lsquic_cubic.c revision 5392f7a3 
1/* Copyright (c) 2017 - 2019 LiteSpeed Technologies Inc.  See LICENSE. */
2/*
3 * lsquic_cubic.c -- LSQUIC CUBIC implementation.
4 */
5
6#include <inttypes.h>
7#include <math.h>
8#include <stddef.h>
9#include <stdlib.h>
10#include <string.h>
11#include <sys/queue.h>
12#ifdef WIN32
13#include <vc_compat.h>
14#endif
15
16#include "lsquic_int_types.h"
17#include "lsquic_types.h"
18#include "lsquic_hash.h"
19#include "lsquic_util.h"
20#include "lsquic_cong_ctl.h"
21#include "lsquic_sfcw.h"
22#include "lsquic_conn_flow.h"
23#include "lsquic_varint.h"
24#include "lsquic_hq.h"
25#include "lsquic_stream.h"
26#include "lsquic_rtt.h"
27#include "lsquic_conn_public.h"
28#include "lsquic_packet_common.h"
29#include "lsquic_packet_out.h"
30#include "lsquic_cubic.h"
31
32#define LSQUIC_LOGGER_MODULE LSQLM_CUBIC
33#define LSQUIC_LOG_CONN_ID lsquic_conn_log_cid(cubic->cu_conn)
34#include "lsquic_logger.h"
35
36#define FAST_CONVERGENCE        1
37#define BETA                    205     /* 205/1024 */
38#define C                       410     /* 410/1024 */
39#define TWO_MINUS_BETA_OVER_TWO 922     /* 922/1024 */
40#define ONE_MINUS_BETA          819     /* 819/1024 */
41#define ONE_OVER_C              2560    /* 2560/1024 */
42
43static void
44cubic_reset (struct lsquic_cubic *cubic)
45{
46    memset(cubic, 0, offsetof(struct lsquic_cubic, cu_conn));
47    cubic->cu_cwnd          = 32 * TCP_MSS;
48    cubic->cu_last_max_cwnd = 32 * TCP_MSS;
49    cubic->cu_tcp_cwnd      = 32 * TCP_MSS;
50}
51
52
53static void
54cubic_update (struct lsquic_cubic *cubic, lsquic_time_t now, unsigned n_bytes)
55{
56    double delta_t, t;
57    lsquic_time_t target;
58
59    if (0 == cubic->cu_epoch_start)
60    {
61        cubic->cu_epoch_start = now;
62        if (cubic->cu_cwnd < cubic->cu_last_max_cwnd)
63        {
64            cubic->cu_K = cbrt(cubic->cu_last_max_cwnd / TCP_MSS / 2);
65            cubic->cu_origin_point = cubic->cu_last_max_cwnd;
66        }
67        else
68        {
69            cubic->cu_K = 0;
70            cubic->cu_origin_point = cubic->cu_cwnd;
71        }
72        LSQ_DEBUG("cwnd: %lu; last_max_cwnd: %lu; K: %lf; origin_point: %lu",
73            cubic->cu_cwnd, cubic->cu_last_max_cwnd, cubic->cu_K, cubic->cu_origin_point);
74    }
75
76    delta_t = (double) (now + cubic->cu_min_delay - cubic->cu_epoch_start) / 1000000;
77    if (delta_t < cubic->cu_K)
78    {
79        t = cubic->cu_K - delta_t;
80        target = cubic->cu_origin_point - t * t * t * 0.4 * TCP_MSS;
81        LSQ_DEBUG("delta_t: %lf; t: %lf; target 1: %"PRIu64, delta_t, t, target);
82    }
83    else
84    {
85        t = delta_t - cubic->cu_K;
86        target = cubic->cu_origin_point + t * t * t * 0.4 * TCP_MSS;
87        LSQ_DEBUG("target 2: %"PRIu64, target);
88    }
89
90    if (cubic->cu_flags & CU_TCP_FRIENDLY)
91    {
92        cubic->cu_tcp_cwnd += n_bytes * TCP_MSS * ONE_MINUS_BETA / 1024
93                            / cubic->cu_tcp_cwnd;
94        LSQ_DEBUG("delta_t: %lf; last_max: %lu; cu_tcp_cwnd: %lu; target: "
95            "%"PRIu64"; over: %d; left: %d", delta_t, cubic->cu_last_max_cwnd,
96            cubic->cu_tcp_cwnd, target, cubic->cu_tcp_cwnd > target,
97            delta_t < cubic->cu_K);
98        if (cubic->cu_tcp_cwnd > target)
99            target = cubic->cu_tcp_cwnd;
100    }
101
102    if (target == 0)
103        target = TCP_MSS;
104
105    cubic->cu_cwnd = target;
106}
107
108
109void
110lsquic_cubic_set_flags (struct lsquic_cubic *cubic, enum cubic_flags flags)
111{
112    LSQ_DEBUG("%s(cubic, 0x%X)", __func__, flags);
113    cubic->cu_flags = flags;
114}
115
116
117static void
118lsquic_cubic_init (void *cong_ctl, const struct lsquic_conn_public *conn_pub,
119                                            enum quic_ft_bit UNUSED_retx_frames)
120{
121    struct lsquic_cubic *const cubic = cong_ctl;
122    cubic_reset(cubic);
123    cubic->cu_ssthresh = 10000 * TCP_MSS; /* Emulate "unbounded" slow start */
124    cubic->cu_conn  = conn_pub->lconn;
125    cubic->cu_rtt_stats = &conn_pub->rtt_stats;
126    cubic->cu_flags = DEFAULT_CUBIC_FLAGS;
127#ifndef NDEBUG
128    const char *s;
129    s = getenv("LSQUIC_CUBIC_SAMPLING_RATE");
130    if (s)
131        cubic->cu_sampling_rate = atoi(s);
132    else
133#endif
134        cubic->cu_sampling_rate = 100000;
135    LSQ_DEBUG("%s(cubic, $conn)", __func__);
136    LSQ_INFO("initialized");
137}
138
139
140#define LOG_CWND(c) do {                                                    \
141    if (LSQ_LOG_ENABLED(LSQ_LOG_INFO)) {                                    \
142        lsquic_time_t now = lsquic_time_now();                              \
143        now -= now % (c)->cu_sampling_rate;                                 \
144        if (now > (c)->cu_last_logged) {                                    \
145            LSQ_INFO("CWND: %lu", (c)->cu_cwnd);                            \
146            (c)->cu_last_logged = now;                                      \
147        }                                                                   \
148    }                                                                       \
149} while (0)
150
151
152static void
153lsquic_cubic_was_quiet (void *cong_ctl, lsquic_time_t now, uint64_t in_flight)
154{
155    struct lsquic_cubic *const cubic = cong_ctl;
156    LSQ_DEBUG("%s(cubic, %"PRIu64")", __func__, now);
157    cubic->cu_epoch_start = 0;
158}
159
160
161static void
162lsquic_cubic_ack (void *cong_ctl, struct lsquic_packet_out *packet_out,
163                  unsigned n_bytes, lsquic_time_t now_time, int app_limited)
164{
165    struct lsquic_cubic *const cubic = cong_ctl;
166    lsquic_time_t rtt;
167
168    rtt = now_time - packet_out->po_sent;
169    LSQ_DEBUG("%s(cubic, %"PRIu64", %"PRIu64", %d, %u)", __func__, now_time, rtt,
170                                                        app_limited, n_bytes);
171    if (0 == cubic->cu_min_delay || rtt < cubic->cu_min_delay)
172    {
173        cubic->cu_min_delay = rtt;
174        LSQ_INFO("min_delay: %"PRIu64, rtt);
175    }
176
177    if (cubic->cu_cwnd <= cubic->cu_ssthresh)
178    {
179        cubic->cu_cwnd += TCP_MSS;
180        LSQ_DEBUG("ACK: slow threshold, cwnd: %lu", cubic->cu_cwnd);
181    }
182    else if (!app_limited)
183    {
184        cubic_update(cubic, now_time, n_bytes);
185        LSQ_DEBUG("ACK: cwnd: %lu", cubic->cu_cwnd);
186    }
187
188    LOG_CWND(cubic);
189}
190
191
192static void
193lsquic_cubic_loss (void *cong_ctl)
194{
195    struct lsquic_cubic *const cubic = cong_ctl;
196    LSQ_DEBUG("%s(cubic)", __func__);
197    cubic->cu_epoch_start = 0;
198    if (FAST_CONVERGENCE && cubic->cu_cwnd < cubic->cu_last_max_cwnd)
199        cubic->cu_last_max_cwnd = cubic->cu_cwnd * TWO_MINUS_BETA_OVER_TWO / 1024;
200    else
201        cubic->cu_last_max_cwnd = cubic->cu_cwnd;
202    cubic->cu_cwnd = cubic->cu_cwnd * ONE_MINUS_BETA / 1024;
203    cubic->cu_tcp_cwnd = cubic->cu_cwnd;
204    cubic->cu_ssthresh = cubic->cu_cwnd;
205    LSQ_INFO("loss detected, last_max_cwnd: %lu, cwnd: %lu",
206        cubic->cu_last_max_cwnd, cubic->cu_cwnd);
207    LOG_CWND(cubic);
208}
209
210
211static void
212lsquic_cubic_timeout (void *cong_ctl)
213{
214    struct lsquic_cubic *const cubic = cong_ctl;
215    unsigned long cwnd;
216
217    cwnd = cubic->cu_cwnd;
218    LSQ_DEBUG("%s(cubic)", __func__);
219    cubic_reset(cubic);
220    cubic->cu_ssthresh = cwnd / 2;
221    cubic->cu_tcp_cwnd = 2 * TCP_MSS;
222    cubic->cu_cwnd = 2 * TCP_MSS;
223    LSQ_INFO("timeout, cwnd: %lu", cubic->cu_cwnd);
224    LOG_CWND(cubic);
225}
226
227
228static void
229lsquic_cubic_cleanup (void *cong_ctl)
230{
231}
232
233
234static uint64_t
235lsquic_cubic_get_cwnd (void *cong_ctl)
236{
237    struct lsquic_cubic *const cubic = cong_ctl;
238    return cubic->cu_cwnd;
239}
240
241
242static int
243in_slow_start (void *cong_ctl)
244{
245    struct lsquic_cubic *const cubic = cong_ctl;
246    return cubic->cu_cwnd < cubic->cu_ssthresh;
247}
248
249
250static uint64_t
251lsquic_cubic_pacing_rate (void *cong_ctl, int in_recovery)
252{
253    struct lsquic_cubic *const cubic = cong_ctl;
254    uint64_t bandwidth, pacing_rate;
255    lsquic_time_t srtt;
256
257    srtt = lsquic_rtt_stats_get_srtt(cubic->cu_rtt_stats);
258    if (srtt == 0)
259        srtt = 50000;
260    bandwidth = cubic->cu_cwnd * 1000000 / srtt;
261    if (in_slow_start(cubic))
262        pacing_rate = bandwidth * 2;
263    else if (in_recovery)
264        pacing_rate = bandwidth;
265    else
266        pacing_rate = bandwidth + bandwidth / 4;
267
268    return pacing_rate;
269}
270
271
272
273const struct cong_ctl_if lsquic_cong_cubic_if =
274{
275    .cci_ack           = lsquic_cubic_ack,
276    .cci_cleanup       = lsquic_cubic_cleanup,
277    .cci_get_cwnd      = lsquic_cubic_get_cwnd,
278    .cci_init          = lsquic_cubic_init,
279    .cci_pacing_rate   = lsquic_cubic_pacing_rate,
280    .cci_loss          = lsquic_cubic_loss,
281    .cci_timeout       = lsquic_cubic_timeout,
282    .cci_was_quiet     = lsquic_cubic_was_quiet,
283};
284