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2874c5fd | 1 | // SPDX-License-Identifier: GPL-2.0-or-later |
e3118e83 DB |
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> | |
e3118e83 DB |
37 | */ |
38 | ||
0e32dfc8 KKD |
39 | #include <linux/btf.h> |
40 | #include <linux/btf_ids.h> | |
e3118e83 DB |
41 | #include <linux/module.h> |
42 | #include <linux/mm.h> | |
43 | #include <net/tcp.h> | |
44 | #include <linux/inet_diag.h> | |
ffd177de | 45 | #include "tcp_dctcp.h" |
e3118e83 DB |
46 | |
47 | #define DCTCP_MAX_ALPHA 1024U | |
48 | ||
49 | struct dctcp { | |
e3058450 ED |
50 | u32 old_delivered; |
51 | u32 old_delivered_ce; | |
e3118e83 DB |
52 | u32 prior_rcv_nxt; |
53 | u32 dctcp_alpha; | |
54 | u32 next_seq; | |
55 | u32 ce_state; | |
ce6dd233 | 56 | u32 loss_cwnd; |
c30f8e0b | 57 | struct tcp_plb_state plb; |
e3118e83 DB |
58 | }; |
59 | ||
60 | static unsigned int dctcp_shift_g __read_mostly = 4; /* g = 1/2^4 */ | |
61 | module_param(dctcp_shift_g, uint, 0644); | |
62 | MODULE_PARM_DESC(dctcp_shift_g, "parameter g for updating dctcp_alpha"); | |
63 | ||
64 | static unsigned int dctcp_alpha_on_init __read_mostly = DCTCP_MAX_ALPHA; | |
65 | module_param(dctcp_alpha_on_init, uint, 0644); | |
66 | MODULE_PARM_DESC(dctcp_alpha_on_init, "parameter for initial alpha value"); | |
67 | ||
e3118e83 DB |
68 | static struct tcp_congestion_ops dctcp_reno; |
69 | ||
70 | static void dctcp_reset(const struct tcp_sock *tp, struct dctcp *ca) | |
71 | { | |
72 | ca->next_seq = tp->snd_nxt; | |
73 | ||
e3058450 ED |
74 | ca->old_delivered = tp->delivered; |
75 | ca->old_delivered_ce = tp->delivered_ce; | |
e3118e83 DB |
76 | } |
77 | ||
400031e0 | 78 | __bpf_kfunc static void dctcp_init(struct sock *sk) |
e3118e83 DB |
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 | ||
e3118e83 DB |
87 | ca->prior_rcv_nxt = tp->rcv_nxt; |
88 | ||
89 | ca->dctcp_alpha = min(dctcp_alpha_on_init, DCTCP_MAX_ALPHA); | |
90 | ||
ce6dd233 | 91 | ca->loss_cwnd = 0; |
e3118e83 DB |
92 | ca->ce_state = 0; |
93 | ||
94 | dctcp_reset(tp, ca); | |
c30f8e0b MAQ |
95 | tcp_plb_init(sk, &ca->plb); |
96 | ||
e3118e83 DB |
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 | ||
400031e0 | 107 | __bpf_kfunc static u32 dctcp_ssthresh(struct sock *sk) |
e3118e83 | 108 | { |
ce6dd233 | 109 | struct dctcp *ca = inet_csk_ca(sk); |
e3118e83 DB |
110 | struct tcp_sock *tp = tcp_sk(sk); |
111 | ||
40570375 ED |
112 | ca->loss_cwnd = tcp_snd_cwnd(tp); |
113 | return max(tcp_snd_cwnd(tp) - ((tcp_snd_cwnd(tp) * ca->dctcp_alpha) >> 11U), 2U); | |
e3118e83 DB |
114 | } |
115 | ||
400031e0 | 116 | __bpf_kfunc static void dctcp_update_alpha(struct sock *sk, u32 flags) |
e3118e83 | 117 | { |
343dfaa1 | 118 | const struct tcp_sock *tp = tcp_sk(sk); |
e3118e83 | 119 | struct dctcp *ca = inet_csk_ca(sk); |
e3118e83 DB |
120 | |
121 | /* Expired RTT */ | |
122 | if (!before(tp->snd_una, ca->next_seq)) { | |
c30f8e0b | 123 | u32 delivered = tp->delivered - ca->old_delivered; |
e3058450 | 124 | u32 delivered_ce = tp->delivered_ce - ca->old_delivered_ce; |
f9c2ff22 | 125 | u32 alpha = ca->dctcp_alpha; |
c30f8e0b MAQ |
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 | } | |
e3118e83 DB |
140 | |
141 | /* alpha = (1 - g) * alpha + g * F */ | |
e3118e83 | 142 | |
c80dbe04 | 143 | alpha -= min_not_zero(alpha, alpha >> dctcp_shift_g); |
e3058450 | 144 | if (delivered_ce) { |
e3058450 | 145 | |
f9c2ff22 | 146 | /* If dctcp_shift_g == 1, a 32bit value would overflow |
e3058450 | 147 | * after 8 M packets. |
f9c2ff22 | 148 | */ |
e3058450 ED |
149 | delivered_ce <<= (10 - dctcp_shift_g); |
150 | delivered_ce /= max(1U, delivered); | |
f9c2ff22 | 151 | |
e3058450 | 152 | alpha = min(alpha + delivered_ce, DCTCP_MAX_ALPHA); |
f9c2ff22 ED |
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); | |
e3118e83 DB |
159 | dctcp_reset(tp, ca); |
160 | } | |
161 | } | |
162 | ||
aecfde23 | 163 | static void dctcp_react_to_loss(struct sock *sk) |
e3118e83 | 164 | { |
aecfde23 KDS |
165 | struct dctcp *ca = inet_csk_ca(sk); |
166 | struct tcp_sock *tp = tcp_sk(sk); | |
e3118e83 | 167 | |
40570375 ED |
168 | ca->loss_cwnd = tcp_snd_cwnd(tp); |
169 | tp->snd_ssthresh = max(tcp_snd_cwnd(tp) >> 1U, 2U); | |
aecfde23 KDS |
170 | } |
171 | ||
400031e0 | 172 | __bpf_kfunc static void dctcp_state(struct sock *sk, u8 new_state) |
aecfde23 KDS |
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 | */ | |
e3118e83 DB |
180 | } |
181 | ||
400031e0 | 182 | __bpf_kfunc static void dctcp_cwnd_event(struct sock *sk, enum tcp_ca_event ev) |
e3118e83 | 183 | { |
ffd177de YC |
184 | struct dctcp *ca = inet_csk_ca(sk); |
185 | ||
e3118e83 DB |
186 | switch (ev) { |
187 | case CA_EVENT_ECN_IS_CE: | |
e3118e83 | 188 | case CA_EVENT_ECN_NO_CE: |
ffd177de | 189 | dctcp_ece_ack_update(sk, ev, &ca->prior_rcv_nxt, &ca->ce_state); |
e3118e83 | 190 | break; |
aecfde23 | 191 | case CA_EVENT_LOSS: |
c30f8e0b | 192 | tcp_plb_update_state_upon_rto(sk, &ca->plb); |
aecfde23 KDS |
193 | dctcp_react_to_loss(sk); |
194 | break; | |
c30f8e0b MAQ |
195 | case CA_EVENT_TX_START: |
196 | tcp_plb_check_rehash(sk, &ca->plb); /* Maybe rehash when inflight is 0 */ | |
197 | break; | |
e3118e83 DB |
198 | default: |
199 | /* Don't care for the rest. */ | |
200 | break; | |
201 | } | |
202 | } | |
203 | ||
64f40ff5 ED |
204 | static size_t dctcp_get_info(struct sock *sk, u32 ext, int *attr, |
205 | union tcp_cc_info *info) | |
e3118e83 DB |
206 | { |
207 | const struct dctcp *ca = inet_csk_ca(sk); | |
e3058450 | 208 | const struct tcp_sock *tp = tcp_sk(sk); |
e3118e83 DB |
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))) { | |
dcf1158b | 215 | memset(&info->dctcp, 0, sizeof(info->dctcp)); |
e3118e83 | 216 | if (inet_csk(sk)->icsk_ca_ops != &dctcp_reno) { |
64f40ff5 ED |
217 | info->dctcp.dctcp_enabled = 1; |
218 | info->dctcp.dctcp_ce_state = (u16) ca->ce_state; | |
219 | info->dctcp.dctcp_alpha = ca->dctcp_alpha; | |
e3058450 ED |
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); | |
e3118e83 DB |
224 | } |
225 | ||
64f40ff5 | 226 | *attr = INET_DIAG_DCTCPINFO; |
dcf1158b | 227 | return sizeof(info->dctcp); |
e3118e83 | 228 | } |
521f1cf1 | 229 | return 0; |
e3118e83 DB |
230 | } |
231 | ||
400031e0 | 232 | __bpf_kfunc static u32 dctcp_cwnd_undo(struct sock *sk) |
ce6dd233 FW |
233 | { |
234 | const struct dctcp *ca = inet_csk_ca(sk); | |
40570375 | 235 | struct tcp_sock *tp = tcp_sk(sk); |
ce6dd233 | 236 | |
40570375 | 237 | return max(tcp_snd_cwnd(tp), ca->loss_cwnd); |
ce6dd233 FW |
238 | } |
239 | ||
e3118e83 DB |
240 | static 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, | |
ce6dd233 | 246 | .undo_cwnd = dctcp_cwnd_undo, |
e3118e83 DB |
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 | ||
254 | static struct tcp_congestion_ops dctcp_reno __read_mostly = { | |
255 | .ssthresh = tcp_reno_ssthresh, | |
256 | .cong_avoid = tcp_reno_cong_avoid, | |
e9799183 | 257 | .undo_cwnd = tcp_reno_undo_cwnd, |
e3118e83 DB |
258 | .get_info = dctcp_get_info, |
259 | .owner = THIS_MODULE, | |
260 | .name = "dctcp-reno", | |
261 | }; | |
262 | ||
a4703e31 | 263 | BTF_SET8_START(tcp_dctcp_check_kfunc_ids) |
0e32dfc8 KKD |
264 | #ifdef CONFIG_X86 |
265 | #ifdef CONFIG_DYNAMIC_FTRACE | |
a4703e31 KKD |
266 | BTF_ID_FLAGS(func, dctcp_init) |
267 | BTF_ID_FLAGS(func, dctcp_update_alpha) | |
268 | BTF_ID_FLAGS(func, dctcp_cwnd_event) | |
269 | BTF_ID_FLAGS(func, dctcp_ssthresh) | |
270 | BTF_ID_FLAGS(func, dctcp_cwnd_undo) | |
271 | BTF_ID_FLAGS(func, dctcp_state) | |
0e32dfc8 KKD |
272 | #endif |
273 | #endif | |
a4703e31 | 274 | BTF_SET8_END(tcp_dctcp_check_kfunc_ids) |
0e32dfc8 | 275 | |
b202d844 | 276 | static const struct btf_kfunc_id_set tcp_dctcp_kfunc_set = { |
a4703e31 KKD |
277 | .owner = THIS_MODULE, |
278 | .set = &tcp_dctcp_check_kfunc_ids, | |
b202d844 | 279 | }; |
0e32dfc8 | 280 | |
e3118e83 DB |
281 | static int __init dctcp_register(void) |
282 | { | |
0e32dfc8 KKD |
283 | int ret; |
284 | ||
e3118e83 | 285 | BUILD_BUG_ON(sizeof(struct dctcp) > ICSK_CA_PRIV_SIZE); |
b202d844 KKD |
286 | |
287 | ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &tcp_dctcp_kfunc_set); | |
288 | if (ret < 0) | |
0e32dfc8 | 289 | return ret; |
b202d844 | 290 | return tcp_register_congestion_control(&dctcp); |
e3118e83 DB |
291 | } |
292 | ||
293 | static void __exit dctcp_unregister(void) | |
294 | { | |
295 | tcp_unregister_congestion_control(&dctcp); | |
296 | } | |
297 | ||
298 | module_init(dctcp_register); | |
299 | module_exit(dctcp_unregister); | |
300 | ||
301 | MODULE_AUTHOR("Daniel Borkmann <dborkman@redhat.com>"); | |
302 | MODULE_AUTHOR("Florian Westphal <fw@strlen.de>"); | |
303 | MODULE_AUTHOR("Glenn Judd <glenn.judd@morganstanley.com>"); | |
304 | ||
305 | MODULE_LICENSE("GPL v2"); | |
306 | MODULE_DESCRIPTION("DataCenter TCP (DCTCP)"); |