Loss recovery at tail

hiren panchasara hiren at strugglingcoder.info
Fri Nov 18 23:13:15 UTC 2016

On 11/18/16 at 09:20P, Michael Tuexen wrote:
> Dear all,
> in the last telco we discussed the behaviour when that last N packets are dropped.
> It was mentioned that multiple retransmission timers where used to recover.
> I wrote a packetdrill script which
> * Get the cwnd to 30 segments
> * Sends 30 segments, which all get lost
> * Observe how the 30 dropped segments are retransmitted.
> It uses only a single timeout as one would expect.
> So this script does NOT reproduce the problem, but I'm attaching it such that
> you can see how the stack behaves.
> Tested with FreeBSD head r308802.

Thanks for testing.

https://reviews.freebsd.org/D8556 was the issue detecting a valid
RTO as bad and resetting snd_nxt to snd_max (instead of snd_una as done by
valid RTO) causing us to not trigger retransmit of missed packets but
wait for RTO for all of lost packets.

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