From 4d418f8da85f0d8be80ce32ca17c67bfd5451c9d Mon Sep 17 00:00:00 2001 From: Randall Stewart Date: Tue, 16 Jun 2020 12:26:23 +0000 Subject: [PATCH] So it turns out rack has a shortcoming in dup-ack counting. It counts the dupacks but then does not properly respond to them. This is because a few missing bits are not present. BBR actually does properly respond (though it also sends a TLP which is interesting and maybe something to fix).. Sponsored by: Netflix Inc. Differential Revision: https://reviews.freebsd.org/D25294 --- sys/netinet/tcp_stacks/rack.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/sys/netinet/tcp_stacks/rack.c b/sys/netinet/tcp_stacks/rack.c index f1cefc8119dd..3fd08fd0c30c 100644 --- a/sys/netinet/tcp_stacks/rack.c +++ b/sys/netinet/tcp_stacks/rack.c @@ -4588,7 +4588,7 @@ rack_timer_start(struct tcpcb *tp, struct tcp_rack *rack, uint32_t cts, int sup_ goto activate_rxt; } /* Convert from ms to usecs */ - if (rsm->r_flags & RACK_SACK_PASSED) { + if ((rsm->r_flags & RACK_SACK_PASSED) || (rsm->r_dupack >= DUP_ACK_THRESHOLD)) { if ((tp->t_flags & TF_SENTFIN) && ((tp->snd_max - tp->snd_una) == 1) && (rsm->r_flags & RACK_HAS_FIN)) { @@ -6237,7 +6237,7 @@ rack_log_output(struct tcpcb *tp, struct tcpopt *to, int32_t len, * or FIN if seq_out is adding more on and a FIN is present * (and we are not resending). */ - if ((th_flags & TH_SYN) && (seq_out == tp->iss)) + if ((th_flags & TH_SYN) && (seq_out == tp->iss)) len++; if (th_flags & TH_FIN) len++; @@ -8190,6 +8190,7 @@ rack_strike_dupack(struct tcp_rack *rack) rsm->r_dupack++; if (rsm->r_dupack >= DUP_ACK_THRESHOLD) { rack->r_wanted_output = 1; + rack->r_timer_override = 1; rack_log_retran_reason(rack, rsm, __LINE__, 1, 3); } else { rack_log_retran_reason(rack, rsm, __LINE__, 0, 3); @@ -11359,7 +11360,8 @@ tcp_rack_output(struct tcpcb *tp, struct tcp_rack *rack, uint32_t tsused) if (rsm->r_flags & RACK_ACKED) { return (NULL); } - if ((rsm->r_flags & RACK_SACK_PASSED) == 0) { + if (((rsm->r_flags & RACK_SACK_PASSED) == 0) && + (rsm->r_dupack < DUP_ACK_THRESHOLD)) { /* Its not yet ready */ return (NULL); }