1 files changed, 62 insertions, 18 deletions

diff --git a/net/ipv4/tcp_westwood.c b/net/ipv4/tcp_westwood.c
index 0c340c3756c2..4247da1384bf 100644
--- a/net/ipv4/tcp_westwood.c
+++ b/net/ipv4/tcp_westwood.c
@@ -1,7 +1,24 @@
 /*
- * TCP Westwood+
+ * TCP Westwood+: end-to-end bandwidth estimation for TCP
  *
- *      Angelo Dell'Aera:       TCP Westwood+ support
+ *      Angelo Dell'Aera: author of the first version of TCP Westwood+ in Linux 2.4
+ *
+ * Support at http://c3lab.poliba.it/index.php/Westwood
+ * Main references in literature:
+ *
+ * - Mascolo S, Casetti, M. Gerla et al.
+ *   "TCP Westwood: bandwidth estimation for TCP" Proc. ACM Mobicom 2001
+ *
+ * - A. Grieco, s. Mascolo
+ *   "Performance evaluation of New Reno, Vegas, Westwood+ TCP" ACM Computer
+ *     Comm. Review, 2004
+ *
+ * - A. Dell'Aera, L. Grieco, S. Mascolo.
+ *   "Linux 2.4 Implementation of Westwood+ TCP with Rate-Halving :
+ *    A Performance Evaluation Over the Internet" (ICC 2004), Paris, June 2004
+ *
+ * Westwood+ employs end-to-end bandwidth measurement to set cwnd and
+ * ssthresh after packet loss. The probing phase is as the original Reno.
  */
 
 #include <linux/config.h>
@@ -22,6 +39,8 @@ struct westwood {
         u32    accounted;
         u32    rtt;
         u32    rtt_min;          /* minimum observed RTT */
+        u8     first_ack;        /* flag which infers that this is the first ack */
+        u8     reset_rtt_min;    /* Reset RTT min to next RTT sample*/
 };
 
 
@@ -49,9 +68,11 @@ static void tcp_westwood_init(struct sock *sk)
         w->bw_est = 0;
         w->accounted = 0;
         w->cumul_ack = 0;
+        w->reset_rtt_min = 1;
         w->rtt_min = w->rtt = TCP_WESTWOOD_INIT_RTT;
         w->rtt_win_sx = tcp_time_stamp;
         w->snd_una = tcp_sk(sk)->snd_una;
+        w->first_ack = 1;
 }
 
 /*
@@ -63,10 +84,16 @@ static inline u32 westwood_do_filter(u32 a, u32 b)
         return (((7 * a) + b) >> 3);
 }
 
-static inline void westwood_filter(struct westwood *w, u32 delta)
+static void westwood_filter(struct westwood *w, u32 delta)
 {
-        w->bw_ns_est = westwood_do_filter(w->bw_ns_est, w->bk / delta);
-        w->bw_est = westwood_do_filter(w->bw_est, w->bw_ns_est);
+        /* If the filter is empty fill it with the first sample of bandwidth  */
+        if (w->bw_ns_est == 0 && w->bw_est == 0) {
+                w->bw_ns_est = w->bk / delta;
+                w->bw_est = w->bw_ns_est;
+        } else {
+                w->bw_ns_est = westwood_do_filter(w->bw_ns_est, w->bk / delta);
+                w->bw_est = westwood_do_filter(w->bw_est, w->bw_ns_est);
+        }
 }
 
 /*
@@ -91,6 +118,15 @@ static void westwood_update_window(struct sock *sk)
         struct westwood *w = inet_csk_ca(sk);
         s32 delta = tcp_time_stamp - w->rtt_win_sx;
 
+        /* Initialize w->snd_una with the first acked sequence number in order
+         * to fix mismatch between tp->snd_una and w->snd_una for the first
+         * bandwidth sample
+         */
+        if (w->first_ack) {
+                w->snd_una = tcp_sk(sk)->snd_una;
+                w->first_ack = 0;
+        }
+
         /*
          * See if a RTT-window has passed.
          * Be careful since if RTT is less than
@@ -108,6 +144,16 @@ static void westwood_update_window(struct sock *sk)
         }
 }
 
+static inline void update_rtt_min(struct westwood *w)
+{
+        if (w->reset_rtt_min) {
+                w->rtt_min = w->rtt;
+                w->reset_rtt_min = 0;   
+        } else
+                w->rtt_min = min(w->rtt, w->rtt_min);
+}
+
+
 /*
  * @westwood_fast_bw
  * It is called when we are in fast path. In particular it is called when
@@ -123,7 +169,7 @@ static inline void westwood_fast_bw(struct sock *sk)
 
         w->bk += tp->snd_una - w->snd_una;
         w->snd_una = tp->snd_una;
-        w->rtt_min = min(w->rtt, w->rtt_min);
+        update_rtt_min(w);
 }
 
 /*
@@ -162,12 +208,6 @@ static inline u32 westwood_acked_count(struct sock *sk)
         return w->cumul_ack;
 }
 
-static inline u32 westwood_bw_rttmin(const struct sock *sk)
-{
-        const struct tcp_sock *tp = tcp_sk(sk);
-        const struct westwood *w = inet_csk_ca(sk);
-        return max_t(u32, (w->bw_est * w->rtt_min) / tp->mss_cache, 2);
-}
 
 /*
  * TCP Westwood
@@ -175,9 +215,11 @@ static inline u32 westwood_bw_rttmin(const struct sock *sk)
  * in packets we use mss_cache). Rttmin is guaranteed to be >= 2
  * so avoids ever returning 0.
  */
-static u32 tcp_westwood_cwnd_min(struct sock *sk)
+static u32 tcp_westwood_bw_rttmin(const struct sock *sk)
 {
-        return westwood_bw_rttmin(sk);
+        const struct tcp_sock *tp = tcp_sk(sk);
+        const struct westwood *w = inet_csk_ca(sk);
+        return max_t(u32, (w->bw_est * w->rtt_min) / tp->mss_cache, 2);
 }
 
 static void tcp_westwood_event(struct sock *sk, enum tcp_ca_event event)
@@ -191,17 +233,19 @@ static void tcp_westwood_event(struct sock *sk, enum tcp_ca_event event)
                 break;
 
         case CA_EVENT_COMPLETE_CWR:
-                tp->snd_cwnd = tp->snd_ssthresh = westwood_bw_rttmin(sk);
+                tp->snd_cwnd = tp->snd_ssthresh = tcp_westwood_bw_rttmin(sk);
                 break;
 
         case CA_EVENT_FRTO:
-                tp->snd_ssthresh = westwood_bw_rttmin(sk);
+                tp->snd_ssthresh = tcp_westwood_bw_rttmin(sk);
+                /* Update RTT_min when next ack arrives */
+                w->reset_rtt_min = 1;
                 break;
 
         case CA_EVENT_SLOW_ACK:
                 westwood_update_window(sk);
                 w->bk += westwood_acked_count(sk);
-                w->rtt_min = min(w->rtt, w->rtt_min);
+                update_rtt_min(w);
                 break;
 
         default:
@@ -235,7 +279,7 @@ static struct tcp_congestion_ops tcp_westwood = {
         .init           = tcp_westwood_init,
         .ssthresh       = tcp_reno_ssthresh,
         .cong_avoid     = tcp_reno_cong_avoid,
-        .min_cwnd       = tcp_westwood_cwnd_min,
+        .min_cwnd       = tcp_westwood_bw_rttmin,
         .cwnd_event     = tcp_westwood_event,
         .get_info       = tcp_westwood_info,
         .pkts_acked     = tcp_westwood_pkts_acked,