[TCP] H-TCP: Better time accounting
Baruch Even [Tue, 21 Mar 2006 06:23:10 +0000 (22:23 -0800)]
Instead of estimating the time since the last congestion event, count
it directly.

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

net/ipv4/tcp_htcp.c

index ac19252..1b2ff53 100644 (file)
@@ -27,13 +27,12 @@ struct htcp {
        u16     alpha;          /* Fixed point arith, << 7 */
        u8      beta;           /* Fixed point arith, << 7 */
        u8      modeswitch;     /* Delay modeswitch until we had at least one congestion event */
-       u8      ccount;         /* Number of RTTs since last congestion event */
-       u8      undo_ccount;
+       u32     last_cong;      /* Time since last congestion event end */
+       u32     undo_last_cong;
        u16     pkts_acked;
        u32     packetcount;
        u32     minRTT;
        u32     maxRTT;
-       u32     snd_cwnd_cnt2;
 
        u32     undo_maxRTT;
        u32     undo_old_maxB;
@@ -46,21 +45,30 @@ struct htcp {
        u32     lasttime;
 };
 
+static inline u32 htcp_cong_time(struct htcp *ca)
+{
+       return jiffies - ca->last_cong;
+}
+
+static inline u32 htcp_ccount(struct htcp *ca)
+{
+       return htcp_cong_time(ca)/ca->minRTT;
+}
+
 static inline void htcp_reset(struct htcp *ca)
 {
-       ca->undo_ccount = ca->ccount;
+       ca->undo_last_cong = ca->last_cong;
        ca->undo_maxRTT = ca->maxRTT;
        ca->undo_old_maxB = ca->old_maxB;
 
-       ca->ccount = 0;
-       ca->snd_cwnd_cnt2 = 0;
+       ca->last_cong = jiffies;
 }
 
 static u32 htcp_cwnd_undo(struct sock *sk)
 {
        const struct tcp_sock *tp = tcp_sk(sk);
        struct htcp *ca = inet_csk_ca(sk);
-       ca->ccount = ca->undo_ccount;
+       ca->last_cong = ca->undo_last_cong;
        ca->maxRTT = ca->undo_maxRTT;
        ca->old_maxB = ca->undo_old_maxB;
        return max(tp->snd_cwnd, (tp->snd_ssthresh<<7)/ca->beta);
@@ -78,7 +86,7 @@ static inline void measure_rtt(struct sock *sk)
                ca->minRTT = srtt;
 
        /* max RTT */
-       if (icsk->icsk_ca_state == TCP_CA_Open && tp->snd_ssthresh < 0xFFFF && ca->ccount > 3) {
+       if (icsk->icsk_ca_state == TCP_CA_Open && tp->snd_ssthresh < 0xFFFF && htcp_ccount(ca) > 3) {
                if (ca->maxRTT < ca->minRTT)
                        ca->maxRTT = ca->minRTT;
                if (ca->maxRTT < srtt && srtt <= ca->maxRTT+msecs_to_jiffies(20))
@@ -113,7 +121,7 @@ static void measure_achieved_throughput(struct sock *sk, u32 pkts_acked)
                        && now - ca->lasttime >= ca->minRTT
                        && ca->minRTT > 0) {
                __u32 cur_Bi = ca->packetcount*HZ/(now - ca->lasttime);
-               if (ca->ccount <= 3) {
+               if (htcp_ccount(ca) <= 3) {
                        /* just after backoff */
                        ca->minB = ca->maxB = ca->Bi = cur_Bi;
                } else {
@@ -158,7 +166,7 @@ static inline void htcp_alpha_update(struct htcp *ca)
 {
        u32 minRTT = ca->minRTT;
        u32 factor = 1;
-       u32 diff = ca->ccount * minRTT; /* time since last backoff */
+       u32 diff = htcp_cong_time(ca);
 
        if (diff > HZ) {
                diff -= HZ;
@@ -223,14 +231,6 @@ 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) {
-                       ca->ccount++;
-                       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
                 */
@@ -238,6 +238,7 @@ static void htcp_cong_avoid(struct sock *sk, u32 ack, u32 rtt,
                        if (tp->snd_cwnd < tp->snd_cwnd_clamp)
                                tp->snd_cwnd++;
                        tp->snd_cwnd_cnt = 0;
+                       htcp_alpha_update(ca);
                } else
                        tp->snd_cwnd_cnt += ca->pkts_acked;
 
@@ -261,11 +262,18 @@ static void htcp_init(struct sock *sk)
        ca->alpha = ALPHA_BASE;
        ca->beta = BETA_MIN;
        ca->pkts_acked = 1;
+       ca->last_cong = jiffies;
 }
 
 static void htcp_state(struct sock *sk, u8 new_state)
 {
        switch (new_state) {
+       case TCP_CA_Open:
+               {
+                       struct htcp *ca = inet_csk_ca(sk);
+                       ca->last_cong = jiffies;
+               }
+               break;
        case TCP_CA_CWR:
        case TCP_CA_Recovery:
        case TCP_CA_Loss: