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2c236f6495
Currently only setting `--styleCheck:hint` as there are some dependency fixes required and the compiler seems to trip over the findnode MessageKind, findnode Message field and the findNode proc. Also over protocol.Protocol usage.
103 lines
3.9 KiB
Nim
103 lines
3.9 KiB
Nim
# Copyright (c) 2021 Status Research & Development GmbH
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# Licensed and distributed under either of
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# * MIT license (license terms in the root directory or at https://opensource.org/licenses/MIT).
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# * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0).
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# at your option. This file may not be copied, modified, or distributed except according to those terms.
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{.push raises: [Defect].}
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import
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chronos,
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./utp_utils
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const targetDelay = milliseconds(100)
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# explanation from reference impl:
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# number of bytes to increase max window size by, per RTT. This is
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# scaled down linearly proportional to off_target. i.e. if all packets
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# in one window have 0 delay, window size will increase by this number.
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# Typically it's less. TCP increases one MSS per RTT, which is 1500
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const maxCwndIncreaseBytesPerRtt = 3000
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const minWindowSize = 10
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proc applyCongestionControl*(
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currentMaxWindowSize: uint32,
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currentSlowStart: bool,
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currentSlowStartTreshold: uint32,
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maxSndBufferSize: uint32,
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currentPacketSize: uint32,
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actualDelay: Duration,
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numOfAckedBytes: uint32,
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minRtt: Duration,
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calculatedDelay: Duration,
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clockDrift: int32
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): (uint32, uint32, bool) =
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if (actualDelay.isZero() or minRtt.isZero() or numOfAckedBytes == 0):
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return (currentMaxWindowSize, currentSlowStartTreshold, currentSlowStart)
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let ourDelay = min(minRtt, calculatedDelay)
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let target = targetDelay
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# Rationale from C reference impl:
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# this is here to compensate for very large clock drift that affects
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# the congestion controller into giving certain endpoints an unfair
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# share of the bandwidth. We have an estimate of the clock drift
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# (clock_drift). The unit of this is microseconds per 5 seconds.
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# empirically, a reasonable cut-off appears to be about 200000
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# (which is pretty high). The main purpose is to compensate for
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# people trying to "cheat" uTP by making their clock run slower,
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# and this definitely catches that without any risk of false positives
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# if clock_drift < -200000 start applying a penalty delay proportional
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# to how far beoynd -200000 the clock drift is
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let clockDriftPenalty: int64 =
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if (clockDrift < -200000):
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let penalty = (-clockDrift - 200000) div 7
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penalty
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else:
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0
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let offTarget = target.microseconds() - (ourDelay.microseconds() + clockDriftPenalty)
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# calculations from reference impl:
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# double window_factor = (double)min(bytes_acked, max_window) / (double)max(max_window, bytes_acked);
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# double delay_factor = off_target / target;
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# double scaled_gain = MAX_CWND_INCREASE_BYTES_PER_RTT * window_factor * delay_factor;
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let windowFactor = float64(min(numOfAckedBytes, currentMaxWindowSize)) / float64(max(currentMaxWindowSize, numOfAckedBytes))
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let delayFactor = float64(offTarget) / float64(target.microseconds())
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let scaledGain = maxCwndIncreaseBytesPerRtt * windowFactor * delayFactor
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let scaledWindow = float64(currentMaxWindowSize) + scaledGain
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let ledbatCwnd: uint32 =
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if scaledWindow < minWindowSize:
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uint32(minWindowSize)
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else:
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uint32(scaledWindow)
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var newSlowStart = currentSlowStart
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var newMaxWindowSize = currentMaxWindowSize
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var newSlowStartTreshold = currentSlowStartTreshold
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if currentSlowStart:
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let slowStartCwnd = currentMaxWindowSize + uint32(windowFactor * float64(currentPacketSize))
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if (slowStartCwnd > currentSlowStartTreshold):
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newSlowStart = false
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elif float64(ourDelay.microseconds()) > float64(target.microseconds()) * 0.9:
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# we are just a litte under target delay, discontinute slows start
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newSlowStart = false
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newSlowStartTreshold = currentMaxWindowSize
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else:
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newMaxWindowSize = max(slowStartCwnd, ledbatCwnd)
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else:
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newMaxWindowSize = ledbatCwnd
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newMaxWindowSize = clamp(newMaxWindowSize, minWindowSize, maxSndBufferSize)
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(newMaxWindowSize, newSlowStartTreshold, newSlowStart)
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