3 files changed, 353 insertions, 0 deletions

diff --git a/net/ipv4/Kconfig b/net/ipv4/Kconfig
index 567b03b1c349..712ebacacb62 100644
--- a/net/ipv4/Kconfig
+++ b/net/ipv4/Kconfig
@@ -433,5 +433,26 @@ config IP_TCPDIAG
 config IP_TCPDIAG_IPV6
         def_bool (IP_TCPDIAG=y && IPV6=y) || (IP_TCPDIAG=m && IPV6)
 
+# TCP Reno is builtin (required as fallback)
+menu "TCP congestion control"
+        depends on INET
+
+config TCP_CONG_BIC
+        tristate "Binary Increase Congestion (BIC) control"
+        depends on INET
+        default y
+        ---help---
+        BIC-TCP is a sender-side only change that ensures a linear RTT
+        fairness under large windows while offering both scalability and
+        bounded TCP-friendliness. The protocol combines two schemes
+        called additive increase and binary search increase. When the
+        congestion window is large, additive increase with a large
+        increment ensures linear RTT fairness as well as good
+        scalability. Under small congestion windows, binary search
+        increase provides TCP friendliness.
+        See http://www.csc.ncsu.edu/faculty/rhee/export/bitcp/
+
+endmenu
+
 source "net/ipv4/ipvs/Kconfig"
 
diff --git a/net/ipv4/Makefile b/net/ipv4/Makefile
index 89c0b4cb470e..1d1cac5ac06a 100644
--- a/net/ipv4/Makefile
+++ b/net/ipv4/Makefile
@@ -31,6 +31,7 @@ obj-$(CONFIG_NETFILTER)	+= netfilter/
 obj-$(CONFIG_IP_VS) += ipvs/
 obj-$(CONFIG_IP_TCPDIAG) += tcp_diag.o 
 obj-$(CONFIG_IP_ROUTE_MULTIPATH_CACHED) += multipath.o
+obj-$(CONFIG_TCP_CONG_BIC) += tcp_bic.o
 
 obj-$(CONFIG_XFRM) += xfrm4_policy.o xfrm4_state.o xfrm4_input.o \
                       xfrm4_output.o
diff --git a/net/ipv4/tcp_bic.c b/net/ipv4/tcp_bic.c
new file mode 100644
index 000000000000..ec38d45d6649
--- /dev/null
+++ b/net/ipv4/tcp_bic.c
@@ -0,0 +1,331 @@
+/*
+ * Binary Increase Congestion control for TCP
+ *
+ * This is from the implementation of BICTCP in
+ * Lison-Xu, Kahaled Harfoush, and Injong Rhee.
+ *  "Binary Increase Congestion Control for Fast, Long Distance
+ *  Networks" in InfoComm 2004
+ * Available from:
+ *  http://www.csc.ncsu.edu/faculty/rhee/export/bitcp.pdf
+ *
+ * Unless BIC is enabled and congestion window is large
+ * this behaves the same as the original Reno.
+ */
+
+#include <linux/config.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <net/tcp.h>
+
+
+#define BICTCP_BETA_SCALE    1024       /* Scale factor beta calculation
+                                         * max_cwnd = snd_cwnd * beta
+                                         */
+#define BICTCP_B                4        /*
+                                          * In binary search,
+                                          * go to point (max+min)/N
+                                          */
+
+static int fast_convergence = 1;
+static int max_increment = 32;
+static int low_window = 14;
+static int beta = 819;          /* = 819/1024 (BICTCP_BETA_SCALE) */
+static int low_utilization_threshold = 153;
+static int low_utilization_period = 2;
+static int initial_ssthresh = 100;
+static int smooth_part = 20;
+
+module_param(fast_convergence, int, 0644);
+MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence");
+module_param(max_increment, int, 0644);
+MODULE_PARM_DESC(max_increment, "Limit on increment allowed during binary search");
+module_param(low_window, int, 0644);
+MODULE_PARM_DESC(low_window, "lower bound on congestion window (for TCP friendliness)");
+module_param(beta, int, 0644);
+MODULE_PARM_DESC(beta, "beta for multiplicative increase");
+module_param(low_utilization_threshold, int, 0644);
+MODULE_PARM_DESC(low_utilization_threshold, "percent (scaled by 1024) for low utilization mode");
+module_param(low_utilization_period, int, 0644);
+MODULE_PARM_DESC(low_utilization_period, "if average delay exceeds then goto to low utilization mode (seconds)");
+module_param(initial_ssthresh, int, 0644);
+MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold");
+module_param(smooth_part, int, 0644);
+MODULE_PARM_DESC(smooth_part, "log(B/(B*Smin))/log(B/(B-1))+B, # of RTT from Wmax-B to Wmax");
+
+
+/* BIC TCP Parameters */
+struct bictcp {
+        u32     cnt;            /* increase cwnd by 1 after ACKs */
+        u32     last_max_cwnd;  /* last maximum snd_cwnd */
+        u32     loss_cwnd;      /* congestion window at last loss */
+        u32     last_cwnd;      /* the last snd_cwnd */
+        u32     last_time;      /* time when updated last_cwnd */
+        u32     delay_min;      /* min delay */
+        u32     delay_max;      /* max delay */
+        u32     last_delay;
+        u8      low_utilization;/* 0: high; 1: low */
+        u32     low_utilization_start;  /* starting time of low utilization detection*/
+        u32     epoch_start;    /* beginning of an epoch */
+#define ACK_RATIO_SHIFT 4
+        u32     delayed_ack;    /* estimate the ratio of Packets/ACKs << 4 */
+};
+
+static inline void bictcp_reset(struct bictcp *ca)
+{
+        ca->cnt = 0;
+        ca->last_max_cwnd = 0;
+        ca->loss_cwnd = 0;
+        ca->last_cwnd = 0;
+        ca->last_time = 0;
+        ca->delay_min = 0;
+        ca->delay_max = 0;
+        ca->last_delay = 0;
+        ca->low_utilization = 0;
+        ca->low_utilization_start = 0;
+        ca->epoch_start = 0;
+        ca->delayed_ack = 2 << ACK_RATIO_SHIFT;
+}
+
+static void bictcp_init(struct tcp_sock *tp)
+{
+        bictcp_reset(tcp_ca(tp));
+        if (initial_ssthresh)
+                tp->snd_ssthresh = initial_ssthresh;
+}
+
+/*
+ * Compute congestion window to use.
+ */
+static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
+{
+        if (ca->last_cwnd == cwnd &&
+            (s32)(tcp_time_stamp - ca->last_time) <= HZ / 32)
+                return;
+
+        ca->last_cwnd = cwnd;
+        ca->last_time = tcp_time_stamp;
+
+        if (ca->epoch_start == 0) /* record the beginning of an epoch */
+                ca->epoch_start = tcp_time_stamp;
+
+        /* start off normal */
+        if (cwnd <= low_window) {
+                ca->cnt = cwnd;
+                return;
+        }
+
+        /* binary increase */
+        if (cwnd < ca->last_max_cwnd) {
+                __u32   dist = (ca->last_max_cwnd - cwnd)
+                        / BICTCP_B;
+
+                if (dist > max_increment)
+                        /* linear increase */
+                        ca->cnt = cwnd / max_increment;
+                else if (dist <= 1U)
+                        /* binary search increase */
+                        ca->cnt = (cwnd * smooth_part) / BICTCP_B;
+                else
+                        /* binary search increase */
+                        ca->cnt = cwnd / dist;
+        } else {
+                /* slow start AMD linear increase */
+                if (cwnd < ca->last_max_cwnd + BICTCP_B)
+                        /* slow start */
+                        ca->cnt = (cwnd * smooth_part) / BICTCP_B;
+                else if (cwnd < ca->last_max_cwnd + max_increment*(BICTCP_B-1))
+                        /* slow start */
+                        ca->cnt = (cwnd * (BICTCP_B-1))
+                                / cwnd-ca->last_max_cwnd;
+                else
+                        /* linear increase */
+                        ca->cnt = cwnd / max_increment;
+        }
+
+        /* if in slow start or link utilization is very low */
+        if ( ca->loss_cwnd == 0 ||
+             (cwnd > ca->loss_cwnd && ca->low_utilization)) {
+                if (ca->cnt > 20) /* increase cwnd 5% per RTT */
+                        ca->cnt = 20;
+        }
+
+        ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack;
+        if (ca->cnt == 0)                       /* cannot be zero */
+                ca->cnt = 1;
+}
+
+
+/* Detect low utilization in congestion avoidance */
+static inline void bictcp_low_utilization(struct tcp_sock *tp, int flag)
+{
+        struct bictcp *ca = tcp_ca(tp);
+        u32 dist, delay;
+
+        /* No time stamp */
+        if (!(tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr) ||
+             /* Discard delay samples right after fast recovery */
+             tcp_time_stamp < ca->epoch_start + HZ ||
+             /* this delay samples may not be accurate */
+             flag == 0) {
+                ca->last_delay = 0;
+                goto notlow;
+        }
+
+        delay = ca->last_delay<<3;      /* use the same scale as tp->srtt*/
+        ca->last_delay = tcp_time_stamp - tp->rx_opt.rcv_tsecr;
+        if (delay == 0)                 /* no previous delay sample */
+                goto notlow;
+
+        /* first time call or link delay decreases */
+        if (ca->delay_min == 0 || ca->delay_min > delay) {
+                ca->delay_min = ca->delay_max = delay;
+                goto notlow;
+        }
+
+        if (ca->delay_max < delay)
+                ca->delay_max = delay;
+
+        /* utilization is low, if avg delay < dist*threshold
+           for checking_period time */
+        dist = ca->delay_max - ca->delay_min;
+        if (dist <= ca->delay_min>>6 ||
+            tp->srtt - ca->delay_min >=  (dist*low_utilization_threshold)>>10)
+                goto notlow;
+
+        if (ca->low_utilization_start == 0) {
+                ca->low_utilization = 0;
+                ca->low_utilization_start = tcp_time_stamp;
+        } else if ((s32)(tcp_time_stamp - ca->low_utilization_start)
+                        > low_utilization_period*HZ) {
+                ca->low_utilization = 1;
+        }
+
+        return;
+
+ notlow:
+        ca->low_utilization = 0;
+        ca->low_utilization_start = 0;
+
+}
+
+static void bictcp_cong_avoid(struct tcp_sock *tp, u32 ack,
+                              u32 seq_rtt, u32 in_flight, int data_acked)
+{
+        struct bictcp *ca = tcp_ca(tp);
+
+        bictcp_low_utilization(tp, data_acked);
+
+        if (in_flight < tp->snd_cwnd)
+                return;
+
+        if (tp->snd_cwnd <= tp->snd_ssthresh) {
+                /* In "safe" area, increase. */
+                if (tp->snd_cwnd < tp->snd_cwnd_clamp)
+                        tp->snd_cwnd++;
+        } else {
+                bictcp_update(ca, tp->snd_cwnd);
+
+                /* In dangerous area, increase slowly.
+                 * In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd
+                 */
+                if (tp->snd_cwnd_cnt >= ca->cnt) {
+                        if (tp->snd_cwnd < tp->snd_cwnd_clamp)
+                                tp->snd_cwnd++;
+                        tp->snd_cwnd_cnt = 0;
+                } else
+                        tp->snd_cwnd_cnt++;
+        }
+
+}
+
+/*
+ *      behave like Reno until low_window is reached,
+ *      then increase congestion window slowly
+ */
+static u32 bictcp_recalc_ssthresh(struct tcp_sock *tp)
+{
+        struct bictcp *ca = tcp_ca(tp);
+
+        ca->epoch_start = 0;    /* end of epoch */
+
+        /* in case of wrong delay_max*/
+        if (ca->delay_min > 0 && ca->delay_max > ca->delay_min)
+                ca->delay_max = ca->delay_min
+                        + ((ca->delay_max - ca->delay_min)* 90) / 100;
+
+        /* Wmax and fast convergence */
+        if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence)
+                ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta))
+                        / (2 * BICTCP_BETA_SCALE);
+        else
+                ca->last_max_cwnd = tp->snd_cwnd;
+
+        ca->loss_cwnd = tp->snd_cwnd;
+
+
+        if (tp->snd_cwnd <= low_window)
+                return max(tp->snd_cwnd >> 1U, 2U);
+        else
+                return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
+}
+
+static u32 bictcp_undo_cwnd(struct tcp_sock *tp)
+{
+        struct bictcp *ca = tcp_ca(tp);
+
+        return max(tp->snd_cwnd, ca->last_max_cwnd);
+}
+
+static u32 bictcp_min_cwnd(struct tcp_sock *tp)
+{
+        return tp->snd_ssthresh;
+}
+
+static void bictcp_state(struct tcp_sock *tp, u8 new_state)
+{
+        if (new_state == TCP_CA_Loss)
+                bictcp_reset(tcp_ca(tp));
+}
+
+/* Track delayed acknowledgement ratio using sliding window
+ * ratio = (15*ratio + sample) / 16
+ */
+static void bictcp_acked(struct tcp_sock *tp, u32 cnt)
+{
+        if (cnt > 0 &&  tp->ca_state == TCP_CA_Open) {
+                struct bictcp *ca = tcp_ca(tp);
+                cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT;
+                ca->delayed_ack += cnt;
+        }
+}
+
+
+static struct tcp_congestion_ops bictcp = {
+        .init           = bictcp_init,
+        .ssthresh       = bictcp_recalc_ssthresh,
+        .cong_avoid     = bictcp_cong_avoid,
+        .set_state      = bictcp_state,
+        .undo_cwnd      = bictcp_undo_cwnd,
+        .min_cwnd       = bictcp_min_cwnd,
+        .pkts_acked     = bictcp_acked,
+        .owner          = THIS_MODULE,
+        .name           = "bic",
+};
+
+static int __init bictcp_register(void)
+{
+        BUG_ON(sizeof(struct bictcp) > TCP_CA_PRIV_SIZE);
+        return tcp_register_congestion_control(&bictcp);
+}
+
+static void __exit bictcp_unregister(void)
+{
+        tcp_unregister_congestion_control(&bictcp);
+}
+
+module_init(bictcp_register);
+module_exit(bictcp_unregister);
+
+MODULE_AUTHOR("Stephen Hemminger");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("BIC TCP");