// SPDX-License-Identifier: GPL-2.0-or-later /* DataCenter TCP (DCTCP) congestion control. * * http://simula.stanford.edu/~alizade/Site/DCTCP.html * * This is an implementation of DCTCP over Reno, an enhancement to the * TCP congestion control algorithm designed for data centers. DCTCP * leverages Explicit Congestion Notification (ECN) in the network to * provide multi-bit feedback to the end hosts. DCTCP's goal is to meet * the following three data center transport requirements: * * - High burst tolerance (incast due to partition/aggregate) * - Low latency (short flows, queries) * - High throughput (continuous data updates, large file transfers) * with commodity shallow buffered switches * * The algorithm is described in detail in the following two papers: * * 1) Mohammad Alizadeh, Albert Greenberg, David A. Maltz, Jitendra Padhye, * Parveen Patel, Balaji Prabhakar, Sudipta Sengupta, and Murari Sridharan: * "Data Center TCP (DCTCP)", Data Center Networks session * Proc. ACM SIGCOMM, New Delhi, 2010. * http://simula.stanford.edu/~alizade/Site/DCTCP_files/dctcp-final.pdf * * 2) Mohammad Alizadeh, Adel Javanmard, and Balaji Prabhakar: * "Analysis of DCTCP: Stability, Convergence, and Fairness" * Proc. ACM SIGMETRICS, San Jose, 2011. * http://simula.stanford.edu/~alizade/Site/DCTCP_files/dctcp_analysis-full.pdf * * Initial prototype from Abdul Kabbani, Masato Yasuda and Mohammad Alizadeh. * * Authors: * * Daniel Borkmann * Florian Westphal * Glenn Judd */ #include #include #include #include #include "tcp_dctcp.h" #define DCTCP_MAX_ALPHA 1024U struct dctcp { u32 old_delivered; u32 old_delivered_ce; u32 prior_rcv_nxt; u32 dctcp_alpha; u32 next_seq; u32 ce_state; u32 loss_cwnd; }; static unsigned int dctcp_shift_g __read_mostly = 4; /* g = 1/2^4 */ module_param(dctcp_shift_g, uint, 0644); MODULE_PARM_DESC(dctcp_shift_g, "parameter g for updating dctcp_alpha"); static unsigned int dctcp_alpha_on_init __read_mostly = DCTCP_MAX_ALPHA; module_param(dctcp_alpha_on_init, uint, 0644); MODULE_PARM_DESC(dctcp_alpha_on_init, "parameter for initial alpha value"); static struct tcp_congestion_ops dctcp_reno; static void dctcp_reset(const struct tcp_sock *tp, struct dctcp *ca) { ca->next_seq = tp->snd_nxt; ca->old_delivered = tp->delivered; ca->old_delivered_ce = tp->delivered_ce; } static void dctcp_init(struct sock *sk) { const struct tcp_sock *tp = tcp_sk(sk); if ((tp->ecn_flags & TCP_ECN_OK) || (sk->sk_state == TCP_LISTEN || sk->sk_state == TCP_CLOSE)) { struct dctcp *ca = inet_csk_ca(sk); ca->prior_rcv_nxt = tp->rcv_nxt; ca->dctcp_alpha = min(dctcp_alpha_on_init, DCTCP_MAX_ALPHA); ca->loss_cwnd = 0; ca->ce_state = 0; dctcp_reset(tp, ca); return; } /* No ECN support? Fall back to Reno. Also need to clear * ECT from sk since it is set during 3WHS for DCTCP. */ inet_csk(sk)->icsk_ca_ops = &dctcp_reno; INET_ECN_dontxmit(sk); } static u32 dctcp_ssthresh(struct sock *sk) { struct dctcp *ca = inet_csk_ca(sk); struct tcp_sock *tp = tcp_sk(sk); ca->loss_cwnd = tp->snd_cwnd; return max(tp->snd_cwnd - ((tp->snd_cwnd * ca->dctcp_alpha) >> 11U), 2U); } static void dctcp_update_alpha(struct sock *sk, u32 flags) { const struct tcp_sock *tp = tcp_sk(sk); struct dctcp *ca = inet_csk_ca(sk); /* Expired RTT */ if (!before(tp->snd_una, ca->next_seq)) { u32 delivered_ce = tp->delivered_ce - ca->old_delivered_ce; u32 alpha = ca->dctcp_alpha; /* alpha = (1 - g) * alpha + g * F */ alpha -= min_not_zero(alpha, alpha >> dctcp_shift_g); if (delivered_ce) { u32 delivered = tp->delivered - ca->old_delivered; /* If dctcp_shift_g == 1, a 32bit value would overflow * after 8 M packets. */ delivered_ce <<= (10 - dctcp_shift_g); delivered_ce /= max(1U, delivered); alpha = min(alpha + delivered_ce, DCTCP_MAX_ALPHA); } /* dctcp_alpha can be read from dctcp_get_info() without * synchro, so we ask compiler to not use dctcp_alpha * as a temporary variable in prior operations. */ WRITE_ONCE(ca->dctcp_alpha, alpha); dctcp_reset(tp, ca); } } static void dctcp_react_to_loss(struct sock *sk) { struct dctcp *ca = inet_csk_ca(sk); struct tcp_sock *tp = tcp_sk(sk); ca->loss_cwnd = tp->snd_cwnd; tp->snd_ssthresh = max(tp->snd_cwnd >> 1U, 2U); } static void dctcp_state(struct sock *sk, u8 new_state) { if (new_state == TCP_CA_Recovery && new_state != inet_csk(sk)->icsk_ca_state) dctcp_react_to_loss(sk); /* We handle RTO in dctcp_cwnd_event to ensure that we perform only * one loss-adjustment per RTT. */ } static void dctcp_cwnd_event(struct sock *sk, enum tcp_ca_event ev) { struct dctcp *ca = inet_csk_ca(sk); switch (ev) { case CA_EVENT_ECN_IS_CE: case CA_EVENT_ECN_NO_CE: dctcp_ece_ack_update(sk, ev, &ca->prior_rcv_nxt, &ca->ce_state); break; case CA_EVENT_LOSS: dctcp_react_to_loss(sk); break; default: /* Don't care for the rest. */ break; } } static size_t dctcp_get_info(struct sock *sk, u32 ext, int *attr, union tcp_cc_info *info) { const struct dctcp *ca = inet_csk_ca(sk); const struct tcp_sock *tp = tcp_sk(sk); /* Fill it also in case of VEGASINFO due to req struct limits. * We can still correctly retrieve it later. */ if (ext & (1 << (INET_DIAG_DCTCPINFO - 1)) || ext & (1 << (INET_DIAG_VEGASINFO - 1))) { memset(&info->dctcp, 0, sizeof(info->dctcp)); if (inet_csk(sk)->icsk_ca_ops != &dctcp_reno) { info->dctcp.dctcp_enabled = 1; info->dctcp.dctcp_ce_state = (u16) ca->ce_state; info->dctcp.dctcp_alpha = ca->dctcp_alpha; info->dctcp.dctcp_ab_ecn = tp->mss_cache * (tp->delivered_ce - ca->old_delivered_ce); info->dctcp.dctcp_ab_tot = tp->mss_cache * (tp->delivered - ca->old_delivered); } *attr = INET_DIAG_DCTCPINFO; return sizeof(info->dctcp); } return 0; } static u32 dctcp_cwnd_undo(struct sock *sk) { const struct dctcp *ca = inet_csk_ca(sk); return max(tcp_sk(sk)->snd_cwnd, ca->loss_cwnd); } static struct tcp_congestion_ops dctcp __read_mostly = { .init = dctcp_init, .in_ack_event = dctcp_update_alpha, .cwnd_event = dctcp_cwnd_event, .ssthresh = dctcp_ssthresh, .cong_avoid = tcp_reno_cong_avoid, .undo_cwnd = dctcp_cwnd_undo, .set_state = dctcp_state, .get_info = dctcp_get_info, .flags = TCP_CONG_NEEDS_ECN, .owner = THIS_MODULE, .name = "dctcp", }; static struct tcp_congestion_ops dctcp_reno __read_mostly = { .ssthresh = tcp_reno_ssthresh, .cong_avoid = tcp_reno_cong_avoid, .undo_cwnd = tcp_reno_undo_cwnd, .get_info = dctcp_get_info, .owner = THIS_MODULE, .name = "dctcp-reno", }; static int __init dctcp_register(void) { BUILD_BUG_ON(sizeof(struct dctcp) > ICSK_CA_PRIV_SIZE); return tcp_register_congestion_control(&dctcp); } static void __exit dctcp_unregister(void) { tcp_unregister_congestion_control(&dctcp); } module_init(dctcp_register); module_exit(dctcp_unregister); MODULE_AUTHOR("Daniel Borkmann "); MODULE_AUTHOR("Florian Westphal "); MODULE_AUTHOR("Glenn Judd "); MODULE_LICENSE("GPL v2"); MODULE_DESCRIPTION("DataCenter TCP (DCTCP)");