Merge branch 'etnaviv/fixes' of https://git.pengutronix.de/git/lst/linux into drm...
[linux-2.6-microblaze.git] / net / ipv4 / tcp_nv.c
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");