2 * Copyright (c) 2018 Cisco and/or its affiliates.
3 * Licensed under the Apache License, Version 2.0 (the "License");
4 * you may not use this file except in compliance with the License.
5 * You may obtain a copy of the License at:
7 * http://www.apache.org/licenses/LICENSE-2.0
9 * Unless required by applicable law or agreed to in writing, software
10 * distributed under the License is distributed on an "AS IS" BASIS,
11 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 * See the License for the specific language governing permissions and
13 * limitations under the License.
16 #include <vnet/tcp/tcp.h>
19 #define beta_cubic 0.7
21 #define west_const (3 * (1 - beta_cubic) / (1 + beta_cubic))
23 typedef struct cubic_cfg_
28 static cubic_cfg_t cubic_cfg = {
29 .fast_convergence = 1,
32 typedef struct cubic_data_
34 /** time period (in seconds) needed to increase the current window
35 * size to W_max if there are no further congestion events */
38 /** time (in sec) since the start of current congestion avoidance */
41 /** Inflection point of the cubic function (in snd_mss segments) */
44 } __clib_packed cubic_data_t;
46 STATIC_ASSERT (sizeof (cubic_data_t) <= TCP_CC_DATA_SZ, "cubic data len");
49 cubic_time (u32 thread_index)
51 return transport_time_now (thread_index);
57 * CUBIC window increase function. Time and K need to be provided in seconds.
60 W_cubic (cubic_data_t * cd, f64 t)
64 /* W_cubic(t) = C*(t-K)^3 + W_max */
65 return cubic_c * diff * diff * diff + cd->w_max;
72 K_cubic (cubic_data_t * cd)
74 /* K = cubic_root(W_max*(1-beta_cubic)/C) */
75 return pow (cd->w_max * (1 - beta_cubic) / cubic_c, 1 / 3.0);
81 * Estimates the window size of AIMD(alpha_aimd, beta_aimd) for
82 * alpha_aimd=3*(1-beta_cubic)/(1+beta_cubic) and beta_aimd=beta_cubic.
83 * Time (t) and rtt should be provided in seconds
86 W_est (cubic_data_t * cd, f64 t, f64 rtt)
88 /* W_est(t) = W_max*beta_cubic+[3*(1-beta_cubic)/(1+beta_cubic)]*(t/RTT) */
89 return cd->w_max * beta_cubic + west_const * (t / rtt);
93 cubic_congestion (tcp_connection_t * tc)
95 cubic_data_t *cd = (cubic_data_t *) tcp_cc_data (tc);
98 w_max = tc->cwnd / tc->snd_mss;
99 if (cubic_cfg.fast_convergence && w_max < cd->w_max)
100 w_max = w_max * ((1.0 + beta_cubic) / 2.0);
103 tc->ssthresh = clib_max (tc->cwnd * beta_cubic, 2 * tc->snd_mss);
107 cubic_recovered (tcp_connection_t * tc)
109 cubic_data_t *cd = (cubic_data_t *) tcp_cc_data (tc);
110 cd->t_start = cubic_time (tc->c_thread_index);
111 cd->K = K_cubic (cd);
112 tc->cwnd = tc->ssthresh;
116 cubic_rcv_ack (tcp_connection_t * tc)
118 cubic_data_t *cd = (cubic_data_t *) tcp_cc_data (tc);
123 /* Constrained by tx fifo, can't grow further */
124 if (tc->cwnd >= tc->tx_fifo_size)
127 if (tcp_in_slowstart (tc))
129 tc->cwnd += clib_min (tc->snd_mss, tc->bytes_acked);
133 t = cubic_time (tc->c_thread_index) - cd->t_start;
134 rtt_sec = clib_min (tc->mrtt_us, (f64) tc->srtt * TCP_TICK);
136 w_cubic = W_cubic (cd, t + rtt_sec) * tc->snd_mss;
137 w_aimd = (u64) W_est (cd, t, rtt_sec) * tc->snd_mss;
138 if (w_cubic < w_aimd)
140 tcp_cwnd_accumulate (tc, tc->cwnd, tc->bytes_acked);
144 if (w_cubic > tc->cwnd)
146 /* For NewReno and slow start, we increment cwnd based on the
147 * number of bytes acked, not the number of acks received. In
148 * particular, for NewReno we increment the cwnd by 1 snd_mss
149 * only after we accumulate 1 cwnd of acked bytes (RFC 3465).
151 * For Cubic, as per RFC 8312 we should increment cwnd by
152 * (w_cubic - cwnd)/cwnd for each ack. Instead of using that,
153 * we compute the number of packets that need to be acked
154 * before adding snd_mss to cwnd and compute the threshold
156 thresh = (tc->snd_mss * tc->cwnd) / (w_cubic - tc->cwnd);
158 /* Make sure we don't increase cwnd more often than every
160 thresh = clib_max (thresh, 2 * tc->snd_mss);
164 /* Practically we can't increment so just inflate threshold */
165 thresh = 50 * tc->cwnd;
167 tcp_cwnd_accumulate (tc, thresh, tc->bytes_acked);
172 cubic_conn_init (tcp_connection_t * tc)
174 cubic_data_t *cd = (cubic_data_t *) tcp_cc_data (tc);
175 tc->ssthresh = tc->snd_wnd;
176 tc->cwnd = tcp_initial_cwnd (tc);
179 cd->t_start = cubic_time (tc->c_thread_index);
183 cubic_unformat_config (unformat_input_t * input)
188 unformat_skip_white_space (input);
190 while (unformat_check_input (input) != UNFORMAT_END_OF_INPUT)
192 if (unformat (input, "no-fast-convergence"))
193 cubic_cfg.fast_convergence = 0;
200 const static tcp_cc_algorithm_t tcp_cubic = {
202 .unformat_cfg = cubic_unformat_config,
203 .congestion = cubic_congestion,
204 .recovered = cubic_recovered,
205 .rcv_ack = cubic_rcv_ack,
206 .rcv_cong_ack = newreno_rcv_cong_ack,
207 .init = cubic_conn_init,
211 cubic_init (vlib_main_t * vm)
213 clib_error_t *error = 0;
215 tcp_cc_algo_register (TCP_CC_CUBIC, &tcp_cubic);
220 VLIB_INIT_FUNCTION (cubic_init);
223 * fd.io coding-style-patch-verification: ON
226 * eval: (c-set-style "gnu")