diff options
Diffstat (limited to 'net/ipv4/tcp_westwood.c')
| -rw-r--r-- | net/ipv4/tcp_westwood.c | 80 |
1 files changed, 62 insertions, 18 deletions
diff --git a/net/ipv4/tcp_westwood.c b/net/ipv4/tcp_westwood.c index 0c340c3756c..4247da1384b 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, |