/*
- * 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>
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*/
};
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;
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);
+ }
}
/*
struct westwood *w = inet_csk_ca(sk);
s32 delta = tcp_time_stamp - w->rtt_win_sx;
- /* Initialise w->snd_una with the first acked sequence number in order
+ /* 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
*/
}
}
+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
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);
}
/*
{
struct tcp_sock *tp = tcp_sk(sk);
struct westwood *w = inet_csk_ca(sk);
-
+
switch(event) {
case CA_EVENT_FAST_ACK:
westwood_fast_bw(sk);
case CA_EVENT_FRTO:
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: