1 files changed, 17 insertions, 22 deletions

diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c
index 6b6002416a73..4b276d1ed980 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;
@@ -205,23 +202,30 @@ 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)
                 return;
 
+        /* The CUBIC function can update ca->cnt at most once per jiffy.
+         * On all cwnd reduction events, ca->epoch_start is set to 0,
+         * which will force a recalculation of ca->cnt.
+         */
+        if (ca->epoch_start && tcp_time_stamp == ca->last_time)
+                goto tcp_friendliness;
+
         ca->last_cwnd = cwnd;
         ca->last_time = tcp_time_stamp;
 
         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) {
@@ -283,6 +287,7 @@ static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
         if (ca->last_max_cwnd == 0 && ca->cnt > 20)
                 ca->cnt = 20;   /* increase cwnd 5% per RTT */
 
+tcp_friendliness:
         /* TCP Friendly */
         if (tcp_friendliness) {
                 u32 scale = beta_scale;
@@ -301,7 +306,6 @@ 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 +321,12 @@ 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);
+                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 +416,10 @@ 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;