If a circuit only sends a tiny amount of data such that its cwnd is not
full, it won't increase its cwnd above the minimum. Since slow start circuits
should never hit the minimum otherwise, we can just ignore them for RTT reset
to handle this.
Since these are derived from the number of SENDMEs in a cwnd/cc update,
and a cwnd should not exceed ~10k, there's plenty of room in uint16_t
for them, even if the network gets significantly faster.
Also provides some stickiness, so that once full, the congestion window is
considered still full for the rest of an update cycle, or the entire
congestion window.
In this way, we avoid increasing the congestion window if it is not fully
utilized, but we can still back off in this case. This substantially reduces
queue use in Shadow.
Since these are derived from the number of SENDMEs in a cwnd/cc update,
and a cwnd should not exceed ~10k, there's plenty of room in uint16_t
for them, even if the network gets significantly faster.
Also provides some stickiness, so that once full, the congestion window is
considered still full for the rest of an update cycle, or the entire
congestion window.
In this way, we avoid increasing the congestion window if it is not fully
utilized, but we can still back off in this case. This substantially reduces
queue use in Shadow.
Having no TotalBuildTimes along a positive CircuitBuildAbandonedCount
count lead to a segfault. We check for that condition and then BUG + log
warn if that is the case.
It should never happened in theory but if someone modified their state
file, it can lead to this problem so instead of segfaulting, warn.
Fixes#40437
Signed-off-by: David Goulet <dgoulet@torproject.org>
