| // 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 <dborkman@redhat.com> |
| * Florian Westphal <fw@strlen.de> |
| * Glenn Judd <glenn.judd@morganstanley.com> |
| */ |
| |
| #include <linux/btf.h> |
| #include <linux/btf_ids.h> |
| #include <linux/module.h> |
| #include <linux/mm.h> |
| #include <net/tcp.h> |
| #include <linux/inet_diag.h> |
| #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; |
| struct tcp_plb_state plb; |
| }; |
| |
| 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); |
| tcp_plb_init(sk, &ca->plb); |
| |
| 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 = tcp_snd_cwnd(tp); |
| return max(tcp_snd_cwnd(tp) - ((tcp_snd_cwnd(tp) * 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 = tp->delivered - ca->old_delivered; |
| u32 delivered_ce = tp->delivered_ce - ca->old_delivered_ce; |
| u32 alpha = ca->dctcp_alpha; |
| u32 ce_ratio = 0; |
| |
| if (delivered > 0) { |
| /* dctcp_alpha keeps EWMA of fraction of ECN marked |
| * packets. Because of EWMA smoothing, PLB reaction can |
| * be slow so we use ce_ratio which is an instantaneous |
| * measure of congestion. ce_ratio is the fraction of |
| * ECN marked packets in the previous RTT. |
| */ |
| if (delivered_ce > 0) |
| ce_ratio = (delivered_ce << TCP_PLB_SCALE) / delivered; |
| tcp_plb_update_state(sk, &ca->plb, (int)ce_ratio); |
| tcp_plb_check_rehash(sk, &ca->plb); |
| } |
| |
| /* alpha = (1 - g) * alpha + g * F */ |
| |
| alpha -= min_not_zero(alpha, alpha >> dctcp_shift_g); |
| if (delivered_ce) { |
| |
| /* 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 = tcp_snd_cwnd(tp); |
| tp->snd_ssthresh = max(tcp_snd_cwnd(tp) >> 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: |
| tcp_plb_update_state_upon_rto(sk, &ca->plb); |
| dctcp_react_to_loss(sk); |
| break; |
| case CA_EVENT_TX_START: |
| tcp_plb_check_rehash(sk, &ca->plb); /* Maybe rehash when inflight is 0 */ |
| 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); |
| struct tcp_sock *tp = tcp_sk(sk); |
| |
| return max(tcp_snd_cwnd(tp), 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", |
| }; |
| |
| BTF_SET8_START(tcp_dctcp_check_kfunc_ids) |
| #ifdef CONFIG_X86 |
| #ifdef CONFIG_DYNAMIC_FTRACE |
| BTF_ID_FLAGS(func, dctcp_init) |
| BTF_ID_FLAGS(func, dctcp_update_alpha) |
| BTF_ID_FLAGS(func, dctcp_cwnd_event) |
| BTF_ID_FLAGS(func, dctcp_ssthresh) |
| BTF_ID_FLAGS(func, dctcp_cwnd_undo) |
| BTF_ID_FLAGS(func, dctcp_state) |
| #endif |
| #endif |
| BTF_SET8_END(tcp_dctcp_check_kfunc_ids) |
| |
| static const struct btf_kfunc_id_set tcp_dctcp_kfunc_set = { |
| .owner = THIS_MODULE, |
| .set = &tcp_dctcp_check_kfunc_ids, |
| }; |
| |
| static int __init dctcp_register(void) |
| { |
| int ret; |
| |
| BUILD_BUG_ON(sizeof(struct dctcp) > ICSK_CA_PRIV_SIZE); |
| |
| ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &tcp_dctcp_kfunc_set); |
| if (ret < 0) |
| return ret; |
| 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)"); |