1 | /* DataCenter TCP (DCTCP) congestion control. |
2 | * |
3 | * http://simula.stanford.edu/~alizade/Site/DCTCP.html |
4 | * |
5 | * This is an implementation of DCTCP over Reno, an enhancement to the |
6 | * TCP congestion control algorithm designed for data centers. DCTCP |
7 | * leverages Explicit Congestion Notification (ECN) in the network to |
8 | * provide multi-bit feedback to the end hosts. DCTCP's goal is to meet |
9 | * the following three data center transport requirements: |
10 | * |
11 | * - High burst tolerance (incast due to partition/aggregate) |
12 | * - Low latency (short flows, queries) |
13 | * - High throughput (continuous data updates, large file transfers) |
14 | * with commodity shallow buffered switches |
15 | * |
16 | * The algorithm is described in detail in the following two papers: |
17 | * |
18 | * 1) Mohammad Alizadeh, Albert Greenberg, David A. Maltz, Jitendra Padhye, |
19 | * Parveen Patel, Balaji Prabhakar, Sudipta Sengupta, and Murari Sridharan: |
20 | * "Data Center TCP (DCTCP)", Data Center Networks session |
21 | * Proc. ACM SIGCOMM, New Delhi, 2010. |
22 | * http://simula.stanford.edu/~alizade/Site/DCTCP_files/dctcp-final.pdf |
23 | * |
24 | * 2) Mohammad Alizadeh, Adel Javanmard, and Balaji Prabhakar: |
25 | * "Analysis of DCTCP: Stability, Convergence, and Fairness" |
26 | * Proc. ACM SIGMETRICS, San Jose, 2011. |
27 | * http://simula.stanford.edu/~alizade/Site/DCTCP_files/dctcp_analysis-full.pdf |
28 | * |
29 | * Initial prototype from Abdul Kabbani, Masato Yasuda and Mohammad Alizadeh. |
30 | * |
31 | * Authors: |
32 | * |
33 | * Daniel Borkmann <dborkman@redhat.com> |
34 | * Florian Westphal <fw@strlen.de> |
35 | * Glenn Judd <glenn.judd@morganstanley.com> |
36 | * |
37 | * This program is free software; you can redistribute it and/or modify |
38 | * it under the terms of the GNU General Public License as published by |
39 | * the Free Software Foundation; either version 2 of the License, or (at |
40 | * your option) any later version. |
41 | */ |
42 | |
43 | #include <linux/module.h> |
44 | #include <linux/mm.h> |
45 | #include <net/tcp.h> |
46 | #include <linux/inet_diag.h> |
47 | #include "tcp_dctcp.h" |
48 | |
49 | #define DCTCP_MAX_ALPHA 1024U |
50 | |
51 | struct dctcp { |
52 | u32 acked_bytes_ecn; |
53 | u32 acked_bytes_total; |
54 | u32 prior_snd_una; |
55 | u32 prior_rcv_nxt; |
56 | u32 dctcp_alpha; |
57 | u32 next_seq; |
58 | u32 ce_state; |
59 | u32 loss_cwnd; |
60 | }; |
61 | |
62 | static unsigned int dctcp_shift_g __read_mostly = 4; /* g = 1/2^4 */ |
63 | module_param(dctcp_shift_g, uint, 0644); |
64 | MODULE_PARM_DESC(dctcp_shift_g, "parameter g for updating dctcp_alpha" ); |
65 | |
66 | static unsigned int dctcp_alpha_on_init __read_mostly = DCTCP_MAX_ALPHA; |
67 | module_param(dctcp_alpha_on_init, uint, 0644); |
68 | MODULE_PARM_DESC(dctcp_alpha_on_init, "parameter for initial alpha value" ); |
69 | |
70 | static unsigned int dctcp_clamp_alpha_on_loss __read_mostly; |
71 | module_param(dctcp_clamp_alpha_on_loss, uint, 0644); |
72 | MODULE_PARM_DESC(dctcp_clamp_alpha_on_loss, |
73 | "parameter for clamping alpha on loss" ); |
74 | |
75 | static struct tcp_congestion_ops dctcp_reno; |
76 | |
77 | static void dctcp_reset(const struct tcp_sock *tp, struct dctcp *ca) |
78 | { |
79 | ca->next_seq = tp->snd_nxt; |
80 | |
81 | ca->acked_bytes_ecn = 0; |
82 | ca->acked_bytes_total = 0; |
83 | } |
84 | |
85 | static void dctcp_init(struct sock *sk) |
86 | { |
87 | const struct tcp_sock *tp = tcp_sk(sk); |
88 | |
89 | if ((tp->ecn_flags & TCP_ECN_OK) || |
90 | (sk->sk_state == TCP_LISTEN || |
91 | sk->sk_state == TCP_CLOSE)) { |
92 | struct dctcp *ca = inet_csk_ca(sk); |
93 | |
94 | ca->prior_snd_una = tp->snd_una; |
95 | ca->prior_rcv_nxt = tp->rcv_nxt; |
96 | |
97 | ca->dctcp_alpha = min(dctcp_alpha_on_init, DCTCP_MAX_ALPHA); |
98 | |
99 | ca->loss_cwnd = 0; |
100 | ca->ce_state = 0; |
101 | |
102 | dctcp_reset(tp, ca); |
103 | return; |
104 | } |
105 | |
106 | /* No ECN support? Fall back to Reno. Also need to clear |
107 | * ECT from sk since it is set during 3WHS for DCTCP. |
108 | */ |
109 | inet_csk(sk)->icsk_ca_ops = &dctcp_reno; |
110 | INET_ECN_dontxmit(sk); |
111 | } |
112 | |
113 | static u32 dctcp_ssthresh(struct sock *sk) |
114 | { |
115 | struct dctcp *ca = inet_csk_ca(sk); |
116 | struct tcp_sock *tp = tcp_sk(sk); |
117 | |
118 | ca->loss_cwnd = tp->snd_cwnd; |
119 | return max(tp->snd_cwnd - ((tp->snd_cwnd * ca->dctcp_alpha) >> 11U), 2U); |
120 | } |
121 | |
122 | static void dctcp_update_alpha(struct sock *sk, u32 flags) |
123 | { |
124 | const struct tcp_sock *tp = tcp_sk(sk); |
125 | struct dctcp *ca = inet_csk_ca(sk); |
126 | u32 acked_bytes = tp->snd_una - ca->prior_snd_una; |
127 | |
128 | /* If ack did not advance snd_una, count dupack as MSS size. |
129 | * If ack did update window, do not count it at all. |
130 | */ |
131 | if (acked_bytes == 0 && !(flags & CA_ACK_WIN_UPDATE)) |
132 | acked_bytes = inet_csk(sk)->icsk_ack.rcv_mss; |
133 | if (acked_bytes) { |
134 | ca->acked_bytes_total += acked_bytes; |
135 | ca->prior_snd_una = tp->snd_una; |
136 | |
137 | if (flags & CA_ACK_ECE) |
138 | ca->acked_bytes_ecn += acked_bytes; |
139 | } |
140 | |
141 | /* Expired RTT */ |
142 | if (!before(tp->snd_una, ca->next_seq)) { |
143 | u64 bytes_ecn = ca->acked_bytes_ecn; |
144 | u32 alpha = ca->dctcp_alpha; |
145 | |
146 | /* alpha = (1 - g) * alpha + g * F */ |
147 | |
148 | alpha -= min_not_zero(alpha, alpha >> dctcp_shift_g); |
149 | if (bytes_ecn) { |
150 | /* If dctcp_shift_g == 1, a 32bit value would overflow |
151 | * after 8 Mbytes. |
152 | */ |
153 | bytes_ecn <<= (10 - dctcp_shift_g); |
154 | do_div(bytes_ecn, max(1U, ca->acked_bytes_total)); |
155 | |
156 | alpha = min(alpha + (u32)bytes_ecn, DCTCP_MAX_ALPHA); |
157 | } |
158 | /* dctcp_alpha can be read from dctcp_get_info() without |
159 | * synchro, so we ask compiler to not use dctcp_alpha |
160 | * as a temporary variable in prior operations. |
161 | */ |
162 | WRITE_ONCE(ca->dctcp_alpha, alpha); |
163 | dctcp_reset(tp, ca); |
164 | } |
165 | } |
166 | |
167 | static void dctcp_state(struct sock *sk, u8 new_state) |
168 | { |
169 | if (dctcp_clamp_alpha_on_loss && new_state == TCP_CA_Loss) { |
170 | struct dctcp *ca = inet_csk_ca(sk); |
171 | |
172 | /* If this extension is enabled, we clamp dctcp_alpha to |
173 | * max on packet loss; the motivation is that dctcp_alpha |
174 | * is an indicator to the extend of congestion and packet |
175 | * loss is an indicator of extreme congestion; setting |
176 | * this in practice turned out to be beneficial, and |
177 | * effectively assumes total congestion which reduces the |
178 | * window by half. |
179 | */ |
180 | ca->dctcp_alpha = DCTCP_MAX_ALPHA; |
181 | } |
182 | } |
183 | |
184 | static void dctcp_cwnd_event(struct sock *sk, enum tcp_ca_event ev) |
185 | { |
186 | struct dctcp *ca = inet_csk_ca(sk); |
187 | |
188 | switch (ev) { |
189 | case CA_EVENT_ECN_IS_CE: |
190 | case CA_EVENT_ECN_NO_CE: |
191 | dctcp_ece_ack_update(sk, ev, &ca->prior_rcv_nxt, &ca->ce_state); |
192 | break; |
193 | default: |
194 | /* Don't care for the rest. */ |
195 | break; |
196 | } |
197 | } |
198 | |
199 | static size_t dctcp_get_info(struct sock *sk, u32 ext, int *attr, |
200 | union tcp_cc_info *info) |
201 | { |
202 | const struct dctcp *ca = inet_csk_ca(sk); |
203 | |
204 | /* Fill it also in case of VEGASINFO due to req struct limits. |
205 | * We can still correctly retrieve it later. |
206 | */ |
207 | if (ext & (1 << (INET_DIAG_DCTCPINFO - 1)) || |
208 | ext & (1 << (INET_DIAG_VEGASINFO - 1))) { |
209 | memset(&info->dctcp, 0, sizeof(info->dctcp)); |
210 | if (inet_csk(sk)->icsk_ca_ops != &dctcp_reno) { |
211 | info->dctcp.dctcp_enabled = 1; |
212 | info->dctcp.dctcp_ce_state = (u16) ca->ce_state; |
213 | info->dctcp.dctcp_alpha = ca->dctcp_alpha; |
214 | info->dctcp.dctcp_ab_ecn = ca->acked_bytes_ecn; |
215 | info->dctcp.dctcp_ab_tot = ca->acked_bytes_total; |
216 | } |
217 | |
218 | *attr = INET_DIAG_DCTCPINFO; |
219 | return sizeof(info->dctcp); |
220 | } |
221 | return 0; |
222 | } |
223 | |
224 | static u32 dctcp_cwnd_undo(struct sock *sk) |
225 | { |
226 | const struct dctcp *ca = inet_csk_ca(sk); |
227 | |
228 | return max(tcp_sk(sk)->snd_cwnd, ca->loss_cwnd); |
229 | } |
230 | |
231 | static struct tcp_congestion_ops dctcp __read_mostly = { |
232 | .init = dctcp_init, |
233 | .in_ack_event = dctcp_update_alpha, |
234 | .cwnd_event = dctcp_cwnd_event, |
235 | .ssthresh = dctcp_ssthresh, |
236 | .cong_avoid = tcp_reno_cong_avoid, |
237 | .undo_cwnd = dctcp_cwnd_undo, |
238 | .set_state = dctcp_state, |
239 | .get_info = dctcp_get_info, |
240 | .flags = TCP_CONG_NEEDS_ECN, |
241 | .owner = THIS_MODULE, |
242 | .name = "dctcp" , |
243 | }; |
244 | |
245 | static struct tcp_congestion_ops dctcp_reno __read_mostly = { |
246 | .ssthresh = tcp_reno_ssthresh, |
247 | .cong_avoid = tcp_reno_cong_avoid, |
248 | .undo_cwnd = tcp_reno_undo_cwnd, |
249 | .get_info = dctcp_get_info, |
250 | .owner = THIS_MODULE, |
251 | .name = "dctcp-reno" , |
252 | }; |
253 | |
254 | static int __init dctcp_register(void) |
255 | { |
256 | BUILD_BUG_ON(sizeof(struct dctcp) > ICSK_CA_PRIV_SIZE); |
257 | return tcp_register_congestion_control(&dctcp); |
258 | } |
259 | |
260 | static void __exit dctcp_unregister(void) |
261 | { |
262 | tcp_unregister_congestion_control(&dctcp); |
263 | } |
264 | |
265 | module_init(dctcp_register); |
266 | module_exit(dctcp_unregister); |
267 | |
268 | MODULE_AUTHOR("Daniel Borkmann <dborkman@redhat.com>" ); |
269 | MODULE_AUTHOR("Florian Westphal <fw@strlen.de>" ); |
270 | MODULE_AUTHOR("Glenn Judd <glenn.judd@morganstanley.com>" ); |
271 | |
272 | MODULE_LICENSE("GPL v2" ); |
273 | MODULE_DESCRIPTION("DataCenter TCP (DCTCP)" ); |
274 | |