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![Eric Dumazet](/assets/img/avatar_default.png)
Upcoming congestion controls for TCP require usec resolution for RTT estimations. Millisecond resolution is simply not enough these days. FQ/pacing in DC environments also require this change for finer control and removal of bimodal behavior due to the current hack in tcp_update_pacing_rate() for 'small rtt' TCP_CONG_RTT_STAMP is no longer needed. As Julian Anastasov pointed out, we need to keep user compatibility : tcp_metrics used to export RTT and RTTVAR in msec resolution, so we added RTT_US and RTTVAR_US. An iproute2 patch is needed to use the new attributes if provided by the kernel. In this example ss command displays a srtt of 32 usecs (10Gbit link) lpk51:~# ./ss -i dst lpk52 Netid State Recv-Q Send-Q Local Address:Port Peer Address:Port tcp ESTAB 0 1 10.246.11.51:42959 10.246.11.52:64614 cubic wscale:6,6 rto:201 rtt:0.032/0.001 ato:40 mss:1448 cwnd:10 send 3620.0Mbps pacing_rate 7240.0Mbps unacked:1 rcv_rtt:993 rcv_space:29559 Updated iproute2 ip command displays : lpk51:~# ./ip tcp_metrics | grep 10.246.11.52 10.246.11.52 age 561.914sec cwnd 10 rtt 274us rttvar 213us source 10.246.11.51 Old binary displays : lpk51:~# ip tcp_metrics | grep 10.246.11.52 10.246.11.52 age 561.914sec cwnd 10 rtt 250us rttvar 125us source 10.246.11.51 With help from Julian Anastasov, Stephen Hemminger and Yuchung Cheng Signed-off-by: Eric Dumazet <edumazet@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Cc: Stephen Hemminger <stephen@networkplumber.org> Cc: Yuchung Cheng <ycheng@google.com> Cc: Larry Brakmo <brakmo@google.com> Cc: Julian Anastasov <ja@ssi.bg> Signed-off-by: David S. Miller <davem@davemloft.net>
194 lines
4.9 KiB
C
194 lines
4.9 KiB
C
/*
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* TCP HYBLA
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*
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* TCP-HYBLA Congestion control algorithm, based on:
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* C.Caini, R.Firrincieli, "TCP-Hybla: A TCP Enhancement
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* for Heterogeneous Networks",
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* International Journal on satellite Communications,
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* September 2004
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* Daniele Lacamera
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* root at danielinux.net
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*/
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#include <linux/module.h>
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#include <net/tcp.h>
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/* Tcp Hybla structure. */
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struct hybla {
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bool hybla_en;
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u32 snd_cwnd_cents; /* Keeps increment values when it is <1, <<7 */
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u32 rho; /* Rho parameter, integer part */
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u32 rho2; /* Rho * Rho, integer part */
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u32 rho_3ls; /* Rho parameter, <<3 */
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u32 rho2_7ls; /* Rho^2, <<7 */
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u32 minrtt_us; /* Minimum smoothed round trip time value seen */
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};
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/* Hybla reference round trip time (default= 1/40 sec = 25 ms), in ms */
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static int rtt0 = 25;
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module_param(rtt0, int, 0644);
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MODULE_PARM_DESC(rtt0, "reference rout trip time (ms)");
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/* This is called to refresh values for hybla parameters */
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static inline void hybla_recalc_param (struct sock *sk)
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{
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struct hybla *ca = inet_csk_ca(sk);
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ca->rho_3ls = max_t(u32,
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tcp_sk(sk)->srtt_us / (rtt0 * USEC_PER_MSEC),
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8U);
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ca->rho = ca->rho_3ls >> 3;
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ca->rho2_7ls = (ca->rho_3ls * ca->rho_3ls) << 1;
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ca->rho2 = ca->rho2_7ls >> 7;
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}
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static void hybla_init(struct sock *sk)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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struct hybla *ca = inet_csk_ca(sk);
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ca->rho = 0;
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ca->rho2 = 0;
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ca->rho_3ls = 0;
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ca->rho2_7ls = 0;
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ca->snd_cwnd_cents = 0;
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ca->hybla_en = true;
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tp->snd_cwnd = 2;
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tp->snd_cwnd_clamp = 65535;
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/* 1st Rho measurement based on initial srtt */
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hybla_recalc_param(sk);
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/* set minimum rtt as this is the 1st ever seen */
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ca->minrtt_us = tp->srtt_us;
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tp->snd_cwnd = ca->rho;
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}
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static void hybla_state(struct sock *sk, u8 ca_state)
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{
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struct hybla *ca = inet_csk_ca(sk);
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ca->hybla_en = (ca_state == TCP_CA_Open);
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}
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static inline u32 hybla_fraction(u32 odds)
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{
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static const u32 fractions[] = {
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128, 139, 152, 165, 181, 197, 215, 234,
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};
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return (odds < ARRAY_SIZE(fractions)) ? fractions[odds] : 128;
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}
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/* TCP Hybla main routine.
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* This is the algorithm behavior:
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* o Recalc Hybla parameters if min_rtt has changed
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* o Give cwnd a new value based on the model proposed
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* o remember increments <1
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*/
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static void hybla_cong_avoid(struct sock *sk, u32 ack, u32 acked,
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u32 in_flight)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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struct hybla *ca = inet_csk_ca(sk);
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u32 increment, odd, rho_fractions;
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int is_slowstart = 0;
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/* Recalculate rho only if this srtt is the lowest */
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if (tp->srtt_us < ca->minrtt_us) {
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hybla_recalc_param(sk);
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ca->minrtt_us = tp->srtt_us;
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}
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if (!tcp_is_cwnd_limited(sk, in_flight))
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return;
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if (!ca->hybla_en) {
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tcp_reno_cong_avoid(sk, ack, acked, in_flight);
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return;
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}
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if (ca->rho == 0)
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hybla_recalc_param(sk);
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rho_fractions = ca->rho_3ls - (ca->rho << 3);
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if (tp->snd_cwnd < tp->snd_ssthresh) {
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/*
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* slow start
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* INC = 2^RHO - 1
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* This is done by splitting the rho parameter
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* into 2 parts: an integer part and a fraction part.
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* Inrement<<7 is estimated by doing:
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* [2^(int+fract)]<<7
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* that is equal to:
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* (2^int) * [(2^fract) <<7]
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* 2^int is straightly computed as 1<<int,
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* while we will use hybla_slowstart_fraction_increment() to
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* calculate 2^fract in a <<7 value.
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*/
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is_slowstart = 1;
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increment = ((1 << min(ca->rho, 16U)) *
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hybla_fraction(rho_fractions)) - 128;
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} else {
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/*
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* congestion avoidance
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* INC = RHO^2 / W
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* as long as increment is estimated as (rho<<7)/window
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* it already is <<7 and we can easily count its fractions.
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*/
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increment = ca->rho2_7ls / tp->snd_cwnd;
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if (increment < 128)
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tp->snd_cwnd_cnt++;
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}
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odd = increment % 128;
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tp->snd_cwnd += increment >> 7;
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ca->snd_cwnd_cents += odd;
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/* check when fractions goes >=128 and increase cwnd by 1. */
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while (ca->snd_cwnd_cents >= 128) {
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tp->snd_cwnd++;
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ca->snd_cwnd_cents -= 128;
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tp->snd_cwnd_cnt = 0;
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}
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/* check when cwnd has not been incremented for a while */
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if (increment == 0 && odd == 0 && tp->snd_cwnd_cnt >= tp->snd_cwnd) {
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tp->snd_cwnd++;
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tp->snd_cwnd_cnt = 0;
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}
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/* clamp down slowstart cwnd to ssthresh value. */
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if (is_slowstart)
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tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
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tp->snd_cwnd = min_t(u32, tp->snd_cwnd, tp->snd_cwnd_clamp);
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}
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static struct tcp_congestion_ops tcp_hybla __read_mostly = {
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.init = hybla_init,
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.ssthresh = tcp_reno_ssthresh,
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.cong_avoid = hybla_cong_avoid,
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.set_state = hybla_state,
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.owner = THIS_MODULE,
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.name = "hybla"
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};
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static int __init hybla_register(void)
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{
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BUILD_BUG_ON(sizeof(struct hybla) > ICSK_CA_PRIV_SIZE);
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return tcp_register_congestion_control(&tcp_hybla);
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}
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static void __exit hybla_unregister(void)
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{
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tcp_unregister_congestion_control(&tcp_hybla);
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}
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module_init(hybla_register);
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module_exit(hybla_unregister);
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MODULE_AUTHOR("Daniele Lacamera");
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MODULE_LICENSE("GPL");
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MODULE_DESCRIPTION("TCP Hybla");
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