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9b44190dc1
The patch series refactor the F-RTO feature (RFC4138/5682). This is to simplify the loss recovery processing. Existing F-RTO was developed during the experimental stage (RFC4138) and has many experimental features. It takes a separate code path from the traditional timeout processing by overloading CA_Disorder instead of using CA_Loss state. This complicates CA_Disorder state handling because it's also used for handling dubious ACKs and undos. While the algorithm in the RFC does not change the congestion control, the implementation intercepts congestion control in various places (e.g., frto_cwnd in tcp_ack()). The new code implements newer F-RTO RFC5682 using CA_Loss processing path. F-RTO becomes a small extension in the timeout processing and interfaces with congestion control and Eifel undo modules. It lets congestion control (module) determines how many to send independently. F-RTO only chooses what to send in order to detect spurious retranmission. If timeout is found spurious it invokes existing Eifel undo algorithms like DSACK or TCP timestamp based detection. The first patch removes all F-RTO code except the sysctl_tcp_frto is left for the new implementation. Since CA_EVENT_FRTO is removed, TCP westwood now computes ssthresh on regular timeout CA_EVENT_LOSS event. Signed-off-by: Yuchung Cheng <ycheng@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Acked-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
305 lines
8.0 KiB
C
305 lines
8.0 KiB
C
/*
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* TCP Westwood+: end-to-end bandwidth estimation for TCP
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*
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* Angelo Dell'Aera: author of the first version of TCP Westwood+ in Linux 2.4
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*
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* Support at http://c3lab.poliba.it/index.php/Westwood
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* Main references in literature:
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*
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* - Mascolo S, Casetti, M. Gerla et al.
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* "TCP Westwood: bandwidth estimation for TCP" Proc. ACM Mobicom 2001
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*
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* - A. Grieco, s. Mascolo
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* "Performance evaluation of New Reno, Vegas, Westwood+ TCP" ACM Computer
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* Comm. Review, 2004
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*
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* - A. Dell'Aera, L. Grieco, S. Mascolo.
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* "Linux 2.4 Implementation of Westwood+ TCP with Rate-Halving :
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* A Performance Evaluation Over the Internet" (ICC 2004), Paris, June 2004
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*
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* Westwood+ employs end-to-end bandwidth measurement to set cwnd and
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* ssthresh after packet loss. The probing phase is as the original Reno.
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*/
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#include <linux/mm.h>
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#include <linux/module.h>
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#include <linux/skbuff.h>
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#include <linux/inet_diag.h>
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#include <net/tcp.h>
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/* TCP Westwood structure */
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struct westwood {
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u32 bw_ns_est; /* first bandwidth estimation..not too smoothed 8) */
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u32 bw_est; /* bandwidth estimate */
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u32 rtt_win_sx; /* here starts a new evaluation... */
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u32 bk;
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u32 snd_una; /* used for evaluating the number of acked bytes */
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u32 cumul_ack;
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u32 accounted;
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u32 rtt;
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u32 rtt_min; /* minimum observed RTT */
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u8 first_ack; /* flag which infers that this is the first ack */
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u8 reset_rtt_min; /* Reset RTT min to next RTT sample*/
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};
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/* TCP Westwood functions and constants */
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#define TCP_WESTWOOD_RTT_MIN (HZ/20) /* 50ms */
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#define TCP_WESTWOOD_INIT_RTT (20*HZ) /* maybe too conservative?! */
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/*
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* @tcp_westwood_create
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* This function initializes fields used in TCP Westwood+,
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* it is called after the initial SYN, so the sequence numbers
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* are correct but new passive connections we have no
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* information about RTTmin at this time so we simply set it to
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* TCP_WESTWOOD_INIT_RTT. This value was chosen to be too conservative
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* since in this way we're sure it will be updated in a consistent
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* way as soon as possible. It will reasonably happen within the first
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* RTT period of the connection lifetime.
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*/
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static void tcp_westwood_init(struct sock *sk)
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{
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struct westwood *w = inet_csk_ca(sk);
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w->bk = 0;
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w->bw_ns_est = 0;
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w->bw_est = 0;
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w->accounted = 0;
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w->cumul_ack = 0;
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w->reset_rtt_min = 1;
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w->rtt_min = w->rtt = TCP_WESTWOOD_INIT_RTT;
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w->rtt_win_sx = tcp_time_stamp;
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w->snd_una = tcp_sk(sk)->snd_una;
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w->first_ack = 1;
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}
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/*
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* @westwood_do_filter
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* Low-pass filter. Implemented using constant coefficients.
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*/
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static inline u32 westwood_do_filter(u32 a, u32 b)
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{
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return ((7 * a) + b) >> 3;
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}
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static void westwood_filter(struct westwood *w, u32 delta)
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{
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/* If the filter is empty fill it with the first sample of bandwidth */
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if (w->bw_ns_est == 0 && w->bw_est == 0) {
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w->bw_ns_est = w->bk / delta;
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w->bw_est = w->bw_ns_est;
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} else {
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w->bw_ns_est = westwood_do_filter(w->bw_ns_est, w->bk / delta);
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w->bw_est = westwood_do_filter(w->bw_est, w->bw_ns_est);
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}
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}
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/*
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* @westwood_pkts_acked
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* Called after processing group of packets.
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* but all westwood needs is the last sample of srtt.
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*/
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static void tcp_westwood_pkts_acked(struct sock *sk, u32 cnt, s32 rtt)
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{
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struct westwood *w = inet_csk_ca(sk);
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if (rtt > 0)
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w->rtt = usecs_to_jiffies(rtt);
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}
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/*
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* @westwood_update_window
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* It updates RTT evaluation window if it is the right moment to do
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* it. If so it calls filter for evaluating bandwidth.
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*/
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static void westwood_update_window(struct sock *sk)
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{
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struct westwood *w = inet_csk_ca(sk);
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s32 delta = tcp_time_stamp - w->rtt_win_sx;
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/* Initialize w->snd_una with the first acked sequence number in order
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* to fix mismatch between tp->snd_una and w->snd_una for the first
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* bandwidth sample
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*/
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if (w->first_ack) {
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w->snd_una = tcp_sk(sk)->snd_una;
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w->first_ack = 0;
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}
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/*
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* See if a RTT-window has passed.
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* Be careful since if RTT is less than
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* 50ms we don't filter but we continue 'building the sample'.
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* This minimum limit was chosen since an estimation on small
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* time intervals is better to avoid...
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* Obviously on a LAN we reasonably will always have
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* right_bound = left_bound + WESTWOOD_RTT_MIN
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*/
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if (w->rtt && delta > max_t(u32, w->rtt, TCP_WESTWOOD_RTT_MIN)) {
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westwood_filter(w, delta);
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w->bk = 0;
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w->rtt_win_sx = tcp_time_stamp;
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}
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}
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static inline void update_rtt_min(struct westwood *w)
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{
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if (w->reset_rtt_min) {
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w->rtt_min = w->rtt;
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w->reset_rtt_min = 0;
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} else
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w->rtt_min = min(w->rtt, w->rtt_min);
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}
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/*
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* @westwood_fast_bw
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* It is called when we are in fast path. In particular it is called when
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* header prediction is successful. In such case in fact update is
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* straight forward and doesn't need any particular care.
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*/
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static inline void westwood_fast_bw(struct sock *sk)
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{
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const struct tcp_sock *tp = tcp_sk(sk);
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struct westwood *w = inet_csk_ca(sk);
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westwood_update_window(sk);
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w->bk += tp->snd_una - w->snd_una;
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w->snd_una = tp->snd_una;
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update_rtt_min(w);
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}
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/*
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* @westwood_acked_count
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* This function evaluates cumul_ack for evaluating bk in case of
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* delayed or partial acks.
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*/
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static inline u32 westwood_acked_count(struct sock *sk)
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{
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const struct tcp_sock *tp = tcp_sk(sk);
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struct westwood *w = inet_csk_ca(sk);
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w->cumul_ack = tp->snd_una - w->snd_una;
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/* If cumul_ack is 0 this is a dupack since it's not moving
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* tp->snd_una.
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*/
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if (!w->cumul_ack) {
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w->accounted += tp->mss_cache;
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w->cumul_ack = tp->mss_cache;
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}
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if (w->cumul_ack > tp->mss_cache) {
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/* Partial or delayed ack */
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if (w->accounted >= w->cumul_ack) {
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w->accounted -= w->cumul_ack;
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w->cumul_ack = tp->mss_cache;
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} else {
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w->cumul_ack -= w->accounted;
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w->accounted = 0;
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}
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}
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w->snd_una = tp->snd_una;
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return w->cumul_ack;
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}
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/*
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* TCP Westwood
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* Here limit is evaluated as Bw estimation*RTTmin (for obtaining it
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* in packets we use mss_cache). Rttmin is guaranteed to be >= 2
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* so avoids ever returning 0.
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*/
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static u32 tcp_westwood_bw_rttmin(const struct sock *sk)
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{
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const struct tcp_sock *tp = tcp_sk(sk);
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const struct westwood *w = inet_csk_ca(sk);
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return max_t(u32, (w->bw_est * w->rtt_min) / tp->mss_cache, 2);
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}
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static void tcp_westwood_event(struct sock *sk, enum tcp_ca_event event)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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struct westwood *w = inet_csk_ca(sk);
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switch (event) {
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case CA_EVENT_FAST_ACK:
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westwood_fast_bw(sk);
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break;
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case CA_EVENT_COMPLETE_CWR:
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tp->snd_cwnd = tp->snd_ssthresh = tcp_westwood_bw_rttmin(sk);
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break;
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case CA_EVENT_LOSS:
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tp->snd_ssthresh = tcp_westwood_bw_rttmin(sk);
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/* Update RTT_min when next ack arrives */
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w->reset_rtt_min = 1;
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break;
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case CA_EVENT_SLOW_ACK:
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westwood_update_window(sk);
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w->bk += westwood_acked_count(sk);
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update_rtt_min(w);
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break;
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default:
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/* don't care */
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break;
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}
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}
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/* Extract info for Tcp socket info provided via netlink. */
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static void tcp_westwood_info(struct sock *sk, u32 ext,
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struct sk_buff *skb)
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{
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const struct westwood *ca = inet_csk_ca(sk);
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if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
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struct tcpvegas_info info = {
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.tcpv_enabled = 1,
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.tcpv_rtt = jiffies_to_usecs(ca->rtt),
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.tcpv_minrtt = jiffies_to_usecs(ca->rtt_min),
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};
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nla_put(skb, INET_DIAG_VEGASINFO, sizeof(info), &info);
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}
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}
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static struct tcp_congestion_ops tcp_westwood __read_mostly = {
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.init = tcp_westwood_init,
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.ssthresh = tcp_reno_ssthresh,
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.cong_avoid = tcp_reno_cong_avoid,
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.min_cwnd = tcp_westwood_bw_rttmin,
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.cwnd_event = tcp_westwood_event,
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.get_info = tcp_westwood_info,
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.pkts_acked = tcp_westwood_pkts_acked,
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.owner = THIS_MODULE,
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.name = "westwood"
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};
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static int __init tcp_westwood_register(void)
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{
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BUILD_BUG_ON(sizeof(struct westwood) > ICSK_CA_PRIV_SIZE);
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return tcp_register_congestion_control(&tcp_westwood);
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}
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static void __exit tcp_westwood_unregister(void)
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{
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tcp_unregister_congestion_control(&tcp_westwood);
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}
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module_init(tcp_westwood_register);
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module_exit(tcp_westwood_unregister);
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MODULE_AUTHOR("Stephen Hemminger, Angelo Dell'Aera");
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MODULE_LICENSE("GPL");
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MODULE_DESCRIPTION("TCP Westwood+");
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