diff options
| -rw-r--r-- | net/ipv4/Kconfig | 10 | ||||
| -rw-r--r-- | net/ipv4/Makefile | 1 | ||||
| -rw-r--r-- | net/ipv4/tcp_compound.c | 407 |
3 files changed, 418 insertions, 0 deletions
diff --git a/net/ipv4/Kconfig b/net/ipv4/Kconfig index 8514106761b0..da33393be45f 100644 --- a/net/ipv4/Kconfig +++ b/net/ipv4/Kconfig @@ -572,6 +572,16 @@ config TCP_CONG_VENO loss packets. See http://www.ntu.edu.sg/home5/ZHOU0022/papers/CPFu03a.pdf +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 00fcd2c1ba78..f30faefc2672 100644 --- a/net/ipv4/Makefile +++ b/net/ipv4/Makefile @@ -46,6 +46,7 @@ obj-$(CONFIG_TCP_CONG_VEGAS) += tcp_vegas.o obj-$(CONFIG_TCP_CONG_VENO) += tcp_veno.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 diff --git a/net/ipv4/tcp_compound.c b/net/ipv4/tcp_compound.c new file mode 100644 index 000000000000..8c1ebfb7659e --- /dev/null +++ b/net/ipv4/tcp_compound.c @@ -0,0 +1,407 @@ +/* + * 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"); |