-
Notifications
You must be signed in to change notification settings - Fork 5
/
manager.go
462 lines (424 loc) · 15.8 KB
/
manager.go
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
// Copyright 2018 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
package flowcontrol
import (
"fmt"
"math"
"sync"
"time"
"github.com/ethereum/go-ethereum/common/mclock"
"github.com/ethereum/go-ethereum/common/prque"
)
// cmNodeFields are ClientNode fields used by the client manager
// Note: these fields are locked by the client manager's mutex
type cmNodeFields struct {
corrBufValue int64 // buffer value adjusted with the extra recharge amount
rcLastIntValue int64 // past recharge integrator value when corrBufValue was last updated
rcFullIntValue int64 // future recharge integrator value when corrBufValue will reach maximum
queueIndex int // position in the recharge queue (-1 if not queued)
}
// FixedPointMultiplier is applied to the recharge integrator and the recharge curve.
//
// Note: fixed point arithmetic is required for the integrator because it is a
// constantly increasing value that can wrap around int64 limits (which behavior is
// also supported by the priority queue). A floating point value would gradually lose
// precision in this application.
// The recharge curve and all recharge values are encoded as fixed point because
// sumRecharge is frequently updated by adding or subtracting individual recharge
// values and perfect precision is required.
const FixedPointMultiplier = 1000000
var (
capacityDropFactor = 0.1
capacityRaiseTC = 1 / (3 * float64(time.Hour)) // time constant for raising the capacity factor
capacityRaiseThresholdRatio = 1.125 // total/connected capacity ratio threshold for raising the capacity factor
)
// ClientManager controls the capacity assigned to the clients of a server.
// Since ServerParams guarantee a safe lower estimate for processable requests
// even in case of all clients being active, ClientManager calculates a
// corrigated buffer value and usually allows a higher remaining buffer value
// to be returned with each reply.
type ClientManager struct {
clock mclock.Clock
lock sync.Mutex
enabledCh chan struct{}
stop chan chan struct{}
curve PieceWiseLinear
sumRecharge, totalRecharge, totalConnected uint64
logTotalCap, totalCapacity float64
logTotalCapRaiseLimit float64
minLogTotalCap, maxLogTotalCap float64
capacityRaiseThreshold uint64
capLastUpdate mclock.AbsTime
totalCapacityCh chan uint64
// recharge integrator is increasing in each moment with a rate of
// (totalRecharge / sumRecharge)*FixedPointMultiplier or 0 if sumRecharge==0
rcLastUpdate mclock.AbsTime // last time the recharge integrator was updated
rcLastIntValue int64 // last updated value of the recharge integrator
// recharge queue is a priority queue with currently recharging client nodes
// as elements. The priority value is rcFullIntValue which allows to quickly
// determine which client will first finish recharge.
rcQueue *prque.Prque
}
// NewClientManager returns a new client manager.
// Client manager enhances flow control performance by allowing client buffers
// to recharge quicker than the minimum guaranteed recharge rate if possible.
// The sum of all minimum recharge rates (sumRecharge) is updated each time
// a clients starts or finishes buffer recharging. Then an adjusted total
// recharge rate is calculated using a piecewise linear recharge curve:
//
// totalRecharge = curve(sumRecharge)
// (totalRecharge >= sumRecharge is enforced)
//
// Then the "bonus" buffer recharge is distributed between currently recharging
// clients proportionally to their minimum recharge rates.
//
// Note: total recharge is proportional to the average number of parallel running
// serving threads. A recharge value of 1000000 corresponds to one thread in average.
// The maximum number of allowed serving threads should always be considerably
// higher than the targeted average number.
//
// Note 2: although it is possible to specify a curve allowing the total target
// recharge starting from zero sumRecharge, it makes sense to add a linear ramp
// starting from zero in order to not let a single low-priority client use up
// the entire server capacity and thus ensure quick availability for others at
// any moment.
func NewClientManager(curve PieceWiseLinear, clock mclock.Clock) *ClientManager {
cm := &ClientManager{
clock: clock,
rcQueue: prque.New(func(a interface{}, i int) { a.(*ClientNode).queueIndex = i }),
capLastUpdate: clock.Now(),
stop: make(chan chan struct{}),
}
if curve != nil {
cm.SetRechargeCurve(curve)
}
go func() {
// regularly recalculate and update total capacity
for {
select {
case <-time.After(time.Minute):
cm.lock.Lock()
cm.updateTotalCapacity(cm.clock.Now(), true)
cm.lock.Unlock()
case stop := <-cm.stop:
close(stop)
return
}
}
}()
return cm
}
// Stop stops the client manager
func (cm *ClientManager) Stop() {
stop := make(chan struct{})
cm.stop <- stop
<-stop
}
// SetRechargeCurve updates the recharge curve
func (cm *ClientManager) SetRechargeCurve(curve PieceWiseLinear) {
cm.lock.Lock()
defer cm.lock.Unlock()
now := cm.clock.Now()
cm.updateRecharge(now)
cm.curve = curve
if len(curve) > 0 {
cm.totalRecharge = curve[len(curve)-1].Y
} else {
cm.totalRecharge = 0
}
}
// SetCapacityRaiseThreshold sets a threshold value used for raising capFactor.
// Either if the difference between total allowed and connected capacity is less
// than this threshold or if their ratio is less than capacityRaiseThresholdRatio
// then capFactor is allowed to slowly raise.
func (cm *ClientManager) SetCapacityLimits(min, max, raiseThreshold uint64) {
if min < 1 {
min = 1
}
cm.minLogTotalCap = math.Log(float64(min))
if max < 1 {
max = 1
}
cm.maxLogTotalCap = math.Log(float64(max))
cm.logTotalCap = cm.maxLogTotalCap
cm.capacityRaiseThreshold = raiseThreshold
cm.refreshCapacity()
}
// connect should be called when a client is connected, before passing it to any
// other ClientManager function
func (cm *ClientManager) connect(node *ClientNode) {
cm.lock.Lock()
defer cm.lock.Unlock()
now := cm.clock.Now()
cm.updateRecharge(now)
node.corrBufValue = int64(node.params.BufLimit)
node.rcLastIntValue = cm.rcLastIntValue
node.queueIndex = -1
cm.updateTotalCapacity(now, true)
cm.totalConnected += node.params.MinRecharge
cm.updateRaiseLimit()
}
// disconnect should be called when a client is disconnected
func (cm *ClientManager) disconnect(node *ClientNode) {
cm.lock.Lock()
defer cm.lock.Unlock()
now := cm.clock.Now()
cm.updateRecharge(cm.clock.Now())
cm.updateTotalCapacity(now, true)
cm.totalConnected -= node.params.MinRecharge
cm.updateRaiseLimit()
}
// accepted is called when a request with given maximum cost is accepted.
// It returns a priority indicator for the request which is used to determine placement
// in the serving queue. Older requests have higher priority by default. If the client
// is almost out of buffer, request priority is reduced.
func (cm *ClientManager) accepted(node *ClientNode, maxCost uint64, now mclock.AbsTime) (priority int64) {
cm.lock.Lock()
defer cm.lock.Unlock()
cm.updateNodeRc(node, -int64(maxCost), &node.params, now)
rcTime := (node.params.BufLimit - uint64(node.corrBufValue)) * FixedPointMultiplier / node.params.MinRecharge
return -int64(now) - int64(rcTime)
}
// processed updates the client buffer according to actual request cost after
// serving has been finished.
//
// Note: processed should always be called for all accepted requests
func (cm *ClientManager) processed(node *ClientNode, maxCost, realCost uint64, now mclock.AbsTime) {
if realCost > maxCost {
realCost = maxCost
}
cm.updateBuffer(node, int64(maxCost-realCost), now)
}
// updateBuffer recalulates the corrected buffer value, adds the given value to it
// and updates the node's actual buffer value if possible
func (cm *ClientManager) updateBuffer(node *ClientNode, add int64, now mclock.AbsTime) {
cm.lock.Lock()
defer cm.lock.Unlock()
cm.updateNodeRc(node, add, &node.params, now)
if node.corrBufValue > node.bufValue {
if node.log != nil {
node.log.add(now, fmt.Sprintf("corrected bv=%d oldBv=%d", node.corrBufValue, node.bufValue))
}
node.bufValue = node.corrBufValue
}
}
// updateParams updates the flow control parameters of a client node
func (cm *ClientManager) updateParams(node *ClientNode, params ServerParams, now mclock.AbsTime) {
cm.lock.Lock()
defer cm.lock.Unlock()
cm.updateRecharge(now)
cm.updateTotalCapacity(now, true)
cm.totalConnected += params.MinRecharge - node.params.MinRecharge
cm.updateRaiseLimit()
cm.updateNodeRc(node, 0, ¶ms, now)
}
// updateRaiseLimit recalculates the limiting value until which logTotalCap
// can be raised when no client freeze events occur
func (cm *ClientManager) updateRaiseLimit() {
if cm.capacityRaiseThreshold == 0 {
cm.logTotalCapRaiseLimit = 0
return
}
limit := float64(cm.totalConnected + cm.capacityRaiseThreshold)
limit2 := float64(cm.totalConnected) * capacityRaiseThresholdRatio
if limit2 > limit {
limit = limit2
}
if limit < 1 {
limit = 1
}
cm.logTotalCapRaiseLimit = math.Log(limit)
}
// updateRecharge updates the recharge integrator and checks the recharge queue
// for nodes with recently filled buffers
func (cm *ClientManager) updateRecharge(now mclock.AbsTime) {
lastUpdate := cm.rcLastUpdate
cm.rcLastUpdate = now
// updating is done in multiple steps if node buffers are filled and sumRecharge
// is decreased before the given target time
for cm.sumRecharge > 0 {
sumRecharge := cm.sumRecharge
if sumRecharge > cm.totalRecharge {
sumRecharge = cm.totalRecharge
}
bonusRatio := float64(1)
v := cm.curve.ValueAt(sumRecharge)
s := float64(sumRecharge)
if v > s && s > 0 {
bonusRatio = v / s
}
dt := now - lastUpdate
// fetch the client that finishes first
rcqNode := cm.rcQueue.PopItem().(*ClientNode) // if sumRecharge > 0 then the queue cannot be empty
// check whether it has already finished
dtNext := mclock.AbsTime(float64(rcqNode.rcFullIntValue-cm.rcLastIntValue) / bonusRatio)
if dt < dtNext {
// not finished yet, put it back, update integrator according
// to current bonusRatio and return
cm.rcQueue.Push(rcqNode, -rcqNode.rcFullIntValue)
cm.rcLastIntValue += int64(bonusRatio * float64(dt))
return
}
lastUpdate += dtNext
// finished recharging, update corrBufValue and sumRecharge if necessary and do next step
if rcqNode.corrBufValue < int64(rcqNode.params.BufLimit) {
rcqNode.corrBufValue = int64(rcqNode.params.BufLimit)
cm.sumRecharge -= rcqNode.params.MinRecharge
}
cm.rcLastIntValue = rcqNode.rcFullIntValue
}
}
// updateNodeRc updates a node's corrBufValue and adds an external correction value.
// It also adds or removes the rcQueue entry and updates ServerParams and sumRecharge if necessary.
func (cm *ClientManager) updateNodeRc(node *ClientNode, bvc int64, params *ServerParams, now mclock.AbsTime) {
cm.updateRecharge(now)
wasFull := true
if node.corrBufValue != int64(node.params.BufLimit) {
wasFull = false
node.corrBufValue += (cm.rcLastIntValue - node.rcLastIntValue) * int64(node.params.MinRecharge) / FixedPointMultiplier
if node.corrBufValue > int64(node.params.BufLimit) {
node.corrBufValue = int64(node.params.BufLimit)
}
node.rcLastIntValue = cm.rcLastIntValue
}
node.corrBufValue += bvc
diff := int64(params.BufLimit - node.params.BufLimit)
if diff > 0 {
node.corrBufValue += diff
}
isFull := false
if node.corrBufValue >= int64(params.BufLimit) {
node.corrBufValue = int64(params.BufLimit)
isFull = true
}
if !wasFull {
cm.sumRecharge -= node.params.MinRecharge
}
if params != &node.params {
node.params = *params
}
if !isFull {
cm.sumRecharge += node.params.MinRecharge
if node.queueIndex != -1 {
cm.rcQueue.Remove(node.queueIndex)
}
node.rcLastIntValue = cm.rcLastIntValue
node.rcFullIntValue = cm.rcLastIntValue + (int64(node.params.BufLimit)-node.corrBufValue)*FixedPointMultiplier/int64(node.params.MinRecharge)
cm.rcQueue.Push(node, -node.rcFullIntValue)
}
}
// reduceTotalCapacity reduces the total capacity allowance in case of a client freeze event
func (cm *ClientManager) reduceTotalCapacity(frozenCap uint64) {
cm.lock.Lock()
defer cm.lock.Unlock()
ratio := float64(1)
if frozenCap < cm.totalConnected {
ratio = float64(frozenCap) / float64(cm.totalConnected)
}
now := cm.clock.Now()
cm.updateTotalCapacity(now, false)
cm.logTotalCap -= capacityDropFactor * ratio
if cm.logTotalCap < cm.minLogTotalCap {
cm.logTotalCap = cm.minLogTotalCap
}
cm.updateTotalCapacity(now, true)
}
// updateTotalCapacity updates the total capacity factor. The capacity factor allows
// the total capacity of the system to go over the allowed total recharge value
// if clients go to frozen state sufficiently rarely.
// The capacity factor is dropped instantly by a small amount if a clients is frozen.
// It is raised slowly (with a large time constant) if the total connected capacity
// is close to the total allowed amount and no clients are frozen.
func (cm *ClientManager) updateTotalCapacity(now mclock.AbsTime, refresh bool) {
dt := now - cm.capLastUpdate
cm.capLastUpdate = now
if cm.logTotalCap < cm.logTotalCapRaiseLimit {
cm.logTotalCap += capacityRaiseTC * float64(dt)
if cm.logTotalCap > cm.logTotalCapRaiseLimit {
cm.logTotalCap = cm.logTotalCapRaiseLimit
}
}
if cm.logTotalCap > cm.maxLogTotalCap {
cm.logTotalCap = cm.maxLogTotalCap
}
if refresh {
cm.refreshCapacity()
}
}
// refreshCapacity recalculates the total capacity value and sends an update to the subscription
// channel if the relative change of the value since the last update is more than 0.1 percent
func (cm *ClientManager) refreshCapacity() {
totalCapacity := math.Exp(cm.logTotalCap)
if totalCapacity >= cm.totalCapacity*0.999 && totalCapacity <= cm.totalCapacity*1.001 {
return
}
cm.totalCapacity = totalCapacity
if cm.totalCapacityCh != nil {
select {
case cm.totalCapacityCh <- uint64(cm.totalCapacity):
default:
}
}
}
// SubscribeTotalCapacity returns all future updates to the total capacity value
// through a channel and also returns the current value
func (cm *ClientManager) SubscribeTotalCapacity(ch chan uint64) uint64 {
cm.lock.Lock()
defer cm.lock.Unlock()
cm.totalCapacityCh = ch
return uint64(cm.totalCapacity)
}
// PieceWiseLinear is used to describe recharge curves
type PieceWiseLinear []struct{ X, Y uint64 }
// ValueAt returns the curve's value at a given point
func (pwl PieceWiseLinear) ValueAt(x uint64) float64 {
l := 0
h := len(pwl)
if h == 0 {
return 0
}
for h != l {
m := (l + h) / 2
if x > pwl[m].X {
l = m + 1
} else {
h = m
}
}
if l == 0 {
return float64(pwl[0].Y)
}
l--
if h == len(pwl) {
return float64(pwl[l].Y)
}
dx := pwl[h].X - pwl[l].X
if dx < 1 {
return float64(pwl[l].Y)
}
return float64(pwl[l].Y) + float64(pwl[h].Y-pwl[l].Y)*float64(x-pwl[l].X)/float64(dx)
}
// Valid returns true if the X coordinates of the curve points are non-strictly monotonic
func (pwl PieceWiseLinear) Valid() bool {
var lastX uint64
for _, i := range pwl {
if i.X < lastX {
return false
}
lastX = i.X
}
return true
}