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 49 struct 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 }; 58 59 static unsigned int dctcp_shift_g __read_mostly = 4; /* g = 1/2^4 */ 60 module_param(dctcp_shift_g, uint, 0644); 61 MODULE_PARM_DESC(dctcp_shift_g, "parameter g for updating dctcp_alpha"); 62 63 static unsigned int dctcp_alpha_on_init __read_mostly = DCTCP_MAX_ALPHA; 64 module_param(dctcp_alpha_on_init, uint, 0644); 65 MODULE_PARM_DESC(dctcp_alpha_on_init, "parameter for initial alpha value"); 66 67 static struct tcp_congestion_ops dctcp_reno; 68 69 static void dctcp_reset(const struct tcp_sock *tp, struct dctcp *ca) 70 { 71 ca->next_seq = tp->snd_nxt; 72 73 ca->old_delivered = tp->delivered; 74 ca->old_delivered_ce = tp->delivered_ce; 75 } 76 77 static void dctcp_init(struct sock *sk) 78 { 79 const struct tcp_sock *tp = tcp_sk(sk); 80 81 if ((tp->ecn_flags & TCP_ECN_OK) || 82 (sk->sk_state == TCP_LISTEN || 83 sk->sk_state == TCP_CLOSE)) { 84 struct dctcp *ca = inet_csk_ca(sk); 85 86 ca->prior_rcv_nxt = tp->rcv_nxt; 87 88 ca->dctcp_alpha = min(dctcp_alpha_on_init, DCTCP_MAX_ALPHA); 89 90 ca->loss_cwnd = 0; 91 ca->ce_state = 0; 92 93 dctcp_reset(tp, ca); 94 return; 95 } 96 97 /* No ECN support? Fall back to Reno. Also need to clear 98 * ECT from sk since it is set during 3WHS for DCTCP. 99 */ 100 inet_csk(sk)->icsk_ca_ops = &dctcp_reno; 101 INET_ECN_dontxmit(sk); 102 } 103 104 static u32 dctcp_ssthresh(struct sock *sk) 105 { 106 struct dctcp *ca = inet_csk_ca(sk); 107 struct tcp_sock *tp = tcp_sk(sk); 108 109 ca->loss_cwnd = tp->snd_cwnd; 110 return max(tp->snd_cwnd - ((tp->snd_cwnd * ca->dctcp_alpha) >> 11U), 2U); 111 } 112 113 static void dctcp_update_alpha(struct sock *sk, u32 flags) 114 { 115 const struct tcp_sock *tp = tcp_sk(sk); 116 struct dctcp *ca = inet_csk_ca(sk); 117 118 /* Expired RTT */ 119 if (!before(tp->snd_una, ca->next_seq)) { 120 u32 delivered_ce = tp->delivered_ce - ca->old_delivered_ce; 121 u32 alpha = ca->dctcp_alpha; 122 123 /* alpha = (1 - g) * alpha + g * F */ 124 125 alpha -= min_not_zero(alpha, alpha >> dctcp_shift_g); 126 if (delivered_ce) { 127 u32 delivered = tp->delivered - ca->old_delivered; 128 129 /* If dctcp_shift_g == 1, a 32bit value would overflow 130 * after 8 M packets. 131 */ 132 delivered_ce <<= (10 - dctcp_shift_g); 133 delivered_ce /= max(1U, delivered); 134 135 alpha = min(alpha + delivered_ce, DCTCP_MAX_ALPHA); 136 } 137 /* dctcp_alpha can be read from dctcp_get_info() without 138 * synchro, so we ask compiler to not use dctcp_alpha 139 * as a temporary variable in prior operations. 140 */ 141 WRITE_ONCE(ca->dctcp_alpha, alpha); 142 dctcp_reset(tp, ca); 143 } 144 } 145 146 static void dctcp_react_to_loss(struct sock *sk) 147 { 148 struct dctcp *ca = inet_csk_ca(sk); 149 struct tcp_sock *tp = tcp_sk(sk); 150 151 ca->loss_cwnd = tp->snd_cwnd; 152 tp->snd_ssthresh = max(tp->snd_cwnd >> 1U, 2U); 153 } 154 155 static void dctcp_state(struct sock *sk, u8 new_state) 156 { 157 if (new_state == TCP_CA_Recovery && 158 new_state != inet_csk(sk)->icsk_ca_state) 159 dctcp_react_to_loss(sk); 160 /* We handle RTO in dctcp_cwnd_event to ensure that we perform only 161 * one loss-adjustment per RTT. 162 */ 163 } 164 165 static void dctcp_cwnd_event(struct sock *sk, enum tcp_ca_event ev) 166 { 167 struct dctcp *ca = inet_csk_ca(sk); 168 169 switch (ev) { 170 case CA_EVENT_ECN_IS_CE: 171 case CA_EVENT_ECN_NO_CE: 172 dctcp_ece_ack_update(sk, ev, &ca->prior_rcv_nxt, &ca->ce_state); 173 break; 174 case CA_EVENT_LOSS: 175 dctcp_react_to_loss(sk); 176 break; 177 default: 178 /* Don't care for the rest. */ 179 break; 180 } 181 } 182 183 static size_t dctcp_get_info(struct sock *sk, u32 ext, int *attr, 184 union tcp_cc_info *info) 185 { 186 const struct dctcp *ca = inet_csk_ca(sk); 187 const struct tcp_sock *tp = tcp_sk(sk); 188 189 /* Fill it also in case of VEGASINFO due to req struct limits. 190 * We can still correctly retrieve it later. 191 */ 192 if (ext & (1 << (INET_DIAG_DCTCPINFO - 1)) || 193 ext & (1 << (INET_DIAG_VEGASINFO - 1))) { 194 memset(&info->dctcp, 0, sizeof(info->dctcp)); 195 if (inet_csk(sk)->icsk_ca_ops != &dctcp_reno) { 196 info->dctcp.dctcp_enabled = 1; 197 info->dctcp.dctcp_ce_state = (u16) ca->ce_state; 198 info->dctcp.dctcp_alpha = ca->dctcp_alpha; 199 info->dctcp.dctcp_ab_ecn = tp->mss_cache * 200 (tp->delivered_ce - ca->old_delivered_ce); 201 info->dctcp.dctcp_ab_tot = tp->mss_cache * 202 (tp->delivered - ca->old_delivered); 203 } 204 205 *attr = INET_DIAG_DCTCPINFO; 206 return sizeof(info->dctcp); 207 } 208 return 0; 209 } 210 211 static u32 dctcp_cwnd_undo(struct sock *sk) 212 { 213 const struct dctcp *ca = inet_csk_ca(sk); 214 215 return max(tcp_sk(sk)->snd_cwnd, ca->loss_cwnd); 216 } 217 218 static struct tcp_congestion_ops dctcp __read_mostly = { 219 .init = dctcp_init, 220 .in_ack_event = dctcp_update_alpha, 221 .cwnd_event = dctcp_cwnd_event, 222 .ssthresh = dctcp_ssthresh, 223 .cong_avoid = tcp_reno_cong_avoid, 224 .undo_cwnd = dctcp_cwnd_undo, 225 .set_state = dctcp_state, 226 .get_info = dctcp_get_info, 227 .flags = TCP_CONG_NEEDS_ECN, 228 .owner = THIS_MODULE, 229 .name = "dctcp", 230 }; 231 232 static struct tcp_congestion_ops dctcp_reno __read_mostly = { 233 .ssthresh = tcp_reno_ssthresh, 234 .cong_avoid = tcp_reno_cong_avoid, 235 .undo_cwnd = tcp_reno_undo_cwnd, 236 .get_info = dctcp_get_info, 237 .owner = THIS_MODULE, 238 .name = "dctcp-reno", 239 }; 240 241 BTF_SET_START(tcp_dctcp_kfunc_ids) 242 #ifdef CONFIG_X86 243 #ifdef CONFIG_DYNAMIC_FTRACE 244 BTF_ID(func, dctcp_init) 245 BTF_ID(func, dctcp_update_alpha) 246 BTF_ID(func, dctcp_cwnd_event) 247 BTF_ID(func, dctcp_ssthresh) 248 BTF_ID(func, dctcp_cwnd_undo) 249 BTF_ID(func, dctcp_state) 250 #endif 251 #endif 252 BTF_SET_END(tcp_dctcp_kfunc_ids) 253 254 static DEFINE_KFUNC_BTF_ID_SET(&tcp_dctcp_kfunc_ids, tcp_dctcp_kfunc_btf_set); 255 256 static int __init dctcp_register(void) 257 { 258 int ret; 259 260 BUILD_BUG_ON(sizeof(struct dctcp) > ICSK_CA_PRIV_SIZE); 261 ret = tcp_register_congestion_control(&dctcp); 262 if (ret) 263 return ret; 264 register_kfunc_btf_id_set(&bpf_tcp_ca_kfunc_list, &tcp_dctcp_kfunc_btf_set); 265 return 0; 266 } 267 268 static void __exit dctcp_unregister(void) 269 { 270 unregister_kfunc_btf_id_set(&bpf_tcp_ca_kfunc_list, &tcp_dctcp_kfunc_btf_set); 271 tcp_unregister_congestion_control(&dctcp); 272 } 273 274 module_init(dctcp_register); 275 module_exit(dctcp_unregister); 276 277 MODULE_AUTHOR("Daniel Borkmann <dborkman@redhat.com>"); 278 MODULE_AUTHOR("Florian Westphal <fw@strlen.de>"); 279 MODULE_AUTHOR("Glenn Judd <glenn.judd@morganstanley.com>"); 280 281 MODULE_LICENSE("GPL v2"); 282 MODULE_DESCRIPTION("DataCenter TCP (DCTCP)"); 283