From 9cd981dcf174d26805a032aefa791436da709bee Mon Sep 17 00:00:00 2001 From: Neal Cardwell Date: Wed, 28 Jan 2015 20:01:38 -0500 Subject: [PATCH] tcp: fix stretch ACK bugs in CUBIC Change CUBIC to properly handle stretch ACKs in additive increase mode by passing in the count of ACKed packets to tcp_cong_avoid_ai(). In addition, because we are now precisely accounting for stretch ACKs, including delayed ACKs, we can now remove the delayed ACK tracking and estimation code that tracked recent delayed ACK behavior in ca->delayed_ack. Reported-by: Eyal Perry Signed-off-by: Neal Cardwell Signed-off-by: Yuchung Cheng Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- net/ipv4/tcp_cubic.c | 31 +++++++++---------------------- 1 file changed, 9 insertions(+), 22 deletions(-) diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c index df4bc4d87e58..ffc045da2fd5 100644 --- a/net/ipv4/tcp_cubic.c +++ b/net/ipv4/tcp_cubic.c @@ -93,9 +93,7 @@ struct bictcp { u32 epoch_start; /* beginning of an epoch */ u32 ack_cnt; /* number of acks */ u32 tcp_cwnd; /* estimated tcp cwnd */ -#define ACK_RATIO_SHIFT 4 -#define ACK_RATIO_LIMIT (32u << ACK_RATIO_SHIFT) - u16 delayed_ack; /* estimate the ratio of Packets/ACKs << 4 */ + u16 unused; u8 sample_cnt; /* number of samples to decide curr_rtt */ u8 found; /* the exit point is found? */ u32 round_start; /* beginning of each round */ @@ -114,7 +112,6 @@ static inline void bictcp_reset(struct bictcp *ca) ca->bic_K = 0; ca->delay_min = 0; ca->epoch_start = 0; - ca->delayed_ack = 2 << ACK_RATIO_SHIFT; ca->ack_cnt = 0; ca->tcp_cwnd = 0; ca->found = 0; @@ -205,12 +202,12 @@ static u32 cubic_root(u64 a) /* * Compute congestion window to use. */ -static inline void bictcp_update(struct bictcp *ca, u32 cwnd) +static inline void bictcp_update(struct bictcp *ca, u32 cwnd, u32 acked) { u32 delta, bic_target, max_cnt; u64 offs, t; - ca->ack_cnt++; /* count the number of ACKs */ + ca->ack_cnt += acked; /* count the number of ACKed packets */ if (ca->last_cwnd == cwnd && (s32)(tcp_time_stamp - ca->last_time) <= HZ / 32) @@ -221,7 +218,7 @@ static inline void bictcp_update(struct bictcp *ca, u32 cwnd) if (ca->epoch_start == 0) { ca->epoch_start = tcp_time_stamp; /* record beginning */ - ca->ack_cnt = 1; /* start counting */ + ca->ack_cnt = acked; /* start counting */ ca->tcp_cwnd = cwnd; /* syn with cubic */ if (ca->last_max_cwnd <= cwnd) { @@ -301,7 +298,6 @@ static inline void bictcp_update(struct bictcp *ca, u32 cwnd) } } - ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack; if (ca->cnt == 0) /* cannot be zero */ ca->cnt = 1; } @@ -317,11 +313,12 @@ static void bictcp_cong_avoid(struct sock *sk, u32 ack, u32 acked) if (tp->snd_cwnd <= tp->snd_ssthresh) { if (hystart && after(ack, ca->end_seq)) bictcp_hystart_reset(sk); - tcp_slow_start(tp, acked); - } else { - bictcp_update(ca, tp->snd_cwnd); - tcp_cong_avoid_ai(tp, ca->cnt, 1); + acked = tcp_slow_start(tp, acked); + if (!acked) + return; } + bictcp_update(ca, tp->snd_cwnd, acked); + tcp_cong_avoid_ai(tp, ca->cnt, acked); } static u32 bictcp_recalc_ssthresh(struct sock *sk) @@ -411,20 +408,10 @@ static void hystart_update(struct sock *sk, u32 delay) */ static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt_us) { - const struct inet_connection_sock *icsk = inet_csk(sk); const struct tcp_sock *tp = tcp_sk(sk); struct bictcp *ca = inet_csk_ca(sk); u32 delay; - if (icsk->icsk_ca_state == TCP_CA_Open) { - u32 ratio = ca->delayed_ack; - - ratio -= ca->delayed_ack >> ACK_RATIO_SHIFT; - ratio += cnt; - - ca->delayed_ack = clamp(ratio, 1U, ACK_RATIO_LIMIT); - } - /* Some calls are for duplicates without timetamps */ if (rtt_us < 0) return; -- 2.20.1