tcp: remove Appropriate Byte Count support

TCP Appropriate Byte Count was added by me, but later disabled.
There is no point in maintaining it since it is a potential source
of bugs and Linux already implements other better window protection
heuristics.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

5 files changed, 1 insertions, 53 deletions

diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index 2622707602d1..960fd29d9b8e 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -633,13 +633,6 @@ static struct ctl_table ipv4_table[] = {
                 .proc_handler   = proc_tcp_congestion_control,
         },
         {
-                .procname       = "tcp_abc",
-                .data           = &sysctl_tcp_abc,
-                .maxlen         = sizeof(int),
-                .mode           = 0644,
-                .proc_handler   = proc_dointvec,
-        },
-        {
                 .procname       = "tcp_mtu_probing",
                 .data           = &sysctl_tcp_mtu_probing,
                 .maxlen         = sizeof(int),
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 3ec1f69c5ceb..2c7e5963c2ea 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2289,7 +2289,6 @@ int tcp_disconnect(struct sock *sk, int flags)
         tp->packets_out = 0;
         tp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
         tp->snd_cwnd_cnt = 0;
-        tp->bytes_acked = 0;
         tp->window_clamp = 0;
         tcp_set_ca_state(sk, TCP_CA_Open);
         tcp_clear_retrans(tp);
diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c
index cdf2e707bb10..019c2389a341 100644
--- a/net/ipv4/tcp_cong.c
+++ b/net/ipv4/tcp_cong.c
@@ -317,28 +317,11 @@ void tcp_slow_start(struct tcp_sock *tp)
                 snd_cwnd = 1U;
         }
 
-        /* RFC3465: ABC Slow start
-         * Increase only after a full MSS of bytes is acked
-         *
-         * TCP sender SHOULD increase cwnd by the number of
-         * previously unacknowledged bytes ACKed by each incoming
-         * acknowledgment, provided the increase is not more than L
-         */
-        if (sysctl_tcp_abc && tp->bytes_acked < tp->mss_cache)
-                return;
-
         if (sysctl_tcp_max_ssthresh > 0 && tp->snd_cwnd > sysctl_tcp_max_ssthresh)
                 cnt = sysctl_tcp_max_ssthresh >> 1;     /* limited slow start */
         else
                 cnt = snd_cwnd;                         /* exponential increase */
 
-        /* RFC3465: ABC
-         * We MAY increase by 2 if discovered delayed ack
-         */
-        if (sysctl_tcp_abc > 1 && tp->bytes_acked >= 2*tp->mss_cache)
-                cnt <<= 1;
-        tp->bytes_acked = 0;
-
         tp->snd_cwnd_cnt += cnt;
         while (tp->snd_cwnd_cnt >= snd_cwnd) {
                 tp->snd_cwnd_cnt -= snd_cwnd;
@@ -378,20 +361,9 @@ void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
         /* In "safe" area, increase. */
         if (tp->snd_cwnd <= tp->snd_ssthresh)
                 tcp_slow_start(tp);
-
         /* In dangerous area, increase slowly. */
-        else if (sysctl_tcp_abc) {
-                /* RFC3465: Appropriate Byte Count
-                 * increase once for each full cwnd acked
-                 */
-                if (tp->bytes_acked >= tp->snd_cwnd*tp->mss_cache) {
-                        tp->bytes_acked -= tp->snd_cwnd*tp->mss_cache;
-                        if (tp->snd_cwnd < tp->snd_cwnd_clamp)
-                                tp->snd_cwnd++;
-                }
-        } else {
+        else
                 tcp_cong_avoid_ai(tp, tp->snd_cwnd);
-        }
 }
 EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
 
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index e376aa9591bc..f56bd1082f54 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -98,7 +98,6 @@ int sysctl_tcp_frto_response __read_mostly;
 int sysctl_tcp_thin_dupack __read_mostly;
 
 int sysctl_tcp_moderate_rcvbuf __read_mostly = 1;
-int sysctl_tcp_abc __read_mostly;
 int sysctl_tcp_early_retrans __read_mostly = 2;
 
 #define FLAG_DATA               0x01 /* Incoming frame contained data.          */
@@ -2007,7 +2006,6 @@ static void tcp_enter_frto_loss(struct sock *sk, int allowed_segments, int flag)
         tp->snd_cwnd_cnt = 0;
         tp->snd_cwnd_stamp = tcp_time_stamp;
         tp->frto_counter = 0;
-        tp->bytes_acked = 0;
 
         tp->reordering = min_t(unsigned int, tp->reordering,
                                sysctl_tcp_reordering);
@@ -2056,7 +2054,6 @@ void tcp_enter_loss(struct sock *sk, int how)
         tp->snd_cwnd_cnt   = 0;
         tp->snd_cwnd_stamp = tcp_time_stamp;
 
-        tp->bytes_acked = 0;
         tcp_clear_retrans_partial(tp);
 
         if (tcp_is_reno(tp))
@@ -2684,7 +2681,6 @@ static void tcp_init_cwnd_reduction(struct sock *sk, const bool set_ssthresh)
         struct tcp_sock *tp = tcp_sk(sk);
 
         tp->high_seq = tp->snd_nxt;
-        tp->bytes_acked = 0;
         tp->snd_cwnd_cnt = 0;
         tp->prior_cwnd = tp->snd_cwnd;
         tp->prr_delivered = 0;
@@ -2735,7 +2731,6 @@ void tcp_enter_cwr(struct sock *sk, const int set_ssthresh)
         struct tcp_sock *tp = tcp_sk(sk);
 
         tp->prior_ssthresh = 0;
-        tp->bytes_acked = 0;
         if (inet_csk(sk)->icsk_ca_state < TCP_CA_CWR) {
                 tp->undo_marker = 0;
                 tcp_init_cwnd_reduction(sk, set_ssthresh);
@@ -3417,7 +3412,6 @@ static void tcp_conservative_spur_to_response(struct tcp_sock *tp)
 {
         tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
         tp->snd_cwnd_cnt = 0;
-        tp->bytes_acked = 0;
         TCP_ECN_queue_cwr(tp);
         tcp_moderate_cwnd(tp);
 }
@@ -3609,15 +3603,6 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
         if (after(ack, prior_snd_una))
                 flag |= FLAG_SND_UNA_ADVANCED;
 
-        if (sysctl_tcp_abc) {
-                if (icsk->icsk_ca_state < TCP_CA_CWR)
-                        tp->bytes_acked += ack - prior_snd_una;
-                else if (icsk->icsk_ca_state == TCP_CA_Loss)
-                        /* we assume just one segment left network */
-                        tp->bytes_acked += min(ack - prior_snd_una,
-                                               tp->mss_cache);
-        }
-
         prior_fackets = tp->fackets_out;
         prior_in_flight = tcp_packets_in_flight(tp);
 
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index f35f2dfb6401..f0409287b5f4 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -446,7 +446,6 @@ struct sock *tcp_create_openreq_child(struct sock *sk, struct request_sock *req,
                  */
                 newtp->snd_cwnd = TCP_INIT_CWND;
                 newtp->snd_cwnd_cnt = 0;
-                newtp->bytes_acked = 0;
 
                 newtp->frto_counter = 0;
                 newtp->frto_highmark = 0;