Release 4.11 net/ipv4/tcp_cdg.c
/*
* CAIA Delay-Gradient (CDG) congestion control
*
* This implementation is based on the paper:
* D.A. Hayes and G. Armitage. "Revisiting TCP congestion control using
* delay gradients." In IFIP Networking, pages 328-341. Springer, 2011.
*
* Scavenger traffic (Less-than-Best-Effort) should disable coexistence
* heuristics using parameters use_shadow=0 and use_ineff=0.
*
* Parameters window, backoff_beta, and backoff_factor are crucial for
* throughput and delay. Future work is needed to determine better defaults,
* and to provide guidelines for use in different environments/contexts.
*
* Except for window, knobs are configured via /sys/module/tcp_cdg/parameters/.
* Parameter window is only configurable when loading tcp_cdg as a module.
*
* Notable differences from paper/FreeBSD:
* o Using Hybrid Slow start and Proportional Rate Reduction.
* o Add toggle for shadow window mechanism. Suggested by David Hayes.
* o Add toggle for non-congestion loss tolerance.
* o Scaling parameter G is changed to a backoff factor;
* conversion is given by: backoff_factor = 1000/(G * window).
* o Limit shadow window to 2 * cwnd, or to cwnd when application limited.
* o More accurate e^-x.
*/
#include <linux/kernel.h>
#include <linux/random.h>
#include <linux/module.h>
#include <linux/sched/clock.h>
#include <net/tcp.h>
#define HYSTART_ACK_TRAIN 1
#define HYSTART_DELAY 2
static int window __read_mostly = 8;
static unsigned int backoff_beta __read_mostly = 0.7071 * 1024;
/* sqrt 0.5 */
static unsigned int backoff_factor __read_mostly = 42;
static unsigned int hystart_detect __read_mostly = 3;
static unsigned int use_ineff __read_mostly = 5;
static bool use_shadow __read_mostly = true;
static bool use_tolerance __read_mostly;
module_param(window, int, 0444);
MODULE_PARM_DESC(window, "gradient window size (power of two <= 256)");
module_param(backoff_beta, uint, 0644);
MODULE_PARM_DESC(backoff_beta, "backoff beta (0-1024)");
module_param(backoff_factor, uint, 0644);
MODULE_PARM_DESC(backoff_factor, "backoff probability scale factor");
module_param(hystart_detect, uint, 0644);
MODULE_PARM_DESC(hystart_detect, "use Hybrid Slow start "
"(0: disabled, 1: ACK train, 2: delay threshold, 3: both)");
module_param(use_ineff, uint, 0644);
MODULE_PARM_DESC(use_ineff, "use ineffectual backoff detection (threshold)");
module_param(use_shadow, bool, 0644);
MODULE_PARM_DESC(use_shadow, "use shadow window heuristic");
module_param(use_tolerance, bool, 0644);
MODULE_PARM_DESC(use_tolerance, "use loss tolerance heuristic");
struct cdg_minmax {
union {
struct {
s32 min;
s32 max;
};
u64 v64;
};
};
enum cdg_state {
CDG_UNKNOWN = 0,
CDG_NONFULL = 1,
CDG_FULL = 2,
CDG_BACKOFF = 3,
};
struct cdg {
struct cdg_minmax rtt;
struct cdg_minmax rtt_prev;
struct cdg_minmax *gradients;
struct cdg_minmax gsum;
bool gfilled;
u8 tail;
u8 state;
u8 delack;
u32 rtt_seq;
u32 undo_cwnd;
u32 shadow_wnd;
u16 backoff_cnt;
u16 sample_cnt;
s32 delay_min;
u32 last_ack;
u32 round_start;
};
/**
* nexp_u32 - negative base-e exponential
* @ux: x in units of micro
*
* Returns exp(ux * -1e-6) * U32_MAX.
*/
static u32 __pure nexp_u32(u32 ux)
{
static const u16 v[] = {
/* exp(-x)*65536-1 for x = 0, 0.000256, 0.000512, ... */
65535,
65518, 65501, 65468, 65401, 65267, 65001, 64470, 63422,
61378, 57484, 50423, 38795, 22965, 8047, 987, 14,
};
u32 msb = ux >> 8;
u32 res;
int i;
/* Cut off when ux >= 2^24 (actual result is <= 222/U32_MAX). */
if (msb > U16_MAX)
return 0;
/* Scale first eight bits linearly: */
res = U32_MAX - (ux & 0xff) * (U32_MAX / 1000000);
/* Obtain e^(x + y + ...) by computing e^x * e^y * ...: */
for (i = 1; msb; i++, msb >>= 1) {
u32 y = v[i & -(msb & 1)] + U32_C(1);
res = ((u64)res * y) >> 16;
}
return res;
}
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| Total | 147 | 100.00% | 1 | 100.00% |
/* Based on the HyStart algorithm (by Ha et al.) that is implemented in
* tcp_cubic. Differences/experimental changes:
* o Using Hayes' delayed ACK filter.
* o Using a usec clock for the ACK train.
* o Reset ACK train when application limited.
* o Invoked at any cwnd (i.e. also when cwnd < 16).
* o Invoked only when cwnd < ssthresh (i.e. not when cwnd == ssthresh).
*/
static void tcp_cdg_hystart_update(struct sock *sk)
{
struct cdg *ca = inet_csk_ca(sk);
struct tcp_sock *tp = tcp_sk(sk);
ca->delay_min = min_not_zero(ca->delay_min, ca->rtt.min);
if (ca->delay_min == 0)
return;
if (hystart_detect & HYSTART_ACK_TRAIN) {
u32 now_us = div_u64(local_clock(), NSEC_PER_USEC);
if (ca->last_ack == 0 || !tcp_is_cwnd_limited(sk)) {
ca->last_ack = now_us;
ca->round_start = now_us;
} else if (before(now_us, ca->last_ack + 3000)) {
u32 base_owd = max(ca->delay_min / 2U, 125U);
ca->last_ack = now_us;
if (after(now_us, ca->round_start + base_owd)) {
NET_INC_STATS(sock_net(sk),
LINUX_MIB_TCPHYSTARTTRAINDETECT);
NET_ADD_STATS(sock_net(sk),
LINUX_MIB_TCPHYSTARTTRAINCWND,
tp->snd_cwnd);
tp->snd_ssthresh = tp->snd_cwnd;
return;
}
}
}
if (hystart_detect & HYSTART_DELAY) {
if (ca->sample_cnt < 8) {
ca->sample_cnt++;
} else {
s32 thresh = max(ca->delay_min + ca->delay_min / 8U,
125U);
if (ca->rtt.min > thresh) {
NET_INC_STATS(sock_net(sk),
LINUX_MIB_TCPHYSTARTDELAYDETECT);
NET_ADD_STATS(sock_net(sk),
LINUX_MIB_TCPHYSTARTDELAYCWND,
tp->snd_cwnd);
tp->snd_ssthresh = tp->snd_cwnd;
}
}
}
}
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static s32 tcp_cdg_grad(struct cdg *ca)
{
s32 gmin = ca->rtt.min - ca->rtt_prev.min;
s32 gmax = ca->rtt.max - ca->rtt_prev.max;
s32 grad;
if (ca->gradients) {
ca->gsum.min += gmin - ca->gradients[ca->tail].min;
ca->gsum.max += gmax - ca->gradients[ca->tail].max;
ca->gradients[ca->tail].min = gmin;
ca->gradients[ca->tail].max = gmax;
ca->tail = (ca->tail + 1) & (window - 1);
gmin = ca->gsum.min;
gmax = ca->gsum.max;
}
/* We keep sums to ignore gradients during cwnd reductions;
* the paper's smoothed gradients otherwise simplify to:
* (rtt_latest - rtt_oldest) / window.
*
* We also drop division by window here.
*/
grad = gmin > 0 ? gmin : gmax;
/* Extrapolate missing values in gradient window: */
if (!ca->gfilled) {
if (!ca->gradients && window > 1)
grad *= window; /* Memory allocation failed. */
else if (ca->tail == 0)
ca->gfilled = true;
else
grad = (grad * window) / (int)ca->tail;
}
/* Backoff was effectual: */
if (gmin <= -32 || gmax <= -32)
ca->backoff_cnt = 0;
if (use_tolerance) {
/* Reduce small variations to zero: */
gmin = DIV_ROUND_CLOSEST(gmin, 64);
gmax = DIV_ROUND_CLOSEST(gmax, 64);
if (gmin > 0 && gmax <= 0)
ca->state = CDG_FULL;
else if ((gmin > 0 && gmax > 0) || gmax < 0)
ca->state = CDG_NONFULL;
}
return grad;
}
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static bool tcp_cdg_backoff(struct sock *sk, u32 grad)
{
struct cdg *ca = inet_csk_ca(sk);
struct tcp_sock *tp = tcp_sk(sk);
if (prandom_u32() <= nexp_u32(grad * backoff_factor))
return false;
if (use_ineff) {
ca->backoff_cnt++;
if (ca->backoff_cnt > use_ineff)
return false;
}
ca->shadow_wnd = max(ca->shadow_wnd, tp->snd_cwnd);
ca->state = CDG_BACKOFF;
tcp_enter_cwr(sk);
return true;
}
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| Total | 100 | 100.00% | 1 | 100.00% |
/* Not called in CWR or Recovery state. */
static void tcp_cdg_cong_avoid(struct sock *sk, u32 ack, u32 acked)
{
struct cdg *ca = inet_csk_ca(sk);
struct tcp_sock *tp = tcp_sk(sk);
u32 prior_snd_cwnd;
u32 incr;
if (tcp_in_slow_start(tp) && hystart_detect)
tcp_cdg_hystart_update(sk);
if (after(ack, ca->rtt_seq) && ca->rtt.v64) {
s32 grad = 0;
if (ca->rtt_prev.v64)
grad = tcp_cdg_grad(ca);
ca->rtt_seq = tp->snd_nxt;
ca->rtt_prev = ca->rtt;
ca->rtt.v64 = 0;
ca->last_ack = 0;
ca->sample_cnt = 0;
if (grad > 0 && tcp_cdg_backoff(sk, grad))
return;
}
if (!tcp_is_cwnd_limited(sk)) {
ca->shadow_wnd = min(ca->shadow_wnd, tp->snd_cwnd);
return;
}
prior_snd_cwnd = tp->snd_cwnd;
tcp_reno_cong_avoid(sk, ack, acked);
incr = tp->snd_cwnd - prior_snd_cwnd;
ca->shadow_wnd = max(ca->shadow_wnd, ca->shadow_wnd + incr);
}
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| Total | 212 | 100.00% | 2 | 100.00% |
static void tcp_cdg_acked(struct sock *sk, const struct ack_sample *sample)
{
struct cdg *ca = inet_csk_ca(sk);
struct tcp_sock *tp = tcp_sk(sk);
if (sample->rtt_us <= 0)
return;
/* A heuristic for filtering delayed ACKs, adapted from:
* D.A. Hayes. "Timing enhancements to the FreeBSD kernel to support
* delay and rate based TCP mechanisms." TR 100219A. CAIA, 2010.
*/
if (tp->sacked_out == 0) {
if (sample->pkts_acked == 1 && ca->delack) {
/* A delayed ACK is only used for the minimum if it is
* provenly lower than an existing non-zero minimum.
*/
ca->rtt.min = min(ca->rtt.min, sample->rtt_us);
ca->delack--;
return;
} else if (sample->pkts_acked > 1 && ca->delack < 5) {
ca->delack++;
}
}
ca->rtt.min = min_not_zero(ca->rtt.min, sample->rtt_us);
ca->rtt.max = max(ca->rtt.max, sample->rtt_us);
}
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static u32 tcp_cdg_ssthresh(struct sock *sk)
{
struct cdg *ca = inet_csk_ca(sk);
struct tcp_sock *tp = tcp_sk(sk);
ca->undo_cwnd = tp->snd_cwnd;
if (ca->state == CDG_BACKOFF)
return max(2U, (tp->snd_cwnd * min(1024U, backoff_beta)) >> 10);
if (ca->state == CDG_NONFULL && use_tolerance)
return tp->snd_cwnd;
ca->shadow_wnd = min(ca->shadow_wnd >> 1, tp->snd_cwnd);
if (use_shadow)
return max3(2U, ca->shadow_wnd, tp->snd_cwnd >> 1);
return max(2U, tp->snd_cwnd >> 1);
}
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| Total | 132 | 100.00% | 1 | 100.00% |
static u32 tcp_cdg_undo_cwnd(struct sock *sk)
{
struct cdg *ca = inet_csk_ca(sk);
return max(tcp_sk(sk)->snd_cwnd, ca->undo_cwnd);
}
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| Person | Tokens | Prop | Commits | CommitProp |
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| Total | 36 | 100.00% | 1 | 100.00% |
static void tcp_cdg_cwnd_event(struct sock *sk, const enum tcp_ca_event ev)
{
struct cdg *ca = inet_csk_ca(sk);
struct tcp_sock *tp = tcp_sk(sk);
struct cdg_minmax *gradients;
switch (ev) {
case CA_EVENT_CWND_RESTART:
gradients = ca->gradients;
if (gradients)
memset(gradients, 0, window * sizeof(gradients[0]));
memset(ca, 0, sizeof(*ca));
ca->gradients = gradients;
ca->rtt_seq = tp->snd_nxt;
ca->shadow_wnd = tp->snd_cwnd;
break;
case CA_EVENT_COMPLETE_CWR:
ca->state = CDG_UNKNOWN;
ca->rtt_seq = tp->snd_nxt;
ca->rtt_prev = ca->rtt;
ca->rtt.v64 = 0;
break;
default:
break;
}
}
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| Kenneth Klette Jonassen | 148 | 99.33% | 1 | 50.00% |
| Soheil Hassas Yeganeh | 1 | 0.67% | 1 | 50.00% |
| Total | 149 | 100.00% | 2 | 100.00% |
static void tcp_cdg_init(struct sock *sk)
{
struct cdg *ca = inet_csk_ca(sk);
struct tcp_sock *tp = tcp_sk(sk);
/* We silently fall back to window = 1 if allocation fails. */
if (window > 1)
ca->gradients = kcalloc(window, sizeof(ca->gradients[0]),
GFP_NOWAIT | __GFP_NOWARN);
ca->rtt_seq = tp->snd_nxt;
ca->shadow_wnd = tp->snd_cwnd;
}
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| Kenneth Klette Jonassen | 77 | 100.00% | 1 | 100.00% |
| Total | 77 | 100.00% | 1 | 100.00% |
static void tcp_cdg_release(struct sock *sk)
{
struct cdg *ca = inet_csk_ca(sk);
kfree(ca->gradients);
}
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| Person | Tokens | Prop | Commits | CommitProp |
| Kenneth Klette Jonassen | 28 | 100.00% | 1 | 100.00% |
| Total | 28 | 100.00% | 1 | 100.00% |
struct tcp_congestion_ops tcp_cdg __read_mostly = {
.cong_avoid = tcp_cdg_cong_avoid,
.cwnd_event = tcp_cdg_cwnd_event,
.pkts_acked = tcp_cdg_acked,
.undo_cwnd = tcp_cdg_undo_cwnd,
.ssthresh = tcp_cdg_ssthresh,
.release = tcp_cdg_release,
.init = tcp_cdg_init,
.owner = THIS_MODULE,
.name = "cdg",
};
static int __init tcp_cdg_register(void)
{
if (backoff_beta > 1024 || window < 1 || window > 256)
return -ERANGE;
if (!is_power_of_2(window))
return -EINVAL;
BUILD_BUG_ON(sizeof(struct cdg) > ICSK_CA_PRIV_SIZE);
tcp_register_congestion_control(&tcp_cdg);
return 0;
}
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| Kenneth Klette Jonassen | 59 | 100.00% | 1 | 100.00% |
| Total | 59 | 100.00% | 1 | 100.00% |
static void __exit tcp_cdg_unregister(void)
{
tcp_unregister_congestion_control(&tcp_cdg);
}
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| Kenneth Klette Jonassen | 15 | 100.00% | 1 | 100.00% |
| Total | 15 | 100.00% | 1 | 100.00% |
module_init(tcp_cdg_register);
module_exit(tcp_cdg_unregister);
MODULE_AUTHOR("Kenneth Klette Jonassen");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("TCP CDG");
Overall Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Kenneth Klette Jonassen | 2028 | 98.30% | 2 | 28.57% |
| Lawrence Brakmo | 19 | 0.92% | 1 | 14.29% |
| Soheil Hassas Yeganeh | 6 | 0.29% | 1 | 14.29% |
| Eric Dumazet | 4 | 0.19% | 1 | 14.29% |
| Ingo Molnar | 3 | 0.15% | 1 | 14.29% |
| Yuchung Cheng | 3 | 0.15% | 1 | 14.29% |
| Total | 2063 | 100.00% | 7 | 100.00% |
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