[TCP] H-TCP: Account for delayed-ACKs

Account for delayed-ACKs in H-TCP.

Delayed-ACKs cause H-TCP to be less aggressive than its design calls
for. It is especially true when the receiver is a Linux machine where
the average delayed ack is over 3 packets with values of 7 not unheard
of.

Signed-off-By: Baruch Even <baruch@ev-en.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/tcp_htcp.c b/net/ipv4/tcp_htcp.c
index fda2f87..ac19252 100644 (file)
--- a/net/ipv4/tcp_htcp.c
+++ b/net/ipv4/tcp_htcp.c
@@ -29,7 +29,8 @@ struct htcp {
        u8      modeswitch;     /* Delay modeswitch until we had at least one congestion event */
        u8      ccount;         /* Number of RTTs since last congestion event */
        u8      undo_ccount;
-       u16     packetcount;
+       u16     pkts_acked;
+       u32     packetcount;
        u32     minRTT;
        u32     maxRTT;
        u32     snd_cwnd_cnt2;
@@ -92,6 +93,12 @@ static void measure_achieved_throughput(struct sock *sk, u32 pkts_acked)
        struct htcp *ca = inet_csk_ca(sk);
        u32 now = tcp_time_stamp;
 
+       if (icsk->icsk_ca_state == TCP_CA_Open)
+               ca->pkts_acked = pkts_acked;
+
+       if (!use_bandwidth_switch)
+               return;
+
        /* achieved throughput calculations */
        if (icsk->icsk_ca_state != TCP_CA_Open &&
            icsk->icsk_ca_state != TCP_CA_Disorder) {
@@ -217,20 +224,24 @@ static void htcp_cong_avoid(struct sock *sk, u32 ack, u32 rtt,
                measure_rtt(sk);
 
                /* keep track of number of round-trip times since last backoff event */
-               if (ca->snd_cwnd_cnt2++ > tp->snd_cwnd) {
+               if (ca->snd_cwnd_cnt2 >= tp->snd_cwnd) {
                        ca->ccount++;
-                       ca->snd_cwnd_cnt2 = 0;
+                       ca->snd_cwnd_cnt2 -= tp->snd_cwnd;
                        htcp_alpha_update(ca);
-               }
+               } else
+                       ca->snd_cwnd_cnt2 += ca->pkts_acked;
 
                /* In dangerous area, increase slowly.
                 * In theory this is tp->snd_cwnd += alpha / tp->snd_cwnd
                 */
-               if ((tp->snd_cwnd_cnt++ * ca->alpha)>>7 >= tp->snd_cwnd) {
+               if ((tp->snd_cwnd_cnt * ca->alpha)>>7 >= tp->snd_cwnd) {
                        if (tp->snd_cwnd < tp->snd_cwnd_clamp)
                                tp->snd_cwnd++;
                        tp->snd_cwnd_cnt = 0;
-               }
+               } else
+                       tp->snd_cwnd_cnt += ca->pkts_acked;
+
+               ca->pkts_acked = 1;
        }
 }
 
@@ -249,6 +260,7 @@ static void htcp_init(struct sock *sk)
        memset(ca, 0, sizeof(struct htcp));
        ca->alpha = ALPHA_BASE;
        ca->beta = BETA_MIN;
+       ca->pkts_acked = 1;
 }
 
 static void htcp_state(struct sock *sk, u8 new_state)
@@ -278,8 +290,6 @@ static int __init htcp_register(void)
 {
        BUG_ON(sizeof(struct htcp) > ICSK_CA_PRIV_SIZE);
        BUILD_BUG_ON(BETA_MIN >= BETA_MAX);
-       if (!use_bandwidth_switch)
-               htcp.pkts_acked = NULL;
        return tcp_register_congestion_control(&htcp);
 }