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tcp: fix stretch ACK bugs in CUBIC

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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 <eyalpe@mellanox.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Neal Cardwell 2015-01-28 20:01:38 -05:00 committed by David S. Miller
parent c22bdca947
commit 9cd981dcf1
1 changed files with 9 additions and 22 deletions
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31
net/ipv4/tcp_cubic.c
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@ -93,9 +93,7 @@ struct bictcp {
u32 epoch_start; /* beginning of an epoch */ u32 epoch_start; /* beginning of an epoch */
u32 ack_cnt; /* number of acks */ u32 ack_cnt; /* number of acks */
u32 tcp_cwnd; /* estimated tcp cwnd */ u32 tcp_cwnd; /* estimated tcp cwnd */
#define ACK_RATIO_SHIFT 4 u16 unused;
#define ACK_RATIO_LIMIT (32u << ACK_RATIO_SHIFT)
u16 delayed_ack; /* estimate the ratio of Packets/ACKs << 4 */
u8 sample_cnt; /* number of samples to decide curr_rtt */ u8 sample_cnt; /* number of samples to decide curr_rtt */
u8 found; /* the exit point is found? */ u8 found; /* the exit point is found? */
u32 round_start; /* beginning of each round */ u32 round_start; /* beginning of each round */
@ -114,7 +112,6 @@ static inline void bictcp_reset(struct bictcp *ca)
ca->bic_K = 0; ca->bic_K = 0;
ca->delay_min = 0; ca->delay_min = 0;
ca->epoch_start = 0; ca->epoch_start = 0;
ca->delayed_ack = 2 << ACK_RATIO_SHIFT;
ca->ack_cnt = 0; ca->ack_cnt = 0;
ca->tcp_cwnd = 0; ca->tcp_cwnd = 0;
ca->found = 0; ca->found = 0;
@ -205,12 +202,12 @@ static u32 cubic_root(u64 a)
/* /*
* Compute congestion window to use. * 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; u32 delta, bic_target, max_cnt;
u64 offs, t; 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 && if (ca->last_cwnd == cwnd &&
(s32)(tcp_time_stamp - ca->last_time) <= HZ / 32) (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) { if (ca->epoch_start == 0) {
ca->epoch_start = tcp_time_stamp; /* record beginning */ 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 */ ca->tcp_cwnd = cwnd; /* syn with cubic */
if (ca->last_max_cwnd <= cwnd) { 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 */ if (ca->cnt == 0) /* cannot be zero */
ca->cnt = 1; 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 (tp->snd_cwnd <= tp->snd_ssthresh) {
if (hystart && after(ack, ca->end_seq)) if (hystart && after(ack, ca->end_seq))
bictcp_hystart_reset(sk); bictcp_hystart_reset(sk);
tcp_slow_start(tp, acked); acked = tcp_slow_start(tp, acked);
} else { if (!acked)
bictcp_update(ca, tp->snd_cwnd); return;
tcp_cong_avoid_ai(tp, ca->cnt, 1);
} }
bictcp_update(ca, tp->snd_cwnd, acked);
tcp_cong_avoid_ai(tp, ca->cnt, acked);
} }
static u32 bictcp_recalc_ssthresh(struct sock *sk) 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) 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); const struct tcp_sock *tp = tcp_sk(sk);
struct bictcp *ca = inet_csk_ca(sk); struct bictcp *ca = inet_csk_ca(sk);
u32 delay; 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 */ /* Some calls are for duplicates without timetamps */
if (rtt_us < 0) if (rtt_us < 0)
return; return;