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 struct tcp_plb_state plb; 58 }; 59 60 static unsigned int dctcp_shift_g __read_mostly = 4; /* g = 1/2^4 */ 61 62 static int dctcp_shift_g_set(const char *val, const struct kernel_param *kp) 63 { 64 return param_set_uint_minmax(val, kp, 0, 10); 65 } 66 67 static const struct kernel_param_ops dctcp_shift_g_ops = { 68 .set = dctcp_shift_g_set, 69 .get = param_get_uint, 70 }; 71 72 module_param_cb(dctcp_shift_g, &dctcp_shift_g_ops, &dctcp_shift_g, 0644); 73 MODULE_PARM_DESC(dctcp_shift_g, "parameter g for updating dctcp_alpha"); 74 75 static unsigned int dctcp_alpha_on_init __read_mostly = DCTCP_MAX_ALPHA; 76 module_param(dctcp_alpha_on_init, uint, 0644); 77 MODULE_PARM_DESC(dctcp_alpha_on_init, "parameter for initial alpha value"); 78 79 static struct tcp_congestion_ops dctcp_reno; 80 81 static void dctcp_reset(const struct tcp_sock *tp, struct dctcp *ca) 82 { 83 ca->next_seq = tp->snd_nxt; 84 85 ca->old_delivered = tp->delivered; 86 ca->old_delivered_ce = tp->delivered_ce; 87 } 88 89 __bpf_kfunc static void dctcp_init(struct sock *sk) 90 { 91 const struct tcp_sock *tp = tcp_sk(sk); 92 93 if ((tp->ecn_flags & TCP_ECN_OK) || 94 (sk->sk_state == TCP_LISTEN || 95 sk->sk_state == TCP_CLOSE)) { 96 struct dctcp *ca = inet_csk_ca(sk); 97 98 ca->prior_rcv_nxt = tp->rcv_nxt; 99 100 ca->dctcp_alpha = min(dctcp_alpha_on_init, DCTCP_MAX_ALPHA); 101 102 ca->loss_cwnd = 0; 103 ca->ce_state = 0; 104 105 dctcp_reset(tp, ca); 106 tcp_plb_init(sk, &ca->plb); 107 108 return; 109 } 110 111 /* No ECN support? Fall back to Reno. Also need to clear 112 * ECT from sk since it is set during 3WHS for DCTCP. 113 */ 114 inet_csk(sk)->icsk_ca_ops = &dctcp_reno; 115 INET_ECN_dontxmit(sk); 116 } 117 118 __bpf_kfunc static u32 dctcp_ssthresh(struct sock *sk) 119 { 120 struct dctcp *ca = inet_csk_ca(sk); 121 struct tcp_sock *tp = tcp_sk(sk); 122 123 ca->loss_cwnd = tcp_snd_cwnd(tp); 124 return max(tcp_snd_cwnd(tp) - ((tcp_snd_cwnd(tp) * ca->dctcp_alpha) >> 11U), 2U); 125 } 126 127 __bpf_kfunc static void dctcp_update_alpha(struct sock *sk, u32 flags) 128 { 129 const struct tcp_sock *tp = tcp_sk(sk); 130 struct dctcp *ca = inet_csk_ca(sk); 131 132 /* Expired RTT */ 133 if (!before(tp->snd_una, ca->next_seq)) { 134 u32 delivered = tp->delivered - ca->old_delivered; 135 u32 delivered_ce = tp->delivered_ce - ca->old_delivered_ce; 136 u32 alpha = ca->dctcp_alpha; 137 u32 ce_ratio = 0; 138 139 if (delivered > 0) { 140 /* dctcp_alpha keeps EWMA of fraction of ECN marked 141 * packets. Because of EWMA smoothing, PLB reaction can 142 * be slow so we use ce_ratio which is an instantaneous 143 * measure of congestion. ce_ratio is the fraction of 144 * ECN marked packets in the previous RTT. 145 */ 146 if (delivered_ce > 0) 147 ce_ratio = (delivered_ce << TCP_PLB_SCALE) / delivered; 148 tcp_plb_update_state(sk, &ca->plb, (int)ce_ratio); 149 tcp_plb_check_rehash(sk, &ca->plb); 150 } 151 152 /* alpha = (1 - g) * alpha + g * F */ 153 154 alpha -= min_not_zero(alpha, alpha >> dctcp_shift_g); 155 if (delivered_ce) { 156 157 /* If dctcp_shift_g == 1, a 32bit value would overflow 158 * after 8 M packets. 159 */ 160 delivered_ce <<= (10 - dctcp_shift_g); 161 delivered_ce /= max(1U, delivered); 162 163 alpha = min(alpha + delivered_ce, DCTCP_MAX_ALPHA); 164 } 165 /* dctcp_alpha can be read from dctcp_get_info() without 166 * synchro, so we ask compiler to not use dctcp_alpha 167 * as a temporary variable in prior operations. 168 */ 169 WRITE_ONCE(ca->dctcp_alpha, alpha); 170 dctcp_reset(tp, ca); 171 } 172 } 173 174 static void dctcp_react_to_loss(struct sock *sk) 175 { 176 struct dctcp *ca = inet_csk_ca(sk); 177 struct tcp_sock *tp = tcp_sk(sk); 178 179 ca->loss_cwnd = tcp_snd_cwnd(tp); 180 tp->snd_ssthresh = max(tcp_snd_cwnd(tp) >> 1U, 2U); 181 } 182 183 __bpf_kfunc static void dctcp_state(struct sock *sk, u8 new_state) 184 { 185 if (new_state == TCP_CA_Recovery && 186 new_state != inet_csk(sk)->icsk_ca_state) 187 dctcp_react_to_loss(sk); 188 /* We handle RTO in dctcp_cwnd_event to ensure that we perform only 189 * one loss-adjustment per RTT. 190 */ 191 } 192 193 __bpf_kfunc static void dctcp_cwnd_event(struct sock *sk, enum tcp_ca_event ev) 194 { 195 struct dctcp *ca = inet_csk_ca(sk); 196 197 switch (ev) { 198 case CA_EVENT_ECN_IS_CE: 199 case CA_EVENT_ECN_NO_CE: 200 dctcp_ece_ack_update(sk, ev, &ca->prior_rcv_nxt, &ca->ce_state); 201 break; 202 case CA_EVENT_LOSS: 203 tcp_plb_update_state_upon_rto(sk, &ca->plb); 204 dctcp_react_to_loss(sk); 205 break; 206 case CA_EVENT_TX_START: 207 tcp_plb_check_rehash(sk, &ca->plb); /* Maybe rehash when inflight is 0 */ 208 break; 209 default: 210 /* Don't care for the rest. */ 211 break; 212 } 213 } 214 215 static size_t dctcp_get_info(struct sock *sk, u32 ext, int *attr, 216 union tcp_cc_info *info) 217 { 218 const struct dctcp *ca = inet_csk_ca(sk); 219 const struct tcp_sock *tp = tcp_sk(sk); 220 221 /* Fill it also in case of VEGASINFO due to req struct limits. 222 * We can still correctly retrieve it later. 223 */ 224 if (ext & (1 << (INET_DIAG_DCTCPINFO - 1)) || 225 ext & (1 << (INET_DIAG_VEGASINFO - 1))) { 226 memset(&info->dctcp, 0, sizeof(info->dctcp)); 227 if (inet_csk(sk)->icsk_ca_ops != &dctcp_reno) { 228 info->dctcp.dctcp_enabled = 1; 229 info->dctcp.dctcp_ce_state = (u16) ca->ce_state; 230 info->dctcp.dctcp_alpha = ca->dctcp_alpha; 231 info->dctcp.dctcp_ab_ecn = tp->mss_cache * 232 (tp->delivered_ce - ca->old_delivered_ce); 233 info->dctcp.dctcp_ab_tot = tp->mss_cache * 234 (tp->delivered - ca->old_delivered); 235 } 236 237 *attr = INET_DIAG_DCTCPINFO; 238 return sizeof(info->dctcp); 239 } 240 return 0; 241 } 242 243 __bpf_kfunc static u32 dctcp_cwnd_undo(struct sock *sk) 244 { 245 const struct dctcp *ca = inet_csk_ca(sk); 246 struct tcp_sock *tp = tcp_sk(sk); 247 248 return max(tcp_snd_cwnd(tp), ca->loss_cwnd); 249 } 250 251 static struct tcp_congestion_ops dctcp __read_mostly = { 252 .init = dctcp_init, 253 .in_ack_event = dctcp_update_alpha, 254 .cwnd_event = dctcp_cwnd_event, 255 .ssthresh = dctcp_ssthresh, 256 .cong_avoid = tcp_reno_cong_avoid, 257 .undo_cwnd = dctcp_cwnd_undo, 258 .set_state = dctcp_state, 259 .get_info = dctcp_get_info, 260 .flags = TCP_CONG_NEEDS_ECN, 261 .owner = THIS_MODULE, 262 .name = "dctcp", 263 }; 264 265 static struct tcp_congestion_ops dctcp_reno __read_mostly = { 266 .ssthresh = tcp_reno_ssthresh, 267 .cong_avoid = tcp_reno_cong_avoid, 268 .undo_cwnd = tcp_reno_undo_cwnd, 269 .get_info = dctcp_get_info, 270 .owner = THIS_MODULE, 271 .name = "dctcp-reno", 272 }; 273 274 BTF_SET8_START(tcp_dctcp_check_kfunc_ids) 275 #ifdef CONFIG_X86 276 #ifdef CONFIG_DYNAMIC_FTRACE 277 BTF_ID_FLAGS(func, dctcp_init) 278 BTF_ID_FLAGS(func, dctcp_update_alpha) 279 BTF_ID_FLAGS(func, dctcp_cwnd_event) 280 BTF_ID_FLAGS(func, dctcp_ssthresh) 281 BTF_ID_FLAGS(func, dctcp_cwnd_undo) 282 BTF_ID_FLAGS(func, dctcp_state) 283 #endif 284 #endif 285 BTF_SET8_END(tcp_dctcp_check_kfunc_ids) 286 287 static const struct btf_kfunc_id_set tcp_dctcp_kfunc_set = { 288 .owner = THIS_MODULE, 289 .set = &tcp_dctcp_check_kfunc_ids, 290 }; 291 292 static int __init dctcp_register(void) 293 { 294 int ret; 295 296 BUILD_BUG_ON(sizeof(struct dctcp) > ICSK_CA_PRIV_SIZE); 297 298 ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &tcp_dctcp_kfunc_set); 299 if (ret < 0) 300 return ret; 301 return tcp_register_congestion_control(&dctcp); 302 } 303 304 static void __exit dctcp_unregister(void) 305 { 306 tcp_unregister_congestion_control(&dctcp); 307 } 308 309 module_init(dctcp_register); 310 module_exit(dctcp_unregister); 311 312 MODULE_AUTHOR("Daniel Borkmann <dborkman@redhat.com>"); 313 MODULE_AUTHOR("Florian Westphal <fw@strlen.de>"); 314 MODULE_AUTHOR("Glenn Judd <glenn.judd@morganstanley.com>"); 315 316 MODULE_LICENSE("GPL v2"); 317 MODULE_DESCRIPTION("DataCenter TCP (DCTCP)"); 318