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