[TCP]: Appropriate Byte Count support

This is an updated version of the RFC3465 ABC patch originally
for Linux 2.6.11-rc4 by Yee-Ting Li. ABC is a way of counting
bytes ack'd rather than packets when updating congestion control.

The orignal ABC described in the RFC applied to a Reno style
algorithm. For advanced congestion control there is little
change after leaving slow start.

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

9 files changed, 63 insertions, 11 deletions

diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index 65895bb51414..ebc09a159f62 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -78,6 +78,11 @@ inet_peer_gc_maxtime - INTEGER
 
 TCP variables: 
 
+tcp_abc - INTEGER
+        Controls Appropriate Byte Count defined in RFC3465. If set to
+        0 then does congestion avoid once per ack. 1 is conservative
+        value, and 2 is more agressive.
+
 tcp_syn_retries - INTEGER
         Number of times initial SYNs for an active TCP connection attempt
         will be retransmitted. Should not be higher than 255. Default value
diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index 22cf5e1ac987..ab2791b3189d 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -390,6 +390,7 @@ enum
         NET_TCP_BIC_BETA=108,
         NET_IPV4_ICMP_ERRORS_USE_INBOUND_IFADDR=109,
         NET_TCP_CONG_CONTROL=110,
+        NET_TCP_ABC=111,
 };
 
 enum {
diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index ac4ca44c75ca..737b32e52956 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -326,6 +326,7 @@ struct tcp_sock {
         __u32   snd_up;         /* Urgent pointer               */
 
         __u32   total_retrans;  /* Total retransmits for entire connection */
+        __u32   bytes_acked;    /* Appropriate Byte Counting - RFC3465 */
 
         unsigned int            keepalive_time;   /* time before keep alive takes place */
         unsigned int            keepalive_intvl;  /* time interval between keep alive probes */
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 54c399886275..44ba4a21cbdc 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -218,6 +218,7 @@ extern int sysctl_tcp_low_latency;
 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 atomic_t tcp_memory_allocated;
 extern atomic_t tcp_sockets_allocated;
@@ -770,6 +771,23 @@ static inline __u32 tcp_current_ssthresh(const struct sock *sk)
  */
 static inline void tcp_slow_start(struct tcp_sock *tp)
 {
+        if (sysctl_tcp_abc) {
+                /* RFC3465: Slow Start
+                 * 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 (tp->bytes_acked < tp->mss_cache)
+                        return;
+
+                /* We MAY increase by 2 if discovered delayed ack */
+                if (sysctl_tcp_abc > 1 && tp->bytes_acked > 2*tp->mss_cache) {
+                        if (tp->snd_cwnd < tp->snd_cwnd_clamp)
+                                tp->snd_cwnd++;
+                }
+        }
+        tp->bytes_acked = 0;
+
         if (tp->snd_cwnd < tp->snd_cwnd_clamp)
                 tp->snd_cwnd++;
 }
@@ -804,6 +822,7 @@ static inline void tcp_enter_cwr(struct sock *sk)
         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) {
                 __tcp_enter_cwr(sk);
                 tcp_set_ca_state(sk, TCP_CA_CWR);
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index 652685623519..01444a02b48b 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -645,6 +645,14 @@ ctl_table ipv4_table[] = {
                 .proc_handler   = &proc_tcp_congestion_control,
                 .strategy       = &sysctl_tcp_congestion_control,
         },
+        {
+                .ctl_name       = NET_TCP_ABC,
+                .procname       = "tcp_abc",
+                .data           = &sysctl_tcp_abc,
+                .maxlen         = sizeof(int),
+                .mode           = 0644,
+                .proc_handler   = &proc_dointvec,
+        },
 
         { .ctl_name = 0 }
 };
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 72b7c22e1ea5..cfaf76133759 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1669,6 +1669,7 @@ int tcp_disconnect(struct sock *sk, int flags)
         tp->packets_out = 0;
         tp->snd_ssthresh = 0x7fffffff;
         tp->snd_cwnd_cnt = 0;
+        tp->bytes_acked = 0;
         tcp_set_ca_state(sk, TCP_CA_Open);
         tcp_clear_retrans(tp);
         inet_csk_delack_init(sk);
diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c
index 6d3e883b48f6..c7cc62c8dc12 100644
--- a/net/ipv4/tcp_cong.c
+++ b/net/ipv4/tcp_cong.c
@@ -192,17 +192,26 @@ void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 rtt, u32 in_flight,
         /* In "safe" area, increase. */
         if (tp->snd_cwnd <= tp->snd_ssthresh)
                 tcp_slow_start(tp);
-        else {
-                /* In dangerous area, increase slowly.
-                 * In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd
-                 */
-                if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
-                        if (tp->snd_cwnd < tp->snd_cwnd_clamp)
-                                tp->snd_cwnd++;
-                        tp->snd_cwnd_cnt = 0;
-                } else
-                        tp->snd_cwnd_cnt++;
-        }
+
+        /* In dangerous area, increase slowly. */
+        else if (sysctl_tcp_abc) {
+                /* RFC3465: Apppriate 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 {
+                /* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd */
+                if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
+                        if (tp->snd_cwnd < tp->snd_cwnd_clamp)
+                                tp->snd_cwnd++;
+                        tp->snd_cwnd_cnt = 0;
+                } else
+                        tp->snd_cwnd_cnt++;
+        }
 }
 EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
 
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index e43065654930..4cb5e6f408dc 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -89,6 +89,7 @@ int sysctl_tcp_frto;
 int sysctl_tcp_nometrics_save;
 
 int sysctl_tcp_moderate_rcvbuf = 1;
+int sysctl_tcp_abc = 1;
 
 #define FLAG_DATA               0x01 /* Incoming frame contained data.          */
 #define FLAG_WIN_UPDATE         0x02 /* Incoming ACK was a window update.       */
@@ -1247,6 +1248,7 @@ 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(tp);
 
         /* Push undo marker, if it was plain RTO and nothing
@@ -1904,6 +1906,7 @@ tcp_fastretrans_alert(struct sock *sk, u32 prior_snd_una,
                         TCP_ECN_queue_cwr(tp);
                 }
 
+                tp->bytes_acked = 0;
                 tp->snd_cwnd_cnt = 0;
                 tcp_set_ca_state(sk, TCP_CA_Recovery);
         }
@@ -2310,6 +2313,9 @@ static int tcp_ack(struct sock *sk, struct sk_buff *skb, int flag)
         if (before(ack, prior_snd_una))
                 goto old_ack;
 
+        if (sysctl_tcp_abc && icsk->icsk_ca_state < TCP_CA_CWR)
+                tp->bytes_acked += ack - prior_snd_una;
+
         if (!(flag&FLAG_SLOWPATH) && after(ack, prior_snd_una)) {
                 /* Window is constant, pure forward advance.
                  * No more checks are required.
@@ -4370,6 +4376,7 @@ discard:
 
 EXPORT_SYMBOL(sysctl_tcp_ecn);
 EXPORT_SYMBOL(sysctl_tcp_reordering);
+EXPORT_SYMBOL(sysctl_tcp_abc);
 EXPORT_SYMBOL(tcp_parse_options);
 EXPORT_SYMBOL(tcp_rcv_established);
 EXPORT_SYMBOL(tcp_rcv_state_process);
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index b1a63b2c6b4a..9203a21e299f 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -380,6 +380,7 @@ struct sock *tcp_create_openreq_child(struct sock *sk, struct request_sock *req,
                  */
                 newtp->snd_cwnd = 2;
                 newtp->snd_cwnd_cnt = 0;
+                newtp->bytes_acked = 0;
 
                 newtp->frto_counter = 0;
                 newtp->frto_highmark = 0;