109c434b8SThomas Gleixner // SPDX-License-Identifier: GPL-2.0-only
2df3271f3SStephen Hemminger /*
3ae27e98aSSangtae Ha * TCP CUBIC: Binary Increase Congestion control for TCP v2.3
46b3d6263SSangtae Ha * Home page:
56b3d6263SSangtae Ha * http://netsrv.csc.ncsu.edu/twiki/bin/view/Main/BIC
6df3271f3SStephen Hemminger * This is from the implementation of CUBIC TCP in
7ae27e98aSSangtae Ha * Sangtae Ha, Injong Rhee and Lisong Xu,
8ae27e98aSSangtae Ha * "CUBIC: A New TCP-Friendly High-Speed TCP Variant"
9ae27e98aSSangtae Ha * in ACM SIGOPS Operating System Review, July 2008.
10df3271f3SStephen Hemminger * Available from:
11ae27e98aSSangtae Ha * http://netsrv.csc.ncsu.edu/export/cubic_a_new_tcp_2008.pdf
12ae27e98aSSangtae Ha *
13ae27e98aSSangtae Ha * CUBIC integrates a new slow start algorithm, called HyStart.
14ae27e98aSSangtae Ha * The details of HyStart are presented in
15ae27e98aSSangtae Ha * Sangtae Ha and Injong Rhee,
16ae27e98aSSangtae Ha * "Taming the Elephants: New TCP Slow Start", NCSU TechReport 2008.
17ae27e98aSSangtae Ha * Available from:
18ae27e98aSSangtae Ha * http://netsrv.csc.ncsu.edu/export/hystart_techreport_2008.pdf
19ae27e98aSSangtae Ha *
20ae27e98aSSangtae Ha * All testing results are available from:
21ae27e98aSSangtae Ha * http://netsrv.csc.ncsu.edu/wiki/index.php/TCP_Testing
22df3271f3SStephen Hemminger *
23df3271f3SStephen Hemminger * Unless CUBIC is enabled and congestion window is large
24df3271f3SStephen Hemminger * this behaves the same as the original Reno.
25df3271f3SStephen Hemminger */
26df3271f3SStephen Hemminger
27df3271f3SStephen Hemminger #include <linux/mm.h>
280e32dfc8SKumar Kartikeya Dwivedi #include <linux/btf.h>
290e32dfc8SKumar Kartikeya Dwivedi #include <linux/btf_ids.h>
30df3271f3SStephen Hemminger #include <linux/module.h>
316f6d6a1aSRoman Zippel #include <linux/math64.h>
32df3271f3SStephen Hemminger #include <net/tcp.h>
33df3271f3SStephen Hemminger
34df3271f3SStephen Hemminger #define BICTCP_BETA_SCALE 1024 /* Scale factor beta calculation
35df3271f3SStephen Hemminger * max_cwnd = snd_cwnd * beta
36df3271f3SStephen Hemminger */
37df3271f3SStephen Hemminger #define BICTCP_HZ 10 /* BIC HZ 2^10 = 1024 */
38df3271f3SStephen Hemminger
39ae27e98aSSangtae Ha /* Two methods of hybrid slow start */
40ae27e98aSSangtae Ha #define HYSTART_ACK_TRAIN 0x1
41ae27e98aSSangtae Ha #define HYSTART_DELAY 0x2
42ae27e98aSSangtae Ha
43ae27e98aSSangtae Ha /* Number of delay samples for detecting the increase of delay */
44ae27e98aSSangtae Ha #define HYSTART_MIN_SAMPLES 8
45cff04e2dSEric Dumazet #define HYSTART_DELAY_MIN (4000U) /* 4 ms */
46cff04e2dSEric Dumazet #define HYSTART_DELAY_MAX (16000U) /* 16 ms */
47ae27e98aSSangtae Ha #define HYSTART_DELAY_THRESH(x) clamp(x, HYSTART_DELAY_MIN, HYSTART_DELAY_MAX)
48ae27e98aSSangtae Ha
4959758f44SStephen Hemminger static int fast_convergence __read_mostly = 1;
506b3d6263SSangtae Ha static int beta __read_mostly = 717; /* = 717/1024 (BICTCP_BETA_SCALE) */
5166e1e3b2SDavid S. Miller static int initial_ssthresh __read_mostly;
5259758f44SStephen Hemminger static int bic_scale __read_mostly = 41;
5359758f44SStephen Hemminger static int tcp_friendliness __read_mostly = 1;
54df3271f3SStephen Hemminger
55ae27e98aSSangtae Ha static int hystart __read_mostly = 1;
56ae27e98aSSangtae Ha static int hystart_detect __read_mostly = HYSTART_ACK_TRAIN | HYSTART_DELAY;
57ae27e98aSSangtae Ha static int hystart_low_window __read_mostly = 16;
58cff04e2dSEric Dumazet static int hystart_ack_delta_us __read_mostly = 2000;
59ae27e98aSSangtae Ha
6059758f44SStephen Hemminger static u32 cube_rtt_scale __read_mostly;
6159758f44SStephen Hemminger static u32 beta_scale __read_mostly;
6259758f44SStephen Hemminger static u64 cube_factor __read_mostly;
6389b3d9aaSStephen Hemminger
6489b3d9aaSStephen Hemminger /* Note parameters that are used for precomputing scale factors are read-only */
65df3271f3SStephen Hemminger module_param(fast_convergence, int, 0644);
66df3271f3SStephen Hemminger MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence");
676b3d6263SSangtae Ha module_param(beta, int, 0644);
68df3271f3SStephen Hemminger MODULE_PARM_DESC(beta, "beta for multiplicative increase");
69df3271f3SStephen Hemminger module_param(initial_ssthresh, int, 0644);
70df3271f3SStephen Hemminger MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold");
7189b3d9aaSStephen Hemminger module_param(bic_scale, int, 0444);
72df3271f3SStephen Hemminger MODULE_PARM_DESC(bic_scale, "scale (scaled by 1024) value for bic function (bic_scale/1024)");
73df3271f3SStephen Hemminger module_param(tcp_friendliness, int, 0644);
74df3271f3SStephen Hemminger MODULE_PARM_DESC(tcp_friendliness, "turn on/off tcp friendliness");
75ae27e98aSSangtae Ha module_param(hystart, int, 0644);
76ae27e98aSSangtae Ha MODULE_PARM_DESC(hystart, "turn on/off hybrid slow start algorithm");
77ae27e98aSSangtae Ha module_param(hystart_detect, int, 0644);
78d6ecf328SChema Gonzalez MODULE_PARM_DESC(hystart_detect, "hybrid slow start detection mechanisms"
79ae27e98aSSangtae Ha " 1: packet-train 2: delay 3: both packet-train and delay");
80ae27e98aSSangtae Ha module_param(hystart_low_window, int, 0644);
81ae27e98aSSangtae Ha MODULE_PARM_DESC(hystart_low_window, "lower bound cwnd for hybrid slow start");
82cff04e2dSEric Dumazet module_param(hystart_ack_delta_us, int, 0644);
83cff04e2dSEric Dumazet MODULE_PARM_DESC(hystart_ack_delta_us, "spacing between ack's indicating train (usecs)");
84df3271f3SStephen Hemminger
85df3271f3SStephen Hemminger /* BIC TCP Parameters */
86df3271f3SStephen Hemminger struct bictcp {
87df3271f3SStephen Hemminger u32 cnt; /* increase cwnd by 1 after ACKs */
88df3271f3SStephen Hemminger u32 last_max_cwnd; /* last maximum snd_cwnd */
89df3271f3SStephen Hemminger u32 last_cwnd; /* the last snd_cwnd */
90df3271f3SStephen Hemminger u32 last_time; /* time when updated last_cwnd */
91df3271f3SStephen Hemminger u32 bic_origin_point;/* origin point of bic function */
92688d1945Sstephen hemminger u32 bic_K; /* time to origin point
93688d1945Sstephen hemminger from the beginning of the current epoch */
94cff04e2dSEric Dumazet u32 delay_min; /* min delay (usec) */
95df3271f3SStephen Hemminger u32 epoch_start; /* beginning of an epoch */
96df3271f3SStephen Hemminger u32 ack_cnt; /* number of acks */
97df3271f3SStephen Hemminger u32 tcp_cwnd; /* estimated tcp cwnd */
989cd981dcSNeal Cardwell u16 unused;
99ae27e98aSSangtae Ha u8 sample_cnt; /* number of samples to decide curr_rtt */
100ae27e98aSSangtae Ha u8 found; /* the exit point is found? */
101ae27e98aSSangtae Ha u32 round_start; /* beginning of each round */
102ae27e98aSSangtae Ha u32 end_seq; /* end_seq of the round */
10317a6e9f1Sstephen hemminger u32 last_ack; /* last time when the ACK spacing is close */
104ae27e98aSSangtae Ha u32 curr_rtt; /* the minimum rtt of current round */
105df3271f3SStephen Hemminger };
106df3271f3SStephen Hemminger
bictcp_reset(struct bictcp * ca)107df3271f3SStephen Hemminger static inline void bictcp_reset(struct bictcp *ca)
108df3271f3SStephen Hemminger {
109f4d133d8SYejune Deng memset(ca, 0, offsetof(struct bictcp, unused));
110ae27e98aSSangtae Ha ca->found = 0;
111ae27e98aSSangtae Ha }
112ae27e98aSSangtae Ha
bictcp_clock_us(const struct sock * sk)113cff04e2dSEric Dumazet static inline u32 bictcp_clock_us(const struct sock *sk)
11417a6e9f1Sstephen hemminger {
115cff04e2dSEric Dumazet return tcp_sk(sk)->tcp_mstamp;
11617a6e9f1Sstephen hemminger }
11717a6e9f1Sstephen hemminger
bictcp_hystart_reset(struct sock * sk)118ae27e98aSSangtae Ha static inline void bictcp_hystart_reset(struct sock *sk)
119ae27e98aSSangtae Ha {
120ae27e98aSSangtae Ha struct tcp_sock *tp = tcp_sk(sk);
121ae27e98aSSangtae Ha struct bictcp *ca = inet_csk_ca(sk);
122ae27e98aSSangtae Ha
123cff04e2dSEric Dumazet ca->round_start = ca->last_ack = bictcp_clock_us(sk);
124ae27e98aSSangtae Ha ca->end_seq = tp->snd_nxt;
12535821fc2SEric Dumazet ca->curr_rtt = ~0U;
126ae27e98aSSangtae Ha ca->sample_cnt = 0;
127df3271f3SStephen Hemminger }
128df3271f3SStephen Hemminger
cubictcp_init(struct sock * sk)129400031e0SDavid Vernet __bpf_kfunc static void cubictcp_init(struct sock *sk)
130df3271f3SStephen Hemminger {
1315a45f008SNeal Cardwell struct bictcp *ca = inet_csk_ca(sk);
1325a45f008SNeal Cardwell
1335a45f008SNeal Cardwell bictcp_reset(ca);
134ae27e98aSSangtae Ha
135ae27e98aSSangtae Ha if (hystart)
136ae27e98aSSangtae Ha bictcp_hystart_reset(sk);
137ae27e98aSSangtae Ha
138ae27e98aSSangtae Ha if (!hystart && initial_ssthresh)
139df3271f3SStephen Hemminger tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
140df3271f3SStephen Hemminger }
141df3271f3SStephen Hemminger
cubictcp_cwnd_event(struct sock * sk,enum tcp_ca_event event)142400031e0SDavid Vernet __bpf_kfunc static void cubictcp_cwnd_event(struct sock *sk, enum tcp_ca_event event)
14330927520SEric Dumazet {
14430927520SEric Dumazet if (event == CA_EVENT_TX_START) {
14530927520SEric Dumazet struct bictcp *ca = inet_csk_ca(sk);
146d635fbe2SEric Dumazet u32 now = tcp_jiffies32;
147c2e7204dSEric Dumazet s32 delta;
148c2e7204dSEric Dumazet
149c2e7204dSEric Dumazet delta = now - tcp_sk(sk)->lsndtime;
15030927520SEric Dumazet
15130927520SEric Dumazet /* We were application limited (idle) for a while.
15230927520SEric Dumazet * Shift epoch_start to keep cwnd growth to cubic curve.
15330927520SEric Dumazet */
154c2e7204dSEric Dumazet if (ca->epoch_start && delta > 0) {
15530927520SEric Dumazet ca->epoch_start += delta;
156c2e7204dSEric Dumazet if (after(ca->epoch_start, now))
157c2e7204dSEric Dumazet ca->epoch_start = now;
158c2e7204dSEric Dumazet }
15930927520SEric Dumazet return;
16030927520SEric Dumazet }
16130927520SEric Dumazet }
16230927520SEric Dumazet
1637e58886bSStephen Hemminger /* calculate the cubic root of x using a table lookup followed by one
1647e58886bSStephen Hemminger * Newton-Raphson iteration.
1657e58886bSStephen Hemminger * Avg err ~= 0.195%
166df3271f3SStephen Hemminger */
cubic_root(u64 a)1679eb2d627SStephen Hemminger static u32 cubic_root(u64 a)
168df3271f3SStephen Hemminger {
1697e58886bSStephen Hemminger u32 x, b, shift;
1707e58886bSStephen Hemminger /*
1717e58886bSStephen Hemminger * cbrt(x) MSB values for x MSB values in [0..63].
1727e58886bSStephen Hemminger * Precomputed then refined by hand - Willy Tarreau
1737e58886bSStephen Hemminger *
1747e58886bSStephen Hemminger * For x in [0..63],
1757e58886bSStephen Hemminger * v = cbrt(x << 18) - 1
1767e58886bSStephen Hemminger * cbrt(x) = (v[x] + 10) >> 6
1779eb2d627SStephen Hemminger */
1787e58886bSStephen Hemminger static const u8 v[] = {
1797e58886bSStephen Hemminger /* 0x00 */ 0, 54, 54, 54, 118, 118, 118, 118,
1807e58886bSStephen Hemminger /* 0x08 */ 123, 129, 134, 138, 143, 147, 151, 156,
1817e58886bSStephen Hemminger /* 0x10 */ 157, 161, 164, 168, 170, 173, 176, 179,
1827e58886bSStephen Hemminger /* 0x18 */ 181, 185, 187, 190, 192, 194, 197, 199,
1837e58886bSStephen Hemminger /* 0x20 */ 200, 202, 204, 206, 209, 211, 213, 215,
1847e58886bSStephen Hemminger /* 0x28 */ 217, 219, 221, 222, 224, 225, 227, 229,
1857e58886bSStephen Hemminger /* 0x30 */ 231, 232, 234, 236, 237, 239, 240, 242,
1867e58886bSStephen Hemminger /* 0x38 */ 244, 245, 246, 248, 250, 251, 252, 254,
1877e58886bSStephen Hemminger };
188df3271f3SStephen Hemminger
1897e58886bSStephen Hemminger b = fls64(a);
1907e58886bSStephen Hemminger if (b < 7) {
1917e58886bSStephen Hemminger /* a in [0..63] */
1927e58886bSStephen Hemminger return ((u32)v[(u32)a] + 35) >> 6;
1937e58886bSStephen Hemminger }
194df3271f3SStephen Hemminger
1957e58886bSStephen Hemminger b = ((b * 84) >> 8) - 1;
1967e58886bSStephen Hemminger shift = (a >> (b * 3));
1977e58886bSStephen Hemminger
1987e58886bSStephen Hemminger x = ((u32)(((u32)v[shift] + 10) << b)) >> 6;
1997e58886bSStephen Hemminger
2007e58886bSStephen Hemminger /*
2017e58886bSStephen Hemminger * Newton-Raphson iteration
2027e58886bSStephen Hemminger * 2
2037e58886bSStephen Hemminger * x = ( 2 * x + a / x ) / 3
2047e58886bSStephen Hemminger * k+1 k k
2057e58886bSStephen Hemminger */
2066f6d6a1aSRoman Zippel x = (2 * x + (u32)div64_u64(a, (u64)x * (u64)(x - 1)));
2077e58886bSStephen Hemminger x = ((x * 341) >> 10);
2089eb2d627SStephen Hemminger return x;
209df3271f3SStephen Hemminger }
210df3271f3SStephen Hemminger
211df3271f3SStephen Hemminger /*
212df3271f3SStephen Hemminger * Compute congestion window to use.
213df3271f3SStephen Hemminger */
bictcp_update(struct bictcp * ca,u32 cwnd,u32 acked)2149cd981dcSNeal Cardwell static inline void bictcp_update(struct bictcp *ca, u32 cwnd, u32 acked)
215df3271f3SStephen Hemminger {
2162ed0edf9SEric Dumazet u32 delta, bic_target, max_cnt;
2172ed0edf9SEric Dumazet u64 offs, t;
218df3271f3SStephen Hemminger
2199cd981dcSNeal Cardwell ca->ack_cnt += acked; /* count the number of ACKed packets */
220df3271f3SStephen Hemminger
221df3271f3SStephen Hemminger if (ca->last_cwnd == cwnd &&
222ac35f562SEric Dumazet (s32)(tcp_jiffies32 - ca->last_time) <= HZ / 32)
223df3271f3SStephen Hemminger return;
224df3271f3SStephen Hemminger
225d6b1a8a9SNeal Cardwell /* The CUBIC function can update ca->cnt at most once per jiffy.
226d6b1a8a9SNeal Cardwell * On all cwnd reduction events, ca->epoch_start is set to 0,
227d6b1a8a9SNeal Cardwell * which will force a recalculation of ca->cnt.
228d6b1a8a9SNeal Cardwell */
229ac35f562SEric Dumazet if (ca->epoch_start && tcp_jiffies32 == ca->last_time)
230d6b1a8a9SNeal Cardwell goto tcp_friendliness;
231d6b1a8a9SNeal Cardwell
232df3271f3SStephen Hemminger ca->last_cwnd = cwnd;
233ac35f562SEric Dumazet ca->last_time = tcp_jiffies32;
234df3271f3SStephen Hemminger
235df3271f3SStephen Hemminger if (ca->epoch_start == 0) {
236ac35f562SEric Dumazet ca->epoch_start = tcp_jiffies32; /* record beginning */
2379cd981dcSNeal Cardwell ca->ack_cnt = acked; /* start counting */
238df3271f3SStephen Hemminger ca->tcp_cwnd = cwnd; /* syn with cubic */
239df3271f3SStephen Hemminger
240df3271f3SStephen Hemminger if (ca->last_max_cwnd <= cwnd) {
241df3271f3SStephen Hemminger ca->bic_K = 0;
242df3271f3SStephen Hemminger ca->bic_origin_point = cwnd;
243df3271f3SStephen Hemminger } else {
24489b3d9aaSStephen Hemminger /* Compute new K based on
24589b3d9aaSStephen Hemminger * (wmax-cwnd) * (srtt>>3 / HZ) / c * 2^(3*bictcp_HZ)
24689b3d9aaSStephen Hemminger */
24789b3d9aaSStephen Hemminger ca->bic_K = cubic_root(cube_factor
24889b3d9aaSStephen Hemminger * (ca->last_max_cwnd - cwnd));
249df3271f3SStephen Hemminger ca->bic_origin_point = ca->last_max_cwnd;
250df3271f3SStephen Hemminger }
251df3271f3SStephen Hemminger }
252df3271f3SStephen Hemminger
253df3271f3SStephen Hemminger /* cubic function - calc*/
254df3271f3SStephen Hemminger /* calculate c * time^3 / rtt,
255df3271f3SStephen Hemminger * while considering overflow in calculation of time^3
25689b3d9aaSStephen Hemminger * (so time^3 is done by using 64 bit)
257df3271f3SStephen Hemminger * and without the support of division of 64bit numbers
25889b3d9aaSStephen Hemminger * (so all divisions are done by using 32 bit)
259df3271f3SStephen Hemminger * also NOTE the unit of those veriables
260df3271f3SStephen Hemminger * time = (t - K) / 2^bictcp_HZ
261df3271f3SStephen Hemminger * c = bic_scale >> 10
262df3271f3SStephen Hemminger * rtt = (srtt >> 3) / HZ
263df3271f3SStephen Hemminger * !!! The following code does not have overflow problems,
264df3271f3SStephen Hemminger * if the cwnd < 1 million packets !!!
265df3271f3SStephen Hemminger */
266df3271f3SStephen Hemminger
267ac35f562SEric Dumazet t = (s32)(tcp_jiffies32 - ca->epoch_start);
268cff04e2dSEric Dumazet t += usecs_to_jiffies(ca->delay_min);
269df3271f3SStephen Hemminger /* change the unit from HZ to bictcp_HZ */
2702ed0edf9SEric Dumazet t <<= BICTCP_HZ;
2712ed0edf9SEric Dumazet do_div(t, HZ);
272df3271f3SStephen Hemminger
273df3271f3SStephen Hemminger if (t < ca->bic_K) /* t - K */
27489b3d9aaSStephen Hemminger offs = ca->bic_K - t;
275df3271f3SStephen Hemminger else
27689b3d9aaSStephen Hemminger offs = t - ca->bic_K;
277df3271f3SStephen Hemminger
27889b3d9aaSStephen Hemminger /* c/rtt * (t-K)^3 */
27989b3d9aaSStephen Hemminger delta = (cube_rtt_scale * offs * offs * offs) >> (10+3*BICTCP_HZ);
280df3271f3SStephen Hemminger if (t < ca->bic_K) /* below origin*/
28189b3d9aaSStephen Hemminger bic_target = ca->bic_origin_point - delta;
282df3271f3SStephen Hemminger else /* above origin*/
28389b3d9aaSStephen Hemminger bic_target = ca->bic_origin_point + delta;
284df3271f3SStephen Hemminger
285df3271f3SStephen Hemminger /* cubic function - calc bictcp_cnt*/
286df3271f3SStephen Hemminger if (bic_target > cwnd) {
287df3271f3SStephen Hemminger ca->cnt = cwnd / (bic_target - cwnd);
288df3271f3SStephen Hemminger } else {
289df3271f3SStephen Hemminger ca->cnt = 100 * cwnd; /* very small increment*/
290df3271f3SStephen Hemminger }
291df3271f3SStephen Hemminger
292b5ccd073SSangtae Ha /*
293b5ccd073SSangtae Ha * The initial growth of cubic function may be too conservative
294b5ccd073SSangtae Ha * when the available bandwidth is still unknown.
295b5ccd073SSangtae Ha */
2965a45f008SNeal Cardwell if (ca->last_max_cwnd == 0 && ca->cnt > 20)
297b5ccd073SSangtae Ha ca->cnt = 20; /* increase cwnd 5% per RTT */
298b5ccd073SSangtae Ha
299d6b1a8a9SNeal Cardwell tcp_friendliness:
300df3271f3SStephen Hemminger /* TCP Friendly */
301df3271f3SStephen Hemminger if (tcp_friendliness) {
30289b3d9aaSStephen Hemminger u32 scale = beta_scale;
303688d1945Sstephen hemminger
30489b3d9aaSStephen Hemminger delta = (cwnd * scale) >> 3;
30589b3d9aaSStephen Hemminger while (ca->ack_cnt > delta) { /* update tcp cwnd */
30689b3d9aaSStephen Hemminger ca->ack_cnt -= delta;
307df3271f3SStephen Hemminger ca->tcp_cwnd++;
308df3271f3SStephen Hemminger }
309df3271f3SStephen Hemminger
310df3271f3SStephen Hemminger if (ca->tcp_cwnd > cwnd) { /* if bic is slower than tcp */
31189b3d9aaSStephen Hemminger delta = ca->tcp_cwnd - cwnd;
31289b3d9aaSStephen Hemminger max_cnt = cwnd / delta;
313df3271f3SStephen Hemminger if (ca->cnt > max_cnt)
314df3271f3SStephen Hemminger ca->cnt = max_cnt;
315df3271f3SStephen Hemminger }
316df3271f3SStephen Hemminger }
317df3271f3SStephen Hemminger
318d578e18cSNeal Cardwell /* The maximum rate of cwnd increase CUBIC allows is 1 packet per
319d578e18cSNeal Cardwell * 2 packets ACKed, meaning cwnd grows at 1.5x per RTT.
320d578e18cSNeal Cardwell */
321d578e18cSNeal Cardwell ca->cnt = max(ca->cnt, 2U);
322df3271f3SStephen Hemminger }
323df3271f3SStephen Hemminger
cubictcp_cong_avoid(struct sock * sk,u32 ack,u32 acked)324400031e0SDavid Vernet __bpf_kfunc static void cubictcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
325df3271f3SStephen Hemminger {
326df3271f3SStephen Hemminger struct tcp_sock *tp = tcp_sk(sk);
327df3271f3SStephen Hemminger struct bictcp *ca = inet_csk_ca(sk);
328df3271f3SStephen Hemminger
32924901551SEric Dumazet if (!tcp_is_cwnd_limited(sk))
330df3271f3SStephen Hemminger return;
331df3271f3SStephen Hemminger
332071d5080SYuchung Cheng if (tcp_in_slow_start(tp)) {
3339cd981dcSNeal Cardwell acked = tcp_slow_start(tp, acked);
3349cd981dcSNeal Cardwell if (!acked)
3359cd981dcSNeal Cardwell return;
336df3271f3SStephen Hemminger }
33740570375SEric Dumazet bictcp_update(ca, tcp_snd_cwnd(tp), acked);
3389cd981dcSNeal Cardwell tcp_cong_avoid_ai(tp, ca->cnt, acked);
339df3271f3SStephen Hemminger }
340df3271f3SStephen Hemminger
cubictcp_recalc_ssthresh(struct sock * sk)341400031e0SDavid Vernet __bpf_kfunc static u32 cubictcp_recalc_ssthresh(struct sock *sk)
342df3271f3SStephen Hemminger {
343df3271f3SStephen Hemminger const struct tcp_sock *tp = tcp_sk(sk);
344df3271f3SStephen Hemminger struct bictcp *ca = inet_csk_ca(sk);
345df3271f3SStephen Hemminger
346df3271f3SStephen Hemminger ca->epoch_start = 0; /* end of epoch */
347df3271f3SStephen Hemminger
348df3271f3SStephen Hemminger /* Wmax and fast convergence */
34940570375SEric Dumazet if (tcp_snd_cwnd(tp) < ca->last_max_cwnd && fast_convergence)
35040570375SEric Dumazet ca->last_max_cwnd = (tcp_snd_cwnd(tp) * (BICTCP_BETA_SCALE + beta))
351df3271f3SStephen Hemminger / (2 * BICTCP_BETA_SCALE);
352df3271f3SStephen Hemminger else
35340570375SEric Dumazet ca->last_max_cwnd = tcp_snd_cwnd(tp);
354df3271f3SStephen Hemminger
35540570375SEric Dumazet return max((tcp_snd_cwnd(tp) * beta) / BICTCP_BETA_SCALE, 2U);
356df3271f3SStephen Hemminger }
357df3271f3SStephen Hemminger
cubictcp_state(struct sock * sk,u8 new_state)358400031e0SDavid Vernet __bpf_kfunc static void cubictcp_state(struct sock *sk, u8 new_state)
359df3271f3SStephen Hemminger {
360ae27e98aSSangtae Ha if (new_state == TCP_CA_Loss) {
361df3271f3SStephen Hemminger bictcp_reset(inet_csk_ca(sk));
362ae27e98aSSangtae Ha bictcp_hystart_reset(sk);
363ae27e98aSSangtae Ha }
364ae27e98aSSangtae Ha }
365ae27e98aSSangtae Ha
366f278b99cSEric Dumazet /* Account for TSO/GRO delays.
367f278b99cSEric Dumazet * Otherwise short RTT flows could get too small ssthresh, since during
368f278b99cSEric Dumazet * slow start we begin with small TSO packets and ca->delay_min would
369f278b99cSEric Dumazet * not account for long aggregation delay when TSO packets get bigger.
370f278b99cSEric Dumazet * Ideally even with a very small RTT we would like to have at least one
371f278b99cSEric Dumazet * TSO packet being sent and received by GRO, and another one in qdisc layer.
372f278b99cSEric Dumazet * We apply another 100% factor because @rate is doubled at this point.
373f278b99cSEric Dumazet * We cap the cushion to 1ms.
374f278b99cSEric Dumazet */
hystart_ack_delay(const struct sock * sk)3759957b38bSEric Dumazet static u32 hystart_ack_delay(const struct sock *sk)
376f278b99cSEric Dumazet {
377f278b99cSEric Dumazet unsigned long rate;
378f278b99cSEric Dumazet
379f278b99cSEric Dumazet rate = READ_ONCE(sk->sk_pacing_rate);
380f278b99cSEric Dumazet if (!rate)
381f278b99cSEric Dumazet return 0;
382f278b99cSEric Dumazet return min_t(u64, USEC_PER_MSEC,
3839957b38bSEric Dumazet div64_ul((u64)sk->sk_gso_max_size * 4 * USEC_PER_SEC, rate));
384f278b99cSEric Dumazet }
385f278b99cSEric Dumazet
hystart_update(struct sock * sk,u32 delay)386ae27e98aSSangtae Ha static void hystart_update(struct sock *sk, u32 delay)
387ae27e98aSSangtae Ha {
388ae27e98aSSangtae Ha struct tcp_sock *tp = tcp_sk(sk);
389ae27e98aSSangtae Ha struct bictcp *ca = inet_csk_ca(sk);
390ede656e8SEric Dumazet u32 threshold;
391ae27e98aSSangtae Ha
3924e1fddc9SEric Dumazet if (after(tp->snd_una, ca->end_seq))
3934e1fddc9SEric Dumazet bictcp_hystart_reset(sk);
3944e1fddc9SEric Dumazet
3956e3a8a93SEric Dumazet if (hystart_detect & HYSTART_ACK_TRAIN) {
396cff04e2dSEric Dumazet u32 now = bictcp_clock_us(sk);
397ae27e98aSSangtae Ha
398ae27e98aSSangtae Ha /* first detection parameter - ack-train detection */
399cff04e2dSEric Dumazet if ((s32)(now - ca->last_ack) <= hystart_ack_delta_us) {
40017a6e9f1Sstephen hemminger ca->last_ack = now;
401ede656e8SEric Dumazet
402f278b99cSEric Dumazet threshold = ca->delay_min + hystart_ack_delay(sk);
403f278b99cSEric Dumazet
404ede656e8SEric Dumazet /* Hystart ack train triggers if we get ack past
405ede656e8SEric Dumazet * ca->delay_min/2.
406ede656e8SEric Dumazet * Pacing might have delayed packets up to RTT/2
407ede656e8SEric Dumazet * during slow start.
408ede656e8SEric Dumazet */
409ede656e8SEric Dumazet if (sk->sk_pacing_status == SK_PACING_NONE)
410ede656e8SEric Dumazet threshold >>= 1;
411ede656e8SEric Dumazet
412ede656e8SEric Dumazet if ((s32)(now - ca->round_start) > threshold) {
413473900a5SEric Dumazet ca->found = 1;
414f278b99cSEric Dumazet pr_debug("hystart_ack_train (%u > %u) delay_min %u (+ ack_delay %u) cwnd %u\n",
415f278b99cSEric Dumazet now - ca->round_start, threshold,
41640570375SEric Dumazet ca->delay_min, hystart_ack_delay(sk), tcp_snd_cwnd(tp));
417c10d9310SEric Dumazet NET_INC_STATS(sock_net(sk),
4186e3a8a93SEric Dumazet LINUX_MIB_TCPHYSTARTTRAINDETECT);
419c10d9310SEric Dumazet NET_ADD_STATS(sock_net(sk),
4206e3a8a93SEric Dumazet LINUX_MIB_TCPHYSTARTTRAINCWND,
42140570375SEric Dumazet tcp_snd_cwnd(tp));
42240570375SEric Dumazet tp->snd_ssthresh = tcp_snd_cwnd(tp);
4236e3a8a93SEric Dumazet }
4246e3a8a93SEric Dumazet }
425ae27e98aSSangtae Ha }
426ae27e98aSSangtae Ha
4276e3a8a93SEric Dumazet if (hystart_detect & HYSTART_DELAY) {
428ae27e98aSSangtae Ha /* obtain the minimum delay of more than sampling packets */
42935821fc2SEric Dumazet if (ca->curr_rtt > delay)
430ae27e98aSSangtae Ha ca->curr_rtt = delay;
431b344579cSNeal Cardwell if (ca->sample_cnt < HYSTART_MIN_SAMPLES) {
432ae27e98aSSangtae Ha ca->sample_cnt++;
433ae27e98aSSangtae Ha } else {
434ae27e98aSSangtae Ha if (ca->curr_rtt > ca->delay_min +
43542eef7a0SEric Dumazet HYSTART_DELAY_THRESH(ca->delay_min >> 3)) {
436473900a5SEric Dumazet ca->found = 1;
437c10d9310SEric Dumazet NET_INC_STATS(sock_net(sk),
4386e3a8a93SEric Dumazet LINUX_MIB_TCPHYSTARTDELAYDETECT);
439c10d9310SEric Dumazet NET_ADD_STATS(sock_net(sk),
4406e3a8a93SEric Dumazet LINUX_MIB_TCPHYSTARTDELAYCWND,
44140570375SEric Dumazet tcp_snd_cwnd(tp));
44240570375SEric Dumazet tp->snd_ssthresh = tcp_snd_cwnd(tp);
443ae27e98aSSangtae Ha }
444df3271f3SStephen Hemminger }
4456e3a8a93SEric Dumazet }
4466e3a8a93SEric Dumazet }
447df3271f3SStephen Hemminger
cubictcp_acked(struct sock * sk,const struct ack_sample * sample)448400031e0SDavid Vernet __bpf_kfunc static void cubictcp_acked(struct sock *sk, const struct ack_sample *sample)
449df3271f3SStephen Hemminger {
450ae27e98aSSangtae Ha const struct tcp_sock *tp = tcp_sk(sk);
451e7d0c885SStephen Hemminger struct bictcp *ca = inet_csk_ca(sk);
452e7d0c885SStephen Hemminger u32 delay;
453df3271f3SStephen Hemminger
454e7d0c885SStephen Hemminger /* Some calls are for duplicates without timetamps */
455756ee172SLawrence Brakmo if (sample->rtt_us < 0)
456e7d0c885SStephen Hemminger return;
457e7d0c885SStephen Hemminger
458e7d0c885SStephen Hemminger /* Discard delay samples right after fast recovery */
459ac35f562SEric Dumazet if (ca->epoch_start && (s32)(tcp_jiffies32 - ca->epoch_start) < HZ)
460e7d0c885SStephen Hemminger return;
461e7d0c885SStephen Hemminger
462cff04e2dSEric Dumazet delay = sample->rtt_us;
463e7d0c885SStephen Hemminger if (delay == 0)
464e7d0c885SStephen Hemminger delay = 1;
465e7d0c885SStephen Hemminger
466e7d0c885SStephen Hemminger /* first time call or link delay decreases */
467e7d0c885SStephen Hemminger if (ca->delay_min == 0 || ca->delay_min > delay)
468e7d0c885SStephen Hemminger ca->delay_min = delay;
469ae27e98aSSangtae Ha
470ae27e98aSSangtae Ha /* hystart triggers when cwnd is larger than some threshold */
471f278b99cSEric Dumazet if (!ca->found && tcp_in_slow_start(tp) && hystart &&
47240570375SEric Dumazet tcp_snd_cwnd(tp) >= hystart_low_window)
473ae27e98aSSangtae Ha hystart_update(sk, delay);
474e7d0c885SStephen Hemminger }
475df3271f3SStephen Hemminger
476a252bebeSStephen Hemminger static struct tcp_congestion_ops cubictcp __read_mostly = {
477d22f6ad1SMartin KaFai Lau .init = cubictcp_init,
478d22f6ad1SMartin KaFai Lau .ssthresh = cubictcp_recalc_ssthresh,
479d22f6ad1SMartin KaFai Lau .cong_avoid = cubictcp_cong_avoid,
480d22f6ad1SMartin KaFai Lau .set_state = cubictcp_state,
481f1722a1bSYuchung Cheng .undo_cwnd = tcp_reno_undo_cwnd,
482d22f6ad1SMartin KaFai Lau .cwnd_event = cubictcp_cwnd_event,
483d22f6ad1SMartin KaFai Lau .pkts_acked = cubictcp_acked,
484df3271f3SStephen Hemminger .owner = THIS_MODULE,
485df3271f3SStephen Hemminger .name = "cubic",
486df3271f3SStephen Hemminger };
487df3271f3SStephen Hemminger
488*6f3189f3SDaniel Xu BTF_KFUNCS_START(tcp_cubic_check_kfunc_ids)
489a4703e31SKumar Kartikeya Dwivedi BTF_ID_FLAGS(func, cubictcp_init)
490a4703e31SKumar Kartikeya Dwivedi BTF_ID_FLAGS(func, cubictcp_recalc_ssthresh)
491a4703e31SKumar Kartikeya Dwivedi BTF_ID_FLAGS(func, cubictcp_cong_avoid)
492a4703e31SKumar Kartikeya Dwivedi BTF_ID_FLAGS(func, cubictcp_state)
493a4703e31SKumar Kartikeya Dwivedi BTF_ID_FLAGS(func, cubictcp_cwnd_event)
494a4703e31SKumar Kartikeya Dwivedi BTF_ID_FLAGS(func, cubictcp_acked)
495*6f3189f3SDaniel Xu BTF_KFUNCS_END(tcp_cubic_check_kfunc_ids)
4960e32dfc8SKumar Kartikeya Dwivedi
497b202d844SKumar Kartikeya Dwivedi static const struct btf_kfunc_id_set tcp_cubic_kfunc_set = {
498b202d844SKumar Kartikeya Dwivedi .owner = THIS_MODULE,
499a4703e31SKumar Kartikeya Dwivedi .set = &tcp_cubic_check_kfunc_ids,
500b202d844SKumar Kartikeya Dwivedi };
5010e32dfc8SKumar Kartikeya Dwivedi
cubictcp_register(void)502df3271f3SStephen Hemminger static int __init cubictcp_register(void)
503df3271f3SStephen Hemminger {
5040e32dfc8SKumar Kartikeya Dwivedi int ret;
5050e32dfc8SKumar Kartikeya Dwivedi
50674975d40SAlexey Dobriyan BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE);
50789b3d9aaSStephen Hemminger
50889b3d9aaSStephen Hemminger /* Precompute a bunch of the scaling factors that are used per-packet
50989b3d9aaSStephen Hemminger * based on SRTT of 100ms
51089b3d9aaSStephen Hemminger */
51189b3d9aaSStephen Hemminger
512688d1945Sstephen hemminger beta_scale = 8*(BICTCP_BETA_SCALE+beta) / 3
513688d1945Sstephen hemminger / (BICTCP_BETA_SCALE - beta);
51489b3d9aaSStephen Hemminger
51522119240SStephen Hemminger cube_rtt_scale = (bic_scale * 10); /* 1024*c/rtt */
51689b3d9aaSStephen Hemminger
51789b3d9aaSStephen Hemminger /* calculate the "K" for (wmax-cwnd) = c/rtt * K^3
51889b3d9aaSStephen Hemminger * so K = cubic_root( (wmax-cwnd)*rtt/c )
51989b3d9aaSStephen Hemminger * the unit of K is bictcp_HZ=2^10, not HZ
52089b3d9aaSStephen Hemminger *
52189b3d9aaSStephen Hemminger * c = bic_scale >> 10
52289b3d9aaSStephen Hemminger * rtt = 100ms
52389b3d9aaSStephen Hemminger *
52489b3d9aaSStephen Hemminger * the following code has been designed and tested for
52589b3d9aaSStephen Hemminger * cwnd < 1 million packets
52689b3d9aaSStephen Hemminger * RTT < 100 seconds
52789b3d9aaSStephen Hemminger * HZ < 1,000,00 (corresponding to 10 nano-second)
52889b3d9aaSStephen Hemminger */
52989b3d9aaSStephen Hemminger
53089b3d9aaSStephen Hemminger /* 1/c * 2^2*bictcp_HZ * srtt */
53189b3d9aaSStephen Hemminger cube_factor = 1ull << (10+3*BICTCP_HZ); /* 2^40 */
53289b3d9aaSStephen Hemminger
53389b3d9aaSStephen Hemminger /* divide by bic_scale and by constant Srtt (100ms) */
53489b3d9aaSStephen Hemminger do_div(cube_factor, bic_scale * 10);
53589b3d9aaSStephen Hemminger
536b202d844SKumar Kartikeya Dwivedi ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &tcp_cubic_kfunc_set);
537b202d844SKumar Kartikeya Dwivedi if (ret < 0)
5380e32dfc8SKumar Kartikeya Dwivedi return ret;
539b202d844SKumar Kartikeya Dwivedi return tcp_register_congestion_control(&cubictcp);
540df3271f3SStephen Hemminger }
541df3271f3SStephen Hemminger
cubictcp_unregister(void)542df3271f3SStephen Hemminger static void __exit cubictcp_unregister(void)
543df3271f3SStephen Hemminger {
544df3271f3SStephen Hemminger tcp_unregister_congestion_control(&cubictcp);
545df3271f3SStephen Hemminger }
546df3271f3SStephen Hemminger
547df3271f3SStephen Hemminger module_init(cubictcp_register);
548df3271f3SStephen Hemminger module_exit(cubictcp_unregister);
549df3271f3SStephen Hemminger
550df3271f3SStephen Hemminger MODULE_AUTHOR("Sangtae Ha, Stephen Hemminger");
551df3271f3SStephen Hemminger MODULE_LICENSE("GPL");
552df3271f3SStephen Hemminger MODULE_DESCRIPTION("CUBIC TCP");
553ae27e98aSSangtae Ha MODULE_VERSION("2.3");
554