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Johannes Würbach 2020-09-27 22:14:53 +02:00
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/*
Copyright 2019 The Kubernetes Authors.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
// Package queueset implements a technique called "fair queuing for
// server requests". One QueueSet is a set of queues operating
// according to this technique.
//
// Fair queuing for server requests is inspired by the fair queuing
// technique from the world of networking. You can find a good paper
// on that at https://dl.acm.org/citation.cfm?doid=75247.75248 or
// http://people.csail.mit.edu/imcgraw/links/research/pubs/networks/WFQ.pdf
// and there is an implementation outline in the Wikipedia article at
// https://en.wikipedia.org/wiki/Fair_queuing .
//
// Fair queuing for server requests differs from traditional fair
// queuing in three ways: (1) we are dispatching application layer
// requests to a server rather than transmitting packets on a network
// link, (2) multiple requests can be executing at once, and (3) the
// service time (execution duration) is not known until the execution
// completes.
//
// The first two differences can easily be handled by straightforward
// adaptation of the concept called "R(t)" in the original paper and
// "virtual time" in the implementation outline. In that
// implementation outline, the notation now() is used to mean reading
// the virtual clock. In the original paper’s terms, "R(t)" is the
// number of "rounds" that have been completed at real time t ---
// where a round consists of virtually transmitting one bit from every
// non-empty queue in the router (regardless of which queue holds the
// packet that is really being transmitted at the moment); in this
// conception, a packet is considered to be "in" its queue until the
// packet’s transmission is finished. For our problem, we can define a
// round to be giving one nanosecond of CPU to every non-empty queue
// in the apiserver (where emptiness is judged based on both queued
// and executing requests from that queue), and define R(t) = (server
// start time) + (1 ns) * (number of rounds since server start). Let
// us write NEQ(t) for that number of non-empty queues in the
// apiserver at time t. Let us also write C for the concurrency
// limit. In the original paper, the partial derivative of R(t) with
// respect to t is
//
// 1 / NEQ(t) .
//
// To generalize from transmitting one packet at a time to executing C
// requests at a time, that derivative becomes
//
// C / NEQ(t) .
//
// However, sometimes there are fewer than C requests available to
// execute. For a given queue "q", let us also write "reqs(q, t)" for
// the number of requests of that queue that are executing at that
// time. The total number of requests executing is sum[over q]
// reqs(q, t) and if that is less than C then virtual time is not
// advancing as fast as it would if all C seats were occupied; in this
// case the numerator of the quotient in that derivative should be
// adjusted proportionally. Putting it all together for fair queing
// for server requests: at a particular time t, the partial derivative
// of R(t) with respect to t is
//
// min( C, sum[over q] reqs(q, t) ) / NEQ(t) .
//
// In terms of the implementation outline, this is the rate at which
// virtual time is advancing at time t (in virtual nanoseconds per
// real nanosecond). Where the networking implementation outline adds
// packet size to a virtual time, in our version this corresponds to
// adding a service time (i.e., duration) to virtual time.
//
// The third difference is handled by modifying the algorithm to
// dispatch based on an initial guess at the request’s service time
// (duration) and then make the corresponding adjustments once the
// request’s actual service time is known. This is similar, although
// not exactly isomorphic, to the original paper’s adjustment by
// `$\delta$` for the sake of promptness.
//
// For implementation simplicity (see below), let us use the same
// initial service time guess for every request; call that duration
// G. A good choice might be the service time limit (1
// minute). Different guesses will give slightly different dynamics,
// but any positive number can be used for G without ruining the
// long-term behavior.
//
// As in ordinary fair queuing, there is a bound on divergence from
// the ideal. In plain fair queuing the bound is one packet; in our
// version it is C requests.
//
// To support efficiently making the necessary adjustments once a
// request’s actual service time is known, the virtual finish time of
// a request and the last virtual finish time of a queue are not
// represented directly but instead computed from queue length,
// request position in the queue, and an alternate state variable that
// holds the queue’s virtual start time. While the queue is empty and
// has no requests executing: the value of its virtual start time
// variable is ignored and its last virtual finish time is considered
// to be in the virtual past. When a request arrives to an empty queue
// with no requests executing, the queue’s virtual start time is set
// to the current virtual time. The virtual finish time of request
// number J in the queue (counting from J=1 for the head) is J * G +
// (queue's virtual start time). While the queue is non-empty: the
// last virtual finish time of the queue is the virtual finish time of
// the last request in the queue. While the queue is empty and has a
// request executing: the last virtual finish time is the queue’s
// virtual start time. When a request is dequeued for service the
// queue’s virtual start time is advanced by G. When a request
// finishes being served, and the actual service time was S, the
// queue’s virtual start time is decremented by G - S.
//
package queueset

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/*
Copyright 2019 The Kubernetes Authors.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
package queueset
import (
"context"
"fmt"
"math"
"sync"
"time"
"github.com/pkg/errors"
"k8s.io/apimachinery/pkg/util/clock"
"k8s.io/apimachinery/pkg/util/runtime"
"k8s.io/apiserver/pkg/util/flowcontrol/counter"
fq "k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing"
"k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing/promise/lockingpromise"
"k8s.io/apiserver/pkg/util/flowcontrol/metrics"
"k8s.io/apiserver/pkg/util/shufflesharding"
"k8s.io/klog"
)
const nsTimeFmt = "2006-01-02 15:04:05.000000000"
// queueSetFactory implements the QueueSetFactory interface
// queueSetFactory makes QueueSet objects.
type queueSetFactory struct {
counter counter.GoRoutineCounter
clock clock.PassiveClock
}
// `*queueSetCompleter` implements QueueSetCompleter. Exactly one of
// the fields `factory` and `theSet` is non-nil.
type queueSetCompleter struct {
factory *queueSetFactory
theSet *queueSet
qCfg fq.QueuingConfig
dealer *shufflesharding.Dealer
}
// queueSet implements the Fair Queuing for Server Requests technique
// described in this package's doc, and a pointer to one implements
// the QueueSet interface. The clock, GoRoutineCounter, and estimated
// service time should not be changed; the fields listed after the
// lock must be accessed only while holding the lock. The methods of
// this type follow the naming convention that the suffix "Locked"
// means the caller must hold the lock; for a method whose name does
// not end in "Locked" either acquires the lock or does not care about
// locking.
type queueSet struct {
clock clock.PassiveClock
counter counter.GoRoutineCounter
estimatedServiceTime float64
lock sync.Mutex
// qCfg holds the current queuing configuration. Its
// DesiredNumQueues may be less than the current number of queues.
// If its DesiredNumQueues is zero then its other queuing
// parameters retain the settings they had when DesiredNumQueues
// was last non-zero (if ever).
qCfg fq.QueuingConfig
// the current dispatching configuration.
dCfg fq.DispatchingConfig
// If `config.DesiredNumQueues` is non-zero then dealer is not nil
// and is good for `config`.
dealer *shufflesharding.Dealer
// queues may be longer than the desired number, while the excess
// queues are still draining.
queues []*queue
// virtualTime is the number of virtual seconds since process startup
virtualTime float64
// lastRealTime is what `clock.Now()` yielded when `virtualTime` was last updated
lastRealTime time.Time
// robinIndex is the index of the last queue dispatched
robinIndex int
// totRequestsWaiting is the sum, over all the queues, of the
// number of requests waiting in that queue
totRequestsWaiting int
// totRequestsExecuting is the total number of requests of this
// queueSet that are currently executing. That is the same as the
// sum, over all the queues, of the number of requests executing
// from that queue.
totRequestsExecuting int
}
// NewQueueSetFactory creates a new QueueSetFactory object
func NewQueueSetFactory(c clock.PassiveClock, counter counter.GoRoutineCounter) fq.QueueSetFactory {
return &queueSetFactory{
counter: counter,
clock: c,
}
}
func (qsf *queueSetFactory) BeginConstruction(qCfg fq.QueuingConfig) (fq.QueueSetCompleter, error) {
dealer, err := checkConfig(qCfg)
if err != nil {
return nil, err
}
return &queueSetCompleter{
factory: qsf,
qCfg: qCfg,
dealer: dealer}, nil
}
// checkConfig returns a non-nil Dealer if the config is valid and
// calls for one, and returns a non-nil error if the given config is
// invalid.
func checkConfig(qCfg fq.QueuingConfig) (*shufflesharding.Dealer, error) {
if qCfg.DesiredNumQueues == 0 {
return nil, nil
}
dealer, err := shufflesharding.NewDealer(qCfg.DesiredNumQueues, qCfg.HandSize)
if err != nil {
err = errors.Wrap(err, "the QueueSetConfig implies an invalid shuffle sharding config (DesiredNumQueues is deckSize)")
}
return dealer, err
}
func (qsc *queueSetCompleter) Complete(dCfg fq.DispatchingConfig) fq.QueueSet {
qs := qsc.theSet
if qs == nil {
qs = &queueSet{
clock: qsc.factory.clock,
counter: qsc.factory.counter,
estimatedServiceTime: 60,
qCfg: qsc.qCfg,
virtualTime: 0,
lastRealTime: qsc.factory.clock.Now(),
}
}
qs.setConfiguration(qsc.qCfg, qsc.dealer, dCfg)
return qs
}
// createQueues is a helper method for initializing an array of n queues
func createQueues(n, baseIndex int) []*queue {
fqqueues := make([]*queue, n)
for i := 0; i < n; i++ {
fqqueues[i] = &queue{index: baseIndex + i, requests: make([]*request, 0)}
}
return fqqueues
}
func (qs *queueSet) BeginConfigChange(qCfg fq.QueuingConfig) (fq.QueueSetCompleter, error) {
dealer, err := checkConfig(qCfg)
if err != nil {
return nil, err
}
return &queueSetCompleter{
theSet: qs,
qCfg: qCfg,
dealer: dealer}, nil
}
// SetConfiguration is used to set the configuration for a queueSet.
// Update handling for when fields are updated is handled here as well -
// eg: if DesiredNum is increased, SetConfiguration reconciles by
// adding more queues.
func (qs *queueSet) setConfiguration(qCfg fq.QueuingConfig, dealer *shufflesharding.Dealer, dCfg fq.DispatchingConfig) {
qs.lockAndSyncTime()
defer qs.lock.Unlock()
if qCfg.DesiredNumQueues > 0 {
// Adding queues is the only thing that requires immediate action
// Removing queues is handled by omitting indexes >DesiredNum from
// chooseQueueIndexLocked
numQueues := len(qs.queues)
if qCfg.DesiredNumQueues > numQueues {
qs.queues = append(qs.queues,
createQueues(qCfg.DesiredNumQueues-numQueues, len(qs.queues))...)
}
} else {
qCfg.QueueLengthLimit = qs.qCfg.QueueLengthLimit
qCfg.HandSize = qs.qCfg.HandSize
qCfg.RequestWaitLimit = qs.qCfg.RequestWaitLimit
}
qs.qCfg = qCfg
qs.dCfg = dCfg
qs.dealer = dealer
qs.dispatchAsMuchAsPossibleLocked()
}
// A decision about a request
type requestDecision int
// Values passed through a request's decision
const (
decisionExecute requestDecision = iota
decisionReject
decisionCancel
)
// StartRequest begins the process of handling a request. We take the
// approach of updating the metrics about total requests queued and
// 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, fsName string, descr1, descr2 interface{}) (fq.Request, bool) {
qs.lockAndSyncTime()
defer qs.lock.Unlock()
var req *request
// ========================================================================
// Step 0:
// Apply only concurrency limit, if zero queues desired
if qs.qCfg.DesiredNumQueues < 1 {
if qs.totRequestsExecuting >= qs.dCfg.ConcurrencyLimit {
klog.V(5).Infof("QS(%s): rejecting request %q %#+v %#+v because %d are executing and the limit is %d", qs.qCfg.Name, fsName, descr1, descr2, qs.totRequestsExecuting, qs.dCfg.ConcurrencyLimit)
metrics.AddReject(qs.qCfg.Name, fsName, "concurrency-limit")
return nil, qs.isIdleLocked()
}
req = qs.dispatchSansQueueLocked(ctx, fsName, descr1, descr2)
return req, false
}
// ========================================================================
// Step 1:
// 1) Start with shuffle sharding, to pick a queue.
// 2) Reject old requests that have been waiting too long
// 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, fsName, descr1, descr2)
// req == nil means that the request was rejected - no remaining
// concurrency shares and at max queue length already
if req == nil {
klog.V(5).Infof("QS(%s): rejecting request %q %#+v %#+v due to queue full", qs.qCfg.Name, fsName, descr1, descr2)
metrics.AddReject(qs.qCfg.Name, fsName, "queue-full")
return nil, qs.isIdleLocked()
}
// ========================================================================
// Step 2:
// The next step is to invoke the method that dequeues as much
// as possible.
// This method runs a loop, as long as there are non-empty
// queues and the number currently executing is less than the
// assured concurrency value. The body of the loop uses the
// fair queuing technique to pick a queue and dispatch a
// request from that queue.
qs.dispatchAsMuchAsPossibleLocked()
// ========================================================================
// Step 3:
// Set up a relay from the context's Done channel to the world
// of well-counted goroutines. We Are Told that every
// request's context's Done channel gets closed by the time
// the request is done being processed.
doneCh := ctx.Done()
if doneCh != nil {
qs.preCreateOrUnblockGoroutine()
go func() {
defer runtime.HandleCrash()
qs.goroutineDoneOrBlocked()
_ = <-doneCh
// Whatever goroutine unblocked the preceding receive MUST
// have already either (a) incremented qs.counter or (b)
// known that said counter is not actually counting or (c)
// known that the count does not need to be accurate.
// BTW, the count only needs to be accurate in a test that
// uses FakeEventClock::Run().
klog.V(6).Infof("QS(%s): Context of request %q %#+v %#+v is Done", qs.qCfg.Name, fsName, descr1, descr2)
qs.cancelWait(req)
qs.goroutineDoneOrBlocked()
}()
}
return req, false
}
func (req *request) Finish(execFn func()) bool {
exec, idle := req.wait()
if !exec {
return idle
}
execFn()
return req.qs.finishRequestAndDispatchAsMuchAsPossible(req)
}
func (req *request) wait() (bool, bool) {
qs := req.qs
qs.lock.Lock()
defer qs.lock.Unlock()
if req.waitStarted {
// This can not happen, because the client is forbidden to
// call Wait twice on the same request
panic(fmt.Sprintf("Multiple calls to the Wait method, QueueSet=%s, startTime=%s, descr1=%#+v, descr2=%#+v", req.qs.qCfg.Name, req.startTime, req.descr1, req.descr2))
}
req.waitStarted = true
// ========================================================================
// Step 4:
// The final step is to wait on a decision from
// somewhere and then act on it.
decisionAny := req.decision.GetLocked()
qs.syncTimeLocked()
decision, isDecision := decisionAny.(requestDecision)
if !isDecision {
panic(fmt.Sprintf("QS(%s): Impossible decision %#+v (of type %T) for request %#+v %#+v", qs.qCfg.Name, decisionAny, decisionAny, req.descr1, req.descr2))
}
switch decision {
case decisionReject:
klog.V(5).Infof("QS(%s): request %#+v %#+v timed out after being enqueued\n", qs.qCfg.Name, req.descr1, req.descr2)
metrics.AddReject(qs.qCfg.Name, req.fsName, "time-out")
return false, qs.isIdleLocked()
case decisionCancel:
// TODO(aaron-prindle) add metrics for this case
klog.V(5).Infof("QS(%s): Ejecting request %#+v %#+v from its queue", qs.qCfg.Name, req.descr1, req.descr2)
return false, qs.isIdleLocked()
case decisionExecute:
klog.V(5).Infof("QS(%s): Dispatching request %#+v %#+v from its queue", qs.qCfg.Name, req.descr1, req.descr2)
return true, false
default:
// This can not happen, all possible values are handled above
panic(decision)
}
}
func (qs *queueSet) IsIdle() bool {
qs.lock.Lock()
defer qs.lock.Unlock()
return qs.isIdleLocked()
}
func (qs *queueSet) isIdleLocked() bool {
return qs.totRequestsWaiting == 0 && qs.totRequestsExecuting == 0
}
// lockAndSyncTime acquires the lock and updates the virtual time.
// Doing them together avoids the mistake of modify some queue state
// before calling syncTimeLocked.
func (qs *queueSet) lockAndSyncTime() {
qs.lock.Lock()
qs.syncTimeLocked()
}
// syncTimeLocked updates the virtual time based on the assumption
// that the current state of the queues has been in effect since
// `qs.lastRealTime`. Thus, it should be invoked after acquiring the
// lock and before modifying the state of any queue.
func (qs *queueSet) syncTimeLocked() {
realNow := qs.clock.Now()
timeSinceLast := realNow.Sub(qs.lastRealTime).Seconds()
qs.lastRealTime = realNow
qs.virtualTime += timeSinceLast * qs.getVirtualTimeRatioLocked()
}
// getVirtualTimeRatio calculates the rate at which virtual time has
// been advancing, according to the logic in `doc.go`.
func (qs *queueSet) getVirtualTimeRatioLocked() float64 {
activeQueues := 0
reqs := 0
for _, queue := range qs.queues {
reqs += queue.requestsExecuting
if len(queue.requests) > 0 || queue.requestsExecuting > 0 {
activeQueues++
}
}
if activeQueues == 0 {
return 0
}
return math.Min(float64(reqs), float64(qs.dCfg.ConcurrencyLimit)) / float64(activeQueues)
}
// timeoutOldRequestsAndRejectOrEnqueueLocked encapsulates the logic required
// to validate and enqueue a request for the queueSet/QueueSet:
// 1) Start with shuffle sharding, to pick a queue.
// 2) Reject old requests that have been waiting too long
// 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
// 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, fsName string, descr1, descr2 interface{}) *request {
// Start with the shuffle sharding, to pick a queue.
queueIdx := qs.chooseQueueIndexLocked(hashValue, descr1, descr2)
queue := qs.queues[queueIdx]
// The next step is the logic to reject requests that have been waiting too long
qs.removeTimedOutRequestsFromQueueLocked(queue, fsName)
// NOTE: currently timeout is only checked for each new request. This means that there can be
// requests that are in the queue longer than the timeout if there are no new requests
// We prefer the simplicity over the promptness, at least for now.
// Create a request and enqueue
req := &request{
qs: qs,
fsName: fsName,
ctx: ctx,
decision: lockingpromise.NewWriteOnce(&qs.lock, qs.counter),
arrivalTime: qs.clock.Now(),
queue: queue,
descr1: descr1,
descr2: descr2,
}
if ok := qs.rejectOrEnqueueLocked(req); !ok {
return nil
}
metrics.ObserveQueueLength(qs.qCfg.Name, fsName, len(queue.requests))
return req
}
// chooseQueueIndexLocked uses shuffle sharding to select a queue index
// using the given hashValue and the shuffle sharding parameters of the queueSet.
func (qs *queueSet) chooseQueueIndexLocked(hashValue uint64, descr1, descr2 interface{}) int {
bestQueueIdx := -1
bestQueueLen := int(math.MaxInt32)
// the dealer uses the current desired number of queues, which is no larger than the number in `qs.queues`.
qs.dealer.Deal(hashValue, func(queueIdx int) {
thisLen := len(qs.queues[queueIdx].requests)
klog.V(7).Infof("QS(%s): For request %#+v %#+v considering queue %d of length %d", qs.qCfg.Name, descr1, descr2, queueIdx, thisLen)
if thisLen < bestQueueLen {
bestQueueIdx, bestQueueLen = queueIdx, thisLen
}
})
klog.V(6).Infof("QS(%s): For request %#+v %#+v chose queue %d, had %d waiting & %d executing", qs.qCfg.Name, descr1, descr2, bestQueueIdx, bestQueueLen, qs.queues[bestQueueIdx].requestsExecuting)
return bestQueueIdx
}
// removeTimedOutRequestsFromQueueLocked rejects old requests that have been enqueued
// past the requestWaitLimit
func (qs *queueSet) removeTimedOutRequestsFromQueueLocked(queue *queue, fsName string) {
timeoutIdx := -1
now := qs.clock.Now()
reqs := queue.requests
// reqs are sorted oldest -> newest
// can short circuit loop (break) if oldest requests are not timing out
// as newer requests also will not have timed out
// now - requestWaitLimit = waitLimit
waitLimit := now.Add(-qs.qCfg.RequestWaitLimit)
for i, req := range reqs {
if waitLimit.After(req.arrivalTime) {
req.decision.SetLocked(decisionReject)
// get index for timed out requests
timeoutIdx = i
metrics.AddRequestsInQueues(qs.qCfg.Name, req.fsName, -1)
} else {
break
}
}
// remove timed out requests from queue
if timeoutIdx != -1 {
// timeoutIdx + 1 to remove the last timeout req
removeIdx := timeoutIdx + 1
// remove all the timeout requests
queue.requests = reqs[removeIdx:]
// decrement the # of requestsEnqueued
qs.totRequestsWaiting -= removeIdx
}
}
// rejectOrEnqueueLocked rejects or enqueues the newly arrived
// request, which has been assigned to a queue. If up against the
// queue length limit and the concurrency limit then returns false.
// Otherwise enqueues and returns true.
func (qs *queueSet) rejectOrEnqueueLocked(request *request) bool {
queue := request.queue
curQueueLength := len(queue.requests)
// rejects the newly arrived request if resource criteria not met
if qs.totRequestsExecuting >= qs.dCfg.ConcurrencyLimit &&
curQueueLength >= qs.qCfg.QueueLengthLimit {
return false
}
qs.enqueueLocked(request)
return true
}
// enqueues a request into its queue.
func (qs *queueSet) enqueueLocked(request *request) {
queue := request.queue
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) {
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)
}
}
queue.Enqueue(request)
qs.totRequestsWaiting++
metrics.AddRequestsInQueues(qs.qCfg.Name, request.fsName, 1)
}
// dispatchAsMuchAsPossibleLocked runs a loop, as long as there
// are non-empty queues and the number currently executing is less than the
// assured concurrency value. The body of the loop uses the fair queuing
// technique to pick a queue, dequeue the request at the head of that
// queue, increment the count of the number executing, and send true
// to the request's channel.
func (qs *queueSet) dispatchAsMuchAsPossibleLocked() {
for qs.totRequestsWaiting != 0 && qs.totRequestsExecuting < qs.dCfg.ConcurrencyLimit {
ok := qs.dispatchLocked()
if !ok {
break
}
}
}
func (qs *queueSet) dispatchSansQueueLocked(ctx context.Context, fsName string, descr1, descr2 interface{}) *request {
now := qs.clock.Now()
req := &request{
qs: qs,
fsName: fsName,
ctx: ctx,
startTime: now,
decision: lockingpromise.NewWriteOnce(&qs.lock, qs.counter),
arrivalTime: now,
descr1: descr1,
descr2: descr2,
}
req.decision.SetLocked(decisionExecute)
qs.totRequestsExecuting++
metrics.AddRequestsExecuting(qs.qCfg.Name, fsName, 1)
if klog.V(5) {
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)
}
return req
}
// dispatchLocked uses the Fair Queuing for Server Requests method to
// select a queue and dispatch the oldest request in that queue. The
// return value indicates whether a request was dispatched; this will
// be false when there are no requests waiting in any queue.
func (qs *queueSet) dispatchLocked() bool {
queue := qs.selectQueueLocked()
if queue == nil {
return false
}
request, ok := queue.Dequeue()
if !ok { // This should never happen. But if it does...
return false
}
request.startTime = qs.clock.Now()
// At this moment the request leaves its queue and starts
// executing. We do not recognize any interim state between
// "queued" and "executing". While that means "executing"
// includes a little overhead from this package, this is not a
// problem because other overhead is also included.
qs.totRequestsWaiting--
qs.totRequestsExecuting++
queue.requestsExecuting++
metrics.AddRequestsInQueues(qs.qCfg.Name, request.fsName, -1)
metrics.AddRequestsExecuting(qs.qCfg.Name, request.fsName, 1)
if klog.V(6) {
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)
}
// When a request is dequeued for service -> qs.virtualStart += G
queue.virtualStart += qs.estimatedServiceTime
request.decision.SetLocked(decisionExecute)
return ok
}
// cancelWait ensures the request is not waiting. This is only
// applicable to a request that has been assigned to a queue.
func (qs *queueSet) cancelWait(req *request) {
qs.lock.Lock()
defer qs.lock.Unlock()
if req.decision.IsSetLocked() {
// The request has already been removed from the queue
// and so we consider its wait to be over.
return
}
req.decision.SetLocked(decisionCancel)
queue := req.queue
// remove the request from the queue as it has timed out
for i := range queue.requests {
if req == queue.requests[i] {
// remove the request
queue.requests = append(queue.requests[:i], queue.requests[i+1:]...)
qs.totRequestsWaiting--
metrics.AddRequestsInQueues(qs.qCfg.Name, req.fsName, -1)
break
}
}
return
}
// selectQueueLocked examines the queues in round robin order and
// returns the first one of those for which the virtual finish time of
// the oldest waiting request is minimal.
func (qs *queueSet) selectQueueLocked() *queue {
minVirtualFinish := math.Inf(1)
var minQueue *queue
var minIndex int
nq := len(qs.queues)
for range qs.queues {
qs.robinIndex = (qs.robinIndex + 1) % nq
queue := qs.queues[qs.robinIndex]
if len(queue.requests) != 0 {
currentVirtualFinish := queue.GetVirtualFinish(0, qs.estimatedServiceTime)
if currentVirtualFinish < minVirtualFinish {
minVirtualFinish = currentVirtualFinish
minQueue = queue
minIndex = qs.robinIndex
}
}
}
// we set the round robin indexing to start at the chose queue
// for the next round. This way the non-selected queues
// win in the case that the virtual finish times are the same
qs.robinIndex = minIndex
return minQueue
}
// finishRequestAndDispatchAsMuchAsPossible is a convenience method
// which calls finishRequest for a given request and then dispatches
// as many requests as possible. This is all of what needs to be done
// once a request finishes execution or is canceled. This returns a bool
// indicating whether the QueueSet is now idle.
func (qs *queueSet) finishRequestAndDispatchAsMuchAsPossible(req *request) bool {
qs.lockAndSyncTime()
defer qs.lock.Unlock()
qs.finishRequestLocked(req)
qs.dispatchAsMuchAsPossibleLocked()
return qs.isIdleLocked()
}
// finishRequestLocked is a callback that should be used when a
// previously dispatched request has completed it's service. This
// callback updates important state in the queueSet
func (qs *queueSet) finishRequestLocked(r *request) {
qs.totRequestsExecuting--
metrics.AddRequestsExecuting(qs.qCfg.Name, r.fsName, -1)
if r.queue == nil {
if klog.V(6) {
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)
}
return
}
S := qs.clock.Since(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.
r.queue.virtualStart -= qs.estimatedServiceTime - S
// request has finished, remove from requests executing
r.queue.requestsExecuting--
if klog.V(6) {
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)
}
// If there are more queues than desired and this one has no
// requests then remove it
if len(qs.queues) > qs.qCfg.DesiredNumQueues &&
len(r.queue.requests) == 0 &&
r.queue.requestsExecuting == 0 {
qs.queues = removeQueueAndUpdateIndexes(qs.queues, r.queue.index)
// decrement here to maintain the invariant that (qs.robinIndex+1) % numQueues
// is the index of the next queue after the one last dispatched from
if qs.robinIndex >= r.queue.index {
qs.robinIndex--
}
}
}
// removeQueueAndUpdateIndexes uses reslicing to remove an index from a slice
// and then updates the 'index' field of the queues to be correct
func removeQueueAndUpdateIndexes(queues []*queue, index int) []*queue {
keptQueues := append(queues[:index], queues[index+1:]...)
for i := index; i < len(keptQueues); i++ {
keptQueues[i].index--
}
return keptQueues
}
// preCreateOrUnblockGoroutine needs to be called before creating a
// goroutine associated with this queueSet or unblocking a blocked
// one, to properly update the accounting used in testing.
func (qs *queueSet) preCreateOrUnblockGoroutine() {
qs.counter.Add(1)
}
// goroutineDoneOrBlocked needs to be called at the end of every
// goroutine associated with this queueSet or when such a goroutine is
// about to wait on some other goroutine to do something; this is to
// properly update the accounting used in testing.
func (qs *queueSet) goroutineDoneOrBlocked() {
qs.counter.Add(-1)
}

96
vendor/k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing/queueset/types.go generated vendored Normal file
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@ -0,0 +1,96 @@
/*
Copyright 2019 The Kubernetes Authors.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
package queueset
import (
"context"
"time"
"k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing/promise"
)
// request is a temporary container for "requests" with additional
// tracking fields required for the functionality FQScheduler
type request struct {
qs *queueSet
fsName string
ctx context.Context
// The relevant queue. Is nil if this request did not go through
// a queue.
queue *queue
// startTime is the real time when the request began executing
startTime time.Time
// decision gets set to a `requestDecision` indicating what to do
// with this request. It gets set exactly once, when the request
// is removed from its queue. The value will be decisionReject,
// decisionCancel, or decisionExecute; decisionTryAnother never
// appears here.
decision promise.LockingWriteOnce
// arrivalTime is the real time when the request entered this system
arrivalTime time.Time
// descr1 and descr2 are not used in any logic but they appear in
// log messages
descr1, descr2 interface{}
// Indicates whether client has called Request::Wait()
waitStarted bool
}
// queue is an array of requests with additional metadata required for
// the FQScheduler
type queue struct {
requests []*request
// virtualStart is the virtual time (virtual seconds since process
// startup) when the oldest request in the queue (if there is any)
// started virtually executing
virtualStart float64
requestsExecuting int
index int
}
// Enqueue enqueues a request into the queue
func (q *queue) Enqueue(request *request) {
q.requests = append(q.requests, request)
}
// Dequeue dequeues a request from the queue
func (q *queue) Dequeue() (*request, bool) {
if len(q.requests) == 0 {
return nil, false
}
request := q.requests[0]
q.requests = q.requests[1:]
return request, true
}
// GetVirtualFinish returns the expected virtual finish time of the request at
// index J in the queue with estimated finish time G
func (q *queue) GetVirtualFinish(J int, G float64) float64 {
// The virtual finish time of request number J in the queue
// (counting from J=1 for the head) is J * G + (virtual start time).
// counting from J=1 for the head (eg: queue.requests[0] -> J=1) - J+1
jg := float64(J+1) * float64(G)
return jg + q.virtualStart
}