1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * TCP NV: TCP with Congestion Avoidance
4 *
5 * TCP-NV is a successor of TCP-Vegas that has been developed to
6 * deal with the issues that occur in modern networks.
7 * Like TCP-Vegas, TCP-NV supports true congestion avoidance,
8 * the ability to detect congestion before packet losses occur.
9 * When congestion (queue buildup) starts to occur, TCP-NV
10 * predicts what the cwnd size should be for the current
11 * throughput and it reduces the cwnd proportionally to
12 * the difference between the current cwnd and the predicted cwnd.
13 *
14 * NV is only recommeneded for traffic within a data center, and when
15 * all the flows are NV (at least those within the data center). This
16 * is due to the inherent unfairness between flows using losses to
17 * detect congestion (congestion control) and those that use queue
18 * buildup to detect congestion (congestion avoidance).
19 *
20 * Note: High NIC coalescence values may lower the performance of NV
21 * due to the increased noise in RTT values. In particular, we have
22 * seen issues with rx-frames values greater than 8.
23 *
24 * TODO:
25 * 1) Add mechanism to deal with reverse congestion.
26 */
27
28 #include <linux/mm.h>
29 #include <linux/module.h>
30 #include <linux/math64.h>
31 #include <net/tcp.h>
32 #include <linux/inet_diag.h>
33
34 /* TCP NV parameters
35 *
36 * nv_pad Max number of queued packets allowed in network
37 * nv_pad_buffer Do not grow cwnd if this closed to nv_pad
38 * nv_reset_period How often (in) seconds)to reset min_rtt
39 * nv_min_cwnd Don't decrease cwnd below this if there are no losses
40 * nv_cong_dec_mult Decrease cwnd by X% (30%) of congestion when detected
41 * nv_ssthresh_factor On congestion set ssthresh to this * <desired cwnd> / 8
42 * nv_rtt_factor RTT averaging factor
43 * nv_loss_dec_factor Decrease cwnd to this (80%) when losses occur
44 * nv_dec_eval_min_calls Wait this many RTT measurements before dec cwnd
45 * nv_inc_eval_min_calls Wait this many RTT measurements before inc cwnd
46 * nv_ssthresh_eval_min_calls Wait this many RTT measurements before stopping
47 * slow-start due to congestion
48 * nv_stop_rtt_cnt Only grow cwnd for this many RTTs after non-congestion
49 * nv_rtt_min_cnt Wait these many RTTs before making congesion decision
50 * nv_cwnd_growth_rate_neg
51 * nv_cwnd_growth_rate_pos
52 * How quickly to double growth rate (not rate) of cwnd when not
53 * congested. One value (nv_cwnd_growth_rate_neg) for when
54 * rate < 1 pkt/RTT (after losses). The other (nv_cwnd_growth_rate_pos)
55 * otherwise.
56 */
57
58 static int nv_pad __read_mostly = 10;
59 static int nv_pad_buffer __read_mostly = 2;
60 static int nv_reset_period __read_mostly = 5; /* in seconds */
61 static int nv_min_cwnd __read_mostly = 2;
62 static int nv_cong_dec_mult __read_mostly = 30 * 128 / 100; /* = 30% */
63 static int nv_ssthresh_factor __read_mostly = 8; /* = 1 */
64 static int nv_rtt_factor __read_mostly = 128; /* = 1/2*old + 1/2*new */
65 static int nv_loss_dec_factor __read_mostly = 819; /* => 80% */
66 static int nv_cwnd_growth_rate_neg __read_mostly = 8;
67 static int nv_cwnd_growth_rate_pos __read_mostly; /* 0 => fixed like Reno */
68 static int nv_dec_eval_min_calls __read_mostly = 60;
69 static int nv_inc_eval_min_calls __read_mostly = 20;
70 static int nv_ssthresh_eval_min_calls __read_mostly = 30;
71 static int nv_stop_rtt_cnt __read_mostly = 10;
72 static int nv_rtt_min_cnt __read_mostly = 2;
73
74 module_param(nv_pad, int, 0644);
75 MODULE_PARM_DESC(nv_pad, "max queued packets allowed in network");
76 module_param(nv_reset_period, int, 0644);
77 MODULE_PARM_DESC(nv_reset_period, "nv_min_rtt reset period (secs)");
78 module_param(nv_min_cwnd, int, 0644);
79 MODULE_PARM_DESC(nv_min_cwnd, "NV will not decrease cwnd below this value"
80 " without losses");
81
82 /* TCP NV Parameters */
83 struct tcpnv {
84 unsigned long nv_min_rtt_reset_jiffies; /* when to switch to
85 * nv_min_rtt_new */
86 s8 cwnd_growth_factor; /* Current cwnd growth factor,
87 * < 0 => less than 1 packet/RTT */
88 u8 available8;
89 u16 available16;
90 u8 nv_allow_cwnd_growth:1, /* whether cwnd can grow */
91 nv_reset:1, /* whether to reset values */
92 nv_catchup:1; /* whether we are growing because
93 * of temporary cwnd decrease */
94 u8 nv_eval_call_cnt; /* call count since last eval */
95 u8 nv_min_cwnd; /* nv won't make a ca decision if cwnd is
96 * smaller than this. It may grow to handle
97 * TSO, LRO and interrupt coalescence because
98 * with these a small cwnd cannot saturate
99 * the link. Note that this is different from
100 * the file local nv_min_cwnd */
101 u8 nv_rtt_cnt; /* RTTs without making ca decision */;
102 u32 nv_last_rtt; /* last rtt */
103 u32 nv_min_rtt; /* active min rtt. Used to determine slope */
104 u32 nv_min_rtt_new; /* min rtt for future use */
105 u32 nv_base_rtt; /* If non-zero it represents the threshold for
106 * congestion */
107 u32 nv_lower_bound_rtt; /* Used in conjunction with nv_base_rtt. It is
108 * set to 80% of nv_base_rtt. It helps reduce
109 * unfairness between flows */
110 u32 nv_rtt_max_rate; /* max rate seen during current RTT */
111 u32 nv_rtt_start_seq; /* current RTT ends when packet arrives
112 * acking beyond nv_rtt_start_seq */
113 u32 nv_last_snd_una; /* Previous value of tp->snd_una. It is
114 * used to determine bytes acked since last
115 * call to bictcp_acked */
116 u32 nv_no_cong_cnt; /* Consecutive no congestion decisions */
117 };
118
119 #define NV_INIT_RTT U32_MAX
120 #define NV_MIN_CWND 4
121 #define NV_MIN_CWND_GROW 2
122 #define NV_TSO_CWND_BOUND 80
123
124 static inline void tcpnv_reset(struct tcpnv *ca, struct sock *sk)
125 {
126 struct tcp_sock *tp = tcp_sk(sk);
127
128 ca->nv_reset = 0;
129 ca->nv_no_cong_cnt = 0;
130 ca->nv_rtt_cnt = 0;
131 ca->nv_last_rtt = 0;
132 ca->nv_rtt_max_rate = 0;
133 ca->nv_rtt_start_seq = tp->snd_una;
134 ca->nv_eval_call_cnt = 0;
135 ca->nv_last_snd_una = tp->snd_una;
136 }
137
138 static void tcpnv_init(struct sock *sk)
139 {
140 struct tcpnv *ca = inet_csk_ca(sk);
141 int base_rtt;
142
143 tcpnv_reset(ca, sk);
144
145 /* See if base_rtt is available from socket_ops bpf program.
146 * It is meant to be used in environments, such as communication
147 * within a datacenter, where we have reasonable estimates of
148 * RTTs
149 */
150 base_rtt = tcp_call_bpf(sk, BPF_SOCK_OPS_BASE_RTT, 0, NULL);
151 if (base_rtt > 0) {
152 ca->nv_base_rtt = base_rtt;
153 ca->nv_lower_bound_rtt = (base_rtt * 205) >> 8; /* 80% */
154 } else {
155 ca->nv_base_rtt = 0;
156 ca->nv_lower_bound_rtt = 0;
157 }
158
159 ca->nv_allow_cwnd_growth = 1;
160 ca->nv_min_rtt_reset_jiffies = jiffies + 2 * HZ;
161 ca->nv_min_rtt = NV_INIT_RTT;
162 ca->nv_min_rtt_new = NV_INIT_RTT;
163 ca->nv_min_cwnd = NV_MIN_CWND;
164 ca->nv_catchup = 0;
165 ca->cwnd_growth_factor = 0;
166 }
167
168 /* If provided, apply upper (base_rtt) and lower (lower_bound_rtt)
169 * bounds to RTT.
170 */
171 inline u32 nv_get_bounded_rtt(struct tcpnv *ca, u32 val)
172 {
173 if (ca->nv_lower_bound_rtt > 0 && val < ca->nv_lower_bound_rtt)
174 return ca->nv_lower_bound_rtt;
175 else if (ca->nv_base_rtt > 0 && val > ca->nv_base_rtt)
176 return ca->nv_base_rtt;
177 else
178 return val;
179 }
180
181 static void tcpnv_cong_avoid(struct sock *sk, u32 ack, u32 acked)
182 {
183 struct tcp_sock *tp = tcp_sk(sk);
184 struct tcpnv *ca = inet_csk_ca(sk);
185 u32 cnt;
186
187 if (!tcp_is_cwnd_limited(sk))
188 return;
189
190 /* Only grow cwnd if NV has not detected congestion */
191 if (!ca->nv_allow_cwnd_growth)
192 return;
193
194 if (tcp_in_slow_start(tp)) {
195 acked = tcp_slow_start(tp, acked);
196 if (!acked)
197 return;
198 }
199
200 if (ca->cwnd_growth_factor < 0) {
201 cnt = tp->snd_cwnd << -ca->cwnd_growth_factor;
202 tcp_cong_avoid_ai(tp, cnt, acked);
203 } else {
204 cnt = max(4U, tp->snd_cwnd >> ca->cwnd_growth_factor);
205 tcp_cong_avoid_ai(tp, cnt, acked);
206 }
207 }
208
209 static u32 tcpnv_recalc_ssthresh(struct sock *sk)
210 {
211 const struct tcp_sock *tp = tcp_sk(sk);
212
213 return max((tp->snd_cwnd * nv_loss_dec_factor) >> 10, 2U);
214 }
215
216 static void tcpnv_state(struct sock *sk, u8 new_state)
217 {
218 struct tcpnv *ca = inet_csk_ca(sk);
219
220 if (new_state == TCP_CA_Open && ca->nv_reset) {
221 tcpnv_reset(ca, sk);
222 } else if (new_state == TCP_CA_Loss || new_state == TCP_CA_CWR ||
223 new_state == TCP_CA_Recovery) {
224 ca->nv_reset = 1;
225 ca->nv_allow_cwnd_growth = 0;
226 if (new_state == TCP_CA_Loss) {
227 /* Reset cwnd growth factor to Reno value */
228 if (ca->cwnd_growth_factor > 0)
229 ca->cwnd_growth_factor = 0;
230 /* Decrease growth rate if allowed */
231 if (nv_cwnd_growth_rate_neg > 0 &&
232 ca->cwnd_growth_factor > -8)
233 ca->cwnd_growth_factor--;
234 }
235 }
236 }
237
238 /* Do congestion avoidance calculations for TCP-NV
239 */
240 static void tcpnv_acked(struct sock *sk, const struct ack_sample *sample)
241 {
242 const struct inet_connection_sock *icsk = inet_csk(sk);
243 struct tcp_sock *tp = tcp_sk(sk);
244 struct tcpnv *ca = inet_csk_ca(sk);
245 unsigned long now = jiffies;
246 u64 rate64;
247 u32 rate, max_win, cwnd_by_slope;
248 u32 avg_rtt;
249 u32 bytes_acked = 0;
250
251 /* Some calls are for duplicates without timetamps */
252 if (sample->rtt_us < 0)
253 return;
254
255 /* If not in TCP_CA_Open or TCP_CA_Disorder states, skip. */
256 if (icsk->icsk_ca_state != TCP_CA_Open &&
257 icsk->icsk_ca_state != TCP_CA_Disorder)
258 return;
259
260 /* Stop cwnd growth if we were in catch up mode */
261 if (ca->nv_catchup && tp->snd_cwnd >= nv_min_cwnd) {
262 ca->nv_catchup = 0;
263 ca->nv_allow_cwnd_growth = 0;
264 }
265
266 bytes_acked = tp->snd_una - ca->nv_last_snd_una;
267 ca->nv_last_snd_una = tp->snd_una;
268
269 if (sample->in_flight == 0)
270 return;
271
272 /* Calculate moving average of RTT */
273 if (nv_rtt_factor > 0) {
274 if (ca->nv_last_rtt > 0) {
275 avg_rtt = (((u64)sample->rtt_us) * nv_rtt_factor +
276 ((u64)ca->nv_last_rtt)
277 * (256 - nv_rtt_factor)) >> 8;
278 } else {
279 avg_rtt = sample->rtt_us;
280 ca->nv_min_rtt = avg_rtt << 1;
281 }
282 ca->nv_last_rtt = avg_rtt;
283 } else {
284 avg_rtt = sample->rtt_us;
285 }
286
287 /* rate in 100's bits per second */
288 rate64 = ((u64)sample->in_flight) * 80000;
289 do_div(rate64, avg_rtt ?: 1);
290 rate = (u32)rate64;
291
292 /* Remember the maximum rate seen during this RTT
293 * Note: It may be more than one RTT. This function should be
294 * called at least nv_dec_eval_min_calls times.
295 */
296 if (ca->nv_rtt_max_rate < rate)
297 ca->nv_rtt_max_rate = rate;
298
299 /* We have valid information, increment counter */
300 if (ca->nv_eval_call_cnt < 255)
301 ca->nv_eval_call_cnt++;
302
303 /* Apply bounds to rtt. Only used to update min_rtt */
304 avg_rtt = nv_get_bounded_rtt(ca, avg_rtt);
305
306 /* update min rtt if necessary */
307 if (avg_rtt < ca->nv_min_rtt)
308 ca->nv_min_rtt = avg_rtt;
309
310 /* update future min_rtt if necessary */
311 if (avg_rtt < ca->nv_min_rtt_new)
312 ca->nv_min_rtt_new = avg_rtt;
313
314 /* nv_min_rtt is updated with the minimum (possibley averaged) rtt
315 * seen in the last sysctl_tcp_nv_reset_period seconds (i.e. a
316 * warm reset). This new nv_min_rtt will be continued to be updated
317 * and be used for another sysctl_tcp_nv_reset_period seconds,
318 * when it will be updated again.
319 * In practice we introduce some randomness, so the actual period used
320 * is chosen randomly from the range:
321 * [sysctl_tcp_nv_reset_period*3/4, sysctl_tcp_nv_reset_period*5/4)
322 */
323 if (time_after_eq(now, ca->nv_min_rtt_reset_jiffies)) {
324 unsigned char rand;
325
326 ca->nv_min_rtt = ca->nv_min_rtt_new;
327 ca->nv_min_rtt_new = NV_INIT_RTT;
328 get_random_bytes(&rand, 1);
329 ca->nv_min_rtt_reset_jiffies =
330 now + ((nv_reset_period * (384 + rand) * HZ) >> 9);
331 /* Every so often we decrease ca->nv_min_cwnd in case previous
332 * value is no longer accurate.
333 */
334 ca->nv_min_cwnd = max(ca->nv_min_cwnd / 2, NV_MIN_CWND);
335 }
336
337 /* Once per RTT check if we need to do congestion avoidance */
338 if (before(ca->nv_rtt_start_seq, tp->snd_una)) {
339 ca->nv_rtt_start_seq = tp->snd_nxt;
340 if (ca->nv_rtt_cnt < 0xff)
341 /* Increase counter for RTTs without CA decision */
342 ca->nv_rtt_cnt++;
343
344 /* If this function is only called once within an RTT
345 * the cwnd is probably too small (in some cases due to
346 * tso, lro or interrupt coalescence), so we increase
347 * ca->nv_min_cwnd.
348 */
349 if (ca->nv_eval_call_cnt == 1 &&
350 bytes_acked >= (ca->nv_min_cwnd - 1) * tp->mss_cache &&
351 ca->nv_min_cwnd < (NV_TSO_CWND_BOUND + 1)) {
352 ca->nv_min_cwnd = min(ca->nv_min_cwnd
353 + NV_MIN_CWND_GROW,
354 NV_TSO_CWND_BOUND + 1);
355 ca->nv_rtt_start_seq = tp->snd_nxt +
356 ca->nv_min_cwnd * tp->mss_cache;
357 ca->nv_eval_call_cnt = 0;
358 ca->nv_allow_cwnd_growth = 1;
359 return;
360 }
361
362 /* Find the ideal cwnd for current rate from slope
363 * slope = 80000.0 * mss / nv_min_rtt
364 * cwnd_by_slope = nv_rtt_max_rate / slope
365 */
366 cwnd_by_slope = (u32)
367 div64_u64(((u64)ca->nv_rtt_max_rate) * ca->nv_min_rtt,
368 80000ULL * tp->mss_cache);
369 max_win = cwnd_by_slope + nv_pad;
370
371 /* If cwnd > max_win, decrease cwnd
372 * if cwnd < max_win, grow cwnd
373 * else leave the same
374 */
375 if (tp->snd_cwnd > max_win) {
376 /* there is congestion, check that it is ok
377 * to make a CA decision
378 * 1. We should have at least nv_dec_eval_min_calls
379 * data points before making a CA decision
380 * 2. We only make a congesion decision after
381 * nv_rtt_min_cnt RTTs
382 */
383 if (ca->nv_rtt_cnt < nv_rtt_min_cnt) {
384 return;
385 } else if (tp->snd_ssthresh == TCP_INFINITE_SSTHRESH) {
386 if (ca->nv_eval_call_cnt <
387 nv_ssthresh_eval_min_calls)
388 return;
389 /* otherwise we will decrease cwnd */
390 } else if (ca->nv_eval_call_cnt <
391 nv_dec_eval_min_calls) {
392 if (ca->nv_allow_cwnd_growth &&
393 ca->nv_rtt_cnt > nv_stop_rtt_cnt)
394 ca->nv_allow_cwnd_growth = 0;
395 return;
396 }
397
398 /* We have enough data to determine we are congested */
399 ca->nv_allow_cwnd_growth = 0;
400 tp->snd_ssthresh =
401 (nv_ssthresh_factor * max_win) >> 3;
402 if (tp->snd_cwnd - max_win > 2) {
403 /* gap > 2, we do exponential cwnd decrease */
404 int dec;
405
406 dec = max(2U, ((tp->snd_cwnd - max_win) *
407 nv_cong_dec_mult) >> 7);
408 tp->snd_cwnd -= dec;
409 } else if (nv_cong_dec_mult > 0) {
410 tp->snd_cwnd = max_win;
411 }
412 if (ca->cwnd_growth_factor > 0)
413 ca->cwnd_growth_factor = 0;
414 ca->nv_no_cong_cnt = 0;
415 } else if (tp->snd_cwnd <= max_win - nv_pad_buffer) {
416 /* There is no congestion, grow cwnd if allowed*/
417 if (ca->nv_eval_call_cnt < nv_inc_eval_min_calls)
418 return;
419
420 ca->nv_allow_cwnd_growth = 1;
421 ca->nv_no_cong_cnt++;
422 if (ca->cwnd_growth_factor < 0 &&
423 nv_cwnd_growth_rate_neg > 0 &&
424 ca->nv_no_cong_cnt > nv_cwnd_growth_rate_neg) {
425 ca->cwnd_growth_factor++;
426 ca->nv_no_cong_cnt = 0;
427 } else if (ca->cwnd_growth_factor >= 0 &&
428 nv_cwnd_growth_rate_pos > 0 &&
429 ca->nv_no_cong_cnt >
430 nv_cwnd_growth_rate_pos) {
431 ca->cwnd_growth_factor++;
432 ca->nv_no_cong_cnt = 0;
433 }
434 } else {
435 /* cwnd is in-between, so do nothing */
436 return;
437 }
438
439 /* update state */
440 ca->nv_eval_call_cnt = 0;
441 ca->nv_rtt_cnt = 0;
442 ca->nv_rtt_max_rate = 0;
443
444 /* Don't want to make cwnd < nv_min_cwnd
445 * (it wasn't before, if it is now is because nv
446 * decreased it).
447 */
448 if (tp->snd_cwnd < nv_min_cwnd)
449 tp->snd_cwnd = nv_min_cwnd;
450 }
451 }
452
453 /* Extract info for Tcp socket info provided via netlink */
454 static size_t tcpnv_get_info(struct sock *sk, u32 ext, int *attr,
455 union tcp_cc_info *info)
456 {
457 const struct tcpnv *ca = inet_csk_ca(sk);
458
459 if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
460 info->vegas.tcpv_enabled = 1;
461 info->vegas.tcpv_rttcnt = ca->nv_rtt_cnt;
462 info->vegas.tcpv_rtt = ca->nv_last_rtt;
463 info->vegas.tcpv_minrtt = ca->nv_min_rtt;
464
465 *attr = INET_DIAG_VEGASINFO;
466 return sizeof(struct tcpvegas_info);
467 }
468 return 0;
469 }
470
471 static struct tcp_congestion_ops tcpnv __read_mostly = {
472 .init = tcpnv_init,
473 .ssthresh = tcpnv_recalc_ssthresh,
474 .cong_avoid = tcpnv_cong_avoid,
475 .set_state = tcpnv_state,
476 .undo_cwnd = tcp_reno_undo_cwnd,
477 .pkts_acked = tcpnv_acked,
478 .get_info = tcpnv_get_info,
479
480 .owner = THIS_MODULE,
481 .name = "nv",
482 };
483
484 static int __init tcpnv_register(void)
485 {
486 BUILD_BUG_ON(sizeof(struct tcpnv) > ICSK_CA_PRIV_SIZE);
487
488 return tcp_register_congestion_control(&tcpnv);
489 }
490
491 static void __exit tcpnv_unregister(void)
492 {
493 tcp_unregister_congestion_control(&tcpnv);
494 }
495
496 module_init(tcpnv_register);
497 module_exit(tcpnv_unregister);
498
499 MODULE_AUTHOR("Lawrence Brakmo");
500 MODULE_LICENSE("GPL");
501 MODULE_DESCRIPTION("TCP NV");
502 MODULE_VERSION("1.0");