/* * Copyright (c) 2018-2019 Cisco and/or its affiliates. * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at: * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ #include <vnet/tcp/tcp.h> #include <math.h> #define beta_cubic 0.7 #define cubic_c 0.4 #define west_const (3 * (1 - beta_cubic) / (1 + beta_cubic)) typedef struct cubic_cfg_ { u8 fast_convergence; u32 ssthresh; } cubic_cfg_t; static cubic_cfg_t cubic_cfg = { .fast_convergence = 1, .ssthresh = 0x7FFFFFFFU, }; typedef struct cubic_data_ { /** time period (in seconds) needed to increase the current window * size to W_max if there are no further congestion events */ f64 K; /** time (in sec) since the start of current congestion avoidance */ f64 t_start; /** Inflection point of the cubic function (in snd_mss segments) */ u32 w_max; } __clib_packed cubic_data_t; STATIC_ASSERT (sizeof (cubic_data_t) <= TCP_CC_DATA_SZ, "cubic data len"); static inline f64 cubic_time (u32 thread_index) { return transport_time_now (thread_index); } /** * RFC 8312 Eq. 1 * * CUBIC window increase function. Time and K need to be provided in seconds. */ static inline u64 W_cubic (cubic_data_t * cd, f64 t) { f64 diff = t - cd->K; /* W_cubic(t) = C*(t-K)^3 + W_max */ return cubic_c * diff * diff * diff + cd->w_max; } /** * RFC 8312 Eq. 2 */ static inline f64 K_cubic (cubic_data_t * cd, u32 wnd) { /* K = cubic_root(W_max*(1-beta_cubic)/C) * Because the current window may be less than W_max * beta_cubic because * of fast convergence, we pass it as parameter */ return pow ((f64) (cd->w_max - wnd) / cubic_c, 1 / 3.0); } /** * RFC 8312 Eq. 4 * * Estimates the window size of AIMD(alpha_aimd, beta_aimd) for * alpha_aimd=3*(1-beta_cubic)/(1+beta_cubic) and beta_aimd=beta_cubic. * Time (t) and rtt should be provided in seconds */ static inline u32 W_est (cubic_data_t * cd, f64 t, f64 rtt) { /* W_est(t) = W_max*beta_cubic+[3*(1-beta_cubic)/(1+beta_cubic)]*(t/RTT) */ return cd->w_max * beta_cubic + west_const * (t / rtt); } static void cubic_congestion (tcp_connection_t * tc) { cubic_data_t *cd = (cubic_data_t *) tcp_cc_data (tc); u32 w_max; w_max = tc->cwnd / tc->snd_mss; if (cubic_cfg.fast_convergence && w_max < cd->w_max) w_max = w_max * ((1.0 + beta_cubic) / 2.0); cd->w_max = w_max; tc->ssthresh = clib_max (tc->cwnd * beta_cubic, 2 * tc->snd_mss); tc->cwnd = tc->ssthresh; } static void cubic_loss (tcp_connection_t * tc) { cubic_data_t *cd = (cubic_data_t *) tcp_cc_data (tc); tc->cwnd = tcp_loss_wnd (tc); cd->t_start = cubic_time (tc->c_thread_index); cd->K = 0; cd->w_max = tc->cwnd / tc->snd_mss; } static void cubic_recovered (tcp_connection_t * tc) { cubic_data_t *cd = (cubic_data_t *) tcp_cc_data (tc); cd->t_start = cubic_time (tc->c_thread_index); tc->cwnd = tc->ssthresh; cd->K = K_cubic (cd, tc->cwnd / tc->snd_mss); } static void cubic_cwnd_accumulate (tcp_connection_t * tc, u32 thresh, u32 bytes_acked) { /* We just updated the threshold and don't know how large the previous * one was. Still, optimistically increase cwnd by one segment and * clear the accumulated bytes. */ if (tc->cwnd_acc_bytes > thresh) { tc->cwnd += tc->snd_mss; tc->cwnd_acc_bytes = 0; } tcp_cwnd_accumulate (tc, thresh, tc->bytes_acked); } static void cubic_rcv_ack (tcp_connection_t * tc, tcp_rate_sample_t * rs) { cubic_data_t *cd = (cubic_data_t *) tcp_cc_data (tc); u64 w_cubic, w_aimd; f64 t, rtt_sec; u32 thresh; /* Constrained by tx fifo, can't grow further */ if (tc->cwnd >= tc->tx_fifo_size) return; if (tcp_in_slowstart (tc)) { tc->cwnd += tc->bytes_acked; return; } t = cubic_time (tc->c_thread_index) - cd->t_start; rtt_sec = clib_min (tc->mrtt_us, (f64) tc->srtt * TCP_TICK); w_cubic = W_cubic (cd, t + rtt_sec) * tc->snd_mss; w_aimd = (u64) W_est (cd, t, rtt_sec) * tc->snd_mss; if (w_cubic < w_aimd) { cubic_cwnd_accumulate (tc, tc->cwnd, tc->bytes_acked); } else { if (w_cubic > tc->cwnd) { /* For NewReno and slow start, we increment cwnd based on the * number of bytes acked, not the number of acks received. In * particular, for NewReno we increment the cwnd by 1 snd_mss * only after we accumulate 1 cwnd of acked bytes (RFC 3465). * * For Cubic, as per RFC 8312 we should increment cwnd by * (w_cubic - cwnd)/cwnd for each ack. Instead of using that, * we compute the number of packets that need to be acked * before adding snd_mss to cwnd and compute the threshold */ thresh = (tc->snd_mss * tc->cwnd) / (w_cubic - tc->cwnd); /* Make sure we don't increase cwnd more often than every segment */ thresh = clib_max (thresh, tc->snd_mss); } else { /* Practically we can't increment so just inflate threshold */ thresh = 50 * tc->cwnd; } cubic_cwnd_accumulate (tc, thresh, tc->bytes_acked); } } static void cubic_conn_init (tcp_connection_t * tc) { cubic_data_t *cd = (cubic_data_t *) tcp_cc_data (tc); tc->ssthresh = cubic_cfg.ssthresh; tc->cwnd = tcp_initial_cwnd (tc); cd->w_max = 0; cd->K = 0; cd->t_start = cubic_time (tc->c_thread_index); } static uword cubic_unformat_config (unformat_input_t * input) { u32 ssthresh = 0x7FFFFFFFU; if (!input) return 0; unformat_skip_white_space (input); while (unformat_check_input (input) != UNFORMAT_END_OF_INPUT) { if (unformat (input, "no-fast-convergence")) cubic_cfg.fast_convergence = 0; else if (unformat (input, "ssthresh %u", &ssthresh)) cubic_cfg.ssthresh = ssthresh; else return 0; } return 1; } const static tcp_cc_algorithm_t tcp_cubic = { .name = "cubic", .unformat_cfg = cubic_unformat_config, .congestion = cubic_congestion, .loss = cubic_loss, .recovered = cubic_recovered, .rcv_ack = cubic_rcv_ack, .rcv_cong_ack = newreno_rcv_cong_ack, .init = cubic_conn_init, }; clib_error_t * cubic_init (vlib_main_t * vm) { clib_error_t *error = 0; tcp_cc_algo_register (TCP_CC_CUBIC, &tcp_cubic); return error; } VLIB_INIT_FUNCTION (cubic_init); /* * fd.io coding-style-patch-verification: ON * * Local Variables: * eval: (c-set-style "gnu") * End: */