[TCP] H-TCP: Better time accounting

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>

1 files changed, 26 insertions, 18 deletions

diff --git a/net/ipv4/tcp_htcp.c b/net/ipv4/tcp_htcp.c
index ac19252e34ce..1b2ff53f98ed 100644
--- a/net/ipv4/tcp_htcp.c
+++ b/net/ipv4/tcp_htcp.c
@@ -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: