[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>

1 files changed, 20 insertions, 11 deletions

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);