| /* 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> |
| * |
| * This program is free software; you can redistribute it and/or modify |
| * it under the terms of the GNU General Public License as published by |
| * the Free Software Foundation; either version 2 of the License, or (at |
| * your option) any later version. |
| */ |
| |
| #include <linux/module.h> |
| #include <linux/mm.h> |
| #include <net/tcp.h> |
| #include <linux/inet_diag.h> |
| |
| #define DCTCP_MAX_ALPHA 1024U |
| |
| struct dctcp { |
| u32 acked_bytes_ecn; |
| u32 acked_bytes_total; |
| u32 prior_snd_una; |
| u32 prior_rcv_nxt; |
| u32 dctcp_alpha; |
| u32 next_seq; |
| u32 ce_state; |
| u32 delayed_ack_reserved; |
| }; |
| |
| 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 unsigned int dctcp_clamp_alpha_on_loss __read_mostly; |
| module_param(dctcp_clamp_alpha_on_loss, uint, 0644); |
| MODULE_PARM_DESC(dctcp_clamp_alpha_on_loss, |
| "parameter for clamping alpha on loss"); |
| |
| 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->acked_bytes_ecn = 0; |
| ca->acked_bytes_total = 0; |
| } |
| |
| 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_snd_una = tp->snd_una; |
| ca->prior_rcv_nxt = tp->rcv_nxt; |
| |
| ca->dctcp_alpha = min(dctcp_alpha_on_init, DCTCP_MAX_ALPHA); |
| |
| ca->delayed_ack_reserved = 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) |
| { |
| const struct dctcp *ca = inet_csk_ca(sk); |
| struct tcp_sock *tp = tcp_sk(sk); |
| |
| return max(tp->snd_cwnd - ((tp->snd_cwnd * ca->dctcp_alpha) >> 11U), 2U); |
| } |
| |
| /* Minimal DCTP CE state machine: |
| * |
| * S: 0 <- last pkt was non-CE |
| * 1 <- last pkt was CE |
| */ |
| |
| static void dctcp_ce_state_0_to_1(struct sock *sk) |
| { |
| struct dctcp *ca = inet_csk_ca(sk); |
| struct tcp_sock *tp = tcp_sk(sk); |
| |
| /* State has changed from CE=0 to CE=1 and delayed |
| * ACK has not sent yet. |
| */ |
| if (!ca->ce_state && ca->delayed_ack_reserved) { |
| u32 tmp_rcv_nxt; |
| |
| /* Save current rcv_nxt. */ |
| tmp_rcv_nxt = tp->rcv_nxt; |
| |
| /* Generate previous ack with CE=0. */ |
| tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR; |
| tp->rcv_nxt = ca->prior_rcv_nxt; |
| |
| tcp_send_ack(sk); |
| |
| /* Recover current rcv_nxt. */ |
| tp->rcv_nxt = tmp_rcv_nxt; |
| } |
| |
| ca->prior_rcv_nxt = tp->rcv_nxt; |
| ca->ce_state = 1; |
| |
| tp->ecn_flags |= TCP_ECN_DEMAND_CWR; |
| } |
| |
| static void dctcp_ce_state_1_to_0(struct sock *sk) |
| { |
| struct dctcp *ca = inet_csk_ca(sk); |
| struct tcp_sock *tp = tcp_sk(sk); |
| |
| /* State has changed from CE=1 to CE=0 and delayed |
| * ACK has not sent yet. |
| */ |
| if (ca->ce_state && ca->delayed_ack_reserved) { |
| u32 tmp_rcv_nxt; |
| |
| /* Save current rcv_nxt. */ |
| tmp_rcv_nxt = tp->rcv_nxt; |
| |
| /* Generate previous ack with CE=1. */ |
| tp->ecn_flags |= TCP_ECN_DEMAND_CWR; |
| tp->rcv_nxt = ca->prior_rcv_nxt; |
| |
| tcp_send_ack(sk); |
| |
| /* Recover current rcv_nxt. */ |
| tp->rcv_nxt = tmp_rcv_nxt; |
| } |
| |
| ca->prior_rcv_nxt = tp->rcv_nxt; |
| ca->ce_state = 0; |
| |
| tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR; |
| } |
| |
| 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); |
| u32 acked_bytes = tp->snd_una - ca->prior_snd_una; |
| |
| /* If ack did not advance snd_una, count dupack as MSS size. |
| * If ack did update window, do not count it at all. |
| */ |
| if (acked_bytes == 0 && !(flags & CA_ACK_WIN_UPDATE)) |
| acked_bytes = inet_csk(sk)->icsk_ack.rcv_mss; |
| if (acked_bytes) { |
| ca->acked_bytes_total += acked_bytes; |
| ca->prior_snd_una = tp->snd_una; |
| |
| if (flags & CA_ACK_ECE) |
| ca->acked_bytes_ecn += acked_bytes; |
| } |
| |
| /* Expired RTT */ |
| if (!before(tp->snd_una, ca->next_seq)) { |
| u64 bytes_ecn = ca->acked_bytes_ecn; |
| u32 alpha = ca->dctcp_alpha; |
| |
| /* alpha = (1 - g) * alpha + g * F */ |
| |
| alpha -= min_not_zero(alpha, alpha >> dctcp_shift_g); |
| if (bytes_ecn) { |
| /* If dctcp_shift_g == 1, a 32bit value would overflow |
| * after 8 Mbytes. |
| */ |
| bytes_ecn <<= (10 - dctcp_shift_g); |
| do_div(bytes_ecn, max(1U, ca->acked_bytes_total)); |
| |
| alpha = min(alpha + (u32)bytes_ecn, 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_state(struct sock *sk, u8 new_state) |
| { |
| if (dctcp_clamp_alpha_on_loss && new_state == TCP_CA_Loss) { |
| struct dctcp *ca = inet_csk_ca(sk); |
| |
| /* If this extension is enabled, we clamp dctcp_alpha to |
| * max on packet loss; the motivation is that dctcp_alpha |
| * is an indicator to the extend of congestion and packet |
| * loss is an indicator of extreme congestion; setting |
| * this in practice turned out to be beneficial, and |
| * effectively assumes total congestion which reduces the |
| * window by half. |
| */ |
| ca->dctcp_alpha = DCTCP_MAX_ALPHA; |
| } |
| } |
| |
| static void dctcp_update_ack_reserved(struct sock *sk, enum tcp_ca_event ev) |
| { |
| struct dctcp *ca = inet_csk_ca(sk); |
| |
| switch (ev) { |
| case CA_EVENT_DELAYED_ACK: |
| if (!ca->delayed_ack_reserved) |
| ca->delayed_ack_reserved = 1; |
| break; |
| case CA_EVENT_NON_DELAYED_ACK: |
| if (ca->delayed_ack_reserved) |
| ca->delayed_ack_reserved = 0; |
| break; |
| default: |
| /* Don't care for the rest. */ |
| break; |
| } |
| } |
| |
| static void dctcp_cwnd_event(struct sock *sk, enum tcp_ca_event ev) |
| { |
| switch (ev) { |
| case CA_EVENT_ECN_IS_CE: |
| dctcp_ce_state_0_to_1(sk); |
| break; |
| case CA_EVENT_ECN_NO_CE: |
| dctcp_ce_state_1_to_0(sk); |
| break; |
| case CA_EVENT_DELAYED_ACK: |
| case CA_EVENT_NON_DELAYED_ACK: |
| dctcp_update_ack_reserved(sk, ev); |
| 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); |
| |
| /* 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, 0, sizeof(struct tcp_dctcp_info)); |
| 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 = ca->acked_bytes_ecn; |
| info->dctcp.dctcp_ab_tot = ca->acked_bytes_total; |
| } |
| |
| *attr = INET_DIAG_DCTCPINFO; |
| return sizeof(*info); |
| } |
| return 0; |
| } |
| |
| 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, |
| .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, |
| .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)"); |