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net/ipv4/tcp_dctcp.c
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// SPDX-License-Identifier: GPL-2.0-or-later |
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/* 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 <dborkman@redhat.com> * Florian Westphal <fw@strlen.de> * Glenn Judd <glenn.judd@morganstanley.com> |
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*/ #include <linux/module.h> #include <linux/mm.h> #include <net/tcp.h> #include <linux/inet_diag.h> |
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#include "tcp_dctcp.h" |
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#define DCTCP_MAX_ALPHA 1024U struct dctcp { |
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u32 old_delivered; u32 old_delivered_ce; |
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u32 prior_rcv_nxt; u32 dctcp_alpha; u32 next_seq; u32 ce_state; |
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u32 loss_cwnd; |
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}; 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"); |
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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; |
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ca->old_delivered = tp->delivered; ca->old_delivered_ce = tp->delivered_ce; |
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} 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); |
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ca->prior_rcv_nxt = tp->rcv_nxt; ca->dctcp_alpha = min(dctcp_alpha_on_init, DCTCP_MAX_ALPHA); |
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ca->loss_cwnd = 0; |
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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) { |
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struct dctcp *ca = inet_csk_ca(sk); |
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struct tcp_sock *tp = tcp_sk(sk); |
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ca->loss_cwnd = tp->snd_cwnd; |
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return max(tp->snd_cwnd - ((tp->snd_cwnd * ca->dctcp_alpha) >> 11U), 2U); } |
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static void dctcp_update_alpha(struct sock *sk, u32 flags) { |
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const struct tcp_sock *tp = tcp_sk(sk); |
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struct dctcp *ca = inet_csk_ca(sk); |
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/* Expired RTT */ if (!before(tp->snd_una, ca->next_seq)) { |
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u32 delivered_ce = tp->delivered_ce - ca->old_delivered_ce; |
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u32 alpha = ca->dctcp_alpha; |
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/* alpha = (1 - g) * alpha + g * F */ |
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alpha -= min_not_zero(alpha, alpha >> dctcp_shift_g); |
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if (delivered_ce) { u32 delivered = tp->delivered - ca->old_delivered; |
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/* If dctcp_shift_g == 1, a 32bit value would overflow |
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* after 8 M packets. |
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*/ |
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delivered_ce <<= (10 - dctcp_shift_g); delivered_ce /= max(1U, delivered); |
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alpha = min(alpha + delivered_ce, DCTCP_MAX_ALPHA); |
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} /* 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); |
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dctcp_reset(tp, ca); } } |
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static void dctcp_react_to_loss(struct sock *sk) |
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{ |
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struct dctcp *ca = inet_csk_ca(sk); struct tcp_sock *tp = tcp_sk(sk); |
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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. */ |
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} |
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static void dctcp_cwnd_event(struct sock *sk, enum tcp_ca_event ev) { |
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struct dctcp *ca = inet_csk_ca(sk); |
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switch (ev) { case CA_EVENT_ECN_IS_CE: |
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case CA_EVENT_ECN_NO_CE: |
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dctcp_ece_ack_update(sk, ev, &ca->prior_rcv_nxt, &ca->ce_state); |
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break; |
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case CA_EVENT_LOSS: dctcp_react_to_loss(sk); break; |
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default: /* Don't care for the rest. */ break; } } |
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static size_t dctcp_get_info(struct sock *sk, u32 ext, int *attr, union tcp_cc_info *info) |
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{ const struct dctcp *ca = inet_csk_ca(sk); |
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const struct tcp_sock *tp = tcp_sk(sk); |
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/* 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))) { |
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memset(&info->dctcp, 0, sizeof(info->dctcp)); |
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if (inet_csk(sk)->icsk_ca_ops != &dctcp_reno) { |
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info->dctcp.dctcp_enabled = 1; info->dctcp.dctcp_ce_state = (u16) ca->ce_state; info->dctcp.dctcp_alpha = ca->dctcp_alpha; |
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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); |
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} |
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*attr = INET_DIAG_DCTCPINFO; |
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return sizeof(info->dctcp); |
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} |
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return 0; |
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} |
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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); } |
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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, |
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.undo_cwnd = dctcp_cwnd_undo, |
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.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, |
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.undo_cwnd = tcp_reno_undo_cwnd, |
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.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 <dborkman@redhat.com>"); MODULE_AUTHOR("Florian Westphal <fw@strlen.de>"); MODULE_AUTHOR("Glenn Judd <glenn.judd@morganstanley.com>"); MODULE_LICENSE("GPL v2"); MODULE_DESCRIPTION("DataCenter TCP (DCTCP)"); |