From: Angelo P. Castellani <[EMAIL PROTECTED]> TCP Compound is a sender-side only change to TCP that uses a mixed Reno/Vegas approach to calculate the cwnd.
For further details look here: ftp://ftp.research.microsoft.com/pub/tr/TR-2005-86.pdf Signed-off-by: Angelo P. Castellani <[EMAIL PROTECTED]> --- This new revision of the TCP Compound implementation fixes some issues present in the previous patch and has been reverted to a stand-alone file (thanks to Stephen suggestion). Regards, Angelo P. Castellani
diff --git a/net/ipv4/Kconfig b/net/ipv4/Kconfig index 326676b..e577eb8 100644 --- a/net/ipv4/Kconfig +++ b/net/ipv4/Kconfig @@ -542,6 +542,16 @@ config TCP_CONG_LP ``fair share`` of bandwidth as targeted by TCP. See http://www-ece.rice.edu/networks/TCP-LP/ +config TCP_CONG_COMPOUND + tristate "TCP Compound" + depends on EXPERIMENTAL + default n + ---help--- + TCP Compound is a sender-side only change to TCP that uses + a mixed Reno/Vegas approach to calculate the cwnd. + For further details look here: + ftp://ftp.research.microsoft.com/pub/tr/TR-2005-86.pdf + endmenu config TCP_CONG_BIC diff --git a/net/ipv4/Makefile b/net/ipv4/Makefile index 5c65487..f0697c4 100644 --- a/net/ipv4/Makefile +++ b/net/ipv4/Makefile @@ -43,6 +43,7 @@ obj-$(CONFIG_TCP_CONG_HTCP) += tcp_htcp. obj-$(CONFIG_TCP_CONG_VEGAS) += tcp_vegas.o obj-$(CONFIG_TCP_CONG_SCALABLE) += tcp_scalable.o obj-$(CONFIG_TCP_CONG_LP) += tcp_lp.o +obj-$(CONFIG_TCP_CONG_COMPOUND) += tcp_compound.o obj-$(CONFIG_XFRM) += xfrm4_policy.o xfrm4_state.o xfrm4_input.o \ xfrm4_output.o
/* * TCP Vegas congestion control * * This is based on the congestion detection/avoidance scheme described in * Lawrence S. Brakmo and Larry L. Peterson. * "TCP Vegas: End to end congestion avoidance on a global internet." * IEEE Journal on Selected Areas in Communication, 13(8):1465--1480, * October 1995. Available from: * ftp://ftp.cs.arizona.edu/xkernel/Papers/jsac.ps * * See http://www.cs.arizona.edu/xkernel/ for their implementation. * The main aspects that distinguish this implementation from the * Arizona Vegas implementation are: * o We do not change the loss detection or recovery mechanisms of * Linux in any way. Linux already recovers from losses quite well, * using fine-grained timers, NewReno, and FACK. * o To avoid the performance penalty imposed by increasing cwnd * only every-other RTT during slow start, we increase during * every RTT during slow start, just like Reno. * o Largely to allow continuous cwnd growth during slow start, * we use the rate at which ACKs come back as the "actual" * rate, rather than the rate at which data is sent. * o To speed convergence to the right rate, we set the cwnd * to achieve the right ("actual") rate when we exit slow start. * o To filter out the noise caused by delayed ACKs, we use the * minimum RTT sample observed during the last RTT to calculate * the actual rate. * o When the sender re-starts from idle, it waits until it has * received ACKs for an entire flight of new data before making * a cwnd adjustment decision. The original Vegas implementation * assumed senders never went idle. * * * TCP Compound based on TCP Vegas * * further details can be found here: * ftp://ftp.research.microsoft.com/pub/tr/TR-2005-86.pdf */ #include <linux/config.h> #include <linux/mm.h> #include <linux/module.h> #include <linux/skbuff.h> #include <linux/inet_diag.h> #include <net/tcp.h> /* Default values of the Vegas variables, in fixed-point representation * with V_PARAM_SHIFT bits to the right of the binary point. */ #define V_PARAM_SHIFT 1 #define TCP_COMPOUND_ALPHA 3U #define TCP_COMPOUND_BETA 1U #define TCP_COMPOUND_KAPPA_POW 3 #define TCP_COMPOUND_KAPPA_NSQRT 2 #define TCP_COMPOUND_GAMMA 30 #define TCP_COMPOUND_ZETA 1 /* TCP compound variables */ struct compound { u32 beg_snd_nxt; /* right edge during last RTT */ u32 beg_snd_una; /* left edge during last RTT */ u32 beg_snd_cwnd; /* saves the size of the cwnd */ u8 doing_vegas_now; /* if true, do vegas for this RTT */ u16 cntRTT; /* # of RTTs measured within last RTT */ u32 minRTT; /* min of RTTs measured within last RTT (in usec) */ u32 baseRTT; /* the min of all Vegas RTT measurements seen (in usec) */ u32 cwnd; u32 dwnd; }; /* There are several situations when we must "re-start" Vegas: * * o when a connection is established * o after an RTO * o after fast recovery * o when we send a packet and there is no outstanding * unacknowledged data (restarting an idle connection) * * In these circumstances we cannot do a Vegas calculation at the * end of the first RTT, because any calculation we do is using * stale info -- both the saved cwnd and congestion feedback are * stale. * * Instead we must wait until the completion of an RTT during * which we actually receive ACKs. */ static inline void vegas_enable(struct sock *sk) { const struct tcp_sock *tp = tcp_sk(sk); struct compound *vegas = inet_csk_ca(sk); /* Begin taking Vegas samples next time we send something. */ vegas->doing_vegas_now = 1; /* Set the beginning of the next send window. */ vegas->beg_snd_nxt = tp->snd_nxt; vegas->cntRTT = 0; vegas->minRTT = 0x7fffffff; } /* Stop taking Vegas samples for now. */ static inline void vegas_disable(struct sock *sk) { struct compound *vegas = inet_csk_ca(sk); vegas->doing_vegas_now = 0; } static void tcp_compound_init(struct sock *sk) { struct compound *vegas = inet_csk_ca(sk); const struct tcp_sock *tp = tcp_sk(sk); vegas->baseRTT = 0x7fffffff; vegas_enable(sk); vegas->dwnd = 0; vegas->cwnd = tp->snd_cwnd; } /* Do RTT sampling needed for Vegas. * Basically we: * o min-filter RTT samples from within an RTT to get the current * propagation delay + queuing delay (we are min-filtering to try to * avoid the effects of delayed ACKs) * o min-filter RTT samples from a much longer window (forever for now) * to find the propagation delay (baseRTT) */ static void tcp_compound_rtt_calc(struct sock *sk, u32 usrtt) { struct compound *vegas = inet_csk_ca(sk); u32 vrtt = usrtt + 1; /* Never allow zero rtt or baseRTT */ /* Filter to find propagation delay: */ if (vrtt < vegas->baseRTT) vegas->baseRTT = vrtt; /* Find the min RTT during the last RTT to find * the current prop. delay + queuing delay: */ vegas->minRTT = min(vegas->minRTT, vrtt); vegas->cntRTT++; } static void tcp_compound_state(struct sock *sk, u8 ca_state) { if (ca_state == TCP_CA_Open) vegas_enable(sk); else vegas_disable(sk); } /* * If the connection is idle and we are restarting, * then we don't want to do any Vegas calculations * until we get fresh RTT samples. So when we * restart, we reset our Vegas state to a clean * slate. After we get acks for this flight of * packets, _then_ we can make Vegas calculations * again. */ static void tcp_compound_cwnd_event(struct sock *sk, enum tcp_ca_event event) { if (event == CA_EVENT_CWND_RESTART || event == CA_EVENT_TX_START) tcp_compound_init(sk); } static void tcp_compound_cong_avoid(struct sock *sk, u32 ack, u32 seq_rtt, u32 in_flight, int flag) { struct tcp_sock *tp = tcp_sk(sk); struct compound *vegas = inet_csk_ca(sk); u8 inc = 0; if (vegas->cwnd + vegas->dwnd > tp->snd_cwnd) { if (vegas->cwnd > tp->snd_cwnd || vegas->dwnd > tp->snd_cwnd) { vegas->cwnd = tp->snd_cwnd; vegas->dwnd = 0; } else vegas->cwnd = tp->snd_cwnd - vegas->dwnd; } if (!tcp_is_cwnd_limited(sk, in_flight)) return; if (vegas->cwnd <= tp->snd_ssthresh) inc = 1; else if (tp->snd_cwnd_cnt < tp->snd_cwnd) tp->snd_cwnd_cnt++; if (tp->snd_cwnd_cnt >= tp->snd_cwnd) { inc = 1; tp->snd_cwnd_cnt = 0; } if (inc && tp->snd_cwnd < tp->snd_cwnd_clamp) vegas->cwnd++; /* The key players are v_beg_snd_una and v_beg_snd_nxt. * * These are so named because they represent the approximate values * of snd_una and snd_nxt at the beginning of the current RTT. More * precisely, they represent the amount of data sent during the RTT. * At the end of the RTT, when we receive an ACK for v_beg_snd_nxt, * we will calculate that (v_beg_snd_nxt - v_beg_snd_una) outstanding * bytes of data have been ACKed during the course of the RTT, giving * an "actual" rate of: * * (v_beg_snd_nxt - v_beg_snd_una) / (rtt duration) * * Unfortunately, v_beg_snd_una is not exactly equal to snd_una, * because delayed ACKs can cover more than one segment, so they * don't line up nicely with the boundaries of RTTs. * * Another unfortunate fact of life is that delayed ACKs delay the * advance of the left edge of our send window, so that the number * of bytes we send in an RTT is often less than our cwnd will allow. * So we keep track of our cwnd separately, in v_beg_snd_cwnd. */ if (after(ack, vegas->beg_snd_nxt)) { /* Do the Vegas once-per-RTT cwnd adjustment. */ u32 old_wnd, old_snd_cwnd; /* Here old_wnd is essentially the window of data that was * sent during the previous RTT, and has all * been acknowledged in the course of the RTT that ended * with the ACK we just received. Likewise, old_snd_cwnd * is the cwnd during the previous RTT. */ if (!tp->mss_cache) return; old_wnd = (vegas->beg_snd_nxt - vegas->beg_snd_una) / tp->mss_cache; old_snd_cwnd = vegas->beg_snd_cwnd; /* Save the extent of the current window so we can use this * at the end of the next RTT. */ vegas->beg_snd_una = vegas->beg_snd_nxt; vegas->beg_snd_nxt = tp->snd_nxt; vegas->beg_snd_cwnd = tp->snd_cwnd; /* We do the Vegas calculations only if we got enough RTT * samples that we can be reasonably sure that we got * at least one RTT sample that wasn't from a delayed ACK. * If we only had 2 samples total, * then that means we're getting only 1 ACK per RTT, which * means they're almost certainly delayed ACKs. * If we have 3 samples, we should be OK. */ if (vegas->cntRTT > 2) { u32 rtt, target_cwnd, diff; u32 brtt, dwnd; /* We have enough RTT samples, so, using the Vegas * algorithm, we determine if we should increase or * decrease cwnd, and by how much. */ /* Pluck out the RTT we are using for the Vegas * calculations. This is the min RTT seen during the * last RTT. Taking the min filters out the effects * of delayed ACKs, at the cost of noticing congestion * a bit later. */ rtt = vegas->minRTT; /* Calculate the cwnd we should have, if we weren't * going too fast. * * This is: * (actual rate in segments) * baseRTT * We keep it as a fixed point number with * V_PARAM_SHIFT bits to the right of the binary point. */ if (!rtt) return; brtt = vegas->baseRTT; target_cwnd = ((old_wnd * brtt) << V_PARAM_SHIFT) / rtt; /* Calculate the difference between the window we had, * and the window we would like to have. This quantity * is the "Diff" from the Arizona Vegas papers. * * Again, this is a fixed point number with * V_PARAM_SHIFT bits to the right of the binary * point. */ diff = (old_wnd << V_PARAM_SHIFT) - target_cwnd; dwnd = vegas->dwnd; if (diff < (TCP_COMPOUND_GAMMA << V_PARAM_SHIFT)) { u32 i, j, x, x2; u64 v; v = 1; for (i = 0; i < TCP_COMPOUND_KAPPA_POW; i++) v *= old_wnd; for (i = 0; i < TCP_COMPOUND_KAPPA_NSQRT; i++) { x = 1; for (j = 0; j < 200; j++) { x2 = ( x + v / x ) / 2; if (x2 == x || !x2) break; x = x2; } v = x; } x = (u32)v >> TCP_COMPOUND_ALPHA; if (x > 1) dwnd = x - 1; else dwnd = 0; dwnd += vegas->dwnd; } else if ((dwnd << V_PARAM_SHIFT) < (diff * TCP_COMPOUND_BETA)) dwnd = 0; else dwnd = ((dwnd << V_PARAM_SHIFT) - (diff * TCP_COMPOUND_BETA)) >> V_PARAM_SHIFT; vegas->dwnd = dwnd; } /* Wipe the slate clean for the next RTT. */ vegas->cntRTT = 0; vegas->minRTT = 0x7fffffff; } tp->snd_cwnd = vegas->cwnd + vegas->dwnd; } /* Extract info for Tcp socket info provided via netlink. */ static void tcp_compound_get_info(struct sock *sk, u32 ext, struct sk_buff *skb) { const struct compound *ca = inet_csk_ca(sk); if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) { struct tcpvegas_info *info; info = RTA_DATA(__RTA_PUT(skb, INET_DIAG_VEGASINFO, sizeof(*info))); info->tcpv_enabled = ca->doing_vegas_now; info->tcpv_rttcnt = ca->cntRTT; info->tcpv_rtt = ca->baseRTT; info->tcpv_minrtt = ca->minRTT; rtattr_failure:; } } static struct tcp_congestion_ops tcp_compound = { .init = tcp_compound_init, .ssthresh = tcp_reno_ssthresh, .cong_avoid = tcp_compound_cong_avoid, .min_cwnd = tcp_reno_min_cwnd, .rtt_sample = tcp_compound_rtt_calc, .set_state = tcp_compound_state, .cwnd_event = tcp_compound_cwnd_event, .get_info = tcp_compound_get_info, .owner = THIS_MODULE, .name = "compound", }; static int __init tcp_compound_register(void) { BUG_ON(sizeof(struct compound) > ICSK_CA_PRIV_SIZE); tcp_register_congestion_control(&tcp_compound); return 0; } static void __exit tcp_compound_unregister(void) { tcp_unregister_congestion_control(&tcp_compound); } module_init(tcp_compound_register); module_exit(tcp_compound_unregister); MODULE_AUTHOR("Angelo P. Castellani / Stephen Hemminger"); MODULE_LICENSE("GPL"); MODULE_DESCRIPTION("TCP Compound");
