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f9c2ff22bb
dctcp_alpha can be read by from dctcp_get_info() without synchro, so use WRITE_ONCE() to prevent compiler from using dctcp_alpha as a temporary variable. Also, playing with small dctcp_shift_g (like 1), can expose an overflow with 32bit values shifted 9 times before divide. Use an u64 field to avoid this problem, and perform the divide only if acked_bytes_ecn is not zero. Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
352 lines
9.4 KiB
C
352 lines
9.4 KiB
C
/* DataCenter TCP (DCTCP) congestion control.
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*
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* http://simula.stanford.edu/~alizade/Site/DCTCP.html
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*
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* This is an implementation of DCTCP over Reno, an enhancement to the
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* TCP congestion control algorithm designed for data centers. DCTCP
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* leverages Explicit Congestion Notification (ECN) in the network to
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* provide multi-bit feedback to the end hosts. DCTCP's goal is to meet
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* the following three data center transport requirements:
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*
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* - High burst tolerance (incast due to partition/aggregate)
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* - Low latency (short flows, queries)
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* - High throughput (continuous data updates, large file transfers)
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* with commodity shallow buffered switches
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*
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* The algorithm is described in detail in the following two papers:
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*
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* 1) Mohammad Alizadeh, Albert Greenberg, David A. Maltz, Jitendra Padhye,
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* Parveen Patel, Balaji Prabhakar, Sudipta Sengupta, and Murari Sridharan:
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* "Data Center TCP (DCTCP)", Data Center Networks session
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* Proc. ACM SIGCOMM, New Delhi, 2010.
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* http://simula.stanford.edu/~alizade/Site/DCTCP_files/dctcp-final.pdf
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*
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* 2) Mohammad Alizadeh, Adel Javanmard, and Balaji Prabhakar:
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* "Analysis of DCTCP: Stability, Convergence, and Fairness"
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* Proc. ACM SIGMETRICS, San Jose, 2011.
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* http://simula.stanford.edu/~alizade/Site/DCTCP_files/dctcp_analysis-full.pdf
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*
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* Initial prototype from Abdul Kabbani, Masato Yasuda and Mohammad Alizadeh.
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*
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* Authors:
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*
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* Daniel Borkmann <dborkman@redhat.com>
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* Florian Westphal <fw@strlen.de>
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* Glenn Judd <glenn.judd@morganstanley.com>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or (at
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* your option) any later version.
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*/
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#include <linux/module.h>
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#include <linux/mm.h>
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#include <net/tcp.h>
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#include <linux/inet_diag.h>
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#define DCTCP_MAX_ALPHA 1024U
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struct dctcp {
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u32 acked_bytes_ecn;
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u32 acked_bytes_total;
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u32 prior_snd_una;
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u32 prior_rcv_nxt;
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u32 dctcp_alpha;
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u32 next_seq;
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u32 ce_state;
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u32 delayed_ack_reserved;
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};
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static unsigned int dctcp_shift_g __read_mostly = 4; /* g = 1/2^4 */
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module_param(dctcp_shift_g, uint, 0644);
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MODULE_PARM_DESC(dctcp_shift_g, "parameter g for updating dctcp_alpha");
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static unsigned int dctcp_alpha_on_init __read_mostly = DCTCP_MAX_ALPHA;
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module_param(dctcp_alpha_on_init, uint, 0644);
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MODULE_PARM_DESC(dctcp_alpha_on_init, "parameter for initial alpha value");
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static unsigned int dctcp_clamp_alpha_on_loss __read_mostly;
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module_param(dctcp_clamp_alpha_on_loss, uint, 0644);
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MODULE_PARM_DESC(dctcp_clamp_alpha_on_loss,
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"parameter for clamping alpha on loss");
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static struct tcp_congestion_ops dctcp_reno;
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static void dctcp_reset(const struct tcp_sock *tp, struct dctcp *ca)
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{
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ca->next_seq = tp->snd_nxt;
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ca->acked_bytes_ecn = 0;
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ca->acked_bytes_total = 0;
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}
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static void dctcp_init(struct sock *sk)
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{
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const struct tcp_sock *tp = tcp_sk(sk);
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if ((tp->ecn_flags & TCP_ECN_OK) ||
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(sk->sk_state == TCP_LISTEN ||
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sk->sk_state == TCP_CLOSE)) {
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struct dctcp *ca = inet_csk_ca(sk);
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ca->prior_snd_una = tp->snd_una;
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ca->prior_rcv_nxt = tp->rcv_nxt;
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ca->dctcp_alpha = min(dctcp_alpha_on_init, DCTCP_MAX_ALPHA);
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ca->delayed_ack_reserved = 0;
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ca->ce_state = 0;
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dctcp_reset(tp, ca);
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return;
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}
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/* No ECN support? Fall back to Reno. Also need to clear
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* ECT from sk since it is set during 3WHS for DCTCP.
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*/
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inet_csk(sk)->icsk_ca_ops = &dctcp_reno;
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INET_ECN_dontxmit(sk);
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}
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static u32 dctcp_ssthresh(struct sock *sk)
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{
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const struct dctcp *ca = inet_csk_ca(sk);
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struct tcp_sock *tp = tcp_sk(sk);
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return max(tp->snd_cwnd - ((tp->snd_cwnd * ca->dctcp_alpha) >> 11U), 2U);
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}
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/* Minimal DCTP CE state machine:
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*
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* S: 0 <- last pkt was non-CE
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* 1 <- last pkt was CE
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*/
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static void dctcp_ce_state_0_to_1(struct sock *sk)
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{
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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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/* State has changed from CE=0 to CE=1 and delayed
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* ACK has not sent yet.
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*/
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if (!ca->ce_state && ca->delayed_ack_reserved) {
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u32 tmp_rcv_nxt;
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/* Save current rcv_nxt. */
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tmp_rcv_nxt = tp->rcv_nxt;
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/* Generate previous ack with CE=0. */
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tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
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tp->rcv_nxt = ca->prior_rcv_nxt;
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tcp_send_ack(sk);
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/* Recover current rcv_nxt. */
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tp->rcv_nxt = tmp_rcv_nxt;
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}
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ca->prior_rcv_nxt = tp->rcv_nxt;
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ca->ce_state = 1;
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tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
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}
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static void dctcp_ce_state_1_to_0(struct sock *sk)
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{
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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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/* State has changed from CE=1 to CE=0 and delayed
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* ACK has not sent yet.
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*/
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if (ca->ce_state && ca->delayed_ack_reserved) {
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u32 tmp_rcv_nxt;
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/* Save current rcv_nxt. */
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tmp_rcv_nxt = tp->rcv_nxt;
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/* Generate previous ack with CE=1. */
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tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
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tp->rcv_nxt = ca->prior_rcv_nxt;
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tcp_send_ack(sk);
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/* Recover current rcv_nxt. */
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tp->rcv_nxt = tmp_rcv_nxt;
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}
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ca->prior_rcv_nxt = tp->rcv_nxt;
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ca->ce_state = 0;
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tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
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}
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static void dctcp_update_alpha(struct sock *sk, u32 flags)
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{
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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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u32 acked_bytes = tp->snd_una - ca->prior_snd_una;
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/* If ack did not advance snd_una, count dupack as MSS size.
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* If ack did update window, do not count it at all.
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*/
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if (acked_bytes == 0 && !(flags & CA_ACK_WIN_UPDATE))
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acked_bytes = inet_csk(sk)->icsk_ack.rcv_mss;
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if (acked_bytes) {
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ca->acked_bytes_total += acked_bytes;
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ca->prior_snd_una = tp->snd_una;
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if (flags & CA_ACK_ECE)
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ca->acked_bytes_ecn += acked_bytes;
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}
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/* Expired RTT */
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if (!before(tp->snd_una, ca->next_seq)) {
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u64 bytes_ecn = ca->acked_bytes_ecn;
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u32 alpha = ca->dctcp_alpha;
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/* alpha = (1 - g) * alpha + g * F */
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alpha -= alpha >> dctcp_shift_g;
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if (bytes_ecn) {
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/* If dctcp_shift_g == 1, a 32bit value would overflow
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* after 8 Mbytes.
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*/
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bytes_ecn <<= (10 - dctcp_shift_g);
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do_div(bytes_ecn, max(1U, ca->acked_bytes_total));
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alpha = min(alpha + (u32)bytes_ecn, DCTCP_MAX_ALPHA);
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}
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/* dctcp_alpha can be read from dctcp_get_info() without
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* synchro, so we ask compiler to not use dctcp_alpha
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* as a temporary variable in prior operations.
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*/
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WRITE_ONCE(ca->dctcp_alpha, alpha);
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dctcp_reset(tp, ca);
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}
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}
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static void dctcp_state(struct sock *sk, u8 new_state)
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{
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if (dctcp_clamp_alpha_on_loss && new_state == TCP_CA_Loss) {
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struct dctcp *ca = inet_csk_ca(sk);
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/* If this extension is enabled, we clamp dctcp_alpha to
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* max on packet loss; the motivation is that dctcp_alpha
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* is an indicator to the extend of congestion and packet
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* loss is an indicator of extreme congestion; setting
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* this in practice turned out to be beneficial, and
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* effectively assumes total congestion which reduces the
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* window by half.
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*/
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ca->dctcp_alpha = DCTCP_MAX_ALPHA;
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}
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}
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static void dctcp_update_ack_reserved(struct sock *sk, enum tcp_ca_event ev)
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{
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struct dctcp *ca = inet_csk_ca(sk);
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switch (ev) {
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case CA_EVENT_DELAYED_ACK:
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if (!ca->delayed_ack_reserved)
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ca->delayed_ack_reserved = 1;
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break;
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case CA_EVENT_NON_DELAYED_ACK:
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if (ca->delayed_ack_reserved)
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ca->delayed_ack_reserved = 0;
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break;
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default:
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/* Don't care for the rest. */
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break;
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}
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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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{
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switch (ev) {
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case CA_EVENT_ECN_IS_CE:
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dctcp_ce_state_0_to_1(sk);
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break;
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case CA_EVENT_ECN_NO_CE:
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dctcp_ce_state_1_to_0(sk);
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break;
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case CA_EVENT_DELAYED_ACK:
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case CA_EVENT_NON_DELAYED_ACK:
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dctcp_update_ack_reserved(sk, ev);
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break;
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default:
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/* Don't care for the rest. */
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break;
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}
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}
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static size_t dctcp_get_info(struct sock *sk, u32 ext, int *attr,
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union tcp_cc_info *info)
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{
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const struct dctcp *ca = inet_csk_ca(sk);
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/* Fill it also in case of VEGASINFO due to req struct limits.
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* We can still correctly retrieve it later.
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*/
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if (ext & (1 << (INET_DIAG_DCTCPINFO - 1)) ||
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ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
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memset(info, 0, sizeof(struct tcp_dctcp_info));
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if (inet_csk(sk)->icsk_ca_ops != &dctcp_reno) {
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info->dctcp.dctcp_enabled = 1;
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info->dctcp.dctcp_ce_state = (u16) ca->ce_state;
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info->dctcp.dctcp_alpha = ca->dctcp_alpha;
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info->dctcp.dctcp_ab_ecn = ca->acked_bytes_ecn;
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info->dctcp.dctcp_ab_tot = ca->acked_bytes_total;
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}
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*attr = INET_DIAG_DCTCPINFO;
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return sizeof(*info);
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}
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return 0;
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}
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static struct tcp_congestion_ops dctcp __read_mostly = {
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.init = dctcp_init,
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.in_ack_event = dctcp_update_alpha,
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.cwnd_event = dctcp_cwnd_event,
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.ssthresh = dctcp_ssthresh,
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.cong_avoid = tcp_reno_cong_avoid,
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.set_state = dctcp_state,
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.get_info = dctcp_get_info,
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.flags = TCP_CONG_NEEDS_ECN,
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.owner = THIS_MODULE,
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.name = "dctcp",
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};
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static struct tcp_congestion_ops dctcp_reno __read_mostly = {
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.ssthresh = tcp_reno_ssthresh,
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.cong_avoid = tcp_reno_cong_avoid,
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.get_info = dctcp_get_info,
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.owner = THIS_MODULE,
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.name = "dctcp-reno",
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};
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static int __init dctcp_register(void)
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{
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BUILD_BUG_ON(sizeof(struct dctcp) > ICSK_CA_PRIV_SIZE);
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return tcp_register_congestion_control(&dctcp);
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}
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static void __exit dctcp_unregister(void)
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{
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tcp_unregister_congestion_control(&dctcp);
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}
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module_init(dctcp_register);
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module_exit(dctcp_unregister);
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MODULE_AUTHOR("Daniel Borkmann <dborkman@redhat.com>");
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MODULE_AUTHOR("Florian Westphal <fw@strlen.de>");
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MODULE_AUTHOR("Glenn Judd <glenn.judd@morganstanley.com>");
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MODULE_LICENSE("GPL v2");
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MODULE_DESCRIPTION("DataCenter TCP (DCTCP)");
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