From a7868ea68d29eb2c037952aeb3b549cf05749a18 Mon Sep 17 00:00:00 2001 From: Baruch Even Date: Thu, 23 Jun 2005 12:28:11 -0700 Subject: [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 Signed-off-by: David S. Miller --- net/ipv4/tcp_htcp.c | 289 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 289 insertions(+) create mode 100644 net/ipv4/tcp_htcp.c (limited to 'net/ipv4/tcp_htcp.c') diff --git a/net/ipv4/tcp_htcp.c b/net/ipv4/tcp_htcp.c new file mode 100644 index 000000000000..40168275acf9 --- /dev/null +++ b/net/ipv4/tcp_htcp.c @@ -0,0 +1,289 @@ +/* + * H-TCP congestion control. The algorithm is detailed in: + * R.N.Shorten, D.J.Leith: + * "H-TCP: TCP for high-speed and long-distance networks" + * Proc. PFLDnet, Argonne, 2004. + * http://www.hamilton.ie/net/htcp3.pdf + */ + +#include +#include +#include +#include + +#define ALPHA_BASE (1<<7) /* 1.0 with shift << 7 */ +#define BETA_MIN (1<<6) /* 0.5 with shift << 7 */ +#define BETA_MAX 102 /* 0.8 with shift << 7 */ + +static int use_rtt_scaling = 1; +module_param(use_rtt_scaling, int, 0644); +MODULE_PARM_DESC(use_rtt_scaling, "turn on/off RTT scaling"); + +static int use_bandwidth_switch = 1; +module_param(use_bandwidth_switch, int, 0644); +MODULE_PARM_DESC(use_bandwidth_switch, "turn on/off bandwidth switcher"); + +struct htcp { + u16 alpha; /* Fixed point arith, << 7 */ + u8 beta; /* Fixed point arith, << 7 */ + u8 modeswitch; /* Delay modeswitch until we had at least one congestion event */ + u8 ccount; /* Number of RTTs since last congestion event */ + u8 undo_ccount; + u16 packetcount; + u32 minRTT; + u32 maxRTT; + u32 snd_cwnd_cnt2; + + u32 undo_maxRTT; + u32 undo_old_maxB; + + /* Bandwidth estimation */ + u32 minB; + u32 maxB; + u32 old_maxB; + u32 Bi; + u32 lasttime; +}; + +static inline void htcp_reset(struct htcp *ca) +{ + ca->undo_ccount = ca->ccount; + ca->undo_maxRTT = ca->maxRTT; + ca->undo_old_maxB = ca->old_maxB; + + ca->ccount = 0; + ca->snd_cwnd_cnt2 = 0; +} + +static u32 htcp_cwnd_undo(struct tcp_sock *tp) +{ + struct htcp *ca = tcp_ca(tp); + ca->ccount = ca->undo_ccount; + ca->maxRTT = ca->undo_maxRTT; + ca->old_maxB = ca->undo_old_maxB; + return max(tp->snd_cwnd, (tp->snd_ssthresh<<7)/ca->beta); +} + +static inline void measure_rtt(struct tcp_sock *tp) +{ + struct htcp *ca = tcp_ca(tp); + u32 srtt = tp->srtt>>3; + + /* keep track of minimum RTT seen so far, minRTT is zero at first */ + if (ca->minRTT > srtt || !ca->minRTT) + ca->minRTT = srtt; + + /* max RTT */ + if (tp->ca_state == TCP_CA_Open && tp->snd_ssthresh < 0xFFFF && ca->ccount > 3) { + if (ca->maxRTT < ca->minRTT) + ca->maxRTT = ca->minRTT; + if (ca->maxRTT < srtt && srtt <= ca->maxRTT+HZ/50) + ca->maxRTT = srtt; + } +} + +static void measure_achieved_throughput(struct tcp_sock *tp, u32 pkts_acked) +{ + struct htcp *ca = tcp_ca(tp); + u32 now = tcp_time_stamp; + + /* achieved throughput calculations */ + if (tp->ca_state != TCP_CA_Open && tp->ca_state != TCP_CA_Disorder) { + ca->packetcount = 0; + ca->lasttime = now; + return; + } + + ca->packetcount += pkts_acked; + + if (ca->packetcount >= tp->snd_cwnd - (ca->alpha>>7? : 1) + && now - ca->lasttime >= ca->minRTT + && ca->minRTT > 0) { + __u32 cur_Bi = ca->packetcount*HZ/(now - ca->lasttime); + if (ca->ccount <= 3) { + /* just after backoff */ + ca->minB = ca->maxB = ca->Bi = cur_Bi; + } else { + ca->Bi = (3*ca->Bi + cur_Bi)/4; + if (ca->Bi > ca->maxB) + ca->maxB = ca->Bi; + if (ca->minB > ca->maxB) + ca->minB = ca->maxB; + } + ca->packetcount = 0; + ca->lasttime = now; + } +} + +static inline void htcp_beta_update(struct htcp *ca, u32 minRTT, u32 maxRTT) +{ + if (use_bandwidth_switch) { + u32 maxB = ca->maxB; + u32 old_maxB = ca->old_maxB; + ca->old_maxB = ca->maxB; + + if (!between(5*maxB, 4*old_maxB, 6*old_maxB)) { + ca->beta = BETA_MIN; + ca->modeswitch = 0; + return; + } + } + + if (ca->modeswitch && minRTT > max(HZ/100, 1) && maxRTT) { + ca->beta = (minRTT<<7)/maxRTT; + if (ca->beta < BETA_MIN) + ca->beta = BETA_MIN; + else if (ca->beta > BETA_MAX) + ca->beta = BETA_MAX; + } else { + ca->beta = BETA_MIN; + ca->modeswitch = 1; + } +} + +static inline void htcp_alpha_update(struct htcp *ca) +{ + u32 minRTT = ca->minRTT; + u32 factor = 1; + u32 diff = ca->ccount * minRTT; /* time since last backoff */ + + if (diff > HZ) { + diff -= HZ; + factor = 1+ ( 10*diff + ((diff/2)*(diff/2)/HZ) )/HZ; + } + + if (use_rtt_scaling && minRTT) { + u32 scale = (HZ<<3)/(10*minRTT); + scale = min(max(scale, 1U<<2), 10U<<3); /* clamping ratio to interval [0.5,10]<<3 */ + factor = (factor<<3)/scale; + if (!factor) + factor = 1; + } + + ca->alpha = 2*factor*((1<<7)-ca->beta); + if (!ca->alpha) + ca->alpha = ALPHA_BASE; +} + +/* After we have the rtt data to calculate beta, we'd still prefer to wait one + * rtt before we adjust our beta to ensure we are working from a consistent + * data. + * + * This function should be called when we hit a congestion event since only at + * that point do we really have a real sense of maxRTT (the queues en route + * were getting just too full now). + */ +static void htcp_param_update(struct tcp_sock *tp) +{ + struct htcp *ca = tcp_ca(tp); + u32 minRTT = ca->minRTT; + u32 maxRTT = ca->maxRTT; + + htcp_beta_update(ca, minRTT, maxRTT); + htcp_alpha_update(ca); + + /* add slowly fading memory for maxRTT to accommodate routing changes etc */ + if (minRTT > 0 && maxRTT > minRTT) + ca->maxRTT = minRTT + ((maxRTT-minRTT)*95)/100; +} + +static u32 htcp_recalc_ssthresh(struct tcp_sock *tp) +{ + struct htcp *ca = tcp_ca(tp); + htcp_param_update(tp); + return max((tp->snd_cwnd * ca->beta) >> 7, 2U); +} + +static void htcp_cong_avoid(struct tcp_sock *tp, u32 ack, u32 rtt, + u32 in_flight, int data_acked) +{ + struct htcp *ca = tcp_ca(tp); + + if (in_flight < tp->snd_cwnd) + return; + + if (tp->snd_cwnd <= tp->snd_ssthresh) { + /* In "safe" area, increase. */ + if (tp->snd_cwnd < tp->snd_cwnd_clamp) + tp->snd_cwnd++; + } else { + measure_rtt(tp); + + /* keep track of number of round-trip times since last backoff event */ + if (ca->snd_cwnd_cnt2++ > tp->snd_cwnd) { + ca->ccount++; + ca->snd_cwnd_cnt2 = 0; + htcp_alpha_update(ca); + } + + /* In dangerous area, increase slowly. + * In theory this is tp->snd_cwnd += alpha / tp->snd_cwnd + */ + if ((tp->snd_cwnd_cnt++ * ca->alpha)>>7 >= tp->snd_cwnd) { + if (tp->snd_cwnd < tp->snd_cwnd_clamp) + tp->snd_cwnd++; + tp->snd_cwnd_cnt = 0; + ca->ccount++; + } + } +} + +/* Lower bound on congestion window. */ +static u32 htcp_min_cwnd(struct tcp_sock *tp) +{ + return tp->snd_ssthresh; +} + + +static void htcp_init(struct tcp_sock *tp) +{ + struct htcp *ca = tcp_ca(tp); + + memset(ca, 0, sizeof(struct htcp)); + ca->alpha = ALPHA_BASE; + ca->beta = BETA_MIN; +} + +static void htcp_state(struct tcp_sock *tp, u8 new_state) +{ + switch (new_state) { + case TCP_CA_CWR: + case TCP_CA_Recovery: + case TCP_CA_Loss: + htcp_reset(tcp_ca(tp)); + break; + } +} + +static struct tcp_congestion_ops htcp = { + .init = htcp_init, + .ssthresh = htcp_recalc_ssthresh, + .min_cwnd = htcp_min_cwnd, + .cong_avoid = htcp_cong_avoid, + .set_state = htcp_state, + .undo_cwnd = htcp_cwnd_undo, + .pkts_acked = measure_achieved_throughput, + .owner = THIS_MODULE, + .name = "htcp", +}; + +static int __init htcp_register(void) +{ + BUG_ON(sizeof(struct htcp) > TCP_CA_PRIV_SIZE); + BUILD_BUG_ON(BETA_MIN >= BETA_MAX); + if (!use_bandwidth_switch) + htcp.pkts_acked = NULL; + return tcp_register_congestion_control(&htcp); +} + +static void __exit htcp_unregister(void) +{ + tcp_unregister_congestion_control(&htcp); +} + +module_init(htcp_register); +module_exit(htcp_unregister); + +MODULE_AUTHOR("Baruch Even"); +MODULE_LICENSE("GPL"); +MODULE_DESCRIPTION("H-TCP"); -- cgit v1.2.3