linux/net/ipv4/tcp_dctcp.c
Thomas Gleixner 2874c5fd28 treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152
Based on 1 normalized pattern(s):

  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

extracted by the scancode license scanner the SPDX license identifier

  GPL-2.0-or-later

has been chosen to replace the boilerplate/reference in 3029 file(s).

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Allison Randal <allison@lohutok.net>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190527070032.746973796@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2019-05-30 11:26:32 -07:00

259 lines
7.2 KiB
C

// 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/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;
};
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);
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 = tp->snd_cwnd;
return max(tp->snd_cwnd - ((tp->snd_cwnd * 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_ce = tp->delivered_ce - ca->old_delivered_ce;
u32 alpha = ca->dctcp_alpha;
/* alpha = (1 - g) * alpha + g * F */
alpha -= min_not_zero(alpha, alpha >> dctcp_shift_g);
if (delivered_ce) {
u32 delivered = tp->delivered - ca->old_delivered;
/* 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 = tp->snd_cwnd;
tp->snd_ssthresh = max(tp->snd_cwnd >> 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:
dctcp_react_to_loss(sk);
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);
return max(tcp_sk(sk)->snd_cwnd, 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",
};
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)");