[TCP]: Add H-TCP congestion control module.
H-TCP is a congestion control algorithm developed at the Hamilton Institute, by Douglas Leith and Robert Shorten. It is extending the standard Reno algorithm with mode switching is thus a relatively simple modification. H-TCP is defined in a layered manner as it is still a research platform. The basic form includes the modification of beta according to the ratio of maxRTT to min RTT and the alpha=2*factor*(1-beta) relation, where factor is dependant on the time since last congestion. The other layers improve convergence by adding appropriate factors to alpha. The following patch implements the H-TCP algorithm in it's basic form. Signed-Off-By: Baruch Even <baruch@ev-en.org> Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Baruch Even
David S. Miller
Родитель
b87d8561d8
Коммит
a7868ea68d
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@ -467,6 +467,18 @@ config TCP_CONG_WESTWOOD
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TCP Westwood+ significantly increases fairness wrt TCP Reno in
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wired networks and throughput over wireless links.
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config TCP_CONG_HTCP
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tristate "H-TCP"
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depends on INET
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default m
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---help---
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H-TCP is a send-side only modifications of the TCP Reno
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protocol stack that optimizes the performance of TCP
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congestion control for high speed network links. It uses a
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modeswitch to change the alpha and beta parameters of TCP Reno
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based on network conditions and in a way so as to be fair with
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other Reno and H-TCP flows.
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config TCP_CONG_HSTCP
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tristate "High Speed TCP"
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depends on INET && EXPERIMENTAL
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@ -499,6 +511,7 @@ config TCP_CONG_VEGAS
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window. TCP Vegas should provide less packet loss, but it is
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not as aggressive as TCP Reno.
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endmenu
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source "net/ipv4/ipvs/Kconfig"
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@ -35,6 +35,7 @@ obj-$(CONFIG_TCP_CONG_BIC) += tcp_bic.o
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obj-$(CONFIG_TCP_CONG_WESTWOOD) += tcp_westwood.o
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obj-$(CONFIG_TCP_CONG_HSTCP) += tcp_highspeed.o
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obj-$(CONFIG_TCP_CONG_HYBLA) += tcp_hybla.o
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obj-$(CONFIG_TCP_CONG_HTCP) += tcp_htcp.o
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obj-$(CONFIG_TCP_CONG_VEGAS) += tcp_vegas.o
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obj-$(CONFIG_XFRM) += xfrm4_policy.o xfrm4_state.o xfrm4_input.o \
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@ -0,0 +1,289 @@
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/*
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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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u8 ccount; /* Number of RTTs since last congestion event */
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u8 undo_ccount;
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u16 packetcount;
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u32 minRTT;
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u32 maxRTT;
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u32 snd_cwnd_cnt2;
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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 void htcp_reset(struct htcp *ca)
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{
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ca->undo_ccount = ca->ccount;
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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->ccount = 0;
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ca->snd_cwnd_cnt2 = 0;
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}
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static u32 htcp_cwnd_undo(struct tcp_sock *tp)
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{
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struct htcp *ca = tcp_ca(tp);
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ca->ccount = ca->undo_ccount;
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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 tcp_sock *tp)
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{
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struct htcp *ca = tcp_ca(tp);
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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 (tp->ca_state == TCP_CA_Open && tp->snd_ssthresh < 0xFFFF && ca->ccount > 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+HZ/50)
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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 tcp_sock *tp, u32 pkts_acked)
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{
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struct htcp *ca = tcp_ca(tp);
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u32 now = tcp_time_stamp;
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/* achieved throughput calculations */
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if (tp->ca_state != TCP_CA_Open && tp->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 (ca->ccount <= 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 > max(HZ/100, 1) && 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 = ca->ccount * minRTT; /* time since last backoff */
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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 tcp_sock *tp)
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{
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struct htcp *ca = tcp_ca(tp);
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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 tcp_sock *tp)
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{
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struct htcp *ca = tcp_ca(tp);
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htcp_param_update(tp);
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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 tcp_sock *tp, u32 ack, u32 rtt,
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u32 in_flight, int data_acked)
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{
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struct htcp *ca = tcp_ca(tp);
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if (in_flight < tp->snd_cwnd)
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return;
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if (tp->snd_cwnd <= tp->snd_ssthresh) {
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/* In "safe" area, increase. */
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if (tp->snd_cwnd < tp->snd_cwnd_clamp)
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tp->snd_cwnd++;
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} else {
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measure_rtt(tp);
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/* keep track of number of round-trip times since last backoff event */
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if (ca->snd_cwnd_cnt2++ > tp->snd_cwnd) {
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ca->ccount++;
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ca->snd_cwnd_cnt2 = 0;
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htcp_alpha_update(ca);
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}
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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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ca->ccount++;
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}
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}
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}
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/* Lower bound on congestion window. */
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static u32 htcp_min_cwnd(struct tcp_sock *tp)
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{
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return tp->snd_ssthresh;
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}
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static void htcp_init(struct tcp_sock *tp)
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{
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struct htcp *ca = tcp_ca(tp);
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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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}
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static void htcp_state(struct tcp_sock *tp, u8 new_state)
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{
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switch (new_state) {
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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(tcp_ca(tp));
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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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.min_cwnd = htcp_min_cwnd,
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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) > TCP_CA_PRIV_SIZE);
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BUILD_BUG_ON(BETA_MIN >= BETA_MAX);
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if (!use_bandwidth_switch)
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htcp.pkts_acked = NULL;
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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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