1 // SPDX-License-Identifier: GPL-2.0 2 /* Copyright (c) 2019 Facebook */ 3 4 /* WARNING: This implemenation is not necessarily the same 5 * as the tcp_dctcp.c. The purpose is mainly for testing 6 * the kernel BPF logic. 7 */ 8 9 #include <stddef.h> 10 #include <linux/bpf.h> 11 #include <linux/types.h> 12 #include <linux/stddef.h> 13 #include <linux/tcp.h> 14 #include <errno.h> 15 #include <bpf/bpf_helpers.h> 16 #include <bpf/bpf_tracing.h> 17 #include "bpf_tcp_helpers.h" 18 19 char _license[] SEC("license") = "GPL"; 20 21 volatile const char fallback[TCP_CA_NAME_MAX]; 22 const char bpf_dctcp[] = "bpf_dctcp"; 23 const char tcp_cdg[] = "cdg"; 24 char cc_res[TCP_CA_NAME_MAX]; 25 int tcp_cdg_res = 0; 26 int stg_result = 0; 27 int ebusy_cnt = 0; 28 29 struct { 30 __uint(type, BPF_MAP_TYPE_SK_STORAGE); 31 __uint(map_flags, BPF_F_NO_PREALLOC); 32 __type(key, int); 33 __type(value, int); 34 } sk_stg_map SEC(".maps"); 35 36 #define DCTCP_MAX_ALPHA 1024U 37 38 struct dctcp { 39 __u32 old_delivered; 40 __u32 old_delivered_ce; 41 __u32 prior_rcv_nxt; 42 __u32 dctcp_alpha; 43 __u32 next_seq; 44 __u32 ce_state; 45 __u32 loss_cwnd; 46 }; 47 48 static unsigned int dctcp_shift_g = 4; /* g = 1/2^4 */ 49 static unsigned int dctcp_alpha_on_init = DCTCP_MAX_ALPHA; 50 51 static __always_inline void dctcp_reset(const struct tcp_sock *tp, 52 struct dctcp *ca) 53 { 54 ca->next_seq = tp->snd_nxt; 55 56 ca->old_delivered = tp->delivered; 57 ca->old_delivered_ce = tp->delivered_ce; 58 } 59 60 SEC("struct_ops/dctcp_init") 61 void BPF_PROG(dctcp_init, struct sock *sk) 62 { 63 const struct tcp_sock *tp = tcp_sk(sk); 64 struct dctcp *ca = inet_csk_ca(sk); 65 int *stg; 66 67 if (!(tp->ecn_flags & TCP_ECN_OK) && fallback[0]) { 68 /* Switch to fallback */ 69 if (bpf_setsockopt(sk, SOL_TCP, TCP_CONGESTION, 70 (void *)fallback, sizeof(fallback)) == -EBUSY) 71 ebusy_cnt++; 72 73 /* Switch back to myself and the recurred dctcp_init() 74 * will get -EBUSY for all bpf_setsockopt(TCP_CONGESTION), 75 * except the last "cdg" one. 76 */ 77 if (bpf_setsockopt(sk, SOL_TCP, TCP_CONGESTION, 78 (void *)bpf_dctcp, sizeof(bpf_dctcp)) == -EBUSY) 79 ebusy_cnt++; 80 81 /* Switch back to fallback */ 82 if (bpf_setsockopt(sk, SOL_TCP, TCP_CONGESTION, 83 (void *)fallback, sizeof(fallback)) == -EBUSY) 84 ebusy_cnt++; 85 86 /* Expecting -ENOTSUPP for tcp_cdg_res */ 87 tcp_cdg_res = bpf_setsockopt(sk, SOL_TCP, TCP_CONGESTION, 88 (void *)tcp_cdg, sizeof(tcp_cdg)); 89 bpf_getsockopt(sk, SOL_TCP, TCP_CONGESTION, 90 (void *)cc_res, sizeof(cc_res)); 91 return; 92 } 93 94 ca->prior_rcv_nxt = tp->rcv_nxt; 95 ca->dctcp_alpha = min(dctcp_alpha_on_init, DCTCP_MAX_ALPHA); 96 ca->loss_cwnd = 0; 97 ca->ce_state = 0; 98 99 stg = bpf_sk_storage_get(&sk_stg_map, (void *)tp, NULL, 0); 100 if (stg) { 101 stg_result = *stg; 102 bpf_sk_storage_delete(&sk_stg_map, (void *)tp); 103 } 104 dctcp_reset(tp, ca); 105 } 106 107 SEC("struct_ops/dctcp_ssthresh") 108 __u32 BPF_PROG(dctcp_ssthresh, struct sock *sk) 109 { 110 struct dctcp *ca = inet_csk_ca(sk); 111 struct tcp_sock *tp = tcp_sk(sk); 112 113 ca->loss_cwnd = tp->snd_cwnd; 114 return max(tp->snd_cwnd - ((tp->snd_cwnd * ca->dctcp_alpha) >> 11U), 2U); 115 } 116 117 SEC("struct_ops/dctcp_update_alpha") 118 void BPF_PROG(dctcp_update_alpha, struct sock *sk, __u32 flags) 119 { 120 const struct tcp_sock *tp = tcp_sk(sk); 121 struct dctcp *ca = inet_csk_ca(sk); 122 123 /* Expired RTT */ 124 if (!before(tp->snd_una, ca->next_seq)) { 125 __u32 delivered_ce = tp->delivered_ce - ca->old_delivered_ce; 126 __u32 alpha = ca->dctcp_alpha; 127 128 /* alpha = (1 - g) * alpha + g * F */ 129 130 alpha -= min_not_zero(alpha, alpha >> dctcp_shift_g); 131 if (delivered_ce) { 132 __u32 delivered = tp->delivered - ca->old_delivered; 133 134 /* If dctcp_shift_g == 1, a 32bit value would overflow 135 * after 8 M packets. 136 */ 137 delivered_ce <<= (10 - dctcp_shift_g); 138 delivered_ce /= max(1U, delivered); 139 140 alpha = min(alpha + delivered_ce, DCTCP_MAX_ALPHA); 141 } 142 ca->dctcp_alpha = alpha; 143 dctcp_reset(tp, ca); 144 } 145 } 146 147 static __always_inline void dctcp_react_to_loss(struct sock *sk) 148 { 149 struct dctcp *ca = inet_csk_ca(sk); 150 struct tcp_sock *tp = tcp_sk(sk); 151 152 ca->loss_cwnd = tp->snd_cwnd; 153 tp->snd_ssthresh = max(tp->snd_cwnd >> 1U, 2U); 154 } 155 156 SEC("struct_ops/dctcp_state") 157 void BPF_PROG(dctcp_state, struct sock *sk, __u8 new_state) 158 { 159 if (new_state == TCP_CA_Recovery && 160 new_state != BPF_CORE_READ_BITFIELD(inet_csk(sk), icsk_ca_state)) 161 dctcp_react_to_loss(sk); 162 /* We handle RTO in dctcp_cwnd_event to ensure that we perform only 163 * one loss-adjustment per RTT. 164 */ 165 } 166 167 static __always_inline void dctcp_ece_ack_cwr(struct sock *sk, __u32 ce_state) 168 { 169 struct tcp_sock *tp = tcp_sk(sk); 170 171 if (ce_state == 1) 172 tp->ecn_flags |= TCP_ECN_DEMAND_CWR; 173 else 174 tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR; 175 } 176 177 /* Minimal DCTP CE state machine: 178 * 179 * S: 0 <- last pkt was non-CE 180 * 1 <- last pkt was CE 181 */ 182 static __always_inline 183 void dctcp_ece_ack_update(struct sock *sk, enum tcp_ca_event evt, 184 __u32 *prior_rcv_nxt, __u32 *ce_state) 185 { 186 __u32 new_ce_state = (evt == CA_EVENT_ECN_IS_CE) ? 1 : 0; 187 188 if (*ce_state != new_ce_state) { 189 /* CE state has changed, force an immediate ACK to 190 * reflect the new CE state. If an ACK was delayed, 191 * send that first to reflect the prior CE state. 192 */ 193 if (inet_csk(sk)->icsk_ack.pending & ICSK_ACK_TIMER) { 194 dctcp_ece_ack_cwr(sk, *ce_state); 195 bpf_tcp_send_ack(sk, *prior_rcv_nxt); 196 } 197 inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOW; 198 } 199 *prior_rcv_nxt = tcp_sk(sk)->rcv_nxt; 200 *ce_state = new_ce_state; 201 dctcp_ece_ack_cwr(sk, new_ce_state); 202 } 203 204 SEC("struct_ops/dctcp_cwnd_event") 205 void BPF_PROG(dctcp_cwnd_event, struct sock *sk, enum tcp_ca_event ev) 206 { 207 struct dctcp *ca = inet_csk_ca(sk); 208 209 switch (ev) { 210 case CA_EVENT_ECN_IS_CE: 211 case CA_EVENT_ECN_NO_CE: 212 dctcp_ece_ack_update(sk, ev, &ca->prior_rcv_nxt, &ca->ce_state); 213 break; 214 case CA_EVENT_LOSS: 215 dctcp_react_to_loss(sk); 216 break; 217 default: 218 /* Don't care for the rest. */ 219 break; 220 } 221 } 222 223 SEC("struct_ops/dctcp_cwnd_undo") 224 __u32 BPF_PROG(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 extern void tcp_reno_cong_avoid(struct sock *sk, __u32 ack, __u32 acked) __ksym; 232 233 SEC("struct_ops/dctcp_reno_cong_avoid") 234 void BPF_PROG(dctcp_cong_avoid, struct sock *sk, __u32 ack, __u32 acked) 235 { 236 tcp_reno_cong_avoid(sk, ack, acked); 237 } 238 239 SEC(".struct_ops") 240 struct tcp_congestion_ops dctcp_nouse = { 241 .init = (void *)dctcp_init, 242 .set_state = (void *)dctcp_state, 243 .flags = TCP_CONG_NEEDS_ECN, 244 .name = "bpf_dctcp_nouse", 245 }; 246 247 SEC(".struct_ops") 248 struct tcp_congestion_ops dctcp = { 249 .init = (void *)dctcp_init, 250 .in_ack_event = (void *)dctcp_update_alpha, 251 .cwnd_event = (void *)dctcp_cwnd_event, 252 .ssthresh = (void *)dctcp_ssthresh, 253 .cong_avoid = (void *)dctcp_cong_avoid, 254 .undo_cwnd = (void *)dctcp_cwnd_undo, 255 .set_state = (void *)dctcp_state, 256 .flags = TCP_CONG_NEEDS_ECN, 257 .name = "bpf_dctcp", 258 }; 259