From fb99886224294b2291d267da41395022fa4200e2 Mon Sep 17 00:00:00 2001 From: Kevin Yang Date: Wed, 22 Aug 2018 17:43:14 -0400 Subject: [PATCH 1/3] tcp_bbr: add bbr_check_probe_rtt_done() helper This patch add a helper function bbr_check_probe_rtt_done() to 1. check the condition to see if bbr should exit probe_rtt mode; 2. process the logic of exiting probe_rtt mode. Fixes: 0f8782ea1497 ("tcp_bbr: add BBR congestion control") Signed-off-by: Kevin Yang Signed-off-by: Neal Cardwell Signed-off-by: Yuchung Cheng Reviewed-by: Soheil Hassas Yeganeh Signed-off-by: David S. Miller --- net/ipv4/tcp_bbr.c | 34 ++++++++++++++++++---------------- 1 file changed, 18 insertions(+), 16 deletions(-) diff --git a/net/ipv4/tcp_bbr.c b/net/ipv4/tcp_bbr.c index 13d34427ca3d..fd7bccf36a26 100644 --- a/net/ipv4/tcp_bbr.c +++ b/net/ipv4/tcp_bbr.c @@ -95,11 +95,10 @@ struct bbr { u32 mode:3, /* current bbr_mode in state machine */ prev_ca_state:3, /* CA state on previous ACK */ packet_conservation:1, /* use packet conservation? */ - restore_cwnd:1, /* decided to revert cwnd to old value */ round_start:1, /* start of packet-timed tx->ack round? */ idle_restart:1, /* restarting after idle? */ probe_rtt_round_done:1, /* a BBR_PROBE_RTT round at 4 pkts? */ - unused:12, + unused:13, lt_is_sampling:1, /* taking long-term ("LT") samples now? */ lt_rtt_cnt:7, /* round trips in long-term interval */ lt_use_bw:1; /* use lt_bw as our bw estimate? */ @@ -396,17 +395,11 @@ static bool bbr_set_cwnd_to_recover_or_restore( cwnd = tcp_packets_in_flight(tp) + acked; } else if (prev_state >= TCP_CA_Recovery && state < TCP_CA_Recovery) { /* Exiting loss recovery; restore cwnd saved before recovery. */ - bbr->restore_cwnd = 1; + cwnd = max(cwnd, bbr->prior_cwnd); bbr->packet_conservation = 0; } bbr->prev_ca_state = state; - if (bbr->restore_cwnd) { - /* Restore cwnd after exiting loss recovery or PROBE_RTT. */ - cwnd = max(cwnd, bbr->prior_cwnd); - bbr->restore_cwnd = 0; - } - if (bbr->packet_conservation) { *new_cwnd = max(cwnd, tcp_packets_in_flight(tp) + acked); return true; /* yes, using packet conservation */ @@ -748,6 +741,20 @@ static void bbr_check_drain(struct sock *sk, const struct rate_sample *rs) bbr_reset_probe_bw_mode(sk); /* we estimate queue is drained */ } +static void bbr_check_probe_rtt_done(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + struct bbr *bbr = inet_csk_ca(sk); + + if (!(bbr->probe_rtt_done_stamp && + after(tcp_jiffies32, bbr->probe_rtt_done_stamp))) + return; + + bbr->min_rtt_stamp = tcp_jiffies32; /* wait a while until PROBE_RTT */ + tp->snd_cwnd = max(tp->snd_cwnd, bbr->prior_cwnd); + bbr_reset_mode(sk); +} + /* The goal of PROBE_RTT mode is to have BBR flows cooperatively and * periodically drain the bottleneck queue, to converge to measure the true * min_rtt (unloaded propagation delay). This allows the flows to keep queues @@ -806,12 +813,8 @@ static void bbr_update_min_rtt(struct sock *sk, const struct rate_sample *rs) } else if (bbr->probe_rtt_done_stamp) { if (bbr->round_start) bbr->probe_rtt_round_done = 1; - if (bbr->probe_rtt_round_done && - after(tcp_jiffies32, bbr->probe_rtt_done_stamp)) { - bbr->min_rtt_stamp = tcp_jiffies32; - bbr->restore_cwnd = 1; /* snap to prior_cwnd */ - bbr_reset_mode(sk); - } + if (bbr->probe_rtt_round_done) + bbr_check_probe_rtt_done(sk); } } /* Restart after idle ends only once we process a new S/ACK for data */ @@ -862,7 +865,6 @@ static void bbr_init(struct sock *sk) bbr->has_seen_rtt = 0; bbr_init_pacing_rate_from_rtt(sk); - bbr->restore_cwnd = 0; bbr->round_start = 0; bbr->idle_restart = 0; bbr->full_bw_reached = 0; From 5490b32dce6932ea7ee8e3b2f76db2957c92af6e Mon Sep 17 00:00:00 2001 From: Kevin Yang Date: Wed, 22 Aug 2018 17:43:15 -0400 Subject: [PATCH 2/3] tcp_bbr: in restart from idle, see if we should exit PROBE_RTT This patch fix the case where BBR does not exit PROBE_RTT mode when it restarts from idle. When BBR restarts from idle and if BBR is in PROBE_RTT mode, BBR should check if it's time to exit PROBE_RTT. If yes, then BBR should exit PROBE_RTT mode and restore the cwnd to its full value. Fixes: 0f8782ea1497 ("tcp_bbr: add BBR congestion control") Signed-off-by: Kevin Yang Signed-off-by: Neal Cardwell Reviewed-by: Yuchung Cheng Reviewed-by: Soheil Hassas Yeganeh Signed-off-by: David S. Miller --- net/ipv4/tcp_bbr.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/net/ipv4/tcp_bbr.c b/net/ipv4/tcp_bbr.c index fd7bccf36a26..1d4bdd3b5e4d 100644 --- a/net/ipv4/tcp_bbr.c +++ b/net/ipv4/tcp_bbr.c @@ -174,6 +174,8 @@ static const u32 bbr_lt_bw_diff = 4000 / 8; /* If we estimate we're policed, use lt_bw for this many round trips: */ static const u32 bbr_lt_bw_max_rtts = 48; +static void bbr_check_probe_rtt_done(struct sock *sk); + /* Do we estimate that STARTUP filled the pipe? */ static bool bbr_full_bw_reached(const struct sock *sk) { @@ -308,6 +310,8 @@ static void bbr_cwnd_event(struct sock *sk, enum tcp_ca_event event) */ if (bbr->mode == BBR_PROBE_BW) bbr_set_pacing_rate(sk, bbr_bw(sk), BBR_UNIT); + else if (bbr->mode == BBR_PROBE_RTT) + bbr_check_probe_rtt_done(sk); } } From 8e995bf14fdb7e33681d5c3312b602fa342b878a Mon Sep 17 00:00:00 2001 From: Kevin Yang Date: Wed, 22 Aug 2018 17:43:16 -0400 Subject: [PATCH 3/3] tcp_bbr: apply PROBE_RTT cwnd cap even if acked==0 This commit fixes a corner case where TCP BBR would enter PROBE_RTT mode but not reduce its cwnd. If a TCP receiver ACKed less than one full segment, the number of delivered/acked packets was 0, so that bbr_set_cwnd() would short-circuit and exit early, without cutting cwnd to the value we want for PROBE_RTT. The fix is to instead make sure that even when 0 full packets are ACKed, we do apply all the appropriate caps, including the cap that applies in PROBE_RTT mode. Fixes: 0f8782ea1497 ("tcp_bbr: add BBR congestion control") Signed-off-by: Kevin Yang Signed-off-by: Neal Cardwell Reviewed-by: Yuchung Cheng Reviewed-by: Soheil Hassas Yeganeh Signed-off-by: David S. Miller --- net/ipv4/tcp_bbr.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/net/ipv4/tcp_bbr.c b/net/ipv4/tcp_bbr.c index 1d4bdd3b5e4d..02ff2dde9609 100644 --- a/net/ipv4/tcp_bbr.c +++ b/net/ipv4/tcp_bbr.c @@ -420,10 +420,10 @@ static void bbr_set_cwnd(struct sock *sk, const struct rate_sample *rs, { struct tcp_sock *tp = tcp_sk(sk); struct bbr *bbr = inet_csk_ca(sk); - u32 cwnd = 0, target_cwnd = 0; + u32 cwnd = tp->snd_cwnd, target_cwnd = 0; if (!acked) - return; + goto done; /* no packet fully ACKed; just apply caps */ if (bbr_set_cwnd_to_recover_or_restore(sk, rs, acked, &cwnd)) goto done;