[tor-bugs] #24694 [Core Tor/Tor]: sched: Use the socket RTT in KIST to compute a more accurate extra space

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#24694: sched: Use the socket RTT in KIST to compute a more accurate extra space
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 Reporter:  dgoulet          |          Owner:  (none)
     Type:  enhancement      |         Status:  new
 Priority:  Medium           |      Milestone:  Tor: 0.3.3.x-final
Component:  Core Tor/Tor     |        Version:
 Severity:  Normal           |     Resolution:
 Keywords:  tor-sched, kist  |  Actual Points:
Parent ID:                   |         Points:
 Reviewer:                   |        Sponsor:
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Comment (by yawning):

 ISTR suggesting to look at `tcpi_snd_ssthresh` as well back in the
 original KIST ticket as well, but I'll bring it up because this ticket is
 about "making better capacity decisions".

 While my suggestion was to increase the scheduling frequency for a
 connection while it was in Slow Start (because `SND.CWND` will double on
 each ACK), instead I would probably be less aggressive about feeding a
 connection more data while `SND.CWND < ssthresh` (because `SND.CWND` will
 overshoot what is possible by the link and you're way over buffered at
 that point).

 My assertion here is that while a connection is in slow start, the
 congestion window is an insufficiently accurate estimate of actual link
 capacity to serve as a good measure for how much buffering to do.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/24694#comment:2>
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