1 /*
2 * Copyright (c) 2013-2021 Apple Inc. All rights reserved.
3 *
4 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
5 *
6 * This file contains Original Code and/or Modifications of Original Code
7 * as defined in and that are subject to the Apple Public Source License
8 * Version 2.0 (the 'License'). You may not use this file except in
9 * compliance with the License. The rights granted to you under the License
10 * may not be used to create, or enable the creation or redistribution of,
11 * unlawful or unlicensed copies of an Apple operating system, or to
12 * circumvent, violate, or enable the circumvention or violation of, any
13 * terms of an Apple operating system software license agreement.
14 *
15 * Please obtain a copy of the License at
16 * http://www.opensource.apple.com/apsl/ and read it before using this file.
17 *
18 * The Original Code and all software distributed under the License are
19 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
20 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
21 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
22 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
23 * Please see the License for the specific language governing rights and
24 * limitations under the License.
25 *
26 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
27 */
28
29 #include "tcp_includes.h"
30
31 #include <sys/param.h>
32 #include <sys/kernel.h>
33 #include <sys/syslog.h>
34 #include <sys/kern_control.h>
35 #include <sys/domain.h>
36
37 #include <netinet/in.h>
38 #include <mach/sdt.h>
39 #include <libkern/OSAtomic.h>
40
41 #include <libkern/OSTypes.h>
42
43 extern struct tcp_cc_algo tcp_cc_newreno;
44 extern struct tcp_cc_algo tcp_cc_ledbat;
45 extern struct tcp_cc_algo tcp_cc_cubic;
46
47 #define SET_SNDSB_IDEAL_SIZE(sndsb, size) \
48 sndsb->sb_idealsize = min(max(tcp_sendspace, tp->snd_ssthresh), \
49 tcp_autosndbuf_max);
50
51 /* Array containing pointers to currently implemented TCP CC algorithms */
52 struct tcp_cc_algo* tcp_cc_algo_list[TCP_CC_ALGO_COUNT];
53
54 static struct tcp_cc_algo tcp_cc_algo_none;
55 /*
56 * Initialize TCP congestion control algorithms.
57 */
58
59 void
tcp_cc_init(void)60 tcp_cc_init(void)
61 {
62 bzero(&tcp_cc_algo_list, sizeof(tcp_cc_algo_list));
63 bzero(&tcp_cc_algo_none, sizeof(tcp_cc_algo_none));
64
65 tcp_cc_algo_list[TCP_CC_ALGO_NONE] = &tcp_cc_algo_none;
66 tcp_cc_algo_list[TCP_CC_ALGO_NEWRENO_INDEX] = &tcp_cc_newreno;
67 tcp_cc_algo_list[TCP_CC_ALGO_BACKGROUND_INDEX] = &tcp_cc_ledbat;
68 tcp_cc_algo_list[TCP_CC_ALGO_CUBIC_INDEX] = &tcp_cc_cubic;
69
70 tcp_ccdbg_control_register();
71 }
72
73 void
tcp_cc_resize_sndbuf(struct tcpcb * tp)74 tcp_cc_resize_sndbuf(struct tcpcb *tp)
75 {
76 struct sockbuf *sb;
77 /*
78 * If the send socket buffer size is bigger than ssthresh,
79 * it is time to trim it because we do not want to hold
80 * too many mbufs in the socket buffer
81 */
82 sb = &tp->t_inpcb->inp_socket->so_snd;
83 if (sb->sb_hiwat > tp->snd_ssthresh &&
84 (sb->sb_flags & SB_AUTOSIZE)) {
85 if (sb->sb_idealsize > tp->snd_ssthresh) {
86 SET_SNDSB_IDEAL_SIZE(sb, tp->snd_ssthresh);
87 }
88 sb->sb_flags |= SB_TRIM;
89 }
90 }
91
92 void
tcp_bad_rexmt_fix_sndbuf(struct tcpcb * tp)93 tcp_bad_rexmt_fix_sndbuf(struct tcpcb *tp)
94 {
95 struct sockbuf *sb;
96 sb = &tp->t_inpcb->inp_socket->so_snd;
97 if ((sb->sb_flags & (SB_TRIM | SB_AUTOSIZE)) == (SB_TRIM | SB_AUTOSIZE)) {
98 /*
99 * If there was a retransmission that was not necessary
100 * then the size of socket buffer can be restored to
101 * what it was before
102 */
103 SET_SNDSB_IDEAL_SIZE(sb, tp->snd_ssthresh);
104 if (sb->sb_hiwat <= sb->sb_idealsize) {
105 sbreserve(sb, sb->sb_idealsize);
106 sb->sb_flags &= ~SB_TRIM;
107 }
108 }
109 }
110
111 /*
112 * Calculate initial cwnd according to RFC3390.
113 */
114 void
tcp_cc_cwnd_init_or_reset(struct tcpcb * tp)115 tcp_cc_cwnd_init_or_reset(struct tcpcb *tp)
116 {
117 if (tp->t_flags & TF_LOCAL) {
118 tp->snd_cwnd = tp->t_maxseg * ss_fltsz_local;
119 } else {
120 if (tcp_cubic_minor_fixes) {
121 tp->snd_cwnd = tcp_initial_cwnd(tp);
122 } else {
123 /* initial congestion window according to RFC 3390 */
124 tp->snd_cwnd = min(4 * tp->t_maxseg,
125 max(2 * tp->t_maxseg, TCP_CC_CWND_INIT_BYTES));
126 }
127 }
128 }
129
130 /*
131 * Indicate whether this ack should be delayed.
132 * Here is the explanation for different settings of tcp_delack_enabled:
133 * - when set to 1, the behavior is same as when set to 2. We kept this
134 * for binary compatibility.
135 * - when set to 2, will "ack every other packet"
136 * - if our last ack wasn't a 0-sized window.
137 * - if the peer hasn't sent us a TH_PUSH data packet (radar 3649245).
138 * If TH_PUSH is set, take this as a clue that we need to ACK
139 * with no delay. This helps higher level protocols who
140 * won't send us more data even if the window is open
141 * because their last "segment" hasn't been ACKed
142 * - when set to 3, will do "streaming detection"
143 * - if we receive more than "maxseg_unacked" full packets
144 * in the last 100ms
145 * - if the connection is not in slow-start or idle or
146 * loss/recovery states
147 * - if those criteria aren't met, it will ack every other packet.
148 */
149 int
tcp_cc_delay_ack(struct tcpcb * tp,struct tcphdr * th)150 tcp_cc_delay_ack(struct tcpcb *tp, struct tcphdr *th)
151 {
152 switch (tcp_delack_enabled) {
153 case 1:
154 case 2:
155 if ((tp->t_flags & TF_RXWIN0SENT) == 0 &&
156 (th->th_flags & TH_PUSH) == 0 &&
157 (tp->t_unacksegs == 1)) {
158 return 1;
159 }
160 break;
161 case 3:
162 if (tcp_ack_strategy == TCP_ACK_STRATEGY_LEGACY) {
163 if ((tp->t_flags & TF_RXWIN0SENT) == 0 &&
164 (th->th_flags & TH_PUSH) == 0 &&
165 ((tp->t_unacksegs == 1) ||
166 ((tp->t_flags & TF_STRETCHACK) &&
167 tp->t_unacksegs < maxseg_unacked))) {
168 return 1;
169 }
170 } else {
171 uint32_t recwin;
172
173 /* Get the receive-window we would announce */
174 recwin = tcp_sbspace(tp);
175 if (recwin > (uint32_t)(TCP_MAXWIN << tp->rcv_scale)) {
176 recwin = (uint32_t)(TCP_MAXWIN << tp->rcv_scale);
177 }
178
179 /* Delay ACK, if:
180 *
181 * 1. We are not sending a zero-window
182 * 2. We are not forcing fast ACKs
183 * 3. We have more than the low-water mark in receive-buffer
184 * 4. The receive-window is not increasing
185 * 5. We have less than or equal of an MSS unacked or
186 * Window actually has been growing larger than the initial value by half of it.
187 * (this makes sure that during ramp-up we ACK every second MSS
188 * until we pass the tcp_recvspace * 1.5-threshold)
189 * 6. We haven't waited for half a BDP
190 * 7. The amount of unacked data is less than the maximum ACK-burst (256 MSS)
191 * We try to avoid having the sender end up hitting huge ACK-ranges.
192 *
193 * (a note on 6: The receive-window is
194 * roughly 2 BDP. Thus, recwin / 4 means half a BDP and
195 * thus we enforce an ACK roughly twice per RTT - even
196 * if the app does not read)
197 */
198 if ((tp->t_flags & TF_RXWIN0SENT) == 0 &&
199 tp->t_forced_acks == 0 &&
200 tp->t_inpcb->inp_socket->so_rcv.sb_cc > tp->t_inpcb->inp_socket->so_rcv.sb_lowat &&
201 recwin <= tp->t_last_recwin &&
202 (tp->rcv_nxt - tp->last_ack_sent <= tp->t_maxseg ||
203 recwin > (uint32_t)(tcp_recvspace + (tcp_recvspace >> 1))) &&
204 (tp->rcv_nxt - tp->last_ack_sent) < (recwin >> 2) &&
205 (tp->rcv_nxt - tp->last_ack_sent) < 256 * tp->t_maxseg) {
206 tp->t_stat.acks_delayed++;
207 return 1;
208 }
209 }
210 break;
211 }
212 return 0;
213 }
214
215 void
tcp_cc_allocate_state(struct tcpcb * tp)216 tcp_cc_allocate_state(struct tcpcb *tp)
217 {
218 if ((tp->tcp_cc_index == TCP_CC_ALGO_CUBIC_INDEX ||
219 tp->tcp_cc_index == TCP_CC_ALGO_BACKGROUND_INDEX) &&
220 tp->t_ccstate == NULL) {
221 tp->t_ccstate = &tp->_t_ccstate;
222
223 bzero(tp->t_ccstate, sizeof(*tp->t_ccstate));
224 }
225 }
226
227 /*
228 * If stretch ack was disabled automatically on long standing connections,
229 * re-evaluate the situation after 15 minutes to enable it.
230 */
231 #define TCP_STRETCHACK_DISABLE_WIN (15 * 60 * TCP_RETRANSHZ)
232 void
tcp_cc_after_idle_stretchack(struct tcpcb * tp)233 tcp_cc_after_idle_stretchack(struct tcpcb *tp)
234 {
235 struct tcp_globals *globals;
236 int32_t tdiff;
237
238 if (!(tp->t_flagsext & TF_DISABLE_STRETCHACK)) {
239 return;
240 }
241
242 globals = tcp_get_globals(tp);
243 tdiff = timer_diff(tcp_globals_now(globals), 0, tp->rcv_nostrack_ts, 0);
244 if (tdiff < 0) {
245 tdiff = -tdiff;
246 }
247
248 if (tdiff > TCP_STRETCHACK_DISABLE_WIN) {
249 tp->t_flagsext &= ~TF_DISABLE_STRETCHACK;
250 tp->t_stretchack_delayed = 0;
251
252 tcp_reset_stretch_ack(tp);
253 }
254 }
255
256 /*
257 * Detect if the congestion window is non-validated according to
258 * draft-ietf-tcpm-newcwv-07
259 */
260 inline uint32_t
tcp_cc_is_cwnd_nonvalidated(struct tcpcb * tp)261 tcp_cc_is_cwnd_nonvalidated(struct tcpcb *tp)
262 {
263 struct socket *so = tp->t_inpcb->inp_socket;
264
265 if (tp->t_pipeack == 0) {
266 tp->t_flagsext &= ~TF_CWND_NONVALIDATED;
267 return 0;
268 }
269
270 /*
271 * The congestion window is validated if the number of bytes acked
272 * is more than half of the current window or if there is more
273 * data to send in the send socket buffer
274 */
275 if (tp->t_pipeack >= (tp->snd_cwnd >> 1) ||
276 (so != NULL && so->so_snd.sb_cc > tp->snd_cwnd)) {
277 tp->t_flagsext &= ~TF_CWND_NONVALIDATED;
278 } else {
279 tp->t_flagsext |= TF_CWND_NONVALIDATED;
280 }
281
282 return tp->t_flagsext & TF_CWND_NONVALIDATED;
283 }
284
285 /*
286 * Adjust congestion window in response to congestion in non-validated
287 * phase.
288 */
289 inline void
tcp_cc_adjust_nonvalidated_cwnd(struct tcpcb * tp)290 tcp_cc_adjust_nonvalidated_cwnd(struct tcpcb *tp)
291 {
292 tp->t_pipeack = tcp_get_max_pipeack(tp);
293 tcp_clear_pipeack_state(tp);
294 tp->snd_cwnd = (max(tp->t_pipeack, tp->t_lossflightsize) >> 1);
295 if (tcp_cubic_minor_fixes) {
296 tp->snd_cwnd = max(tp->snd_cwnd, tp->t_maxseg);
297 } else {
298 tp->snd_cwnd = max(tp->snd_cwnd, TCP_CC_CWND_INIT_BYTES);
299 }
300 tp->snd_cwnd += tp->t_maxseg * tcprexmtthresh;
301 tp->t_flagsext &= ~TF_CWND_NONVALIDATED;
302 }
303
304 /*
305 * Return maximum of all the pipeack samples. Since the number of samples
306 * TCP_PIPEACK_SAMPLE_COUNT is 3 at this time, it will be simpler to do
307 * a comparision. We should change ths if the number of samples increases.
308 */
309 inline uint32_t
tcp_get_max_pipeack(struct tcpcb * tp)310 tcp_get_max_pipeack(struct tcpcb *tp)
311 {
312 uint32_t max_pipeack = 0;
313 max_pipeack = (tp->t_pipeack_sample[0] > tp->t_pipeack_sample[1]) ?
314 tp->t_pipeack_sample[0] : tp->t_pipeack_sample[1];
315 max_pipeack = (tp->t_pipeack_sample[2] > max_pipeack) ?
316 tp->t_pipeack_sample[2] : max_pipeack;
317
318 return max_pipeack;
319 }
320
321 inline void
tcp_clear_pipeack_state(struct tcpcb * tp)322 tcp_clear_pipeack_state(struct tcpcb *tp)
323 {
324 bzero(tp->t_pipeack_sample, sizeof(tp->t_pipeack_sample));
325 tp->t_pipeack_ind = 0;
326 tp->t_lossflightsize = 0;
327 }
328