err := qscOfPL(meal.cfgCtl.queueSetFactory, nil, proto, requestWaitLimit)
+	obsPair := meal.cfgCtlr.obsPairGenerator.Generate(1, 1, []string{proto.Name})
+	qsCompleter, err := queueSetCompleterForPL(meal.cfgCtlr.queueSetFactory, nil, proto, requestWaitLimit, obsPair)
 	if err != nil {
 		// This can not happen because proto is one of the mandatory
 		// objects and these are not erroneous
@@ -605,6 +614,7 @@ func (meal *cfgMeal) imaginePL(proto *fctypesv1a1.PriorityLevelConfiguration, re
 	meal.newPLStates[proto.Name] = &priorityLevelState{
 		pl:          proto,
 		qsCompleter: qsCompleter,
+		obsPair:     obsPair,
 	}
 	if proto.Spec.Limited != nil {
 		meal.shareSum += float64(proto.Spec.Limited.AssuredConcurrencyShares)
@@ -624,14 +634,14 @@ func (immediateRequest) Finish(execute func()) bool {
 // The returned bool indicates whether the request is exempt from
 // limitation.  The startWaitingTime is when the request started
 // waiting in its queue, or `Time{}` if this did not happen.
-func (cfgCtl *configController) startRequest(ctx context.Context, rd RequestDigest) (fs *fctypesv1a1.FlowSchema, pl *fctypesv1a1.PriorityLevelConfiguration, isExempt bool, req fq.Request, startWaitingTime time.Time) {
+func (cfgCtlr *configController) startRequest(ctx context.Context, rd RequestDigest, queueNoteFn fq.QueueNoteFn) (fs *fctypesv1a1.FlowSchema, pl *fctypesv1a1.PriorityLevelConfiguration, isExempt bool, req fq.Request, startWaitingTime time.Time) {
 	klog.V(7).Infof("startRequest(%#+v)", rd)
-	cfgCtl.lock.Lock()
+	cfgCtlr.lock.Lock()
-	defer cfgCtl.lock.Unlock()
+	defer cfgCtlr.lock.Unlock()
-	for _, fs := range cfgCtl.flowSchemas {
+	for _, fs := range cfgCtlr.flowSchemas {
 		if matchesFlowSchema(rd, fs) {
 			plName := fs.Spec.PriorityLevelConfiguration.Name
-			plState := cfgCtl.priorityLevelStates[plName]
+			plState := cfgCtlr.priorityLevelStates[plName]
 			if plState.pl.Spec.Type == fctypesv1a1.PriorityLevelEnablementExempt {
 				klog.V(7).Infof("startRequest(%#+v) => fsName=%q, distMethod=%#+v, plName=%q, immediate", rd, fs.Name, fs.Spec.DistinguisherMethod, plName)
 				return fs, plState.pl, true, immediateRequest{}, time.Time{}
@@ -649,9 +659,9 @@ func (cfgCtl *configController) startRequest(ctx context.Context, rd RequestDige
 			}
 			startWaitingTime = time.Now()
 			klog.V(7).Infof("startRequest(%#+v) => fsName=%q, distMethod=%#+v, plName=%q, numQueues=%d", rd, fs.Name, fs.Spec.DistinguisherMethod, plName, numQueues)
-			req, idle := plState.queues.StartRequest(ctx, hashValue, flowDistinguisher, fs.Name, rd.RequestInfo, rd.User)
+			req, idle := plState.queues.StartRequest(ctx, hashValue, flowDistinguisher, fs.Name, rd.RequestInfo, rd.User, queueNoteFn)
 			if idle {
-				cfgCtl.maybeReapLocked(plName, plState)
+				cfgCtlr.maybeReapLocked(plName, plState)
 			}
 			return fs, plState.pl, false, req, startWaitingTime
 		}
@@ -660,7 +670,7 @@ func (cfgCtl *configController) startRequest(ctx context.Context, rd RequestDige
 	// FlowSchema that matches everything.  If somehow control reaches
 	// here, panic with some relevant information.
 	var catchAll *fctypesv1a1.FlowSchema
-	for _, fs := range cfgCtl.flowSchemas {
+	for _, fs := range cfgCtlr.flowSchemas {
 		if fs.Name == fctypesv1a1.FlowSchemaNameCatchAll {
 			catchAll = fs
 		}
@@ -669,10 +679,10 @@ func (cfgCtl *configController) startRequest(ctx context.Context, rd RequestDige
 }
 
 // Call this after getting a clue that the given priority level is undesired and idle
-func (cfgCtl *configController) maybeReap(plName string) {
+func (cfgCtlr *configController) maybeReap(plName string) {
-	cfgCtl.lock.Lock()
+	cfgCtlr.lock.Lock()
-	defer cfgCtl.lock.Unlock()
+	defer cfgCtlr.lock.Unlock()
-	plState := cfgCtl.priorityLevelStates[plName]
+	plState := cfgCtlr.priorityLevelStates[plName]
 	if plState == nil {
 		klog.V(7).Infof("plName=%s, plState==nil", plName)
 		return
@@ -685,17 +695,17 @@ func (cfgCtl *configController) maybeReap(plName string) {
 		}
 	}
 	klog.V(3).Infof("Triggered API priority and fairness config reloading because priority level %s is undesired and idle", plName)
-	cfgCtl.configQueue.Add(0)
+	cfgCtlr.configQueue.Add(0)
 }
 
 // Call this if both (1) plState.queues is non-nil and reported being
-// idle, and (2) cfgCtl's lock has not been released since then.
+// idle, and (2) cfgCtlr's lock has not been released since then.
-func (cfgCtl *configController) maybeReapLocked(plName string, plState *priorityLevelState) {
+func (cfgCtlr *configController) maybeReapLocked(plName string, plState *priorityLevelState) {
 	if !(plState.quiescing && plState.numPending == 0) {
 		return
 	}
 	klog.V(3).Infof("Triggered API priority and fairness config reloading because priority level %s is undesired and idle", plName)
-	cfgCtl.configQueue.Add(0)
+	cfgCtlr.configQueue.Add(0)
 }
 
 // computeFlowDistinguisher extracts the flow distinguisher according to the given method

staging/src/k8s.io/apiserver/pkg/util/flowcontrol/apf_controller_debug.go

@@ -34,20 +34,20 @@ const (
 	queryIncludeRequestDetails = "includeRequestDetails"
 )
 
-func (cfgCtl *configController) Install(c *mux.PathRecorderMux) {
+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", cfgCtl.dumpPriorityLevels)
+	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", cfgCtl.dumpQueues)
+	c.UnlistedHandleFunc("/debug/api_priority_and_fairness/dump_queues", cfgCtlr.dumpQueues)
 	// 3. row per request
-	c.UnlistedHandleFunc("/debug/api_priority_and_fairness/dump_requests", cfgCtl.dumpRequests)
+	c.UnlistedHandleFunc("/debug/api_priority_and_fairness/dump_requests", cfgCtlr.dumpRequests)
 }
 
-func (cfgCtl *configController) dumpPriorityLevels(w http.ResponseWriter, r *http.Request) {
+func (cfgCtlr *configController) dumpPriorityLevels(w http.ResponseWriter, r *http.Request) {
-	cfgCtl.lock.Lock()
+	cfgCtlr.lock.Lock()
-	defer cfgCtl.lock.Unlock()
+	defer cfgCtlr.lock.Unlock()
 	tabWriter := tabwriter.NewWriter(w, 8, 0, 1, ' ', 0)
 	columnHeaders := []string{
 		"PriorityLevelName", // 1
@@ -59,7 +59,7 @@ func (cfgCtl *configController) dumpPriorityLevels(w http.ResponseWriter, r *htt
 	}
 	tabPrint(tabWriter, rowForHeaders(columnHeaders))
 	endline(tabWriter)
-	for _, plState := range cfgCtl.priorityLevelStates {
+	for _, plState := range cfgCtlr.priorityLevelStates {
 		if plState.queues == nil {
 			tabPrint(tabWriter, row(
 				plState.pl.Name, // 1
@@ -93,9 +93,9 @@ func (cfgCtl *configController) dumpPriorityLevels(w http.ResponseWriter, r *htt
 	runtime.HandleError(tabWriter.Flush())
 }
 
-func (cfgCtl *configController) dumpQueues(w http.ResponseWriter, r *http.Request) {
+func (cfgCtlr *configController) dumpQueues(w http.ResponseWriter, r *http.Request) {
-	cfgCtl.lock.Lock()
+	cfgCtlr.lock.Lock()
-	defer cfgCtl.lock.Unlock()
+	defer cfgCtlr.lock.Unlock()
 	tabWriter := tabwriter.NewWriter(w, 8, 0, 1, ' ', 0)
 	columnHeaders := []string{
 		"PriorityLevelName", // 1
@@ -106,7 +106,7 @@ func (cfgCtl *configController) dumpQueues(w http.ResponseWriter, r *http.Reques
 	}
 	tabPrint(tabWriter, rowForHeaders(columnHeaders))
 	endline(tabWriter)
-	for _, plState := range cfgCtl.priorityLevelStates {
+	for _, plState := range cfgCtlr.priorityLevelStates {
 		if plState.queues == nil {
 			tabPrint(tabWriter, row(
 				plState.pl.Name, // 1
@@ -133,9 +133,9 @@ func (cfgCtl *configController) dumpQueues(w http.ResponseWriter, r *http.Reques
 	runtime.HandleError(tabWriter.Flush())
 }
 
-func (cfgCtl *configController) dumpRequests(w http.ResponseWriter, r *http.Request) {
+func (cfgCtlr *configController) dumpRequests(w http.ResponseWriter, r *http.Request) {
-	cfgCtl.lock.Lock()
+	cfgCtlr.lock.Lock()
-	defer cfgCtl.lock.Unlock()
+	defer cfgCtlr.lock.Unlock()
 
 	includeRequestDetails := len(r.URL.Query().Get(queryIncludeRequestDetails)) > 0
 
@@ -161,7 +161,7 @@ func (cfgCtl *configController) dumpRequests(w http.ResponseWriter, r *http.Requ
 		}))
 	}
 	endline(tabWriter)
-	for _, plState := range cfgCtl.priorityLevelStates {
+	for _, plState := range cfgCtlr.priorityLevelStates {
 		if plState.queues == nil {
 			tabPrint(tabWriter, row(
 				plState.pl.Name, // 1

staging/src/k8s.io/apiserver/pkg/util/flowcontrol/apf_filter.go

@@ -45,6 +45,7 @@ type Interface interface {
 	Handle(ctx context.Context,
 		requestDigest RequestDigest,
 		noteFn func(fs *fctypesv1a1.FlowSchema, pl *fctypesv1a1.PriorityLevelConfiguration),
+		queueNoteFn fq.QueueNoteFn,
 		execFn func(),
 	)
 
@@ -72,6 +73,7 @@ func New(
 		flowcontrolClient,
 		serverConcurrencyLimit,
 		requestWaitLimit,
+		metrics.PriorityLevelConcurrencyObserverPairGenerator,
 		fqs.NewQueueSetFactory(&clock.RealClock{}, grc),
 	)
 }
@@ -82,15 +84,17 @@ func NewTestable(
 	flowcontrolClient fcclientv1a1.FlowcontrolV1alpha1Interface,
 	serverConcurrencyLimit int,
 	requestWaitLimit time.Duration,
+	obsPairGenerator metrics.TimedObserverPairGenerator,
 	queueSetFactory fq.QueueSetFactory,
 ) Interface {
-	return newTestableController(informerFactory, flowcontrolClient, serverConcurrencyLimit, requestWaitLimit, queueSetFactory)
+	return newTestableController(informerFactory, flowcontrolClient, serverConcurrencyLimit, requestWaitLimit, obsPairGenerator, queueSetFactory)
 }
 
-func (cfgCtl *configController) Handle(ctx context.Context, requestDigest RequestDigest,
+func (cfgCtlr *configController) Handle(ctx context.Context, requestDigest RequestDigest,
 	noteFn func(fs *fctypesv1a1.FlowSchema, pl *fctypesv1a1.PriorityLevelConfiguration),
+	queueNoteFn fq.QueueNoteFn,
 	execFn func()) {
-	fs, pl, isExempt, req, startWaitingTime := cfgCtl.startRequest(ctx, requestDigest)
+	fs, pl, isExempt, req, startWaitingTime := cfgCtlr.startRequest(ctx, requestDigest, queueNoteFn)
 	queued := startWaitingTime != time.Time{}
 	noteFn(fs, pl)
 	if req == nil {
@@ -117,6 +121,6 @@ func (cfgCtl *configController) Handle(ctx context.Context, requestDigest Reques
 	}
 	klog.V(7).Infof("Handle(%#+v) => fsName=%q, distMethod=%#+v, plName=%q, isExempt=%v, queued=%v, Finish() => idle=%v", requestDigest, fs.Name, fs.Spec.DistinguisherMethod, pl.Name, isExempt, queued, idle)
 	if idle {
-		cfgCtl.maybeReap(pl.Name)
+		cfgCtlr.maybeReap(pl.Name)
 	}
 }

staging/src/k8s.io/apiserver/pkg/util/flowcontrol/controller_test.go

@@ -31,6 +31,7 @@ import (
 	"k8s.io/apiserver/pkg/util/flowcontrol/debug"
 	fq "k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing"
 	fcfmt "k8s.io/apiserver/pkg/util/flowcontrol/format"
+	"k8s.io/apiserver/pkg/util/flowcontrol/metrics"
 	"k8s.io/client-go/informers"
 	clientsetfake "k8s.io/client-go/kubernetes/fake"
 	fcclient "k8s.io/client-go/kubernetes/typed/flowcontrol/v1alpha1"
@@ -50,16 +51,16 @@ var mandPLs = func() map[string]*fcv1a1.PriorityLevelConfiguration {
 	return ans
 }()
 
-type ctlTestState struct {
+type ctlrTestState struct {
 	t               *testing.T
-	cfgCtl          *configController
+	cfgCtlr         *configController
 	fcIfc           fcclient.FlowcontrolV1alpha1Interface
 	existingPLs     map[string]*fcv1a1.PriorityLevelConfiguration
 	existingFSs     map[string]*fcv1a1.FlowSchema
 	heldRequestsMap map[string][]heldRequest
 	requestWG       sync.WaitGroup
 	lock            sync.Mutex
-	queues          map[string]*ctlTestQueueSet
+	queues          map[string]*ctlrTestQueueSet
 }
 
 type heldRequest struct {
@@ -67,45 +68,45 @@ type heldRequest struct {
 	finishCh chan struct{}
 }
 
-var _ fq.QueueSetFactory = (*ctlTestState)(nil)
+var _ fq.QueueSetFactory = (*ctlrTestState)(nil)
 
-type ctlTestQueueSetCompleter struct {
+type ctlrTestQueueSetCompleter struct {
-	cts *ctlTestState
+	cts *ctlrTestState
-	cqs *ctlTestQueueSet
+	cqs *ctlrTestQueueSet
 	qc  fq.QueuingConfig
 }
 
-type ctlTestQueueSet struct {
+type ctlrTestQueueSet struct {
-	cts         *ctlTestState
+	cts         *ctlrTestState
 	qc          fq.QueuingConfig
 	dc          fq.DispatchingConfig
 	countActive int
 }
 
-type ctlTestRequest struct {
+type ctlrTestRequest struct {
-	cqs            *ctlTestQueueSet
+	cqs            *ctlrTestQueueSet
 	qsName         string
 	descr1, descr2 interface{}
 }
 
-func (cts *ctlTestState) BeginConstruction(qc fq.QueuingConfig) (fq.QueueSetCompleter, error) {
+func (cts *ctlrTestState) BeginConstruction(qc fq.QueuingConfig, ip metrics.TimedObserverPair) (fq.QueueSetCompleter, error) {
-	return ctlTestQueueSetCompleter{cts, nil, qc}, nil
+	return ctlrTestQueueSetCompleter{cts, nil, qc}, nil
 }
 
-func (cqs *ctlTestQueueSet) BeginConfigChange(qc fq.QueuingConfig) (fq.QueueSetCompleter, error) {
+func (cqs *ctlrTestQueueSet) BeginConfigChange(qc fq.QueuingConfig) (fq.QueueSetCompleter, error) {
-	return ctlTestQueueSetCompleter{cqs.cts, cqs, qc}, nil
+	return ctlrTestQueueSetCompleter{cqs.cts, cqs, qc}, nil
 }
 
-func (cqs *ctlTestQueueSet) Dump(bool) debug.QueueSetDump {
+func (cqs *ctlrTestQueueSet) Dump(bool) debug.QueueSetDump {
 	return debug.QueueSetDump{}
 }
 
-func (cqc ctlTestQueueSetCompleter) Complete(dc fq.DispatchingConfig) fq.QueueSet {
+func (cqc ctlrTestQueueSetCompleter) Complete(dc fq.DispatchingConfig) fq.QueueSet {
 	cqc.cts.lock.Lock()
 	defer cqc.cts.lock.Unlock()
 	qs := cqc.cqs
 	if qs == nil {
-		qs = &ctlTestQueueSet{cts: cqc.cts, qc: cqc.qc, dc: dc}
+		qs = &ctlrTestQueueSet{cts: cqc.cts, qc: cqc.qc, dc: dc}
 		cqc.cts.queues[cqc.qc.Name] = qs
 	} else {
 		qs.qc, qs.dc = cqc.qc, dc
@@ -113,22 +114,22 @@ func (cqc ctlTestQueueSetCompleter) Complete(dc fq.DispatchingConfig) fq.QueueSe
 	return qs
 }
 
-func (cqs *ctlTestQueueSet) IsIdle() bool {
+func (cqs *ctlrTestQueueSet) IsIdle() bool {
 	cqs.cts.lock.Lock()
 	defer cqs.cts.lock.Unlock()
 	klog.V(7).Infof("For %p QS %s, countActive==%d", cqs, cqs.qc.Name, cqs.countActive)
 	return cqs.countActive == 0
 }
 
-func (cqs *ctlTestQueueSet) StartRequest(ctx context.Context, hashValue uint64, flowDistinguisher, fsName string, descr1, descr2 interface{}) (req fq.Request, idle bool) {
+func (cqs *ctlrTestQueueSet) StartRequest(ctx context.Context, hashValue uint64, flowDistinguisher, fsName string, descr1, descr2 interface{}, queueNoteFn fq.QueueNoteFn) (req fq.Request, idle bool) {
 	cqs.cts.lock.Lock()
 	defer cqs.cts.lock.Unlock()
 	cqs.countActive++
 	cqs.cts.t.Logf("Queued %q %#+v %#+v for %p QS=%s, countActive:=%d", fsName, descr1, descr2, cqs, cqs.qc.Name, cqs.countActive)
-	return &ctlTestRequest{cqs, cqs.qc.Name, descr1, descr2}, false
+	return &ctlrTestRequest{cqs, cqs.qc.Name, descr1, descr2}, false
 }
 
-func (ctr *ctlTestRequest) Finish(execute func()) bool {
+func (ctr *ctlrTestRequest) Finish(execute func()) bool {
 	execute()
 	ctr.cqs.cts.lock.Lock()
 	defer ctr.cqs.cts.lock.Unlock()
@@ -137,13 +138,13 @@ func (ctr *ctlTestRequest) Finish(execute func()) bool {
 	return ctr.cqs.countActive == 0
 }
 
-func (cts *ctlTestState) getQueueSetNames() sets.String {
+func (cts *ctlrTestState) getQueueSetNames() sets.String {
 	cts.lock.Lock()
 	defer cts.lock.Unlock()
 	return sets.StringKeySet(cts.queues)
 }
 
-func (cts *ctlTestState) getNonIdleQueueSetNames() sets.String {
+func (cts *ctlrTestState) getNonIdleQueueSetNames() sets.String {
 	cts.lock.Lock()
 	defer cts.lock.Unlock()
 	ans := sets.NewString()
@@ -155,14 +156,14 @@ func (cts *ctlTestState) getNonIdleQueueSetNames() sets.String {
 	return ans
 }
 
-func (cts *ctlTestState) hasNonIdleQueueSet(name string) bool {
+func (cts *ctlrTestState) hasNonIdleQueueSet(name string) bool {
 	cts.lock.Lock()
 	defer cts.lock.Unlock()
 	qs := cts.queues[name]
 	return qs != nil && qs.countActive > 0
 }
 
-func (cts *ctlTestState) addHeldRequest(plName string, rd RequestDigest, finishCh chan struct{}) {
+func (cts *ctlrTestState) addHeldRequest(plName string, rd RequestDigest, finishCh chan struct{}) {
 	cts.lock.Lock()
 	defer cts.lock.Unlock()
 	hrs := cts.heldRequestsMap[plName]
@@ -171,7 +172,7 @@ func (cts *ctlTestState) addHeldRequest(plName string, rd RequestDigest, finishC
 	cts.t.Logf("Holding %#+v for %s, count:=%d", rd, plName, len(hrs))
 }
 
-func (cts *ctlTestState) popHeldRequest() (plName string, hr *heldRequest, nCount int) {
+func (cts *ctlrTestState) popHeldRequest() (plName string, hr *heldRequest, nCount int) {
 	cts.lock.Lock()
 	defer cts.lock.Unlock()
 	var hrs []heldRequest
@@ -219,21 +220,22 @@ func TestConfigConsumer(t *testing.T) {
 			clientset := clientsetfake.NewSimpleClientset()
 			informerFactory := informers.NewSharedInformerFactory(clientset, 0)
 			flowcontrolClient := clientset.FlowcontrolV1alpha1()
-			cts := &ctlTestState{t: t,
+			cts := &ctlrTestState{t: t,
 				fcIfc:           flowcontrolClient,
 				existingFSs:     map[string]*fcv1a1.FlowSchema{},
 				existingPLs:     map[string]*fcv1a1.PriorityLevelConfiguration{},
 				heldRequestsMap: map[string][]heldRequest{},
-				queues:          map[string]*ctlTestQueueSet{},
+				queues:          map[string]*ctlrTestQueueSet{},
 			}
-			ctl := newTestableController(
+			ctlr := newTestableController(
 				informerFactory,
 				flowcontrolClient,
 				100,         // server concurrency limit
 				time.Minute, // request wait limit
+				metrics.PriorityLevelConcurrencyObserverPairGenerator,
 				cts,
 			)
-			cts.cfgCtl = ctl
+			cts.cfgCtlr = ctlr
 			persistingPLNames := sets.NewString()
 			trialStep := fmt.Sprintf("trial%d-0", i)
 			_, _, desiredPLNames, newBadPLNames := genPLs(rng, trialStep, persistingPLNames, 0)
@@ -290,7 +292,7 @@ func TestConfigConsumer(t *testing.T) {
 				for _, newFS := range newFSs {
 					t.Logf("For %s, digesting newFS=%s", trialStep, fcfmt.Fmt(newFS))
 				}
-				_ = ctl.lockAndDigestConfigObjects(newPLs, newFSs)
+				_ = ctlr.lockAndDigestConfigObjects(newPLs, newFSs)
 			}
 			for plName, hr, nCount := cts.popHeldRequest(); hr != nil; plName, hr, nCount = cts.popHeldRequest() {
 				desired := desiredPLNames.Has(plName) || mandPLs[plName] != nil
@@ -302,9 +304,9 @@ func TestConfigConsumer(t *testing.T) {
 	}
 }
 
-func checkNewFS(cts *ctlTestState, rng *rand.Rand, trialName string, ftr *fsTestingRecord, catchAlls map[bool]*fcv1a1.FlowSchema) {
+func checkNewFS(cts *ctlrTestState, rng *rand.Rand, trialName string, ftr *fsTestingRecord, catchAlls map[bool]*fcv1a1.FlowSchema) {
 	t := cts.t
-	ctl := cts.cfgCtl
+	ctlr := cts.cfgCtlr
 	fs := ftr.fs
 	expectedPLName := fs.Spec.PriorityLevelConfiguration.Name
 	ctx := context.Background()
@@ -320,17 +322,18 @@ func checkNewFS(cts *ctlTestState, rng *rand.Rand, trialName string, ftr *fsTest
 				startWG.Add(1)
 				go func(matches, isResource bool, rdu RequestDigest) {
 					expectedMatch := matches && ftr.wellFormed && (fsPrecedes(fs, catchAlls[isResource]) || fs.Name == catchAlls[isResource].Name)
-					ctl.Handle(ctx, rdu, func(matchFS *fcv1a1.FlowSchema, matchPL *fcv1a1.PriorityLevelConfiguration) {
+					ctlr.Handle(ctx, rdu, func(matchFS *fcv1a1.FlowSchema, matchPL *fcv1a1.PriorityLevelConfiguration) {
 						matchIsExempt := matchPL.Spec.Type == fcv1a1.PriorityLevelEnablementExempt
 						t.Logf("Considering FlowSchema %s, expectedMatch=%v, isResource=%v: Handle(%#+v) => note(fs=%s, pl=%s, isExempt=%v)", fs.Name, expectedMatch, isResource, rdu, matchFS.Name, matchPL.Name, matchIsExempt)
-						if e, a := expectedMatch, matchFS.Name == fs.Name; e != a {
+						if a := matchFS.Name == fs.Name; expectedMatch != a {
-							t.Errorf("Fail at %s/%s: rd=%#+v, expectedMatch=%v, actualMatch=%v, matchFSName=%q, catchAlls=%#+v", trialName, fs.Name, rdu, e, a, matchFS.Name, catchAlls)
+							t.Errorf("Fail at %s/%s: rd=%#+v, expectedMatch=%v, actualMatch=%v, matchFSName=%q, catchAlls=%#+v", trialName, fs.Name, rdu, expectedMatch, a, matchFS.Name, catchAlls)
 						}
 						if matchFS.Name == fs.Name {
-							if e, a := fs.Spec.PriorityLevelConfiguration.Name, matchPL.Name; e != a {
+							if fs.Spec.PriorityLevelConfiguration.Name != matchPL.Name {
-								t.Errorf("Fail at %s/%s: e=%v, a=%v", trialName, fs.Name, e, a)
+								t.Errorf("Fail at %s/%s: expected=%v, actual=%v", trialName, fs.Name, fs.Spec.PriorityLevelConfiguration.Name, matchPL.Name)
 							}
 						}
+					}, func(inQueue bool) {
 					}, func() {
 						startWG.Done()
 						_ = <-finishCh

staging/src/k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing/BUILD

@@ -1,12 +1,19 @@
-load("@io_bazel_rules_go//go:def.bzl", "go_library")
+load("@io_bazel_rules_go//go:def.bzl", "go_library", "go_test")
 
 go_library(
     name = "go_default_library",
-    srcs = ["interface.go"],
+    srcs = [
+        "integrator.go",
+        "interface.go",
+    ],
     importmap = "k8s.io/kubernetes/vendor/k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing",
     importpath = "k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing",
     visibility = ["//visibility:public"],
-    deps = ["//staging/src/k8s.io/apiserver/pkg/util/flowcontrol/debug:go_default_library"],
+    deps = [
+        "//staging/src/k8s.io/apimachinery/pkg/util/clock:go_default_library",
+        "//staging/src/k8s.io/apiserver/pkg/util/flowcontrol/debug:go_default_library",
+        "//staging/src/k8s.io/apiserver/pkg/util/flowcontrol/metrics:go_default_library",
+    ],
 )
 
 filegroup(
@@ -27,3 +34,10 @@ filegroup(
     tags = ["automanaged"],
     visibility = ["//visibility:public"],
 )
+
+go_test(
+    name = "go_default_test",
+    srcs = ["integrator_test.go"],
+    embed = [":go_default_library"],
+    deps = ["//staging/src/k8s.io/apimachinery/pkg/util/clock:go_default_library"],
+)

staging/src/k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing/integrator.go

@@ -0,0 +1,180 @@
+/*
+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"
+
+	"k8s.io/apimachinery/pkg/util/clock"
+	"k8s.io/apiserver/pkg/util/flowcontrol/metrics"
+)
+
+// 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.  As a `metrics.TimedObserver` this fixes X1=1 and
+// ignores attempts to change X1.
+type Integrator interface {
+	metrics.TimedObserver
+
+	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 {
+	clock clock.PassiveClock
+	sync.Mutex
+	lastTime time.Time
+	x        float64
+	moments  Moments
+	min, max float64
+}
+
+// NewIntegrator makes one that uses the given clock
+func NewIntegrator(clock clock.PassiveClock) Integrator {
+	return &integrator{
+		clock:    clock,
+		lastTime: clock.Now(),
+	}
+}
+
+func (igr *integrator) SetX1(x1 float64) {
+}
+
+func (igr *integrator) Set(x float64) {
+	igr.Lock()
+	igr.setLocked(x)
+	igr.Unlock()
+}
+
+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) Add(deltaX float64) {
+	igr.Lock()
+	igr.setLocked(igr.x + deltaX)
+	igr.Unlock()
+}
+
+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()
+}

staging/src/k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing/integrator_test.go

@@ -0,0 +1,53 @@
+/*
+Copyright 2020 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"
+	"testing"
+	"time"
+
+	"k8s.io/apimachinery/pkg/util/clock"
+)
+
+func TestIntegrator(t *testing.T) {
+	now := time.Now()
+	clk := clock.NewFakeClock(now)
+	igr := NewIntegrator(clk)
+	igr.Add(3)
+	clk.Step(time.Second)
+	results := igr.GetResults()
+	rToo := igr.Reset()
+	if e := (IntegratorResults{Duration: time.Second.Seconds(), Average: 3, Deviation: 0, Min: 0, Max: 3}); !e.Equal(&results) {
+		t.Errorf("expected %#+v, got %#+v", e, results)
+	}
+	if !results.Equal(&rToo) {
+		t.Errorf("expected %#+v, got %#+v", results, rToo)
+	}
+	igr.Set(2)
+	results = igr.GetResults()
+	if e := (IntegratorResults{Duration: 0, Average: math.NaN(), Deviation: math.NaN(), Min: 2, Max: 3}); !e.Equal(&results) {
+		t.Errorf("expected %#+v, got %#+v", e, results)
+	}
+	clk.Step(time.Millisecond)
+	igr.Add(-1)
+	clk.Step(time.Millisecond)
+	results = igr.GetResults()
+	if e := (IntegratorResults{Duration: 2 * time.Millisecond.Seconds(), Average: 1.5, Deviation: 0.5, Min: 1, Max: 3}); !e.Equal(&results) {
+		t.Errorf("expected %#+v, got %#+v", e, results)
+	}
+}

staging/src/k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing/interface.go

@@ -21,6 +21,7 @@ import (
 	"time"
 
 	"k8s.io/apiserver/pkg/util/flowcontrol/debug"
+	"k8s.io/apiserver/pkg/util/flowcontrol/metrics"
 )
 
 // QueueSetFactory is used to create QueueSet objects.  Creation, like
@@ -30,7 +31,7 @@ import (
 // before committing to a concurrency allotment for the second.
 type QueueSetFactory interface {
 	// BeginConstruction does the first phase of creating a QueueSet
-	BeginConstruction(QueuingConfig) (QueueSetCompleter, error)
+	BeginConstruction(QueuingConfig, metrics.TimedObserverPair) (QueueSetCompleter, error)
 }
 
 // QueueSetCompleter finishes the two-step process of creating or
@@ -79,7 +80,7 @@ type QueueSet interface {
 	// 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, hashValue uint64, flowDistinguisher, fsName string, descr1, descr2 interface{}) (req Request, idle bool)
+	StartRequest(ctx context.Context, 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
@@ -88,6 +89,9 @@ type QueueSet interface {
 	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

staging/src/k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing/queueset/BUILD

@@ -31,6 +31,7 @@ go_test(
     srcs = ["queueset_test.go"],
     embed = [":go_default_library"],
     deps = [
+        "//staging/src/k8s.io/apimachinery/pkg/util/clock:go_default_library",
         "//staging/src/k8s.io/apiserver/pkg/util/flowcontrol/counter:go_default_library",
         "//staging/src/k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing:go_default_library",
         "//staging/src/k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing/testing:go_default_library",

staging/src/k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing/queueset/queueset.go

@@ -49,6 +49,7 @@ type queueSetFactory struct {
 // the fields `factory` and `theSet` is non-nil.
 type queueSetCompleter struct {
 	factory *queueSetFactory
+	obsPair metrics.TimedObserverPair
 	theSet  *queueSet
 	qCfg    fq.QueuingConfig
 	dealer  *shufflesharding.Dealer
@@ -67,6 +68,7 @@ type queueSet struct {
 	clock                clock.PassiveClock
 	counter              counter.GoRoutineCounter
 	estimatedServiceTime float64
+	obsPair              metrics.TimedObserverPair
 
 	lock sync.Mutex
 
@@ -116,13 +118,14 @@ func NewQueueSetFactory(c clock.PassiveClock, counter counter.GoRoutineCounter)
 	}
 }
 
-func (qsf *queueSetFactory) BeginConstruction(qCfg fq.QueuingConfig) (fq.QueueSetCompleter, error) {
+func (qsf *queueSetFactory) BeginConstruction(qCfg fq.QueuingConfig, obsPair metrics.TimedObserverPair) (fq.QueueSetCompleter, error) {
 	dealer, err := checkConfig(qCfg)
 	if err != nil {
 		return nil, err
 	}
 	return &queueSetCompleter{
 		factory: qsf,
+		obsPair: obsPair,
 		qCfg:    qCfg,
 		dealer:  dealer}, nil
 }
@@ -148,6 +151,7 @@ func (qsc *queueSetCompleter) Complete(dCfg fq.DispatchingConfig) fq.QueueSet {
 			clock:                qsc.factory.clock,
 			counter:              qsc.factory.counter,
 			estimatedServiceTime: 60,
+			obsPair:              qsc.obsPair,
 			qCfg:                 qsc.qCfg,
 			virtualTime:          0,
 			lastRealTime:         qsc.factory.clock.Now(),
@@ -203,6 +207,12 @@ func (qs *queueSet) setConfiguration(qCfg fq.QueuingConfig, dealer *shuffleshard
 	qs.qCfg = qCfg
 	qs.dCfg = dCfg
 	qs.dealer = dealer
+	qll := qCfg.QueueLengthLimit
+	if qll < 1 {
+		qll = 1
+	}
+	qs.obsPair.RequestsWaiting.SetX1(float64(qll))
+	qs.obsPair.RequestsExecuting.SetX1(float64(dCfg.ConcurrencyLimit))
 
 	qs.dispatchAsMuchAsPossibleLocked()
 }
@@ -222,7 +232,7 @@ const (
 // executing at each point where there is a change in that quantity,
 // because the metrics --- and only the metrics --- track that
 // quantity per FlowSchema.
-func (qs *queueSet) StartRequest(ctx context.Context, hashValue uint64, flowDistinguisher, fsName string, descr1, descr2 interface{}) (fq.Request, bool) {
+func (qs *queueSet) StartRequest(ctx context.Context, hashValue uint64, flowDistinguisher, fsName string, descr1, descr2 interface{}, queueNoteFn fq.QueueNoteFn) (fq.Request, bool) {
 	qs.lockAndSyncTime()
 	defer qs.lock.Unlock()
 	var req *request
@@ -247,7 +257,7 @@ func (qs *queueSet) StartRequest(ctx context.Context, hashValue uint64, flowDist
 	// 3) Reject current request if there is not enough concurrency shares and
 	// we are at max queue length
 	// 4) If not rejected, create a request and enqueue
-	req = qs.timeoutOldRequestsAndRejectOrEnqueueLocked(ctx, hashValue, flowDistinguisher, fsName, descr1, descr2)
+	req = qs.timeoutOldRequestsAndRejectOrEnqueueLocked(ctx, hashValue, flowDistinguisher, fsName, descr1, descr2, queueNoteFn)
 	// req == nil means that the request was rejected - no remaining
 	// concurrency shares and at max queue length already
 	if req == nil {
@@ -295,6 +305,12 @@ func (qs *queueSet) StartRequest(ctx context.Context, hashValue uint64, flowDist
 	return req, false
 }
 
+func (req *request) NoteQueued(inQueue bool) {
+	if req.queueNoteFn != nil {
+		req.queueNoteFn(inQueue)
+	}
+}
+
 func (req *request) Finish(execFn func()) bool {
 	exec, idle := req.wait()
 	if !exec {
@@ -399,7 +415,7 @@ func (qs *queueSet) getVirtualTimeRatioLocked() float64 {
 // returns the enqueud request on a successful enqueue
 // returns nil in the case that there is no available concurrency or
 // the queuelengthlimit has been reached
-func (qs *queueSet) timeoutOldRequestsAndRejectOrEnqueueLocked(ctx context.Context, hashValue uint64, flowDistinguisher, fsName string, descr1, descr2 interface{}) *request {
+func (qs *queueSet) timeoutOldRequestsAndRejectOrEnqueueLocked(ctx context.Context, hashValue uint64, flowDistinguisher, fsName string, descr1, descr2 interface{}, queueNoteFn fq.QueueNoteFn) *request {
 	//	Start with the shuffle sharding, to pick a queue.
 	queueIdx := qs.chooseQueueIndexLocked(hashValue, descr1, descr2)
 	queue := qs.queues[queueIdx]
@@ -420,6 +436,7 @@ func (qs *queueSet) timeoutOldRequestsAndRejectOrEnqueueLocked(ctx context.Conte
 		queue:             queue,
 		descr1:            descr1,
 		descr2:            descr2,
+		queueNoteFn:       queueNoteFn,
 	}
 	if ok := qs.rejectOrEnqueueLocked(req); !ok {
 		return nil
@@ -463,6 +480,7 @@ func (qs *queueSet) removeTimedOutRequestsFromQueueLocked(queue *queue, fsName s
 			// get index for timed out requests
 			timeoutIdx = i
 			metrics.AddRequestsInQueues(qs.qCfg.Name, req.fsName, -1)
+			req.NoteQueued(false)
 		} else {
 			break
 		}
@@ -475,6 +493,7 @@ func (qs *queueSet) removeTimedOutRequestsFromQueueLocked(queue *queue, fsName s
 		queue.requests = reqs[removeIdx:]
 		// decrement the # of requestsEnqueued
 		qs.totRequestsWaiting -= removeIdx
+		qs.obsPair.RequestsWaiting.Add(float64(-removeIdx))
 	}
 }
 
@@ -498,16 +517,19 @@ func (qs *queueSet) rejectOrEnqueueLocked(request *request) bool {
 // enqueues a request into its queue.
 func (qs *queueSet) enqueueLocked(request *request) {
 	queue := request.queue
+	now := qs.clock.Now()
 	if len(queue.requests) == 0 && queue.requestsExecuting == 0 {
 		// the queue’s virtual start time is set to the virtual time.
 		queue.virtualStart = qs.virtualTime
 		if klog.V(6).Enabled() {
-			klog.Infof("QS(%s) at r=%s v=%.9fs: initialized queue %d virtual start time due to request %#+v %#+v", qs.qCfg.Name, qs.clock.Now().Format(nsTimeFmt), queue.virtualStart, queue.index, request.descr1, request.descr2)
+			klog.Infof("QS(%s) at r=%s v=%.9fs: initialized queue %d virtual start time due to request %#+v %#+v", qs.qCfg.Name, now.Format(nsTimeFmt), queue.virtualStart, queue.index, request.descr1, request.descr2)
 		}
 	}
 	queue.Enqueue(request)
 	qs.totRequestsWaiting++
 	metrics.AddRequestsInQueues(qs.qCfg.Name, request.fsName, 1)
+	request.NoteQueued(true)
+	qs.obsPair.RequestsWaiting.Add(1)
 }
 
 // dispatchAsMuchAsPossibleLocked runs a loop, as long as there
@@ -541,6 +563,7 @@ func (qs *queueSet) dispatchSansQueueLocked(ctx context.Context, flowDistinguish
 	req.decision.SetLocked(decisionExecute)
 	qs.totRequestsExecuting++
 	metrics.AddRequestsExecuting(qs.qCfg.Name, fsName, 1)
+	qs.obsPair.RequestsExecuting.Add(1)
 	if klog.V(5).Enabled() {
 		klog.Infof("QS(%s) at r=%s v=%.9fs: immediate dispatch of request %q %#+v %#+v, qs will have %d executing", qs.qCfg.Name, now.Format(nsTimeFmt), qs.virtualTime, fsName, descr1, descr2, qs.totRequestsExecuting)
 	}
@@ -570,7 +593,10 @@ func (qs *queueSet) dispatchLocked() bool {
 	qs.totRequestsExecuting++
 	queue.requestsExecuting++
 	metrics.AddRequestsInQueues(qs.qCfg.Name, request.fsName, -1)
+	request.NoteQueued(false)
 	metrics.AddRequestsExecuting(qs.qCfg.Name, request.fsName, 1)
+	qs.obsPair.RequestsWaiting.Add(-1)
+	qs.obsPair.RequestsExecuting.Add(1)
 	if klog.V(6).Enabled() {
 		klog.Infof("QS(%s) at r=%s v=%.9fs: dispatching request %#+v %#+v from queue %d with virtual start time %.9fs, queue will have %d waiting & %d executing", qs.qCfg.Name, request.startTime.Format(nsTimeFmt), qs.virtualTime, request.descr1, request.descr2, queue.index, queue.virtualStart, len(queue.requests), queue.requestsExecuting)
 	}
@@ -599,6 +625,8 @@ func (qs *queueSet) cancelWait(req *request) {
 			queue.requests = append(queue.requests[:i], queue.requests[i+1:]...)
 			qs.totRequestsWaiting--
 			metrics.AddRequestsInQueues(qs.qCfg.Name, req.fsName, -1)
+			req.NoteQueued(false)
+			qs.obsPair.RequestsWaiting.Add(-1)
 			break
 		}
 	}
@@ -650,17 +678,19 @@ func (qs *queueSet) finishRequestAndDispatchAsMuchAsPossible(req *request) bool
 // previously dispatched request has completed it's service.  This
 // callback updates important state in the queueSet
 func (qs *queueSet) finishRequestLocked(r *request) {
+	now := qs.clock.Now()
 	qs.totRequestsExecuting--
 	metrics.AddRequestsExecuting(qs.qCfg.Name, r.fsName, -1)
+	qs.obsPair.RequestsExecuting.Add(-1)
 
 	if r.queue == nil {
 		if klog.V(6).Enabled() {
-			klog.Infof("QS(%s) at r=%s v=%.9fs: request %#+v %#+v finished, qs will have %d executing", qs.qCfg.Name, qs.clock.Now().Format(nsTimeFmt), qs.virtualTime, r.descr1, r.descr2, qs.totRequestsExecuting)
+			klog.Infof("QS(%s) at r=%s v=%.9fs: request %#+v %#+v finished, qs will have %d executing", qs.qCfg.Name, now.Format(nsTimeFmt), qs.virtualTime, r.descr1, r.descr2, qs.totRequestsExecuting)
 		}
 		return
 	}
 
-	S := qs.clock.Since(r.startTime).Seconds()
+	S := now.Sub(r.startTime).Seconds()
 
 	// When a request finishes being served, and the actual service time was S,
 	// the queue’s virtual start time is decremented by G - S.
@@ -670,7 +700,7 @@ func (qs *queueSet) finishRequestLocked(r *request) {
 	r.queue.requestsExecuting--
 
 	if klog.V(6).Enabled() {
-		klog.Infof("QS(%s) at r=%s v=%.9fs: request %#+v %#+v finished, adjusted queue %d virtual start time to %.9fs due to service time %.9fs, queue will have %d waiting & %d executing", qs.qCfg.Name, qs.clock.Now().Format(nsTimeFmt), qs.virtualTime, r.descr1, r.descr2, r.queue.index, r.queue.virtualStart, S, len(r.queue.requests), r.queue.requestsExecuting)
+		klog.Infof("QS(%s) at r=%s v=%.9fs: request %#+v %#+v finished, adjusted queue %d virtual start time to %.9fs due to service time %.9fs, queue will have %d waiting & %d executing", qs.qCfg.Name, now.Format(nsTimeFmt), qs.virtualTime, r.descr1, r.descr2, r.queue.index, r.queue.virtualStart, S, len(r.queue.requests), r.queue.requestsExecuting)
 	}
 
 	// If there are more queues than desired and this one has no

staging/src/k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing/queueset/queueset_test.go

@@ -26,10 +26,11 @@ import (
 	"testing"
 	"time"
 
+	"k8s.io/apimachinery/pkg/util/clock"
 	"k8s.io/apiserver/pkg/util/flowcontrol/counter"
 	fq "k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing"
 	test "k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing/testing"
-	"k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing/testing/clock"
+	testclock "k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing/testing/clock"
 	"k8s.io/apiserver/pkg/util/flowcontrol/metrics"
 	"k8s.io/klog/v2"
 )
@@ -128,7 +129,7 @@ type uniformScenario struct {
 	expectAllRequests                        bool
 	evalInqueueMetrics, evalExecutingMetrics bool
 	rejectReason                             string
-	clk                                      *clock.FakeEventClock
+	clk                                      *testclock.FakeEventClock
 	counter                                  counter.GoRoutineCounter
 }
 
@@ -137,7 +138,7 @@ func (us uniformScenario) exercise(t *testing.T) {
 		t:               t,
 		uniformScenario: us,
 		startTime:       time.Now(),
-		integrators:     make([]test.Integrator, len(us.clients)),
+		integrators:     make([]fq.Integrator, len(us.clients)),
 		executions:      make([]int32, len(us.clients)),
 		rejects:         make([]int32, len(us.clients)),
 	}
@@ -152,7 +153,7 @@ type uniformScenarioState struct {
 	uniformScenario
 	startTime                          time.Time
 	doSplit                            bool
-	integrators                        []test.Integrator
+	integrators                        []fq.Integrator
 	failedCount                        uint64
 	expectedInqueue, expectedExecuting string
 	executions, rejects                []int32
@@ -164,7 +165,7 @@ func (uss *uniformScenarioState) exercise() {
 		metrics.Reset()
 	}
 	for i, uc := range uss.clients {
-		uss.integrators[i] = test.NewIntegrator(uss.clk)
+		uss.integrators[i] = fq.NewIntegrator(uss.clk)
 		fsName := fmt.Sprintf("client%d", i)
 		uss.expectedInqueue = uss.expectedInqueue + fmt.Sprintf(`				apiserver_flowcontrol_current_inqueue_requests{flowSchema=%q,priorityLevel=%q} 0%s`, fsName, uss.name, "\n")
 		for j := 0; j < uc.nThreads; j++ {
@@ -193,7 +194,7 @@ type uniformScenarioThread struct {
 	i, j   int
 	nCalls int
 	uc     uniformClient
-	igr    test.Integrator
+	igr    fq.Integrator
 	fsName string
 }
 
@@ -223,7 +224,7 @@ func (ust *uniformScenarioThread) callK(k int) {
 	if k >= ust.nCalls {
 		return
 	}
-	req, idle := ust.uss.qs.StartRequest(context.Background(), ust.uc.hash, "", ust.fsName, ust.uss.name, []int{ust.i, ust.j, k})
+	req, idle := ust.uss.qs.StartRequest(context.Background(), ust.uc.hash, "", ust.fsName, ust.uss.name, []int{ust.i, ust.j, k}, nil)
 	ust.uss.t.Logf("%s: %d, %d, %d got req=%p, idle=%v", ust.uss.clk.Now().Format(nsTimeFmt), ust.i, ust.j, k, req, idle)
 	if req == nil {
 		atomic.AddUint64(&ust.uss.failedCount, 1)
@@ -236,7 +237,8 @@ func (ust *uniformScenarioThread) callK(k int) {
 	var executed bool
 	idle2 := req.Finish(func() {
 		executed = true
-		ust.uss.t.Logf("%s: %d, %d, %d executing", ust.uss.clk.Now().Format(nsTimeFmt), ust.i, ust.j, k)
+		execStart := ust.uss.clk.Now()
+		ust.uss.t.Logf("%s: %d, %d, %d executing", execStart.Format(nsTimeFmt), ust.i, ust.j, k)
 		atomic.AddInt32(&ust.uss.executions[ust.i], 1)
 		ust.igr.Add(1)
 		ust.uss.clk.EventAfterDuration(ust.genCallK(k+1), ust.uc.execDuration+ust.uc.thinkDuration)
@@ -339,7 +341,7 @@ func (uss *uniformScenarioState) finalReview() {
 	}
 }
 
-func ClockWait(clk *clock.FakeEventClock, counter counter.GoRoutineCounter, duration time.Duration) {
+func ClockWait(clk *testclock.FakeEventClock, counter counter.GoRoutineCounter, duration time.Duration) {
 	dunch := make(chan struct{})
 	clk.EventAfterDuration(func(time.Time) {
 		counter.Add(1)
@@ -359,8 +361,8 @@ func init() {
 func TestNoRestraint(t *testing.T) {
 	metrics.Register()
 	now := time.Now()
-	clk, counter := clock.NewFakeEventClock(now, 0, nil)
+	clk, counter := testclock.NewFakeEventClock(now, 0, nil)
-	nrc, err := test.NewNoRestraintFactory().BeginConstruction(fq.QueuingConfig{})
+	nrc, err := test.NewNoRestraintFactory().BeginConstruction(fq.QueuingConfig{}, newObserverPair(clk))
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -384,7 +386,7 @@ func TestUniformFlowsHandSize1(t *testing.T) {
 	metrics.Register()
 	now := time.Now()
 
-	clk, counter := clock.NewFakeEventClock(now, 0, nil)
+	clk, counter := testclock.NewFakeEventClock(now, 0, nil)
 	qsf := NewQueueSetFactory(clk, counter)
 	qCfg := fq.QueuingConfig{
 		Name:             "TestUniformFlowsHandSize1",
@@ -393,7 +395,7 @@ func TestUniformFlowsHandSize1(t *testing.T) {
 		HandSize:         1,
 		RequestWaitLimit: 10 * time.Minute,
 	}
-	qsc, err := qsf.BeginConstruction(qCfg)
+	qsc, err := qsf.BeginConstruction(qCfg, newObserverPair(clk))
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -420,7 +422,7 @@ func TestUniformFlowsHandSize3(t *testing.T) {
 	metrics.Register()
 	now := time.Now()
 
-	clk, counter := clock.NewFakeEventClock(now, 0, nil)
+	clk, counter := testclock.NewFakeEventClock(now, 0, nil)
 	qsf := NewQueueSetFactory(clk, counter)
 	qCfg := fq.QueuingConfig{
 		Name:             "TestUniformFlowsHandSize3",
@@ -429,7 +431,7 @@ func TestUniformFlowsHandSize3(t *testing.T) {
 		HandSize:         3,
 		RequestWaitLimit: 10 * time.Minute,
 	}
-	qsc, err := qsf.BeginConstruction(qCfg)
+	qsc, err := qsf.BeginConstruction(qCfg, newObserverPair(clk))
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -455,7 +457,7 @@ func TestDifferentFlowsExpectEqual(t *testing.T) {
 	metrics.Register()
 	now := time.Now()
 
-	clk, counter := clock.NewFakeEventClock(now, 0, nil)
+	clk, counter := testclock.NewFakeEventClock(now, 0, nil)
 	qsf := NewQueueSetFactory(clk, counter)
 	qCfg := fq.QueuingConfig{
 		Name:             "DiffFlowsExpectEqual",
@@ -464,7 +466,7 @@ func TestDifferentFlowsExpectEqual(t *testing.T) {
 		HandSize:         1,
 		RequestWaitLimit: 10 * time.Minute,
 	}
-	qsc, err := qsf.BeginConstruction(qCfg)
+	qsc, err := qsf.BeginConstruction(qCfg, newObserverPair(clk))
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -491,7 +493,7 @@ func TestDifferentFlowsExpectUnequal(t *testing.T) {
 	metrics.Register()
 	now := time.Now()
 
-	clk, counter := clock.NewFakeEventClock(now, 0, nil)
+	clk, counter := testclock.NewFakeEventClock(now, 0, nil)
 	qsf := NewQueueSetFactory(clk, counter)
 	qCfg := fq.QueuingConfig{
 		Name:             "DiffFlowsExpectUnequal",
@@ -500,7 +502,7 @@ func TestDifferentFlowsExpectUnequal(t *testing.T) {
 		HandSize:         1,
 		RequestWaitLimit: 10 * time.Minute,
 	}
-	qsc, err := qsf.BeginConstruction(qCfg)
+	qsc, err := qsf.BeginConstruction(qCfg, newObserverPair(clk))
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -527,7 +529,7 @@ func TestWindup(t *testing.T) {
 	metrics.Register()
 	now := time.Now()
 
-	clk, counter := clock.NewFakeEventClock(now, 0, nil)
+	clk, counter := testclock.NewFakeEventClock(now, 0, nil)
 	qsf := NewQueueSetFactory(clk, counter)
 	qCfg := fq.QueuingConfig{
 		Name:             "TestWindup",
@@ -536,7 +538,7 @@ func TestWindup(t *testing.T) {
 		HandSize:         1,
 		RequestWaitLimit: 10 * time.Minute,
 	}
-	qsc, err := qsf.BeginConstruction(qCfg)
+	qsc, err := qsf.BeginConstruction(qCfg, newObserverPair(clk))
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -562,13 +564,13 @@ func TestDifferentFlowsWithoutQueuing(t *testing.T) {
 	metrics.Register()
 	now := time.Now()
 
-	clk, counter := clock.NewFakeEventClock(now, 0, nil)
+	clk, counter := testclock.NewFakeEventClock(now, 0, nil)
 	qsf := NewQueueSetFactory(clk, counter)
 	qCfg := fq.QueuingConfig{
 		Name:             "TestDifferentFlowsWithoutQueuing",
 		DesiredNumQueues: 0,
 	}
-	qsc, err := qsf.BeginConstruction(qCfg)
+	qsc, err := qsf.BeginConstruction(qCfg, newObserverPair(clk))
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -594,7 +596,7 @@ func TestTimeout(t *testing.T) {
 	metrics.Register()
 	now := time.Now()
 
-	clk, counter := clock.NewFakeEventClock(now, 0, nil)
+	clk, counter := testclock.NewFakeEventClock(now, 0, nil)
 	qsf := NewQueueSetFactory(clk, counter)
 	qCfg := fq.QueuingConfig{
 		Name:             "TestTimeout",
@@ -603,7 +605,7 @@ func TestTimeout(t *testing.T) {
 		HandSize:         1,
 		RequestWaitLimit: 0,
 	}
-	qsc, err := qsf.BeginConstruction(qCfg)
+	qsc, err := qsf.BeginConstruction(qCfg, newObserverPair(clk))
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -629,7 +631,7 @@ func TestContextCancel(t *testing.T) {
 	metrics.Register()
 	metrics.Reset()
 	now := time.Now()
-	clk, counter := clock.NewFakeEventClock(now, 0, nil)
+	clk, counter := testclock.NewFakeEventClock(now, 0, nil)
 	qsf := NewQueueSetFactory(clk, counter)
 	qCfg := fq.QueuingConfig{
 		Name:             "TestContextCancel",
@@ -638,18 +640,26 @@ func TestContextCancel(t *testing.T) {
 		HandSize:         1,
 		RequestWaitLimit: 15 * time.Second,
 	}
-	qsc, err := qsf.BeginConstruction(qCfg)
+	qsc, err := qsf.BeginConstruction(qCfg, newObserverPair(clk))
 	if err != nil {
 		t.Fatal(err)
 	}
 	qs := qsc.Complete(fq.DispatchingConfig{ConcurrencyLimit: 1})
 	counter.Add(1) // account for the goroutine running this test
 	ctx1 := context.Background()
-	req1, _ := qs.StartRequest(ctx1, 1, "", "fs1", "test", "one")
+	b2i := map[bool]int{false: 0, true: 1}
+	var qnc [2][2]int32
+	req1, _ := qs.StartRequest(ctx1, 1, "", "fs1", "test", "one", func(inQueue bool) { atomic.AddInt32(&qnc[0][b2i[inQueue]], 1) })
 	if req1 == nil {
 		t.Error("Request rejected")
 		return
 	}
+	if a := atomic.AddInt32(&qnc[0][0], 0); a != 1 {
+		t.Errorf("Got %d calls to queueNoteFn1(false), expected 1", a)
+	}
+	if a := atomic.AddInt32(&qnc[0][1], 0); a != 1 {
+		t.Errorf("Got %d calls to queueNoteFn1(true), expected 1", a)
+	}
 	var executed1 bool
 	idle1 := req1.Finish(func() {
 		executed1 = true
@@ -657,11 +667,17 @@ func TestContextCancel(t *testing.T) {
 		tBefore := time.Now()
 		go func() {
 			time.Sleep(time.Second)
+			if a := atomic.AddInt32(&qnc[1][0], 0); a != 0 {
+				t.Errorf("Got %d calls to queueNoteFn2(false), expected 0", a)
+			}
+			if a := atomic.AddInt32(&qnc[1][1], 0); a != 1 {
+				t.Errorf("Got %d calls to queueNoteFn2(true), expected 1", a)
+			}
 			// account for unblocking the goroutine that waits on cancelation
 			counter.Add(1)
 			cancel2()
 		}()
-		req2, idle2a := qs.StartRequest(ctx2, 2, "", "fs2", "test", "two")
+		req2, idle2a := qs.StartRequest(ctx2, 2, "", "fs2", "test", "two", func(inQueue bool) { atomic.AddInt32(&qnc[1][b2i[inQueue]], 1) })
 		if idle2a {
 			t.Error("2nd StartRequest returned idle")
 		}
@@ -672,6 +688,9 @@ func TestContextCancel(t *testing.T) {
 			if idle2b {
 				t.Error("2nd Finish returned idle")
 			}
+			if a := atomic.AddInt32(&qnc[1][0], 0); a != 1 {
+				t.Errorf("Got %d calls to queueNoteFn2(false), expected 1", a)
+			}
 		}
 		tAfter := time.Now()
 		dt := tAfter.Sub(tBefore)
@@ -686,3 +705,7 @@ func TestContextCancel(t *testing.T) {
 		t.Error("Not idle at the end")
 	}
 }
+
+func newObserverPair(clk clock.PassiveClock) metrics.TimedObserverPair {
+	return metrics.PriorityLevelConcurrencyObserverPairGenerator.Generate(1, 1, []string{"test"})
+}

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

@@ -22,6 +22,7 @@ import (
 
 	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"
 )
 
@@ -58,6 +59,8 @@ type request struct {
 
 	// Indicates whether client has called Request::Wait()
 	waitStarted bool
+
+	queueNoteFn fq.QueueNoteFn
 }
 
 // queue is an array of requests with additional metadata required for

staging/src/k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing/testing/BUILD

@@ -2,17 +2,14 @@ load("@io_bazel_rules_go//go:def.bzl", "go_library")
 
 go_library(
     name = "go_default_library",
-    srcs = [
+    srcs = ["no-restraint.go"],
-        "integrator.go",
-        "no-restraint.go",
-    ],
     importmap = "k8s.io/kubernetes/vendor/k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing/testing",
     importpath = "k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing/testing",
     visibility = ["//visibility:public"],
     deps = [
-        "//staging/src/k8s.io/apimachinery/pkg/util/clock:go_default_library",
         "//staging/src/k8s.io/apiserver/pkg/util/flowcontrol/debug:go_default_library",
         "//staging/src/k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing:go_default_library",
+        "//staging/src/k8s.io/apiserver/pkg/util/flowcontrol/metrics:go_default_library",
     ],
 )
 

staging/src/k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing/testing/integrator.go

@@ -1,116 +0,0 @@
-/*
-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 testing
-
-import (
-	"math"
-	"sync"
-	"time"
-
-	"k8s.io/apimachinery/pkg/util/clock"
-)
-
-// Integrator computes the integral of some variable X over time as
-// read from a particular clock.  The integral starts when the
-// Integrator is created, and ends at the latest operation on the
-// Integrator.
-type Integrator interface {
-	Set(float64) // set the value of X
-	Add(float64) // add the given quantity to X
-	GetResults() IntegratorResults
-	Reset() IntegratorResults // restart the integration from now
-}
-
-// IntegratorResults holds statistical abstracts of the integration
-type IntegratorResults struct {
-	Duration  float64 //seconds
-	Average   float64
-	Deviation float64 //sqrt(avg((value-avg)^2))
-}
-
-type integrator struct {
-	sync.Mutex
-	clk       clock.PassiveClock
-	lastTime  time.Time
-	x         float64
-	integrals [3]float64 // integral of x^0, x^1, and x^2
-}
-
-// NewIntegrator makes one that uses the given clock
-func NewIntegrator(clk clock.PassiveClock) Integrator {
-	return &integrator{
-		clk:      clk,
-		lastTime: clk.Now(),
-	}
-}
-
-func (igr *integrator) Set(x float64) {
-	igr.Lock()
-	igr.updateLocked()
-	igr.x = x
-	igr.Unlock()
-}
-
-func (igr *integrator) Add(deltaX float64) {
-	igr.Lock()
-	igr.updateLocked()
-	igr.x += deltaX
-	igr.Unlock()
-}
-
-func (igr *integrator) updateLocked() {
-	now := igr.clk.Now()
-	dt := now.Sub(igr.lastTime).Seconds()
-	igr.lastTime = now
-	igr.integrals[0] += dt
-	igr.integrals[1] += dt * igr.x
-	igr.integrals[2] += dt * igr.x * igr.x
-}
-
-func (igr *integrator) GetResults() (results IntegratorResults) {
-	igr.Lock()
-	defer func() { igr.Unlock() }()
-	return igr.getResultsLocked()
-}
-
-func (igr *integrator) getResultsLocked() (results IntegratorResults) {
-	igr.updateLocked()
-	results.Duration = igr.integrals[0]
-	if results.Duration <= 0 {
-		results.Average = math.NaN()
-		results.Deviation = math.NaN()
-		return
-	}
-	results.Average = igr.integrals[1] / igr.integrals[0]
-	// Deviation is sqrt( Integral( (x - xbar)^2 dt) / Duration )
-	// = 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.integrals[2]/igr.integrals[0] - results.Average*results.Average
-	if variance > 0 {
-		results.Deviation = math.Sqrt(variance)
-	}
-	return
-}
-
-func (igr *integrator) Reset() (results IntegratorResults) {
-	igr.Lock()
-	defer func() { igr.Unlock() }()
-	results = igr.getResultsLocked()
-	igr.integrals = [3]float64{0, 0, 0}
-	return
-}

staging/src/k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing/testing/no-restraint.go

@@ -21,6 +21,7 @@ import (
 
 	"k8s.io/apiserver/pkg/util/flowcontrol/debug"
 	fq "k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing"
+	"k8s.io/apiserver/pkg/util/flowcontrol/metrics"
 )
 
 // NewNoRestraintFactory makes a QueueSetFactory that produces
@@ -38,7 +39,7 @@ type noRestraint struct{}
 
 type noRestraintRequest struct{}
 
-func (noRestraintFactory) BeginConstruction(qCfg fq.QueuingConfig) (fq.QueueSetCompleter, error) {
+func (noRestraintFactory) BeginConstruction(fq.QueuingConfig, metrics.TimedObserverPair) (fq.QueueSetCompleter, error) {
 	return noRestraintCompleter{}, nil
 }
 
@@ -54,7 +55,7 @@ func (noRestraint) IsIdle() bool {
 	return false
 }
 
-func (noRestraint) StartRequest(ctx context.Context, hashValue uint64, flowDistinguisher, fsName string, descr1, descr2 interface{}) (fq.Request, bool) {
+func (noRestraint) StartRequest(ctx context.Context, hashValue uint64, flowDistinguisher, fsName string, descr1, descr2 interface{}, queueNoteFn fq.QueueNoteFn) (fq.Request, bool) {
 	return noRestraintRequest{}, false
 }
 

staging/src/k8s.io/apiserver/pkg/util/flowcontrol/gen_test.go

@@ -31,6 +31,7 @@ import (
 	"k8s.io/apiserver/pkg/endpoints/request"
 	fqtesting "k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing/testing"
 	fcfmt "k8s.io/apiserver/pkg/util/flowcontrol/format"
+	"k8s.io/apiserver/pkg/util/flowcontrol/metrics"
 )
 
 var noRestraintQSF = fqtesting.NewNoRestraintFactory()
@@ -55,7 +56,7 @@ func genPL(rng *rand.Rand, name string) *fcv1a1.PriorityLevelConfiguration {
 			HandSize:         hs,
 			QueueLengthLimit: 5}
 	}
-	_, err := qscOfPL(noRestraintQSF, nil, plc, time.Minute)
+	_, err := queueSetCompleterForPL(noRestraintQSF, nil, plc, time.Minute, metrics.PriorityLevelConcurrencyObserverPairGenerator.Generate(1, 1, []string{"test"}))
 	if err != nil {
 		panic(err)
 	}

staging/src/k8s.io/apiserver/pkg/util/flowcontrol/metrics/BUILD

@@ -2,14 +2,20 @@ load("@io_bazel_rules_go//go:def.bzl", "go_library")
 
 go_library(
     name = "go_default_library",
-    srcs = ["metrics.go"],
+    srcs = [
+        "metrics.go",
+        "sample_and_watermark.go",
+        "timed_observer.go",
+    ],
     importmap = "k8s.io/kubernetes/vendor/k8s.io/apiserver/pkg/util/flowcontrol/metrics",
     importpath = "k8s.io/apiserver/pkg/util/flowcontrol/metrics",
     visibility = ["//visibility:public"],
     deps = [
+        "//staging/src/k8s.io/apimachinery/pkg/util/clock:go_default_library",
         "//staging/src/k8s.io/component-base/metrics:go_default_library",
         "//staging/src/k8s.io/component-base/metrics/legacyregistry:go_default_library",
         "//staging/src/k8s.io/component-base/metrics/testutil:go_default_library",
+        "//vendor/k8s.io/klog/v2:go_default_library",
     ],
 )
 

staging/src/k8s.io/apiserver/pkg/util/flowcontrol/metrics/metrics.go

@@ -21,6 +21,7 @@ import (
 	"sync"
 	"time"
 
+	"k8s.io/apimachinery/pkg/util/clock"
 	compbasemetrics "k8s.io/component-base/metrics"
 	"k8s.io/component-base/metrics/legacyregistry"
 	basemetricstestutil "k8s.io/component-base/metrics/testutil"
@@ -32,8 +33,11 @@ const (
 )
 
 const (
+	requestKind   = "request_kind"
 	priorityLevel = "priorityLevel"
 	flowSchema    = "flowSchema"
+	phase         = "phase"
+	mark          = "mark"
 )
 
 var (
@@ -69,6 +73,14 @@ 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{
@@ -88,6 +100,47 @@ var (
 		},
 		[]string{priorityLevel, flowSchema},
 	)
+
+	// PriorityLevelConcurrencyObserverPairGenerator creates pairs that observe concurrency for priority levels
+	PriorityLevelConcurrencyObserverPairGenerator = NewSampleAndWaterMarkHistogramsPairGenerator(clock.RealClock{}, time.Millisecond,
+		&compbasemetrics.HistogramOpts{
+			Namespace:      namespace,
+			Subsystem:      subsystem,
+			Name:           "priority_level_request_count_samples",
+			Help:           "Periodic observations of the number of requests",
+			Buckets:        []float64{0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1},
+			StabilityLevel: compbasemetrics.ALPHA,
+		},
+		&compbasemetrics.HistogramOpts{
+			Namespace:      namespace,
+			Subsystem:      subsystem,
+			Name:           "priority_level_request_count_watermarks",
+			Help:           "Watermarks of the number of requests",
+			Buckets:        []float64{0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1},
+			StabilityLevel: compbasemetrics.ALPHA,
+		},
+		[]string{priorityLevel})
+
+	// ReadWriteConcurrencyObserverPairGenerator creates pairs that observe concurrency broken down by mutating vs readonly
+	ReadWriteConcurrencyObserverPairGenerator = NewSampleAndWaterMarkHistogramsPairGenerator(clock.RealClock{}, time.Millisecond,
+		&compbasemetrics.HistogramOpts{
+			Namespace:      namespace,
+			Subsystem:      subsystem,
+			Name:           "read_vs_write_request_count_samples",
+			Help:           "Periodic observations of the number of requests",
+			Buckets:        []float64{0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1},
+			StabilityLevel: compbasemetrics.ALPHA,
+		},
+		&compbasemetrics.HistogramOpts{
+			Namespace:      namespace,
+			Subsystem:      subsystem,
+			Name:           "read_vs_write_request_count_watermarks",
+			Help:           "Watermarks of the number of requests",
+			Buckets:        []float64{0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1},
+			StabilityLevel: compbasemetrics.ALPHA,
+		},
+		[]string{requestKind})
+
 	apiserverCurrentInqueueRequests = compbasemetrics.NewGaugeVec(
 		&compbasemetrics.GaugeOpts{
 			Namespace: namespace,
@@ -145,7 +198,7 @@ var (
 		},
 		[]string{priorityLevel, flowSchema},
 	)
-	metrics = []compbasemetrics.Registerable{
+	metrics = Registerables{
 		apiserverRejectedRequestsTotal,
 		apiserverDispatchedRequestsTotal,
 		apiserverCurrentInqueueRequests,
@@ -154,7 +207,9 @@ var (
 		apiserverCurrentExecutingRequests,
 		apiserverRequestWaitingSeconds,
 		apiserverRequestExecutionSeconds,
-	}
+	}.
+		Append(PriorityLevelConcurrencyObserverPairGenerator.metrics()...).
+		Append(ReadWriteConcurrencyObserverPairGenerator.metrics()...)
 )
 
 // AddRequestsInQueues adds the given delta to the gauge of the # of requests in the queues of the specified flowSchema and priorityLevel

staging/src/k8s.io/apiserver/pkg/util/flowcontrol/metrics/sample_and_watermark.go

@@ -0,0 +1,192 @@
+/*
+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 (
+	"sync"
+	"time"
+
+	"k8s.io/apimachinery/pkg/util/clock"
+	compbasemetrics "k8s.io/component-base/metrics"
+	"k8s.io/klog/v2"
+)
+
+const (
+	labelNameMark       = "mark"
+	labelValueLo        = "low"
+	labelValueHi        = "high"
+	labelNamePhase      = "phase"
+	labelValueWaiting   = "waiting"
+	labelValueExecuting = "executing"
+)
+
+// SampleAndWaterMarkPairGenerator makes pairs of TimedObservers that
+// track samples and watermarks.
+type SampleAndWaterMarkPairGenerator struct {
+	urGenerator SampleAndWaterMarkObserverGenerator
+}
+
+var _ TimedObserverPairGenerator = SampleAndWaterMarkPairGenerator{}
+
+// NewSampleAndWaterMarkHistogramsPairGenerator makes a new pair generator
+func NewSampleAndWaterMarkHistogramsPairGenerator(clock clock.PassiveClock, samplePeriod time.Duration, sampleOpts, waterMarkOpts *compbasemetrics.HistogramOpts, labelNames []string) SampleAndWaterMarkPairGenerator {
+	return SampleAndWaterMarkPairGenerator{
+		urGenerator: NewSampleAndWaterMarkHistogramsGenerator(clock, samplePeriod, sampleOpts, waterMarkOpts, append([]string{labelNamePhase}, labelNames...)),
+	}
+}
+
+// Generate makes a new pair
+func (spg SampleAndWaterMarkPairGenerator) Generate(waiting1, executing1 float64, labelValues []string) TimedObserverPair {
+	return TimedObserverPair{
+		RequestsWaiting:   spg.urGenerator.Generate(0, waiting1, append([]string{labelValueWaiting}, labelValues...)),
+		RequestsExecuting: spg.urGenerator.Generate(0, executing1, append([]string{labelValueExecuting}, labelValues...)),
+	}
+}
+
+func (spg SampleAndWaterMarkPairGenerator) metrics() Registerables {
+	return spg.urGenerator.metrics()
+}
+
+// SampleAndWaterMarkObserverGenerator creates TimedObservers that
+// populate histograms of samples and low- and high-water-marks.  The
+// generator has a samplePeriod, and the histograms get an observation
+// every samplePeriod.
+type SampleAndWaterMarkObserverGenerator struct {
+	*sampleAndWaterMarkObserverGenerator
+}
+
+type sampleAndWaterMarkObserverGenerator struct {
+	clock        clock.PassiveClock
+	samplePeriod time.Duration
+	samples      *compbasemetrics.HistogramVec
+	waterMarks   *compbasemetrics.HistogramVec
+}
+
+var _ TimedObserverGenerator = (*sampleAndWaterMarkObserverGenerator)(nil)
+
+// NewSampleAndWaterMarkHistogramsGenerator makes a new one
+func NewSampleAndWaterMarkHistogramsGenerator(clock clock.PassiveClock, samplePeriod time.Duration, sampleOpts, waterMarkOpts *compbasemetrics.HistogramOpts, labelNames []string) SampleAndWaterMarkObserverGenerator {
+	return SampleAndWaterMarkObserverGenerator{
+		&sampleAndWaterMarkObserverGenerator{
+			clock:        clock,
+			samplePeriod: samplePeriod,
+			samples:      compbasemetrics.NewHistogramVec(sampleOpts, labelNames),
+			waterMarks:   compbasemetrics.NewHistogramVec(waterMarkOpts, append([]string{labelNameMark}, labelNames...)),
+		}}
+}
+
+func (swg *sampleAndWaterMarkObserverGenerator) quantize(when time.Time) int64 {
+	return when.UnixNano() / int64(swg.samplePeriod)
+}
+
+// Generate makes a new TimedObserver
+func (swg *sampleAndWaterMarkObserverGenerator) Generate(x, x1 float64, labelValues []string) TimedObserver {
+	relX := x / x1
+	when := swg.clock.Now()
+	return &sampleAndWaterMarkHistograms{
+		sampleAndWaterMarkObserverGenerator: swg,
+		labelValues:                         labelValues,
+		loLabelValues:                       append([]string{labelValueLo}, labelValues...),
+		hiLabelValues:                       append([]string{labelValueHi}, labelValues...),
+		x1:                                  x1,
+		sampleAndWaterMarkAccumulator: sampleAndWaterMarkAccumulator{
+			lastSet:    when,
+			lastSetInt: swg.quantize(when),
+			x:          x,
+			relX:       relX,
+			loRelX:     relX,
+			hiRelX:     relX,
+		}}
+}
+
+func (swg *sampleAndWaterMarkObserverGenerator) metrics() Registerables {
+	return Registerables{swg.samples, swg.waterMarks}
+}
+
+type sampleAndWaterMarkHistograms struct {
+	*sampleAndWaterMarkObserverGenerator
+	labelValues                  []string
+	loLabelValues, hiLabelValues []string
+
+	sync.Mutex
+	x1 float64
+	sampleAndWaterMarkAccumulator
+}
+
+type sampleAndWaterMarkAccumulator struct {
+	lastSet        time.Time
+	lastSetInt     int64 // lastSet / samplePeriod
+	x              float64
+	relX           float64 // x / x1
+	loRelX, hiRelX float64
+}
+
+var _ TimedObserver = (*sampleAndWaterMarkHistograms)(nil)
+
+func (saw *sampleAndWaterMarkHistograms) Add(deltaX float64) {
+	saw.innerSet(func() {
+		saw.x += deltaX
+	})
+}
+
+func (saw *sampleAndWaterMarkHistograms) Set(x float64) {
+	saw.innerSet(func() {
+		saw.x = x
+	})
+}
+
+func (saw *sampleAndWaterMarkHistograms) SetX1(x1 float64) {
+	saw.innerSet(func() {
+		saw.x1 = x1
+	})
+}
+
+func (saw *sampleAndWaterMarkHistograms) innerSet(updateXOrX1 func()) {
+	saw.Lock()
+	when := saw.clock.Now()
+	whenInt := saw.quantize(when)
+	acc := saw.sampleAndWaterMarkAccumulator
+	wellOrdered := !when.Before(acc.lastSet)
+	if wellOrdered {
+		updateXOrX1()
+		saw.relX = saw.x / saw.x1
+		if acc.lastSetInt < whenInt {
+			saw.loRelX, saw.hiRelX = acc.relX, acc.relX
+			saw.lastSetInt = whenInt
+		}
+		if saw.relX < saw.loRelX {
+			saw.loRelX = saw.relX
+		} else if saw.relX > saw.hiRelX {
+			saw.hiRelX = saw.relX
+		}
+		saw.lastSet = when
+	}
+	saw.Unlock()
+	if !wellOrdered {
+		lastSetS := acc.lastSet.Format(time.RFC3339Nano)
+		whenS := when.Format(time.RFC3339Nano)
+		klog.Fatalf("Time went backwards from %s to %s for labelValues=%#+v", lastSetS, whenS, saw.labelValues)
+		panic(append([]string{lastSetS, whenS}, saw.labelValues...))
+	}
+	for acc.lastSetInt < whenInt {
+		saw.samples.WithLabelValues(saw.labelValues...).Observe(acc.relX)
+		saw.waterMarks.WithLabelValues(saw.loLabelValues...).Observe(acc.loRelX)
+		saw.waterMarks.WithLabelValues(saw.hiLabelValues...).Observe(acc.hiRelX)
+		acc.lastSetInt++
+		acc.loRelX, acc.hiRelX = acc.relX, acc.relX
+	}
+}

staging/src/k8s.io/apiserver/pkg/util/flowcontrol/metrics/timed_observer.go

@@ -0,0 +1,52 @@
+/*
+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
+
+// TimedObserver gets informed about the values assigned to a variable
+// `X float64` over time, and reports on the ratio `X/X1`.
+type TimedObserver interface {
+	// Add notes a change to the variable
+	Add(deltaX float64)
+
+	// Set notes a setting of the variable
+	Set(x float64)
+
+	// SetX1 changes the value to use for X1
+	SetX1(x1 float64)
+}
+
+// TimedObserverGenerator creates related observers that are
+// differentiated by a series of label values
+type TimedObserverGenerator interface {
+	Generate(x, x1 float64, labelValues []string) TimedObserver
+}
+
+// TimedObserverPair is a corresponding pair of observers, one for the
+// number of requests waiting in queue(s) and one for the number of
+// requests being executed
+type TimedObserverPair struct {
+	// RequestsWaiting is given observations of the number of currently queued requests
+	RequestsWaiting TimedObserver
+
+	// RequestsExecuting is given observations of the number of requests currently executing
+	RequestsExecuting TimedObserver
+}
+
+// TimedObserverPairGenerator generates pairs
+type TimedObserverPairGenerator interface {
+	Generate(waiting1, executing1 float64, labelValues []string) TimedObserverPair
+}