--- /dev/null
+/* 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)) {
+ /* For avoiding denominator == 1. */
+ if (ca->acked_bytes_total == 0)
+ ca->acked_bytes_total = 1;
+
+ /* alpha = (1 - g) * alpha + g * F */
+ ca->dctcp_alpha = ca->dctcp_alpha -
+ (ca->dctcp_alpha >> dctcp_shift_g) +
+ (ca->acked_bytes_ecn << (10U - dctcp_shift_g)) /
+ ca->acked_bytes_total;
+
+ if (ca->dctcp_alpha > DCTCP_MAX_ALPHA)
+ /* Clamp dctcp_alpha to max. */
+ ca->dctcp_alpha = DCTCP_MAX_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)");
Code Review / kvmfornfv.git / blobdiff