--- /dev/null
+/*
+ * TCP Illinois congestion control.
+ * Home page:
+ * http://www.ews.uiuc.edu/~shaoliu/tcpillinois/index.html
+ *
+ * The algorithm is described in:
+ * "TCP-Illinois: A Loss and Delay-Based Congestion Control Algorithm
+ * for High-Speed Networks"
+ * http://www.ifp.illinois.edu/~srikant/Papers/liubassri06perf.pdf
+ *
+ * Implemented from description in paper and ns-2 simulation.
+ * Copyright (C) 2007 Stephen Hemminger <shemminger@linux-foundation.org>
+ */
+
+#include <linux/module.h>
+#include <linux/skbuff.h>
+#include <linux/inet_diag.h>
+#include <asm/div64.h>
+#include <net/tcp.h>
+
+#define ALPHA_SHIFT 7
+#define ALPHA_SCALE (1u<<ALPHA_SHIFT)
+#define ALPHA_MIN ((3*ALPHA_SCALE)/10) /* ~0.3 */
+#define ALPHA_MAX (10*ALPHA_SCALE) /* 10.0 */
+#define ALPHA_BASE ALPHA_SCALE /* 1.0 */
+#define RTT_MAX (U32_MAX / ALPHA_MAX) /* 3.3 secs */
+
+#define BETA_SHIFT 6
+#define BETA_SCALE (1u<<BETA_SHIFT)
+#define BETA_MIN (BETA_SCALE/8) /* 0.125 */
+#define BETA_MAX (BETA_SCALE/2) /* 0.5 */
+#define BETA_BASE BETA_MAX
+
+static int win_thresh __read_mostly = 15;
+module_param(win_thresh, int, 0);
+MODULE_PARM_DESC(win_thresh, "Window threshold for starting adaptive sizing");
+
+static int theta __read_mostly = 5;
+module_param(theta, int, 0);
+MODULE_PARM_DESC(theta, "# of fast RTT's before full growth");
+
+/* TCP Illinois Parameters */
+struct illinois {
+ u64 sum_rtt; /* sum of rtt's measured within last rtt */
+ u16 cnt_rtt; /* # of rtts measured within last rtt */
+ u32 base_rtt; /* min of all rtt in usec */
+ u32 max_rtt; /* max of all rtt in usec */
+ u32 end_seq; /* right edge of current RTT */
+ u32 alpha; /* Additive increase */
+ u32 beta; /* Muliplicative decrease */
+ u16 acked; /* # packets acked by current ACK */
+ u8 rtt_above; /* average rtt has gone above threshold */
+ u8 rtt_low; /* # of rtts measurements below threshold */
+};
+
+static void rtt_reset(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct illinois *ca = inet_csk_ca(sk);
+
+ ca->end_seq = tp->snd_nxt;
+ ca->cnt_rtt = 0;
+ ca->sum_rtt = 0;
+
+ /* TODO: age max_rtt? */
+}
+
+static void tcp_illinois_init(struct sock *sk)
+{
+ struct illinois *ca = inet_csk_ca(sk);
+
+ ca->alpha = ALPHA_MAX;
+ ca->beta = BETA_BASE;
+ ca->base_rtt = 0x7fffffff;
+ ca->max_rtt = 0;
+
+ ca->acked = 0;
+ ca->rtt_low = 0;
+ ca->rtt_above = 0;
+
+ rtt_reset(sk);
+}
+
+/* Measure RTT for each ack. */
+static void tcp_illinois_acked(struct sock *sk, u32 pkts_acked, s32 rtt)
+{
+ struct illinois *ca = inet_csk_ca(sk);
+
+ ca->acked = pkts_acked;
+
+ /* dup ack, no rtt sample */
+ if (rtt < 0)
+ return;
+
+ /* ignore bogus values, this prevents wraparound in alpha math */
+ if (rtt > RTT_MAX)
+ rtt = RTT_MAX;
+
+ /* keep track of minimum RTT seen so far */
+ if (ca->base_rtt > rtt)
+ ca->base_rtt = rtt;
+
+ /* and max */
+ if (ca->max_rtt < rtt)
+ ca->max_rtt = rtt;
+
+ ++ca->cnt_rtt;
+ ca->sum_rtt += rtt;
+}
+
+/* Maximum queuing delay */
+static inline u32 max_delay(const struct illinois *ca)
+{
+ return ca->max_rtt - ca->base_rtt;
+}
+
+/* Average queuing delay */
+static inline u32 avg_delay(const struct illinois *ca)
+{
+ u64 t = ca->sum_rtt;
+
+ do_div(t, ca->cnt_rtt);
+ return t - ca->base_rtt;
+}
+
+/*
+ * Compute value of alpha used for additive increase.
+ * If small window then use 1.0, equivalent to Reno.
+ *
+ * For larger windows, adjust based on average delay.
+ * A. If average delay is at minimum (we are uncongested),
+ * then use large alpha (10.0) to increase faster.
+ * B. If average delay is at maximum (getting congested)
+ * then use small alpha (0.3)
+ *
+ * The result is a convex window growth curve.
+ */
+static u32 alpha(struct illinois *ca, u32 da, u32 dm)
+{
+ u32 d1 = dm / 100; /* Low threshold */
+
+ if (da <= d1) {
+ /* If never got out of low delay zone, then use max */
+ if (!ca->rtt_above)
+ return ALPHA_MAX;
+
+ /* Wait for 5 good RTT's before allowing alpha to go alpha max.
+ * This prevents one good RTT from causing sudden window increase.
+ */
+ if (++ca->rtt_low < theta)
+ return ca->alpha;
+
+ ca->rtt_low = 0;
+ ca->rtt_above = 0;
+ return ALPHA_MAX;
+ }
+
+ ca->rtt_above = 1;
+
+ /*
+ * Based on:
+ *
+ * (dm - d1) amin amax
+ * k1 = -------------------
+ * amax - amin
+ *
+ * (dm - d1) amin
+ * k2 = ---------------- - d1
+ * amax - amin
+ *
+ * k1
+ * alpha = ----------
+ * k2 + da
+ */
+
+ dm -= d1;
+ da -= d1;
+ return (dm * ALPHA_MAX) /
+ (dm + (da * (ALPHA_MAX - ALPHA_MIN)) / ALPHA_MIN);
+}
+
+/*
+ * Beta used for multiplicative decrease.
+ * For small window sizes returns same value as Reno (0.5)
+ *
+ * If delay is small (10% of max) then beta = 1/8
+ * If delay is up to 80% of max then beta = 1/2
+ * In between is a linear function
+ */
+static u32 beta(u32 da, u32 dm)
+{
+ u32 d2, d3;
+
+ d2 = dm / 10;
+ if (da <= d2)
+ return BETA_MIN;
+
+ d3 = (8 * dm) / 10;
+ if (da >= d3 || d3 <= d2)
+ return BETA_MAX;
+
+ /*
+ * Based on:
+ *
+ * bmin d3 - bmax d2
+ * k3 = -------------------
+ * d3 - d2
+ *
+ * bmax - bmin
+ * k4 = -------------
+ * d3 - d2
+ *
+ * b = k3 + k4 da
+ */
+ return (BETA_MIN * d3 - BETA_MAX * d2 + (BETA_MAX - BETA_MIN) * da)
+ / (d3 - d2);
+}
+
+/* Update alpha and beta values once per RTT */
+static void update_params(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct illinois *ca = inet_csk_ca(sk);
+
+ if (tp->snd_cwnd < win_thresh) {
+ ca->alpha = ALPHA_BASE;
+ ca->beta = BETA_BASE;
+ } else if (ca->cnt_rtt > 0) {
+ u32 dm = max_delay(ca);
+ u32 da = avg_delay(ca);
+
+ ca->alpha = alpha(ca, da, dm);
+ ca->beta = beta(da, dm);
+ }
+
+ rtt_reset(sk);
+}
+
+/*
+ * In case of loss, reset to default values
+ */
+static void tcp_illinois_state(struct sock *sk, u8 new_state)
+{
+ struct illinois *ca = inet_csk_ca(sk);
+
+ if (new_state == TCP_CA_Loss) {
+ ca->alpha = ALPHA_BASE;
+ ca->beta = BETA_BASE;
+ ca->rtt_low = 0;
+ ca->rtt_above = 0;
+ rtt_reset(sk);
+ }
+}
+
+/*
+ * Increase window in response to successful acknowledgment.
+ */
+static void tcp_illinois_cong_avoid(struct sock *sk, u32 ack, u32 acked)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct illinois *ca = inet_csk_ca(sk);
+
+ if (after(ack, ca->end_seq))
+ update_params(sk);
+
+ /* RFC2861 only increase cwnd if fully utilized */
+ if (!tcp_is_cwnd_limited(sk))
+ return;
+
+ /* In slow start */
+ if (tp->snd_cwnd <= tp->snd_ssthresh)
+ tcp_slow_start(tp, acked);
+
+ else {
+ u32 delta;
+
+ /* snd_cwnd_cnt is # of packets since last cwnd increment */
+ tp->snd_cwnd_cnt += ca->acked;
+ ca->acked = 1;
+
+ /* This is close approximation of:
+ * tp->snd_cwnd += alpha/tp->snd_cwnd
+ */
+ delta = (tp->snd_cwnd_cnt * ca->alpha) >> ALPHA_SHIFT;
+ if (delta >= tp->snd_cwnd) {
+ tp->snd_cwnd = min(tp->snd_cwnd + delta / tp->snd_cwnd,
+ (u32)tp->snd_cwnd_clamp);
+ tp->snd_cwnd_cnt = 0;
+ }
+ }
+}
+
+static u32 tcp_illinois_ssthresh(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct illinois *ca = inet_csk_ca(sk);
+
+ /* Multiplicative decrease */
+ return max(tp->snd_cwnd - ((tp->snd_cwnd * ca->beta) >> BETA_SHIFT), 2U);
+}
+
+/* Extract info for Tcp socket info provided via netlink. */
+static size_t tcp_illinois_info(struct sock *sk, u32 ext, int *attr,
+ union tcp_cc_info *info)
+{
+ const struct illinois *ca = inet_csk_ca(sk);
+
+ if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
+ info->vegas.tcpv_enabled = 1;
+ info->vegas.tcpv_rttcnt = ca->cnt_rtt;
+ info->vegas.tcpv_minrtt = ca->base_rtt;
+ info->vegas.tcpv_rtt = 0;
+
+ if (info->vegas.tcpv_rttcnt > 0) {
+ u64 t = ca->sum_rtt;
+
+ do_div(t, info->vegas.tcpv_rttcnt);
+ info->vegas.tcpv_rtt = t;
+ }
+ *attr = INET_DIAG_VEGASINFO;
+ return sizeof(struct tcpvegas_info);
+ }
+ return 0;
+}
+
+static struct tcp_congestion_ops tcp_illinois __read_mostly = {
+ .init = tcp_illinois_init,
+ .ssthresh = tcp_illinois_ssthresh,
+ .cong_avoid = tcp_illinois_cong_avoid,
+ .set_state = tcp_illinois_state,
+ .get_info = tcp_illinois_info,
+ .pkts_acked = tcp_illinois_acked,
+
+ .owner = THIS_MODULE,
+ .name = "illinois",
+};
+
+static int __init tcp_illinois_register(void)
+{
+ BUILD_BUG_ON(sizeof(struct illinois) > ICSK_CA_PRIV_SIZE);
+ return tcp_register_congestion_control(&tcp_illinois);
+}
+
+static void __exit tcp_illinois_unregister(void)
+{
+ tcp_unregister_congestion_control(&tcp_illinois);
+}
+
+module_init(tcp_illinois_register);
+module_exit(tcp_illinois_unregister);
+
+MODULE_AUTHOR("Stephen Hemminger, Shao Liu");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("TCP Illinois");
+MODULE_VERSION("1.0");
Code Review / kvmfornfv.git / blobdiff