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Merge branch 'tor-gitlab/mr/75'

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David Goulet 2023-01-10 16:17:06 -05:00
commit 773fc92000
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proposals/324-rtt-congestion-control.txt
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@ -144,20 +144,22 @@ measured by the RTT estimator, and if these heurtics detect a stall or a jump,
we do not use that value to update RTT or BDP, nor do we update any congestion
control algorithm information that round.
If the time delta is 0, that is always treated as a clock stall.
If the time delta is 0, that is always treated as a clock stall, the RTT is
not used, congestion control is not updated, and this fact is cached globally.
If we have measured at least 'cc_bwe_min' RTT values or we have successfully
exited slow start, then every sendme ACK, the new candidate RTT is compared to
the stored EWMA RTT. If the new RTT is either 5000 times larger than the EWMA
RTT, or 5000 times smaller than the stored EWMA RTT, then we do not record that
estimate, and do not update BDP or the congestion control algorithms for that
SENDME ack.
If the circuit does not yet have an EWMA RTT or it is still in Slow Start, then
no further checks are performed, and the RTT is used.
Moreover, if a clock stall is detected by *any* circuit, this fact is
cached, and this cached value is used on circuits for which we do not
have enough data to compute the above heueristics. This cached value is
also exported for use by the edge connection rate calculations done by
[XON_ADVISORY].
If the circuit has stored an EWMA RTT and has exited Slow Start, then every
sendme ACK, the new candidate RTT is compared to the stored EWMA RTT. If the
new RTT is 5000 times larger than the EWMA RTT, then the circuit does not
record that estimate, and does not update BDP or the congestion control
algorithms for that SENDME ack. If the new RTT is 5000 times smaller than the
EWMA RTT, then the circuit uses the globally cached value from above (ie: it
assumes the clock is stalled *only* if there was previously *also* a 0-delta RTT).
If both ratio checks pass, the globally cached clock stall state is set to
false (no stall), and the RTT value is used.
2.1.2. N_EWMA Smoothing [N_EWMA_SMOOTHING]