--- /dev/null
+/*
+ * TCP Westwood+: end-to-end bandwidth estimation for TCP
+ *
+ * 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/mm.h>
+#include <linux/module.h>
+#include <linux/skbuff.h>
+#include <linux/inet_diag.h>
+#include <net/tcp.h>
+
+/* TCP Westwood structure */
+struct westwood {
+ u32 bw_ns_est; /* first bandwidth estimation..not too smoothed 8) */
+ u32 bw_est; /* bandwidth estimate */
+ u32 rtt_win_sx; /* here starts a new evaluation... */
+ u32 bk;
+ u32 snd_una; /* used for evaluating the number of acked bytes */
+ u32 cumul_ack;
+ 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*/
+};
+
+/* TCP Westwood functions and constants */
+#define TCP_WESTWOOD_RTT_MIN (HZ/20) /* 50ms */
+#define TCP_WESTWOOD_INIT_RTT (20*HZ) /* maybe too conservative?! */
+
+/*
+ * @tcp_westwood_create
+ * This function initializes fields used in TCP Westwood+,
+ * it is called after the initial SYN, so the sequence numbers
+ * are correct but new passive connections we have no
+ * information about RTTmin at this time so we simply set it to
+ * TCP_WESTWOOD_INIT_RTT. This value was chosen to be too conservative
+ * since in this way we're sure it will be updated in a consistent
+ * way as soon as possible. It will reasonably happen within the first
+ * RTT period of the connection lifetime.
+ */
+static void tcp_westwood_init(struct sock *sk)
+{
+ struct westwood *w = inet_csk_ca(sk);
+
+ w->bk = 0;
+ w->bw_ns_est = 0;
+ 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;
+}
+
+/*
+ * @westwood_do_filter
+ * Low-pass filter. Implemented using constant coefficients.
+ */
+static inline u32 westwood_do_filter(u32 a, u32 b)
+{
+ return ((7 * a) + b) >> 3;
+}
+
+static void westwood_filter(struct westwood *w, u32 delta)
+{
+ /* 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);
+ }
+}
+
+/*
+ * @westwood_pkts_acked
+ * Called after processing group of packets.
+ * but all westwood needs is the last sample of srtt.
+ */
+static void tcp_westwood_pkts_acked(struct sock *sk, u32 cnt, s32 rtt)
+{
+ struct westwood *w = inet_csk_ca(sk);
+
+ if (rtt > 0)
+ w->rtt = usecs_to_jiffies(rtt);
+}
+
+/*
+ * @westwood_update_window
+ * It updates RTT evaluation window if it is the right moment to do
+ * it. If so it calls filter for evaluating bandwidth.
+ */
+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
+ * 50ms we don't filter but we continue 'building the sample'.
+ * This minimum limit was chosen since an estimation on small
+ * time intervals is better to avoid...
+ * Obviously on a LAN we reasonably will always have
+ * right_bound = left_bound + WESTWOOD_RTT_MIN
+ */
+ if (w->rtt && delta > max_t(u32, w->rtt, TCP_WESTWOOD_RTT_MIN)) {
+ westwood_filter(w, delta);
+
+ w->bk = 0;
+ w->rtt_win_sx = tcp_time_stamp;
+ }
+}
+
+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
+ * header prediction is successful. In such case in fact update is
+ * straight forward and doesn't need any particular care.
+ */
+static inline void westwood_fast_bw(struct sock *sk)
+{
+ const struct tcp_sock *tp = tcp_sk(sk);
+ struct westwood *w = inet_csk_ca(sk);
+
+ westwood_update_window(sk);
+
+ w->bk += tp->snd_una - w->snd_una;
+ w->snd_una = tp->snd_una;
+ update_rtt_min(w);
+}
+
+/*
+ * @westwood_acked_count
+ * This function evaluates cumul_ack for evaluating bk in case of
+ * delayed or partial acks.
+ */
+static inline u32 westwood_acked_count(struct sock *sk)
+{
+ const struct tcp_sock *tp = tcp_sk(sk);
+ struct westwood *w = inet_csk_ca(sk);
+
+ w->cumul_ack = tp->snd_una - w->snd_una;
+
+ /* If cumul_ack is 0 this is a dupack since it's not moving
+ * tp->snd_una.
+ */
+ if (!w->cumul_ack) {
+ w->accounted += tp->mss_cache;
+ w->cumul_ack = tp->mss_cache;
+ }
+
+ if (w->cumul_ack > tp->mss_cache) {
+ /* Partial or delayed ack */
+ if (w->accounted >= w->cumul_ack) {
+ w->accounted -= w->cumul_ack;
+ w->cumul_ack = tp->mss_cache;
+ } else {
+ w->cumul_ack -= w->accounted;
+ w->accounted = 0;
+ }
+ }
+
+ w->snd_una = tp->snd_una;
+
+ return w->cumul_ack;
+}
+
+/*
+ * TCP Westwood
+ * Here limit is evaluated as Bw estimation*RTTmin (for obtaining it
+ * in packets we use mss_cache). Rttmin is guaranteed to be >= 2
+ * so avoids ever returning 0.
+ */
+static u32 tcp_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);
+}
+
+static void tcp_westwood_ack(struct sock *sk, u32 ack_flags)
+{
+ if (ack_flags & CA_ACK_SLOWPATH) {
+ struct westwood *w = inet_csk_ca(sk);
+
+ westwood_update_window(sk);
+ w->bk += westwood_acked_count(sk);
+
+ update_rtt_min(w);
+ return;
+ }
+
+ westwood_fast_bw(sk);
+}
+
+static void tcp_westwood_event(struct sock *sk, enum tcp_ca_event event)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct westwood *w = inet_csk_ca(sk);
+
+ switch (event) {
+ case CA_EVENT_COMPLETE_CWR:
+ tp->snd_cwnd = tp->snd_ssthresh = tcp_westwood_bw_rttmin(sk);
+ break;
+ case CA_EVENT_LOSS:
+ tp->snd_ssthresh = tcp_westwood_bw_rttmin(sk);
+ /* Update RTT_min when next ack arrives */
+ w->reset_rtt_min = 1;
+ break;
+ default:
+ /* don't care */
+ break;
+ }
+}
+
+/* Extract info for Tcp socket info provided via netlink. */
+static size_t tcp_westwood_info(struct sock *sk, u32 ext, int *attr,
+ union tcp_cc_info *info)
+{
+ const struct westwood *ca = inet_csk_ca(sk);
+
+ if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
+ info->vegas.tcpv_enabled = 1;
+ info->vegas.tcpv_rttcnt = 0;
+ info->vegas.tcpv_rtt = jiffies_to_usecs(ca->rtt),
+ info->vegas.tcpv_minrtt = jiffies_to_usecs(ca->rtt_min),
+
+ *attr = INET_DIAG_VEGASINFO;
+ return sizeof(struct tcpvegas_info);
+ }
+ return 0;
+}
+
+static struct tcp_congestion_ops tcp_westwood __read_mostly = {
+ .init = tcp_westwood_init,
+ .ssthresh = tcp_reno_ssthresh,
+ .cong_avoid = tcp_reno_cong_avoid,
+ .cwnd_event = tcp_westwood_event,
+ .in_ack_event = tcp_westwood_ack,
+ .get_info = tcp_westwood_info,
+ .pkts_acked = tcp_westwood_pkts_acked,
+
+ .owner = THIS_MODULE,
+ .name = "westwood"
+};
+
+static int __init tcp_westwood_register(void)
+{
+ BUILD_BUG_ON(sizeof(struct westwood) > ICSK_CA_PRIV_SIZE);
+ return tcp_register_congestion_control(&tcp_westwood);
+}
+
+static void __exit tcp_westwood_unregister(void)
+{
+ tcp_unregister_congestion_control(&tcp_westwood);
+}
+
+module_init(tcp_westwood_register);
+module_exit(tcp_westwood_unregister);
+
+MODULE_AUTHOR("Stephen Hemminger, Angelo Dell'Aera");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("TCP Westwood+");
Code Review / kvmfornfv.git / blobdiff