// 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 <[email protected]>
* Florian Westphal <[email protected]>
* Glenn Judd <[email protected]>
*/
#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 */
static int dctcp_shift_g_set(const char *val, const struct kernel_param *kp)
{
return param_set_uint_minmax(val, kp, 0, 10);
}
static const struct kernel_param_ops dctcp_shift_g_ops = {
.set = dctcp_shift_g_set,
.get = param_get_uint,
};
module_param_cb(dctcp_shift_g, &dctcp_shift_g_ops, &dctcp_shift_g, 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;
}
__bpf_kfunc 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);
}
__bpf_kfunc 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);
}
__bpf_kfunc 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);
}
__bpf_kfunc 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.
*/
}
__bpf_kfunc 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;
}
__bpf_kfunc 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_KFUNCS_START(tcp_dctcp_check_kfunc_ids)
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)
BTF_KFUNCS_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 <[email protected]>");
MODULE_AUTHOR("Florian Westphal <[email protected]>");
MODULE_AUTHOR("Glenn Judd <[email protected]>");
MODULE_LICENSE("GPL v2");
MODULE_DESCRIPTION("DataCenter TCP (DCTCP)");
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