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![Stephen Hemminger](/assets/img/avatar_default.png)
Many of the TCP congestion methods all just use ssthresh as the minimum congestion window on decrease. Rather than duplicating the code, just have that be the default if that handle in the ops structure is not set. Minor behaviour change to TCP compound. It probably wants to use this (ssthresh) as lower bound, rather than ssthresh/2 because the latter causes undershoot on loss. Signed-off-by: Stephen Hemminger <shemminger@osdl.org> Signed-off-by: David S. Miller <davem@davemloft.net>
305 lines
7.3 KiB
C
305 lines
7.3 KiB
C
/*
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* H-TCP congestion control. The algorithm is detailed in:
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* R.N.Shorten, D.J.Leith:
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* "H-TCP: TCP for high-speed and long-distance networks"
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* Proc. PFLDnet, Argonne, 2004.
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* http://www.hamilton.ie/net/htcp3.pdf
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*/
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#include <linux/config.h>
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#include <linux/mm.h>
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#include <linux/module.h>
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#include <net/tcp.h>
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#define ALPHA_BASE (1<<7) /* 1.0 with shift << 7 */
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#define BETA_MIN (1<<6) /* 0.5 with shift << 7 */
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#define BETA_MAX 102 /* 0.8 with shift << 7 */
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static int use_rtt_scaling = 1;
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module_param(use_rtt_scaling, int, 0644);
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MODULE_PARM_DESC(use_rtt_scaling, "turn on/off RTT scaling");
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static int use_bandwidth_switch = 1;
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module_param(use_bandwidth_switch, int, 0644);
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MODULE_PARM_DESC(use_bandwidth_switch, "turn on/off bandwidth switcher");
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struct htcp {
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u16 alpha; /* Fixed point arith, << 7 */
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u8 beta; /* Fixed point arith, << 7 */
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u8 modeswitch; /* Delay modeswitch until we had at least one congestion event */
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u32 last_cong; /* Time since last congestion event end */
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u32 undo_last_cong;
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u16 pkts_acked;
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u32 packetcount;
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u32 minRTT;
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u32 maxRTT;
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u32 undo_maxRTT;
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u32 undo_old_maxB;
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/* Bandwidth estimation */
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u32 minB;
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u32 maxB;
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u32 old_maxB;
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u32 Bi;
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u32 lasttime;
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};
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static inline u32 htcp_cong_time(struct htcp *ca)
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{
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return jiffies - ca->last_cong;
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}
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static inline u32 htcp_ccount(struct htcp *ca)
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{
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return htcp_cong_time(ca)/ca->minRTT;
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}
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static inline void htcp_reset(struct htcp *ca)
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{
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ca->undo_last_cong = ca->last_cong;
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ca->undo_maxRTT = ca->maxRTT;
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ca->undo_old_maxB = ca->old_maxB;
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ca->last_cong = jiffies;
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}
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static u32 htcp_cwnd_undo(struct sock *sk)
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{
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const struct tcp_sock *tp = tcp_sk(sk);
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struct htcp *ca = inet_csk_ca(sk);
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ca->last_cong = ca->undo_last_cong;
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ca->maxRTT = ca->undo_maxRTT;
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ca->old_maxB = ca->undo_old_maxB;
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return max(tp->snd_cwnd, (tp->snd_ssthresh<<7)/ca->beta);
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}
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static inline void measure_rtt(struct sock *sk)
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{
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const struct inet_connection_sock *icsk = inet_csk(sk);
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const struct tcp_sock *tp = tcp_sk(sk);
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struct htcp *ca = inet_csk_ca(sk);
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u32 srtt = tp->srtt>>3;
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/* keep track of minimum RTT seen so far, minRTT is zero at first */
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if (ca->minRTT > srtt || !ca->minRTT)
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ca->minRTT = srtt;
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/* max RTT */
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if (icsk->icsk_ca_state == TCP_CA_Open && tp->snd_ssthresh < 0xFFFF && htcp_ccount(ca) > 3) {
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if (ca->maxRTT < ca->minRTT)
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ca->maxRTT = ca->minRTT;
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if (ca->maxRTT < srtt && srtt <= ca->maxRTT+msecs_to_jiffies(20))
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ca->maxRTT = srtt;
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}
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}
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static void measure_achieved_throughput(struct sock *sk, u32 pkts_acked)
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{
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const struct inet_connection_sock *icsk = inet_csk(sk);
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const struct tcp_sock *tp = tcp_sk(sk);
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struct htcp *ca = inet_csk_ca(sk);
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u32 now = tcp_time_stamp;
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if (icsk->icsk_ca_state == TCP_CA_Open)
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ca->pkts_acked = pkts_acked;
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if (!use_bandwidth_switch)
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return;
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/* achieved throughput calculations */
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if (icsk->icsk_ca_state != TCP_CA_Open &&
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icsk->icsk_ca_state != TCP_CA_Disorder) {
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ca->packetcount = 0;
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ca->lasttime = now;
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return;
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}
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ca->packetcount += pkts_acked;
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if (ca->packetcount >= tp->snd_cwnd - (ca->alpha>>7? : 1)
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&& now - ca->lasttime >= ca->minRTT
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&& ca->minRTT > 0) {
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__u32 cur_Bi = ca->packetcount*HZ/(now - ca->lasttime);
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if (htcp_ccount(ca) <= 3) {
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/* just after backoff */
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ca->minB = ca->maxB = ca->Bi = cur_Bi;
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} else {
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ca->Bi = (3*ca->Bi + cur_Bi)/4;
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if (ca->Bi > ca->maxB)
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ca->maxB = ca->Bi;
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if (ca->minB > ca->maxB)
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ca->minB = ca->maxB;
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}
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ca->packetcount = 0;
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ca->lasttime = now;
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}
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}
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static inline void htcp_beta_update(struct htcp *ca, u32 minRTT, u32 maxRTT)
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{
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if (use_bandwidth_switch) {
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u32 maxB = ca->maxB;
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u32 old_maxB = ca->old_maxB;
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ca->old_maxB = ca->maxB;
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if (!between(5*maxB, 4*old_maxB, 6*old_maxB)) {
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ca->beta = BETA_MIN;
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ca->modeswitch = 0;
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return;
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}
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}
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if (ca->modeswitch && minRTT > msecs_to_jiffies(10) && maxRTT) {
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ca->beta = (minRTT<<7)/maxRTT;
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if (ca->beta < BETA_MIN)
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ca->beta = BETA_MIN;
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else if (ca->beta > BETA_MAX)
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ca->beta = BETA_MAX;
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} else {
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ca->beta = BETA_MIN;
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ca->modeswitch = 1;
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}
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}
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static inline void htcp_alpha_update(struct htcp *ca)
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{
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u32 minRTT = ca->minRTT;
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u32 factor = 1;
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u32 diff = htcp_cong_time(ca);
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if (diff > HZ) {
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diff -= HZ;
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factor = 1+ ( 10*diff + ((diff/2)*(diff/2)/HZ) )/HZ;
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}
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if (use_rtt_scaling && minRTT) {
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u32 scale = (HZ<<3)/(10*minRTT);
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scale = min(max(scale, 1U<<2), 10U<<3); /* clamping ratio to interval [0.5,10]<<3 */
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factor = (factor<<3)/scale;
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if (!factor)
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factor = 1;
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}
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ca->alpha = 2*factor*((1<<7)-ca->beta);
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if (!ca->alpha)
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ca->alpha = ALPHA_BASE;
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}
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/* After we have the rtt data to calculate beta, we'd still prefer to wait one
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* rtt before we adjust our beta to ensure we are working from a consistent
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* data.
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*
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* This function should be called when we hit a congestion event since only at
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* that point do we really have a real sense of maxRTT (the queues en route
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* were getting just too full now).
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*/
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static void htcp_param_update(struct sock *sk)
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{
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struct htcp *ca = inet_csk_ca(sk);
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u32 minRTT = ca->minRTT;
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u32 maxRTT = ca->maxRTT;
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htcp_beta_update(ca, minRTT, maxRTT);
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htcp_alpha_update(ca);
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/* add slowly fading memory for maxRTT to accommodate routing changes etc */
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if (minRTT > 0 && maxRTT > minRTT)
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ca->maxRTT = minRTT + ((maxRTT-minRTT)*95)/100;
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}
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static u32 htcp_recalc_ssthresh(struct sock *sk)
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{
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const struct tcp_sock *tp = tcp_sk(sk);
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const struct htcp *ca = inet_csk_ca(sk);
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htcp_param_update(sk);
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return max((tp->snd_cwnd * ca->beta) >> 7, 2U);
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}
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static void htcp_cong_avoid(struct sock *sk, u32 ack, u32 rtt,
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u32 in_flight, int data_acked)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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struct htcp *ca = inet_csk_ca(sk);
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if (!tcp_is_cwnd_limited(sk, in_flight))
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return;
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if (tp->snd_cwnd <= tp->snd_ssthresh)
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tcp_slow_start(tp);
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else {
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measure_rtt(sk);
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/* In dangerous area, increase slowly.
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* In theory this is tp->snd_cwnd += alpha / tp->snd_cwnd
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*/
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if ((tp->snd_cwnd_cnt * ca->alpha)>>7 >= tp->snd_cwnd) {
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if (tp->snd_cwnd < tp->snd_cwnd_clamp)
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tp->snd_cwnd++;
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tp->snd_cwnd_cnt = 0;
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htcp_alpha_update(ca);
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} else
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tp->snd_cwnd_cnt += ca->pkts_acked;
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ca->pkts_acked = 1;
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}
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}
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static void htcp_init(struct sock *sk)
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{
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struct htcp *ca = inet_csk_ca(sk);
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memset(ca, 0, sizeof(struct htcp));
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ca->alpha = ALPHA_BASE;
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ca->beta = BETA_MIN;
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ca->pkts_acked = 1;
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ca->last_cong = jiffies;
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}
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static void htcp_state(struct sock *sk, u8 new_state)
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{
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switch (new_state) {
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case TCP_CA_Open:
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{
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struct htcp *ca = inet_csk_ca(sk);
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ca->last_cong = jiffies;
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}
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break;
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case TCP_CA_CWR:
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case TCP_CA_Recovery:
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case TCP_CA_Loss:
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htcp_reset(inet_csk_ca(sk));
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break;
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}
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}
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static struct tcp_congestion_ops htcp = {
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.init = htcp_init,
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.ssthresh = htcp_recalc_ssthresh,
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.cong_avoid = htcp_cong_avoid,
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.set_state = htcp_state,
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.undo_cwnd = htcp_cwnd_undo,
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.pkts_acked = measure_achieved_throughput,
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.owner = THIS_MODULE,
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.name = "htcp",
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};
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static int __init htcp_register(void)
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{
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BUG_ON(sizeof(struct htcp) > ICSK_CA_PRIV_SIZE);
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BUILD_BUG_ON(BETA_MIN >= BETA_MAX);
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return tcp_register_congestion_control(&htcp);
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}
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static void __exit htcp_unregister(void)
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{
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tcp_unregister_congestion_control(&htcp);
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}
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module_init(htcp_register);
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module_exit(htcp_unregister);
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MODULE_AUTHOR("Baruch Even");
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MODULE_LICENSE("GPL");
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MODULE_DESCRIPTION("H-TCP");
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