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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 | ||
39 | #include <linux/module.h> | |
40 | #include <linux/mm.h> | |
41 | #include <net/tcp.h> | |
42 | #include <linux/inet_diag.h> | |
ffd177de | 43 | #include "tcp_dctcp.h" |
e3118e83 DB |
44 | |
45 | #define DCTCP_MAX_ALPHA 1024U | |
46 | ||
47 | struct dctcp { | |
e3058450 ED |
48 | u32 old_delivered; |
49 | u32 old_delivered_ce; | |
e3118e83 DB |
50 | u32 prior_rcv_nxt; |
51 | u32 dctcp_alpha; | |
52 | u32 next_seq; | |
53 | u32 ce_state; | |
ce6dd233 | 54 | u32 loss_cwnd; |
e3118e83 DB |
55 | }; |
56 | ||
57 | static unsigned int dctcp_shift_g __read_mostly = 4; /* g = 1/2^4 */ | |
58 | module_param(dctcp_shift_g, uint, 0644); | |
59 | MODULE_PARM_DESC(dctcp_shift_g, "parameter g for updating dctcp_alpha"); | |
60 | ||
61 | static unsigned int dctcp_alpha_on_init __read_mostly = DCTCP_MAX_ALPHA; | |
62 | module_param(dctcp_alpha_on_init, uint, 0644); | |
63 | MODULE_PARM_DESC(dctcp_alpha_on_init, "parameter for initial alpha value"); | |
64 | ||
e3118e83 DB |
65 | static struct tcp_congestion_ops dctcp_reno; |
66 | ||
67 | static void dctcp_reset(const struct tcp_sock *tp, struct dctcp *ca) | |
68 | { | |
69 | ca->next_seq = tp->snd_nxt; | |
70 | ||
e3058450 ED |
71 | ca->old_delivered = tp->delivered; |
72 | ca->old_delivered_ce = tp->delivered_ce; | |
e3118e83 DB |
73 | } |
74 | ||
75 | static void dctcp_init(struct sock *sk) | |
76 | { | |
77 | const struct tcp_sock *tp = tcp_sk(sk); | |
78 | ||
79 | if ((tp->ecn_flags & TCP_ECN_OK) || | |
80 | (sk->sk_state == TCP_LISTEN || | |
81 | sk->sk_state == TCP_CLOSE)) { | |
82 | struct dctcp *ca = inet_csk_ca(sk); | |
83 | ||
e3118e83 DB |
84 | ca->prior_rcv_nxt = tp->rcv_nxt; |
85 | ||
86 | ca->dctcp_alpha = min(dctcp_alpha_on_init, DCTCP_MAX_ALPHA); | |
87 | ||
ce6dd233 | 88 | ca->loss_cwnd = 0; |
e3118e83 DB |
89 | ca->ce_state = 0; |
90 | ||
91 | dctcp_reset(tp, ca); | |
92 | return; | |
93 | } | |
94 | ||
95 | /* No ECN support? Fall back to Reno. Also need to clear | |
96 | * ECT from sk since it is set during 3WHS for DCTCP. | |
97 | */ | |
98 | inet_csk(sk)->icsk_ca_ops = &dctcp_reno; | |
99 | INET_ECN_dontxmit(sk); | |
100 | } | |
101 | ||
102 | static u32 dctcp_ssthresh(struct sock *sk) | |
103 | { | |
ce6dd233 | 104 | struct dctcp *ca = inet_csk_ca(sk); |
e3118e83 DB |
105 | struct tcp_sock *tp = tcp_sk(sk); |
106 | ||
ce6dd233 | 107 | ca->loss_cwnd = tp->snd_cwnd; |
e3118e83 DB |
108 | return max(tp->snd_cwnd - ((tp->snd_cwnd * ca->dctcp_alpha) >> 11U), 2U); |
109 | } | |
110 | ||
e3118e83 DB |
111 | static void dctcp_update_alpha(struct sock *sk, u32 flags) |
112 | { | |
343dfaa1 | 113 | const struct tcp_sock *tp = tcp_sk(sk); |
e3118e83 | 114 | struct dctcp *ca = inet_csk_ca(sk); |
e3118e83 DB |
115 | |
116 | /* Expired RTT */ | |
117 | if (!before(tp->snd_una, ca->next_seq)) { | |
e3058450 | 118 | u32 delivered_ce = tp->delivered_ce - ca->old_delivered_ce; |
f9c2ff22 | 119 | u32 alpha = ca->dctcp_alpha; |
e3118e83 DB |
120 | |
121 | /* alpha = (1 - g) * alpha + g * F */ | |
e3118e83 | 122 | |
c80dbe04 | 123 | alpha -= min_not_zero(alpha, alpha >> dctcp_shift_g); |
e3058450 ED |
124 | if (delivered_ce) { |
125 | u32 delivered = tp->delivered - ca->old_delivered; | |
126 | ||
f9c2ff22 | 127 | /* If dctcp_shift_g == 1, a 32bit value would overflow |
e3058450 | 128 | * after 8 M packets. |
f9c2ff22 | 129 | */ |
e3058450 ED |
130 | delivered_ce <<= (10 - dctcp_shift_g); |
131 | delivered_ce /= max(1U, delivered); | |
f9c2ff22 | 132 | |
e3058450 | 133 | alpha = min(alpha + delivered_ce, DCTCP_MAX_ALPHA); |
f9c2ff22 ED |
134 | } |
135 | /* dctcp_alpha can be read from dctcp_get_info() without | |
136 | * synchro, so we ask compiler to not use dctcp_alpha | |
137 | * as a temporary variable in prior operations. | |
138 | */ | |
139 | WRITE_ONCE(ca->dctcp_alpha, alpha); | |
e3118e83 DB |
140 | dctcp_reset(tp, ca); |
141 | } | |
142 | } | |
143 | ||
aecfde23 | 144 | static void dctcp_react_to_loss(struct sock *sk) |
e3118e83 | 145 | { |
aecfde23 KDS |
146 | struct dctcp *ca = inet_csk_ca(sk); |
147 | struct tcp_sock *tp = tcp_sk(sk); | |
e3118e83 | 148 | |
aecfde23 KDS |
149 | ca->loss_cwnd = tp->snd_cwnd; |
150 | tp->snd_ssthresh = max(tp->snd_cwnd >> 1U, 2U); | |
151 | } | |
152 | ||
153 | static void dctcp_state(struct sock *sk, u8 new_state) | |
154 | { | |
155 | if (new_state == TCP_CA_Recovery && | |
156 | new_state != inet_csk(sk)->icsk_ca_state) | |
157 | dctcp_react_to_loss(sk); | |
158 | /* We handle RTO in dctcp_cwnd_event to ensure that we perform only | |
159 | * one loss-adjustment per RTT. | |
160 | */ | |
e3118e83 DB |
161 | } |
162 | ||
e3118e83 DB |
163 | static void dctcp_cwnd_event(struct sock *sk, enum tcp_ca_event ev) |
164 | { | |
ffd177de YC |
165 | struct dctcp *ca = inet_csk_ca(sk); |
166 | ||
e3118e83 DB |
167 | switch (ev) { |
168 | case CA_EVENT_ECN_IS_CE: | |
e3118e83 | 169 | case CA_EVENT_ECN_NO_CE: |
ffd177de | 170 | dctcp_ece_ack_update(sk, ev, &ca->prior_rcv_nxt, &ca->ce_state); |
e3118e83 | 171 | break; |
aecfde23 KDS |
172 | case CA_EVENT_LOSS: |
173 | dctcp_react_to_loss(sk); | |
174 | break; | |
e3118e83 DB |
175 | default: |
176 | /* Don't care for the rest. */ | |
177 | break; | |
178 | } | |
179 | } | |
180 | ||
64f40ff5 ED |
181 | static size_t dctcp_get_info(struct sock *sk, u32 ext, int *attr, |
182 | union tcp_cc_info *info) | |
e3118e83 DB |
183 | { |
184 | const struct dctcp *ca = inet_csk_ca(sk); | |
e3058450 | 185 | const struct tcp_sock *tp = tcp_sk(sk); |
e3118e83 DB |
186 | |
187 | /* Fill it also in case of VEGASINFO due to req struct limits. | |
188 | * We can still correctly retrieve it later. | |
189 | */ | |
190 | if (ext & (1 << (INET_DIAG_DCTCPINFO - 1)) || | |
191 | ext & (1 << (INET_DIAG_VEGASINFO - 1))) { | |
dcf1158b | 192 | memset(&info->dctcp, 0, sizeof(info->dctcp)); |
e3118e83 | 193 | if (inet_csk(sk)->icsk_ca_ops != &dctcp_reno) { |
64f40ff5 ED |
194 | info->dctcp.dctcp_enabled = 1; |
195 | info->dctcp.dctcp_ce_state = (u16) ca->ce_state; | |
196 | info->dctcp.dctcp_alpha = ca->dctcp_alpha; | |
e3058450 ED |
197 | info->dctcp.dctcp_ab_ecn = tp->mss_cache * |
198 | (tp->delivered_ce - ca->old_delivered_ce); | |
199 | info->dctcp.dctcp_ab_tot = tp->mss_cache * | |
200 | (tp->delivered - ca->old_delivered); | |
e3118e83 DB |
201 | } |
202 | ||
64f40ff5 | 203 | *attr = INET_DIAG_DCTCPINFO; |
dcf1158b | 204 | return sizeof(info->dctcp); |
e3118e83 | 205 | } |
521f1cf1 | 206 | return 0; |
e3118e83 DB |
207 | } |
208 | ||
ce6dd233 FW |
209 | static u32 dctcp_cwnd_undo(struct sock *sk) |
210 | { | |
211 | const struct dctcp *ca = inet_csk_ca(sk); | |
212 | ||
213 | return max(tcp_sk(sk)->snd_cwnd, ca->loss_cwnd); | |
214 | } | |
215 | ||
e3118e83 DB |
216 | static struct tcp_congestion_ops dctcp __read_mostly = { |
217 | .init = dctcp_init, | |
218 | .in_ack_event = dctcp_update_alpha, | |
219 | .cwnd_event = dctcp_cwnd_event, | |
220 | .ssthresh = dctcp_ssthresh, | |
221 | .cong_avoid = tcp_reno_cong_avoid, | |
ce6dd233 | 222 | .undo_cwnd = dctcp_cwnd_undo, |
e3118e83 DB |
223 | .set_state = dctcp_state, |
224 | .get_info = dctcp_get_info, | |
225 | .flags = TCP_CONG_NEEDS_ECN, | |
226 | .owner = THIS_MODULE, | |
227 | .name = "dctcp", | |
228 | }; | |
229 | ||
230 | static struct tcp_congestion_ops dctcp_reno __read_mostly = { | |
231 | .ssthresh = tcp_reno_ssthresh, | |
232 | .cong_avoid = tcp_reno_cong_avoid, | |
e9799183 | 233 | .undo_cwnd = tcp_reno_undo_cwnd, |
e3118e83 DB |
234 | .get_info = dctcp_get_info, |
235 | .owner = THIS_MODULE, | |
236 | .name = "dctcp-reno", | |
237 | }; | |
238 | ||
239 | static int __init dctcp_register(void) | |
240 | { | |
241 | BUILD_BUG_ON(sizeof(struct dctcp) > ICSK_CA_PRIV_SIZE); | |
242 | return tcp_register_congestion_control(&dctcp); | |
243 | } | |
244 | ||
245 | static void __exit dctcp_unregister(void) | |
246 | { | |
247 | tcp_unregister_congestion_control(&dctcp); | |
248 | } | |
249 | ||
250 | module_init(dctcp_register); | |
251 | module_exit(dctcp_unregister); | |
252 | ||
253 | MODULE_AUTHOR("Daniel Borkmann <dborkman@redhat.com>"); | |
254 | MODULE_AUTHOR("Florian Westphal <fw@strlen.de>"); | |
255 | MODULE_AUTHOR("Glenn Judd <glenn.judd@morganstanley.com>"); | |
256 | ||
257 | MODULE_LICENSE("GPL v2"); | |
258 | MODULE_DESCRIPTION("DataCenter TCP (DCTCP)"); |