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>

9 files changed, 1 insertions, 67 deletions

diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index 19ac1802bfd4..dc2dc87d2557 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -130,17 +130,6 @@ somaxconn - INTEGER
         Defaults to 128.  See also tcp_max_syn_backlog for additional tuning
         for TCP sockets.
 
-tcp_abc - INTEGER
-        Controls Appropriate Byte Count (ABC) defined in RFC3465.
-        ABC is a way of increasing congestion window (cwnd) more slowly
-        in response to partial acknowledgments.
-        Possible values are:
-                0 increase cwnd once per acknowledgment (no ABC)
-                1 increase cwnd once per acknowledgment of full sized segment
-                2 allow increase cwnd by two if acknowledgment is
-                  of two segments to compensate for delayed acknowledgments.
-        Default: 0 (off)
-
 tcp_abort_on_overflow - BOOLEAN
         If listening service is too slow to accept new connections,
         reset them. Default state is FALSE. It means that if overflow
diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 4e1d2283e3cc..6d0d46138ae8 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -246,7 +246,6 @@ struct tcp_sock {
         u32     sacked_out;     /* SACK'd packets                       */
         u32     fackets_out;    /* FACK'd packets                       */
         u32     tso_deferred;
-        u32     bytes_acked;    /* Appropriate Byte Counting - RFC3465 */
 
         /* from STCP, retrans queue hinting */
         struct sk_buff* lost_skb_hint;
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 614af8b7758e..23f2e98d4b65 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -279,7 +279,6 @@ extern int sysctl_tcp_dma_copybreak;
 extern int sysctl_tcp_nometrics_save;
 extern int sysctl_tcp_moderate_rcvbuf;
 extern int sysctl_tcp_tso_win_divisor;
-extern int sysctl_tcp_abc;
 extern int sysctl_tcp_mtu_probing;
 extern int sysctl_tcp_base_mss;
 extern int sysctl_tcp_workaround_signed_windows;
diff --git a/kernel/sysctl_binary.c b/kernel/sysctl_binary.c
index 5a6384450501..b669ca1fa103 100644
--- a/kernel/sysctl_binary.c
+++ b/kernel/sysctl_binary.c
@@ -387,7 +387,6 @@ static const struct bin_table bin_net_ipv4_table[] = {
         { CTL_INT,      NET_TCP_MODERATE_RCVBUF,                "tcp_moderate_rcvbuf" },
         { CTL_INT,      NET_TCP_TSO_WIN_DIVISOR,                "tcp_tso_win_divisor" },
         { CTL_STR,      NET_TCP_CONG_CONTROL,                   "tcp_congestion_control" },
-        { CTL_INT,      NET_TCP_ABC,                            "tcp_abc" },
         { CTL_INT,      NET_TCP_MTU_PROBING,                    "tcp_mtu_probing" },
         { CTL_INT,      NET_TCP_BASE_MSS,                       "tcp_base_mss" },
         { CTL_INT,      NET_IPV4_TCP_WORKAROUND_SIGNED_WINDOWS, "tcp_workaround_signed_windows" },
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)