--- /dev/null
+/*
+ * TCP CUBIC: Binary Increase Congestion control for TCP v2.0
+ *
+ * This is from the implementation of CUBIC TCP in
+ * Injong Rhee, Lisong Xu.
+ * "CUBIC: A New TCP-Friendly High-Speed TCP Variant
+ * in PFLDnet 2005
+ * Available from:
+ * http://www.csc.ncsu.edu/faculty/rhee/export/bitcp/cubic-paper.pdf
+ *
+ * Unless CUBIC 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
+ */
+#define BICTCP_HZ 10 /* BIC HZ 2^10 = 1024 */
+
+static int fast_convergence = 1;
+static int max_increment = 16;
+static int beta = 819; /* = 819/1024 (BICTCP_BETA_SCALE) */
+static int initial_ssthresh = 100;
+static int bic_scale = 41;
+static int tcp_friendliness = 1;
+
+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(beta, int, 0644);
+MODULE_PARM_DESC(beta, "beta for multiplicative increase");
+module_param(initial_ssthresh, int, 0644);
+MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold");
+module_param(bic_scale, int, 0644);
+MODULE_PARM_DESC(bic_scale, "scale (scaled by 1024) value for bic function (bic_scale/1024)");
+module_param(tcp_friendliness, int, 0644);
+MODULE_PARM_DESC(tcp_friendliness, "turn on/off tcp friendliness");
+
+
+/* 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 bic_origin_point;/* origin point of bic function */
+ u32 bic_K; /* time to origin point from the beginning of the current epoch */
+ u32 delay_min; /* min delay */
+ u32 epoch_start; /* beginning of an epoch */
+ u32 ack_cnt; /* number of acks */
+ u32 tcp_cwnd; /* estimated tcp cwnd */
+#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->bic_origin_point = 0;
+ ca->bic_K = 0;
+ ca->delay_min = 0;
+ ca->epoch_start = 0;
+ ca->delayed_ack = 2 << ACK_RATIO_SHIFT;
+ ca->ack_cnt = 0;
+ ca->tcp_cwnd = 0;
+}
+
+static void bictcp_init(struct sock *sk)
+{
+ bictcp_reset(inet_csk_ca(sk));
+ if (initial_ssthresh)
+ tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
+}
+
+/* 65536 times the cubic root */
+static const u64 cubic_table[8]
+ = {0, 65536, 82570, 94519, 104030, 112063, 119087, 125367};
+
+/*
+ * calculate the cubic root of x
+ * the basic idea is that x can be expressed as i*8^j
+ * so cubic_root(x) = cubic_root(i)*2^j
+ * in the following code, x is i, and y is 2^j
+ * because of integer calculation, there are errors in calculation
+ * so finally use binary search to find out the exact solution
+ */
+static u32 cubic_root(u64 x)
+{
+ u64 y, app, target, start, end, mid, start_diff, end_diff;
+
+ if (x == 0)
+ return 0;
+
+ target = x;
+
+ /* first estimate lower and upper bound */
+ y = 1;
+ while (x >= 8){
+ x = (x >> 3);
+ y = (y << 1);
+ }
+ start = (y*cubic_table[x])>>16;
+ if (x==7)
+ end = (y<<1);
+ else
+ end = (y*cubic_table[x+1]+65535)>>16;
+
+ /* binary search for more accurate one */
+ while (start < end-1) {
+ mid = (start+end) >> 1;
+ app = mid*mid*mid;
+ if (app < target)
+ start = mid;
+ else if (app > target)
+ end = mid;
+ else
+ return mid;
+ }
+
+ /* find the most accurate one from start and end */
+ app = start*start*start;
+ if (app < target)
+ start_diff = target - app;
+ else
+ start_diff = app - target;
+ app = end*end*end;
+ if (app < target)
+ end_diff = target - app;
+ else
+ end_diff = app - target;
+
+ if (start_diff < end_diff)
+ return (u32)start;
+ else
+ return (u32)end;
+}
+
+static inline u32 bictcp_K(u32 dist, u32 srtt)
+{
+ u64 d64;
+ u32 d32;
+ u32 count;
+ u32 result;
+
+ /* calculate the "K" for (wmax-cwnd) = c/rtt * K^3
+ so K = cubic_root( (wmax-cwnd)*rtt/c )
+ the unit of K is bictcp_HZ=2^10, not HZ
+
+ c = bic_scale >> 10
+ rtt = (tp->srtt >> 3 ) / HZ
+
+ the following code has been designed and tested for
+ cwnd < 1 million packets
+ RTT < 100 seconds
+ HZ < 1,000,00 (corresponding to 10 nano-second)
+
+ */
+
+ /* 1/c * 2^2*bictcp_HZ */
+ d32 = (1 << (10+2*BICTCP_HZ)) / bic_scale;
+ d64 = (__u64)d32;
+
+ /* srtt * 2^count / HZ
+ 1) to get a better accuracy of the following d32,
+ the larger the "count", the better the accuracy
+ 2) and avoid overflow of the following d64
+ the larger the "count", the high possibility of overflow
+ 3) so find a "count" between bictcp_hz-3 and bictcp_hz
+ "count" may be less than bictcp_HZ,
+ then d64 becomes 0. that is OK
+ */
+ d32 = srtt;
+ count = 0;
+ while (((d32 & 0x80000000)==0) && (count < BICTCP_HZ)){
+ d32 = d32 << 1;
+ count++;
+ }
+ d32 = d32 / HZ;
+
+ /* (wmax-cwnd) * (srtt>>3 / HZ) / c * 2^(3*bictcp_HZ) */
+ d64 = (d64 * dist * d32) >> (count+3-BICTCP_HZ);
+
+ /* cubic root */
+ d64 = cubic_root(d64);
+
+ result = (u32)d64;
+ return result;
+}
+
+/*
+ * Compute congestion window to use.
+ */
+static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
+{
+ u64 d64;
+ u32 d32, t, srtt, bic_target, min_cnt, max_cnt;
+
+ ca->ack_cnt++; /* count the number of ACKs */
+
+ 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;
+
+ srtt = (HZ << 3)/10; /* use real time-based growth function */
+
+ if (ca->epoch_start == 0) {
+ ca->epoch_start = tcp_time_stamp; /* record the beginning of an epoch */
+ ca->ack_cnt = 1; /* start counting */
+ ca->tcp_cwnd = cwnd; /* syn with cubic */
+
+ if (ca->last_max_cwnd <= cwnd) {
+ ca->bic_K = 0;
+ ca->bic_origin_point = cwnd;
+ } else {
+ ca->bic_K = bictcp_K(ca->last_max_cwnd-cwnd, srtt);
+ ca->bic_origin_point = ca->last_max_cwnd;
+ }
+ }
+
+ /* cubic function - calc*/
+ /* calculate c * time^3 / rtt,
+ * while considering overflow in calculation of time^3
+ * (so time^3 is done by using d64)
+ * and without the support of division of 64bit numbers
+ * (so all divisions are done by using d32)
+ * also NOTE the unit of those veriables
+ * time = (t - K) / 2^bictcp_HZ
+ * c = bic_scale >> 10
+ * rtt = (srtt >> 3) / HZ
+ * !!! The following code does not have overflow problems,
+ * if the cwnd < 1 million packets !!!
+ */
+
+ /* change the unit from HZ to bictcp_HZ */
+ t = ((tcp_time_stamp + ca->delay_min - ca->epoch_start)
+ << BICTCP_HZ) / HZ;
+
+ if (t < ca->bic_K) /* t - K */
+ d32 = ca->bic_K - t;
+ else
+ d32 = t - ca->bic_K;
+
+ d64 = (u64)d32;
+ d32 = (bic_scale << 3) * HZ / srtt; /* 1024*c/rtt */
+ d64 = (d32 * d64 * d64 * d64) >> (10+3*BICTCP_HZ); /* c/rtt * (t-K)^3 */
+ d32 = (u32)d64;
+ if (t < ca->bic_K) /* below origin*/
+ bic_target = ca->bic_origin_point - d32;
+ else /* above origin*/
+ bic_target = ca->bic_origin_point + d32;
+
+ /* cubic function - calc bictcp_cnt*/
+ if (bic_target > cwnd) {
+ ca->cnt = cwnd / (bic_target - cwnd);
+ } else {
+ ca->cnt = 100 * cwnd; /* very small increment*/
+ }
+
+ if (ca->delay_min > 0) {
+ /* max increment = Smax * rtt / 0.1 */
+ min_cnt = (cwnd * HZ * 8)/(10 * max_increment * ca->delay_min);
+ if (ca->cnt < min_cnt)
+ ca->cnt = min_cnt;
+ }
+
+ /* slow start and low utilization */
+ if (ca->loss_cwnd == 0) /* could be aggressive in slow start */
+ ca->cnt = 50;
+
+ /* TCP Friendly */
+ if (tcp_friendliness) {
+ u32 scale = 8*(BICTCP_BETA_SCALE+beta)/3/(BICTCP_BETA_SCALE-beta);
+ d32 = (cwnd * scale) >> 3;
+ while (ca->ack_cnt > d32) { /* update tcp cwnd */
+ ca->ack_cnt -= d32;
+ ca->tcp_cwnd++;
+ }
+
+ if (ca->tcp_cwnd > cwnd){ /* if bic is slower than tcp */
+ d32 = ca->tcp_cwnd - cwnd;
+ max_cnt = cwnd / d32;
+ if (ca->cnt > max_cnt)
+ ca->cnt = max_cnt;
+ }
+ }
+
+ ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack;
+ if (ca->cnt == 0) /* cannot be zero */
+ ca->cnt = 1;
+}
+
+
+/* Keep track of minimum rtt */
+static inline void measure_delay(struct sock *sk)
+{
+ const struct tcp_sock *tp = tcp_sk(sk);
+ struct bictcp *ca = inet_csk_ca(sk);
+ u32 delay;
+
+ /* No time stamp */
+ if (!(tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr) ||
+ /* Discard delay samples right after fast recovery */
+ (s32)(tcp_time_stamp - ca->epoch_start) < HZ)
+ return;
+
+ delay = tcp_time_stamp - tp->rx_opt.rcv_tsecr;
+ if (delay == 0)
+ delay = 1;
+
+ /* first time call or link delay decreases */
+ if (ca->delay_min == 0 || ca->delay_min > delay)
+ ca->delay_min = delay;
+}
+
+static void bictcp_cong_avoid(struct sock *sk, u32 ack,
+ u32 seq_rtt, u32 in_flight, int data_acked)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct bictcp *ca = inet_csk_ca(sk);
+
+ if (data_acked)
+ measure_delay(sk);
+
+ if (!tcp_is_cwnd_limited(sk, in_flight))
+ return;
+
+ if (tp->snd_cwnd <= tp->snd_ssthresh)
+ tcp_slow_start(tp);
+ 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++;
+ }
+
+}
+
+static u32 bictcp_recalc_ssthresh(struct sock *sk)
+{
+ const struct tcp_sock *tp = tcp_sk(sk);
+ struct bictcp *ca = inet_csk_ca(sk);
+
+ ca->epoch_start = 0; /* end of epoch */
+
+ /* 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;
+
+ return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
+}
+
+static u32 bictcp_undo_cwnd(struct sock *sk)
+{
+ struct bictcp *ca = inet_csk_ca(sk);
+
+ return max(tcp_sk(sk)->snd_cwnd, ca->last_max_cwnd);
+}
+
+static u32 bictcp_min_cwnd(struct sock *sk)
+{
+ return tcp_sk(sk)->snd_ssthresh;
+}
+
+static void bictcp_state(struct sock *sk, u8 new_state)
+{
+ if (new_state == TCP_CA_Loss)
+ bictcp_reset(inet_csk_ca(sk));
+}
+
+/* Track delayed acknowledgment ratio using sliding window
+ * ratio = (15*ratio + sample) / 16
+ */
+static void bictcp_acked(struct sock *sk, u32 cnt)
+{
+ const struct inet_connection_sock *icsk = inet_csk(sk);
+
+ if (cnt > 0 && icsk->icsk_ca_state == TCP_CA_Open) {
+ struct bictcp *ca = inet_csk_ca(sk);
+ cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT;
+ ca->delayed_ack += cnt;
+ }
+}
+
+
+static struct tcp_congestion_ops cubictcp = {
+ .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 = "cubic",
+};
+
+static int __init cubictcp_register(void)
+{
+ BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE);
+ return tcp_register_congestion_control(&cubictcp);
+}
+
+static void __exit cubictcp_unregister(void)
+{
+ tcp_unregister_congestion_control(&cubictcp);
+}
+
+module_init(cubictcp_register);
+module_exit(cubictcp_unregister);
+
+MODULE_AUTHOR("Sangtae Ha, Stephen Hemminger");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("CUBIC TCP");
+MODULE_VERSION("2.0");
projects / linux-2.6 / commitdiff