395 lines
11 KiB
C
395 lines
11 KiB
C
/*
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* TCP CUBIC: Binary Increase Congestion control for TCP v2.1
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*
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* This is from the implementation of CUBIC TCP in
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* Injong Rhee, Lisong Xu.
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* "CUBIC: A New TCP-Friendly High-Speed TCP Variant
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* in PFLDnet 2005
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* Available from:
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* http://www.csc.ncsu.edu/faculty/rhee/export/bitcp/cubic-paper.pdf
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*
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* Unless CUBIC is enabled and congestion window is large
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* this behaves the same 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 <net/tcp.h>
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#include <asm/div64.h>
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#define BICTCP_BETA_SCALE 1024 /* Scale factor beta calculation
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* max_cwnd = snd_cwnd * beta
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*/
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#define BICTCP_B 4 /*
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* In binary search,
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* go to point (max+min)/N
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*/
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#define BICTCP_HZ 10 /* BIC HZ 2^10 = 1024 */
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static int fast_convergence __read_mostly = 1;
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static int max_increment __read_mostly = 16;
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static int beta __read_mostly = 819; /* = 819/1024 (BICTCP_BETA_SCALE) */
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static int initial_ssthresh __read_mostly;
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static int bic_scale __read_mostly = 41;
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static int tcp_friendliness __read_mostly = 1;
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static u32 cube_rtt_scale __read_mostly;
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static u32 beta_scale __read_mostly;
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static u64 cube_factor __read_mostly;
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/* Note parameters that are used for precomputing scale factors are read-only */
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module_param(fast_convergence, int, 0644);
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MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence");
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module_param(max_increment, int, 0644);
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MODULE_PARM_DESC(max_increment, "Limit on increment allowed during binary search");
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module_param(beta, int, 0444);
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MODULE_PARM_DESC(beta, "beta for multiplicative increase");
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module_param(initial_ssthresh, int, 0644);
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MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold");
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module_param(bic_scale, int, 0444);
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MODULE_PARM_DESC(bic_scale, "scale (scaled by 1024) value for bic function (bic_scale/1024)");
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module_param(tcp_friendliness, int, 0644);
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MODULE_PARM_DESC(tcp_friendliness, "turn on/off tcp friendliness");
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/* BIC TCP Parameters */
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struct bictcp {
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u32 cnt; /* increase cwnd by 1 after ACKs */
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u32 last_max_cwnd; /* last maximum snd_cwnd */
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u32 loss_cwnd; /* congestion window at last loss */
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u32 last_cwnd; /* the last snd_cwnd */
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u32 last_time; /* time when updated last_cwnd */
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u32 bic_origin_point;/* origin point of bic function */
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u32 bic_K; /* time to origin point from the beginning of the current epoch */
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u32 delay_min; /* min delay */
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u32 epoch_start; /* beginning of an epoch */
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u32 ack_cnt; /* number of acks */
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u32 tcp_cwnd; /* estimated tcp cwnd */
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#define ACK_RATIO_SHIFT 4
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u32 delayed_ack; /* estimate the ratio of Packets/ACKs << 4 */
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};
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static inline void bictcp_reset(struct bictcp *ca)
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{
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ca->cnt = 0;
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ca->last_max_cwnd = 0;
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ca->loss_cwnd = 0;
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ca->last_cwnd = 0;
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ca->last_time = 0;
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ca->bic_origin_point = 0;
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ca->bic_K = 0;
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ca->delay_min = 0;
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ca->epoch_start = 0;
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ca->delayed_ack = 2 << ACK_RATIO_SHIFT;
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ca->ack_cnt = 0;
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ca->tcp_cwnd = 0;
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}
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static void bictcp_init(struct sock *sk)
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{
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bictcp_reset(inet_csk_ca(sk));
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if (initial_ssthresh)
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tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
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}
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/* calculate the cubic root of x using a table lookup followed by one
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* Newton-Raphson iteration.
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* Avg err ~= 0.195%
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*/
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static u32 cubic_root(u64 a)
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{
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u32 x, b, shift;
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/*
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* cbrt(x) MSB values for x MSB values in [0..63].
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* Precomputed then refined by hand - Willy Tarreau
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*
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* For x in [0..63],
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* v = cbrt(x << 18) - 1
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* cbrt(x) = (v[x] + 10) >> 6
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*/
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static const u8 v[] = {
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/* 0x00 */ 0, 54, 54, 54, 118, 118, 118, 118,
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/* 0x08 */ 123, 129, 134, 138, 143, 147, 151, 156,
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/* 0x10 */ 157, 161, 164, 168, 170, 173, 176, 179,
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/* 0x18 */ 181, 185, 187, 190, 192, 194, 197, 199,
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/* 0x20 */ 200, 202, 204, 206, 209, 211, 213, 215,
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/* 0x28 */ 217, 219, 221, 222, 224, 225, 227, 229,
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/* 0x30 */ 231, 232, 234, 236, 237, 239, 240, 242,
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/* 0x38 */ 244, 245, 246, 248, 250, 251, 252, 254,
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};
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b = fls64(a);
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if (b < 7) {
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/* a in [0..63] */
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return ((u32)v[(u32)a] + 35) >> 6;
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}
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b = ((b * 84) >> 8) - 1;
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shift = (a >> (b * 3));
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x = ((u32)(((u32)v[shift] + 10) << b)) >> 6;
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/*
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* Newton-Raphson iteration
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* 2
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* x = ( 2 * x + a / x ) / 3
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* k+1 k k
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*/
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x = (2 * x + (u32)div64_64(a, (u64)x * (u64)(x - 1)));
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x = ((x * 341) >> 10);
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return x;
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}
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/*
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* Compute congestion window to use.
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*/
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static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
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{
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u64 offs;
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u32 delta, t, bic_target, min_cnt, max_cnt;
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ca->ack_cnt++; /* count the number of ACKs */
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if (ca->last_cwnd == cwnd &&
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(s32)(tcp_time_stamp - ca->last_time) <= HZ / 32)
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return;
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ca->last_cwnd = cwnd;
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ca->last_time = tcp_time_stamp;
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if (ca->epoch_start == 0) {
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ca->epoch_start = tcp_time_stamp; /* record the beginning of an epoch */
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ca->ack_cnt = 1; /* start counting */
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ca->tcp_cwnd = cwnd; /* syn with cubic */
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if (ca->last_max_cwnd <= cwnd) {
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ca->bic_K = 0;
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ca->bic_origin_point = cwnd;
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} else {
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/* Compute new K based on
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* (wmax-cwnd) * (srtt>>3 / HZ) / c * 2^(3*bictcp_HZ)
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*/
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ca->bic_K = cubic_root(cube_factor
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* (ca->last_max_cwnd - cwnd));
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ca->bic_origin_point = ca->last_max_cwnd;
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}
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}
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/* cubic function - calc*/
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/* calculate c * time^3 / rtt,
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* while considering overflow in calculation of time^3
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* (so time^3 is done by using 64 bit)
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* and without the support of division of 64bit numbers
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* (so all divisions are done by using 32 bit)
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* also NOTE the unit of those veriables
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* time = (t - K) / 2^bictcp_HZ
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* c = bic_scale >> 10
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* rtt = (srtt >> 3) / HZ
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* !!! The following code does not have overflow problems,
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* if the cwnd < 1 million packets !!!
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*/
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/* change the unit from HZ to bictcp_HZ */
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t = ((tcp_time_stamp + (ca->delay_min>>3) - ca->epoch_start)
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<< BICTCP_HZ) / HZ;
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if (t < ca->bic_K) /* t - K */
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offs = ca->bic_K - t;
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else
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offs = t - ca->bic_K;
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/* c/rtt * (t-K)^3 */
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delta = (cube_rtt_scale * offs * offs * offs) >> (10+3*BICTCP_HZ);
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if (t < ca->bic_K) /* below origin*/
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bic_target = ca->bic_origin_point - delta;
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else /* above origin*/
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bic_target = ca->bic_origin_point + delta;
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/* cubic function - calc bictcp_cnt*/
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if (bic_target > cwnd) {
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ca->cnt = cwnd / (bic_target - cwnd);
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} else {
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ca->cnt = 100 * cwnd; /* very small increment*/
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}
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if (ca->delay_min > 0) {
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/* max increment = Smax * rtt / 0.1 */
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min_cnt = (cwnd * HZ * 8)/(10 * max_increment * ca->delay_min);
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/* use concave growth when the target is above the origin */
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if (ca->cnt < min_cnt && t >= ca->bic_K)
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ca->cnt = min_cnt;
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}
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/* slow start and low utilization */
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if (ca->loss_cwnd == 0) /* could be aggressive in slow start */
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ca->cnt = 50;
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/* TCP Friendly */
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if (tcp_friendliness) {
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u32 scale = beta_scale;
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delta = (cwnd * scale) >> 3;
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while (ca->ack_cnt > delta) { /* update tcp cwnd */
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ca->ack_cnt -= delta;
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ca->tcp_cwnd++;
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}
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if (ca->tcp_cwnd > cwnd){ /* if bic is slower than tcp */
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delta = ca->tcp_cwnd - cwnd;
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max_cnt = cwnd / delta;
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if (ca->cnt > max_cnt)
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ca->cnt = max_cnt;
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}
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}
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ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack;
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if (ca->cnt == 0) /* cannot be zero */
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ca->cnt = 1;
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}
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static void bictcp_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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struct bictcp *ca = inet_csk_ca(sk);
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if (!tcp_is_cwnd_limited(sk, in_flight))
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return;
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if (tp->snd_cwnd <= tp->snd_ssthresh)
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tcp_slow_start(tp);
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else {
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bictcp_update(ca, tp->snd_cwnd);
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/* In dangerous area, increase slowly.
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* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd
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*/
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if (tp->snd_cwnd_cnt >= ca->cnt) {
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if (tp->snd_cwnd < tp->snd_cwnd_clamp)
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tp->snd_cwnd++;
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tp->snd_cwnd_cnt = 0;
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} else
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tp->snd_cwnd_cnt++;
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}
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}
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static u32 bictcp_recalc_ssthresh(struct sock *sk)
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{
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const struct tcp_sock *tp = tcp_sk(sk);
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struct bictcp *ca = inet_csk_ca(sk);
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ca->epoch_start = 0; /* end of epoch */
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/* Wmax and fast convergence */
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if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence)
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ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta))
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/ (2 * BICTCP_BETA_SCALE);
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else
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ca->last_max_cwnd = tp->snd_cwnd;
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ca->loss_cwnd = tp->snd_cwnd;
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return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
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}
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static u32 bictcp_undo_cwnd(struct sock *sk)
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{
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struct bictcp *ca = inet_csk_ca(sk);
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return max(tcp_sk(sk)->snd_cwnd, ca->last_max_cwnd);
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}
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static void bictcp_state(struct sock *sk, u8 new_state)
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{
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if (new_state == TCP_CA_Loss)
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bictcp_reset(inet_csk_ca(sk));
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}
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/* Track delayed acknowledgment ratio using sliding window
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* ratio = (15*ratio + sample) / 16
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*/
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static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt_us)
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{
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const struct inet_connection_sock *icsk = inet_csk(sk);
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struct bictcp *ca = inet_csk_ca(sk);
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u32 delay;
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if (icsk->icsk_ca_state == TCP_CA_Open) {
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cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT;
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ca->delayed_ack += cnt;
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}
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/* Some calls are for duplicates without timetamps */
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if (rtt_us < 0)
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return;
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/* Discard delay samples right after fast recovery */
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if ((s32)(tcp_time_stamp - ca->epoch_start) < HZ)
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return;
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delay = usecs_to_jiffies(rtt_us) << 3;
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if (delay == 0)
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delay = 1;
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/* first time call or link delay decreases */
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if (ca->delay_min == 0 || ca->delay_min > delay)
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ca->delay_min = delay;
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}
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static struct tcp_congestion_ops cubictcp = {
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.init = bictcp_init,
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.ssthresh = bictcp_recalc_ssthresh,
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.cong_avoid = bictcp_cong_avoid,
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.set_state = bictcp_state,
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.undo_cwnd = bictcp_undo_cwnd,
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.pkts_acked = bictcp_acked,
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.owner = THIS_MODULE,
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.name = "cubic",
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};
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static int __init cubictcp_register(void)
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{
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BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE);
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/* Precompute a bunch of the scaling factors that are used per-packet
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* based on SRTT of 100ms
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*/
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beta_scale = 8*(BICTCP_BETA_SCALE+beta)/ 3 / (BICTCP_BETA_SCALE - beta);
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cube_rtt_scale = (bic_scale * 10); /* 1024*c/rtt */
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/* calculate the "K" for (wmax-cwnd) = c/rtt * K^3
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* so K = cubic_root( (wmax-cwnd)*rtt/c )
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* the unit of K is bictcp_HZ=2^10, not HZ
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*
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* c = bic_scale >> 10
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* rtt = 100ms
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*
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* the following code has been designed and tested for
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* cwnd < 1 million packets
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* RTT < 100 seconds
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* HZ < 1,000,00 (corresponding to 10 nano-second)
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*/
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/* 1/c * 2^2*bictcp_HZ * srtt */
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cube_factor = 1ull << (10+3*BICTCP_HZ); /* 2^40 */
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/* divide by bic_scale and by constant Srtt (100ms) */
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do_div(cube_factor, bic_scale * 10);
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return tcp_register_congestion_control(&cubictcp);
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}
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static void __exit cubictcp_unregister(void)
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{
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tcp_unregister_congestion_control(&cubictcp);
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}
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module_init(cubictcp_register);
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module_exit(cubictcp_unregister);
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MODULE_AUTHOR("Sangtae Ha, Stephen Hemminger");
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MODULE_LICENSE("GPL");
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MODULE_DESCRIPTION("CUBIC TCP");
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MODULE_VERSION("2.1");
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