FD.io VPP  v19.08.3-2-gbabecb413
Vector Packet Processing
tcp_cubic.c
Go to the documentation of this file.
1 /*
2  * Copyright (c) 2018-2019 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:
6  *
7  * http://www.apache.org/licenses/LICENSE-2.0
8  *
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.
14  */
15 
16 #include <vnet/tcp/tcp.h>
17 #include <math.h>
18 
19 #define beta_cubic 0.7
20 #define cubic_c 0.4
21 #define west_const (3 * (1 - beta_cubic) / (1 + beta_cubic))
22 
23 typedef struct cubic_cfg_
24 {
27 } cubic_cfg_t;
28 
29 static cubic_cfg_t cubic_cfg = {
30  .fast_convergence = 1,
31  .ssthresh = 0x7FFFFFFFU,
32 };
33 
34 typedef struct cubic_data_
35 {
36  /** time period (in seconds) needed to increase the current window
37  * size to W_max if there are no further congestion events */
38  f64 K;
39 
40  /** time (in sec) since the start of current congestion avoidance */
42 
43  /** Inflection point of the cubic function (in snd_mss segments) */
45 
46 } __clib_packed cubic_data_t;
47 
48 STATIC_ASSERT (sizeof (cubic_data_t) <= TCP_CC_DATA_SZ, "cubic data len");
49 
50 static inline f64
51 cubic_time (u32 thread_index)
52 {
53  return transport_time_now (thread_index);
54 }
55 
56 /**
57  * RFC 8312 Eq. 1
58  *
59  * CUBIC window increase function. Time and K need to be provided in seconds.
60  */
61 static inline u64
62 W_cubic (cubic_data_t * cd, f64 t)
63 {
64  f64 diff = t - cd->K;
65 
66  /* W_cubic(t) = C*(t-K)^3 + W_max */
67  return cubic_c * diff * diff * diff + cd->w_max;
68 }
69 
70 /**
71  * RFC 8312 Eq. 2
72  */
73 static inline f64
74 K_cubic (cubic_data_t * cd, u32 wnd)
75 {
76  /* K = cubic_root(W_max*(1-beta_cubic)/C)
77  * Because the current window may be less than W_max * beta_cubic because
78  * of fast convergence, we pass it as parameter */
79  return pow ((f64) (cd->w_max - wnd) / cubic_c, 1 / 3.0);
80 }
81 
82 /**
83  * RFC 8312 Eq. 4
84  *
85  * Estimates the window size of AIMD(alpha_aimd, beta_aimd) for
86  * alpha_aimd=3*(1-beta_cubic)/(1+beta_cubic) and beta_aimd=beta_cubic.
87  * Time (t) and rtt should be provided in seconds
88  */
89 static inline u32
90 W_est (cubic_data_t * cd, f64 t, f64 rtt)
91 {
92  /* W_est(t) = W_max*beta_cubic+[3*(1-beta_cubic)/(1+beta_cubic)]*(t/RTT) */
93  return cd->w_max * beta_cubic + west_const * (t / rtt);
94 }
95 
96 static void
98 {
99  cubic_data_t *cd = (cubic_data_t *) tcp_cc_data (tc);
100  u32 w_max;
101 
102  w_max = tc->cwnd / tc->snd_mss;
103  if (cubic_cfg.fast_convergence && w_max < cd->w_max)
104  w_max = w_max * ((1.0 + beta_cubic) / 2.0);
105 
106  cd->w_max = w_max;
107  tc->ssthresh = clib_max (tc->cwnd * beta_cubic, 2 * tc->snd_mss);
108  tc->cwnd = tc->ssthresh;
109 }
110 
111 static void
113 {
114  cubic_data_t *cd = (cubic_data_t *) tcp_cc_data (tc);
115 
116  tc->cwnd = tcp_loss_wnd (tc);
117  cd->t_start = cubic_time (tc->c_thread_index);
118  cd->K = 0;
119  cd->w_max = tc->cwnd / tc->snd_mss;
120 }
121 
122 static void
124 {
125  cubic_data_t *cd = (cubic_data_t *) tcp_cc_data (tc);
126  cd->t_start = cubic_time (tc->c_thread_index);
127  tc->cwnd = tc->ssthresh;
128  cd->K = K_cubic (cd, tc->cwnd / tc->snd_mss);
129 }
130 
131 static void
132 cubic_cwnd_accumulate (tcp_connection_t * tc, u32 thresh, u32 bytes_acked)
133 {
134  /* We just updated the threshold and don't know how large the previous
135  * one was. Still, optimistically increase cwnd by one segment and
136  * clear the accumulated bytes. */
137  if (tc->cwnd_acc_bytes > thresh)
138  {
139  tc->cwnd += tc->snd_mss;
140  tc->cwnd_acc_bytes = 0;
141  }
142 
143  tcp_cwnd_accumulate (tc, thresh, tc->bytes_acked);
144 }
145 
146 static void
148 {
149  cubic_data_t *cd = (cubic_data_t *) tcp_cc_data (tc);
150  u64 w_cubic, w_aimd;
151  f64 t, rtt_sec;
152  u32 thresh;
153 
154  /* Constrained by tx fifo, can't grow further */
155  if (tc->cwnd >= tc->tx_fifo_size)
156  return;
157 
158  if (tcp_in_slowstart (tc))
159  {
160  tc->cwnd += tc->bytes_acked;
161  return;
162  }
163 
164  t = cubic_time (tc->c_thread_index) - cd->t_start;
165  rtt_sec = clib_min (tc->mrtt_us, (f64) tc->srtt * TCP_TICK);
166 
167  w_cubic = W_cubic (cd, t + rtt_sec) * tc->snd_mss;
168  w_aimd = (u64) W_est (cd, t, rtt_sec) * tc->snd_mss;
169  if (w_cubic < w_aimd)
170  {
171  cubic_cwnd_accumulate (tc, tc->cwnd, tc->bytes_acked);
172  }
173  else
174  {
175  if (w_cubic > tc->cwnd)
176  {
177  /* For NewReno and slow start, we increment cwnd based on the
178  * number of bytes acked, not the number of acks received. In
179  * particular, for NewReno we increment the cwnd by 1 snd_mss
180  * only after we accumulate 1 cwnd of acked bytes (RFC 3465).
181  *
182  * For Cubic, as per RFC 8312 we should increment cwnd by
183  * (w_cubic - cwnd)/cwnd for each ack. Instead of using that,
184  * we compute the number of packets that need to be acked
185  * before adding snd_mss to cwnd and compute the threshold
186  */
187  thresh = (tc->snd_mss * tc->cwnd) / (w_cubic - tc->cwnd);
188 
189  /* Make sure we don't increase cwnd more often than every segment */
190  thresh = clib_max (thresh, tc->snd_mss);
191  }
192  else
193  {
194  /* Practically we can't increment so just inflate threshold */
195  thresh = 50 * tc->cwnd;
196  }
197  cubic_cwnd_accumulate (tc, thresh, tc->bytes_acked);
198  }
199 }
200 
201 static void
203 {
204  cubic_data_t *cd = (cubic_data_t *) tcp_cc_data (tc);
205  tc->ssthresh = cubic_cfg.ssthresh;
206  tc->cwnd = tcp_initial_cwnd (tc);
207  cd->w_max = 0;
208  cd->K = 0;
209  cd->t_start = cubic_time (tc->c_thread_index);
210 }
211 
212 static uword
214 {
215  u32 ssthresh = 0x7FFFFFFFU;
216 
217  if (!input)
218  return 0;
219 
221 
223  {
224  if (unformat (input, "no-fast-convergence"))
225  cubic_cfg.fast_convergence = 0;
226  else if (unformat (input, "ssthresh %u", &ssthresh))
227  cubic_cfg.ssthresh = ssthresh;
228  else
229  return 0;
230  }
231  return 1;
232 }
233 
234 const static tcp_cc_algorithm_t tcp_cubic = {
235  .name = "cubic",
236  .unformat_cfg = cubic_unformat_config,
237  .congestion = cubic_congestion,
238  .loss = cubic_loss,
239  .recovered = cubic_recovered,
240  .rcv_ack = cubic_rcv_ack,
241  .rcv_cong_ack = newreno_rcv_cong_ack,
242  .init = cubic_conn_init,
243 };
244 
245 clib_error_t *
247 {
248  clib_error_t *error = 0;
249 
250  tcp_cc_algo_register (TCP_CC_CUBIC, &tcp_cubic);
251 
252  return error;
253 }
254 
256 
257 /*
258  * fd.io coding-style-patch-verification: ON
259  *
260  * Local Variables:
261  * eval: (c-set-style "gnu")
262  * End:
263  */
#define clib_min(x, y)
Definition: clib.h:302
static u64 W_cubic(cubic_data_t *cd, f64 t)
RFC 8312 Eq.
Definition: tcp_cubic.c:62
static clib_time_type_t transport_time_now(u32 thread_index)
Definition: session.h:513
struct cubic_data_ cubic_data_t
unsigned long u64
Definition: types.h:89
f64 K
time period (in seconds) needed to increase the current window size to W_max if there are no further ...
Definition: tcp_cubic.c:38
static uword cubic_unformat_config(unformat_input_t *input)
Definition: tcp_cubic.c:213
struct _tcp_connection tcp_connection_t
static u32 W_est(cubic_data_t *cd, f64 t, f64 rtt)
RFC 8312 Eq.
Definition: tcp_cubic.c:90
unsigned char u8
Definition: types.h:56
static void cubic_cwnd_accumulate(tcp_connection_t *tc, u32 thresh, u32 bytes_acked)
Definition: tcp_cubic.c:132
double f64
Definition: types.h:142
#define beta_cubic
Definition: tcp_cubic.c:19
#define TCP_TICK
TCP tick period (s)
Definition: tcp.h:27
u32 w_max
Inflection point of the cubic function (in snd_mss segments)
Definition: tcp_cubic.c:44
#define VLIB_INIT_FUNCTION(x)
Definition: init.h:173
static f64 cubic_time(u32 thread_index)
Definition: tcp_cubic.c:51
#define tcp_in_slowstart(tc)
Definition: tcp.h:466
unsigned int u32
Definition: types.h:88
static void cubic_recovered(tcp_connection_t *tc)
Definition: tcp_cubic.c:123
static void cubic_loss(tcp_connection_t *tc)
Definition: tcp_cubic.c:112
static void * tcp_cc_data(tcp_connection_t *tc)
Definition: tcp.h:1232
struct _unformat_input_t unformat_input_t
static void tcp_cwnd_accumulate(tcp_connection_t *tc, u32 thresh, u32 bytes)
Definition: tcp.h:930
void newreno_rcv_cong_ack(tcp_connection_t *tc, tcp_cc_ack_t ack_type, tcp_rate_sample_t *rs)
Definition: tcp_newreno.c:61
static f64 K_cubic(cubic_data_t *cd, u32 wnd)
RFC 8312 Eq.
Definition: tcp_cubic.c:74
#define west_const
Definition: tcp_cubic.c:21
static void cubic_congestion(tcp_connection_t *tc)
Definition: tcp_cubic.c:97
#define UNFORMAT_END_OF_INPUT
Definition: format.h:145
STATIC_ASSERT(sizeof(cubic_data_t)<=TCP_CC_DATA_SZ, "cubic data len")
vlib_main_t * vm
Definition: buffer.c:323
f64 t_start
time (in sec) since the start of current congestion avoidance
Definition: tcp_cubic.c:41
struct cubic_cfg_ cubic_cfg_t
static void cubic_rcv_ack(tcp_connection_t *tc, tcp_rate_sample_t *rs)
Definition: tcp_cubic.c:147
u8 fast_convergence
Definition: tcp_cubic.c:25
void tcp_cc_algo_register(tcp_cc_algorithm_type_e type, const tcp_cc_algorithm_t *vft)
Register exiting cc algo type.
Definition: tcp.c:87
struct _tcp_cc_algorithm tcp_cc_algorithm_t
Definition: tcp.h:305
#define clib_max(x, y)
Definition: clib.h:295
#define cubic_c
Definition: tcp_cubic.c:20
clib_error_t * cubic_init(vlib_main_t *vm)
Definition: tcp_cubic.c:246
static u32 tcp_initial_cwnd(const tcp_connection_t *tc)
Initial cwnd as per RFC5681.
Definition: tcp.h:910
#define TCP_CC_DATA_SZ
Definition: tcp.h:33
u64 uword
Definition: types.h:112
static u32 tcp_loss_wnd(const tcp_connection_t *tc)
Definition: tcp.h:943
uword unformat_skip_white_space(unformat_input_t *input)
Definition: unformat.c:821
static void cubic_conn_init(tcp_connection_t *tc)
Definition: tcp_cubic.c:202
u32 ssthresh
Definition: tcp_cubic.c:26
uword unformat(unformat_input_t *i, const char *fmt,...)
Definition: unformat.c:978
static uword unformat_check_input(unformat_input_t *i)
Definition: format.h:171