+++ /dev/null
-/*
- *
- * Copyright 2017 gRPC 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 transport
-
-import (
- "sync"
- "time"
-)
-
-const (
- // bdpLimit is the maximum value the flow control windows
- // will be increased to.
- bdpLimit = (1 << 20) * 4
- // alpha is a constant factor used to keep a moving average
- // of RTTs.
- alpha = 0.9
- // If the current bdp sample is greater than or equal to
- // our beta * our estimated bdp and the current bandwidth
- // sample is the maximum bandwidth observed so far, we
- // increase our bbp estimate by a factor of gamma.
- beta = 0.66
- // To put our bdp to be smaller than or equal to twice the real BDP,
- // we should multiply our current sample with 4/3, however to round things out
- // we use 2 as the multiplication factor.
- gamma = 2
-)
-
-// Adding arbitrary data to ping so that its ack can be identified.
-// Easter-egg: what does the ping message say?
-var bdpPing = &ping{data: [8]byte{2, 4, 16, 16, 9, 14, 7, 7}}
-
-type bdpEstimator struct {
- // sentAt is the time when the ping was sent.
- sentAt time.Time
-
- mu sync.Mutex
- // bdp is the current bdp estimate.
- bdp uint32
- // sample is the number of bytes received in one measurement cycle.
- sample uint32
- // bwMax is the maximum bandwidth noted so far (bytes/sec).
- bwMax float64
- // bool to keep track of the beginning of a new measurement cycle.
- isSent bool
- // Callback to update the window sizes.
- updateFlowControl func(n uint32)
- // sampleCount is the number of samples taken so far.
- sampleCount uint64
- // round trip time (seconds)
- rtt float64
-}
-
-// timesnap registers the time bdp ping was sent out so that
-// network rtt can be calculated when its ack is received.
-// It is called (by controller) when the bdpPing is
-// being written on the wire.
-func (b *bdpEstimator) timesnap(d [8]byte) {
- if bdpPing.data != d {
- return
- }
- b.sentAt = time.Now()
-}
-
-// add adds bytes to the current sample for calculating bdp.
-// It returns true only if a ping must be sent. This can be used
-// by the caller (handleData) to make decision about batching
-// a window update with it.
-func (b *bdpEstimator) add(n uint32) bool {
- b.mu.Lock()
- defer b.mu.Unlock()
- if b.bdp == bdpLimit {
- return false
- }
- if !b.isSent {
- b.isSent = true
- b.sample = n
- b.sentAt = time.Time{}
- b.sampleCount++
- return true
- }
- b.sample += n
- return false
-}
-
-// calculate is called when an ack for a bdp ping is received.
-// Here we calculate the current bdp and bandwidth sample and
-// decide if the flow control windows should go up.
-func (b *bdpEstimator) calculate(d [8]byte) {
- // Check if the ping acked for was the bdp ping.
- if bdpPing.data != d {
- return
- }
- b.mu.Lock()
- rttSample := time.Since(b.sentAt).Seconds()
- if b.sampleCount < 10 {
- // Bootstrap rtt with an average of first 10 rtt samples.
- b.rtt += (rttSample - b.rtt) / float64(b.sampleCount)
- } else {
- // Heed to the recent past more.
- b.rtt += (rttSample - b.rtt) * float64(alpha)
- }
- b.isSent = false
- // The number of bytes accumulated so far in the sample is smaller
- // than or equal to 1.5 times the real BDP on a saturated connection.
- bwCurrent := float64(b.sample) / (b.rtt * float64(1.5))
- if bwCurrent > b.bwMax {
- b.bwMax = bwCurrent
- }
- // If the current sample (which is smaller than or equal to the 1.5 times the real BDP) is
- // greater than or equal to 2/3rd our perceived bdp AND this is the maximum bandwidth seen so far, we
- // should update our perception of the network BDP.
- if float64(b.sample) >= beta*float64(b.bdp) && bwCurrent == b.bwMax && b.bdp != bdpLimit {
- sampleFloat := float64(b.sample)
- b.bdp = uint32(gamma * sampleFloat)
- if b.bdp > bdpLimit {
- b.bdp = bdpLimit
- }
- bdp := b.bdp
- b.mu.Unlock()
- b.updateFlowControl(bdp)
- return
- }
- b.mu.Unlock()
-}
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