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1// SPDX-License-Identifier: GPL-2.0-or-later
2/* DataCenter TCP (DCTCP) congestion control.
3 *
4 * http://simula.stanford.edu/~alizade/Site/DCTCP.html
5 *
6 * This is an implementation of DCTCP over Reno, an enhancement to the
7 * TCP congestion control algorithm designed for data centers. DCTCP
8 * leverages Explicit Congestion Notification (ECN) in the network to
9 * provide multi-bit feedback to the end hosts. DCTCP's goal is to meet
10 * the following three data center transport requirements:
11 *
12 * - High burst tolerance (incast due to partition/aggregate)
13 * - Low latency (short flows, queries)
14 * - High throughput (continuous data updates, large file transfers)
15 * with commodity shallow buffered switches
16 *
17 * The algorithm is described in detail in the following two papers:
18 *
19 * 1) Mohammad Alizadeh, Albert Greenberg, David A. Maltz, Jitendra Padhye,
20 * Parveen Patel, Balaji Prabhakar, Sudipta Sengupta, and Murari Sridharan:
21 * "Data Center TCP (DCTCP)", Data Center Networks session
22 * Proc. ACM SIGCOMM, New Delhi, 2010.
23 * http://simula.stanford.edu/~alizade/Site/DCTCP_files/dctcp-final.pdf
24 *
25 * 2) Mohammad Alizadeh, Adel Javanmard, and Balaji Prabhakar:
26 * "Analysis of DCTCP: Stability, Convergence, and Fairness"
27 * Proc. ACM SIGMETRICS, San Jose, 2011.
28 * http://simula.stanford.edu/~alizade/Site/DCTCP_files/dctcp_analysis-full.pdf
29 *
30 * Initial prototype from Abdul Kabbani, Masato Yasuda and Mohammad Alizadeh.
31 *
32 * Authors:
33 *
34 * Daniel Borkmann <dborkman@redhat.com>
35 * Florian Westphal <fw@strlen.de>
36 * Glenn Judd <glenn.judd@morganstanley.com>
37 */
38
39#include <linux/btf.h>
40#include <linux/btf_ids.h>
41#include <linux/module.h>
42#include <linux/mm.h>
43#include <net/tcp.h>
44#include <linux/inet_diag.h>
45#include "tcp_dctcp.h"
46
47#define DCTCP_MAX_ALPHA 1024U
48
49struct dctcp {
50 u32 old_delivered;
51 u32 old_delivered_ce;
52 u32 prior_rcv_nxt;
53 u32 dctcp_alpha;
54 u32 next_seq;
55 u32 ce_state;
56 u32 loss_cwnd;
57 struct tcp_plb_state plb;
58};
59
60static unsigned int dctcp_shift_g __read_mostly = 4; /* g = 1/2^4 */
61module_param(dctcp_shift_g, uint, 0644);
62MODULE_PARM_DESC(dctcp_shift_g, "parameter g for updating dctcp_alpha");
63
64static unsigned int dctcp_alpha_on_init __read_mostly = DCTCP_MAX_ALPHA;
65module_param(dctcp_alpha_on_init, uint, 0644);
66MODULE_PARM_DESC(dctcp_alpha_on_init, "parameter for initial alpha value");
67
68static struct tcp_congestion_ops dctcp_reno;
69
70static void dctcp_reset(const struct tcp_sock *tp, struct dctcp *ca)
71{
72 ca->next_seq = tp->snd_nxt;
73
74 ca->old_delivered = tp->delivered;
75 ca->old_delivered_ce = tp->delivered_ce;
76}
77
78__bpf_kfunc static void dctcp_init(struct sock *sk)
79{
80 const struct tcp_sock *tp = tcp_sk(sk);
81
82 if ((tp->ecn_flags & TCP_ECN_OK) ||
83 (sk->sk_state == TCP_LISTEN ||
84 sk->sk_state == TCP_CLOSE)) {
85 struct dctcp *ca = inet_csk_ca(sk);
86
87 ca->prior_rcv_nxt = tp->rcv_nxt;
88
89 ca->dctcp_alpha = min(dctcp_alpha_on_init, DCTCP_MAX_ALPHA);
90
91 ca->loss_cwnd = 0;
92 ca->ce_state = 0;
93
94 dctcp_reset(tp, ca);
95 tcp_plb_init(sk, &ca->plb);
96
97 return;
98 }
99
100 /* No ECN support? Fall back to Reno. Also need to clear
101 * ECT from sk since it is set during 3WHS for DCTCP.
102 */
103 inet_csk(sk)->icsk_ca_ops = &dctcp_reno;
104 INET_ECN_dontxmit(sk);
105}
106
107__bpf_kfunc static u32 dctcp_ssthresh(struct sock *sk)
108{
109 struct dctcp *ca = inet_csk_ca(sk);
110 struct tcp_sock *tp = tcp_sk(sk);
111
112 ca->loss_cwnd = tcp_snd_cwnd(tp);
113 return max(tcp_snd_cwnd(tp) - ((tcp_snd_cwnd(tp) * ca->dctcp_alpha) >> 11U), 2U);
114}
115
116__bpf_kfunc static void dctcp_update_alpha(struct sock *sk, u32 flags)
117{
118 const struct tcp_sock *tp = tcp_sk(sk);
119 struct dctcp *ca = inet_csk_ca(sk);
120
121 /* Expired RTT */
122 if (!before(tp->snd_una, ca->next_seq)) {
123 u32 delivered = tp->delivered - ca->old_delivered;
124 u32 delivered_ce = tp->delivered_ce - ca->old_delivered_ce;
125 u32 alpha = ca->dctcp_alpha;
126 u32 ce_ratio = 0;
127
128 if (delivered > 0) {
129 /* dctcp_alpha keeps EWMA of fraction of ECN marked
130 * packets. Because of EWMA smoothing, PLB reaction can
131 * be slow so we use ce_ratio which is an instantaneous
132 * measure of congestion. ce_ratio is the fraction of
133 * ECN marked packets in the previous RTT.
134 */
135 if (delivered_ce > 0)
136 ce_ratio = (delivered_ce << TCP_PLB_SCALE) / delivered;
137 tcp_plb_update_state(sk, &ca->plb, (int)ce_ratio);
138 tcp_plb_check_rehash(sk, &ca->plb);
139 }
140
141 /* alpha = (1 - g) * alpha + g * F */
142
143 alpha -= min_not_zero(alpha, alpha >> dctcp_shift_g);
144 if (delivered_ce) {
145
146 /* If dctcp_shift_g == 1, a 32bit value would overflow
147 * after 8 M packets.
148 */
149 delivered_ce <<= (10 - dctcp_shift_g);
150 delivered_ce /= max(1U, delivered);
151
152 alpha = min(alpha + delivered_ce, DCTCP_MAX_ALPHA);
153 }
154 /* dctcp_alpha can be read from dctcp_get_info() without
155 * synchro, so we ask compiler to not use dctcp_alpha
156 * as a temporary variable in prior operations.
157 */
158 WRITE_ONCE(ca->dctcp_alpha, alpha);
159 dctcp_reset(tp, ca);
160 }
161}
162
163static void dctcp_react_to_loss(struct sock *sk)
164{
165 struct dctcp *ca = inet_csk_ca(sk);
166 struct tcp_sock *tp = tcp_sk(sk);
167
168 ca->loss_cwnd = tcp_snd_cwnd(tp);
169 tp->snd_ssthresh = max(tcp_snd_cwnd(tp) >> 1U, 2U);
170}
171
172__bpf_kfunc static void dctcp_state(struct sock *sk, u8 new_state)
173{
174 if (new_state == TCP_CA_Recovery &&
175 new_state != inet_csk(sk)->icsk_ca_state)
176 dctcp_react_to_loss(sk);
177 /* We handle RTO in dctcp_cwnd_event to ensure that we perform only
178 * one loss-adjustment per RTT.
179 */
180}
181
182__bpf_kfunc static void dctcp_cwnd_event(struct sock *sk, enum tcp_ca_event ev)
183{
184 struct dctcp *ca = inet_csk_ca(sk);
185
186 switch (ev) {
187 case CA_EVENT_ECN_IS_CE:
188 case CA_EVENT_ECN_NO_CE:
189 dctcp_ece_ack_update(sk, ev, &ca->prior_rcv_nxt, &ca->ce_state);
190 break;
191 case CA_EVENT_LOSS:
192 tcp_plb_update_state_upon_rto(sk, &ca->plb);
193 dctcp_react_to_loss(sk);
194 break;
195 case CA_EVENT_TX_START:
196 tcp_plb_check_rehash(sk, &ca->plb); /* Maybe rehash when inflight is 0 */
197 break;
198 default:
199 /* Don't care for the rest. */
200 break;
201 }
202}
203
204static size_t dctcp_get_info(struct sock *sk, u32 ext, int *attr,
205 union tcp_cc_info *info)
206{
207 const struct dctcp *ca = inet_csk_ca(sk);
208 const struct tcp_sock *tp = tcp_sk(sk);
209
210 /* Fill it also in case of VEGASINFO due to req struct limits.
211 * We can still correctly retrieve it later.
212 */
213 if (ext & (1 << (INET_DIAG_DCTCPINFO - 1)) ||
214 ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
215 memset(&info->dctcp, 0, sizeof(info->dctcp));
216 if (inet_csk(sk)->icsk_ca_ops != &dctcp_reno) {
217 info->dctcp.dctcp_enabled = 1;
218 info->dctcp.dctcp_ce_state = (u16) ca->ce_state;
219 info->dctcp.dctcp_alpha = ca->dctcp_alpha;
220 info->dctcp.dctcp_ab_ecn = tp->mss_cache *
221 (tp->delivered_ce - ca->old_delivered_ce);
222 info->dctcp.dctcp_ab_tot = tp->mss_cache *
223 (tp->delivered - ca->old_delivered);
224 }
225
226 *attr = INET_DIAG_DCTCPINFO;
227 return sizeof(info->dctcp);
228 }
229 return 0;
230}
231
232__bpf_kfunc static u32 dctcp_cwnd_undo(struct sock *sk)
233{
234 const struct dctcp *ca = inet_csk_ca(sk);
235 struct tcp_sock *tp = tcp_sk(sk);
236
237 return max(tcp_snd_cwnd(tp), ca->loss_cwnd);
238}
239
240static struct tcp_congestion_ops dctcp __read_mostly = {
241 .init = dctcp_init,
242 .in_ack_event = dctcp_update_alpha,
243 .cwnd_event = dctcp_cwnd_event,
244 .ssthresh = dctcp_ssthresh,
245 .cong_avoid = tcp_reno_cong_avoid,
246 .undo_cwnd = dctcp_cwnd_undo,
247 .set_state = dctcp_state,
248 .get_info = dctcp_get_info,
249 .flags = TCP_CONG_NEEDS_ECN,
250 .owner = THIS_MODULE,
251 .name = "dctcp",
252};
253
254static struct tcp_congestion_ops dctcp_reno __read_mostly = {
255 .ssthresh = tcp_reno_ssthresh,
256 .cong_avoid = tcp_reno_cong_avoid,
257 .undo_cwnd = tcp_reno_undo_cwnd,
258 .get_info = dctcp_get_info,
259 .owner = THIS_MODULE,
260 .name = "dctcp-reno",
261};
262
263BTF_SET8_START(tcp_dctcp_check_kfunc_ids)
264#ifdef CONFIG_X86
265#ifdef CONFIG_DYNAMIC_FTRACE
266BTF_ID_FLAGS(func, dctcp_init)
267BTF_ID_FLAGS(func, dctcp_update_alpha)
268BTF_ID_FLAGS(func, dctcp_cwnd_event)
269BTF_ID_FLAGS(func, dctcp_ssthresh)
270BTF_ID_FLAGS(func, dctcp_cwnd_undo)
271BTF_ID_FLAGS(func, dctcp_state)
272#endif
273#endif
274BTF_SET8_END(tcp_dctcp_check_kfunc_ids)
275
276static const struct btf_kfunc_id_set tcp_dctcp_kfunc_set = {
277 .owner = THIS_MODULE,
278 .set = &tcp_dctcp_check_kfunc_ids,
279};
280
281static int __init dctcp_register(void)
282{
283 int ret;
284
285 BUILD_BUG_ON(sizeof(struct dctcp) > ICSK_CA_PRIV_SIZE);
286
287 ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &tcp_dctcp_kfunc_set);
288 if (ret < 0)
289 return ret;
290 return tcp_register_congestion_control(&dctcp);
291}
292
293static void __exit dctcp_unregister(void)
294{
295 tcp_unregister_congestion_control(&dctcp);
296}
297
298module_init(dctcp_register);
299module_exit(dctcp_unregister);
300
301MODULE_AUTHOR("Daniel Borkmann <dborkman@redhat.com>");
302MODULE_AUTHOR("Florian Westphal <fw@strlen.de>");
303MODULE_AUTHOR("Glenn Judd <glenn.judd@morganstanley.com>");
304
305MODULE_LICENSE("GPL v2");
306MODULE_DESCRIPTION("DataCenter TCP (DCTCP)");